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  • 1.
    Bergkvist, Tommy
    et al.
    KTH, Superseded Departments, Electrical Systems.
    Hellsten, Torbjörn
    KTH, Superseded Departments, Electrical Systems.
    Self-consistent calculations of the distribution function and wave field during ICRF heating and global Alfvén wave excitation2004In: Proceeding of Theory of Fusions Plasmas, 2004, 123-132 p.Conference paper (Refereed)
  • 2.
    Bergkvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Hellsten, Torbjörn A K
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Non-linear Alfvén eigenmode dynamics of a burning plasma in the presence of ion cyclotron resonance heating2006In: EPS Conf. Plasma Phys., EPS, 2006, 1792-1795 p.Conference paper (Refereed)
    Abstract [en]

    Alfvén eigenmodes (AEs) excited by α particles in a burning plasma can degrade the heating efficiency by spatial redistribution of the resonant α particles. Changes of the orbit invariants in phase space by collisions and other waves, such as magnetosonic waves during ion cyclotron resonance heating (ICRH), lead to changes in the phase between the αs and AEs, causing a decorrelation of the interactions. ICRH lead to an increased decorrelation of the AE interactions and hence a stronger radial redistribution of the thermonuclear α particles by the AEs. Renewal of the distribution function by thermonuclear reactions and losses of α particles to the wall lead to a continuous drive of the AEs and a radial redistribution of the α particles. The redistribution results in a degradation of the heating efficiency.

  • 3.
    Bergkvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Effects of ICRH on the dynamics of fast particle excited alfven eigenmodes2007In: Radio Frequency Power in Plasmas, American Institute of Physics (AIP), 2007, Vol. 933, 455-458 p.Conference paper (Refereed)
    Abstract [en]

    ICRH is often used in experiments to simulate destabilization of Alfvén eigenmodes by thermonuclear α-particles. Whereas the slowing down distribution of α-particles is nearly isotropic, the ICRH creates an anisotropic distribution function with non-standard orbits. The ICRH does not only build up gradients in phase space, which destabilizes the AEs, but it also provides a strong phase decorrelation mechanism between ions and AEs. Renewal of the distribution function by thermonuclear reactions and losses of α-particles to the wall lead to a continuous drive of the AEs. Simulations of the non-linear dynamics of AEs and the impact they have on the heating profile due to particle redistribution are presented.

  • 4.
    Bergkvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Non-linear Alfvén Eigenmode Dynamic of Burning Plasma in the Presence of Ion Cyclotron Resonance Heating2006In: 33rd EPS Plasma Physics Conference, 2006Conference paper (Other academic)
    Abstract [en]

    Alfvén eigenmodes (AEs) excited by a particles in a burning plasma can degrade theheating efficiency by spatial redistribution of the resonant a particles. Changes of the orbitinvariants in phase space by collisions and other waves, such as magnetosonic waves duringion cyclotron resonance heating (ICRH), lead to changes in the phase between the as andAEs, causing a decorrelation of the interactions. ICRH lead to an increased decorrelation ofthe AE interactions and hence a stronger radial redistribution of the thermonuclear a particlesby the AEs. Renewal of the distribution function by thermonuclear reactions and lossesof a particles to the wall lead to a continuous drive of the AEs and a radial redistributionof the a particles. The redistribution results in a degradation of the heating efficiency.

  • 5.
    Bergkvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Non-linear dynamics of Alfvén eigenmodes excited by thermonulcear alpha particles in the presence of ion cyclotron resonance heating2007In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, no 9, 1131-1141 p.Article in journal (Refereed)
    Abstract [en]

    Alfvén eigenmodes (AEs) excited by thermonuclear α-particles can degrade the heating efficiency by spatial redistribution of the resonant α-particles. Changes of the orbit invariants in phase space by collisions and interactions with other waves, such as magnetosonic waves during ion cyclotron resonance heating (ICRH), lead to changes in the phase between the α-particles and AEs, causing a decorrelation of the interactions and stronger redistribution of the α-particles. Cyclotron interactions increase the decorrelation of the AE interactions with the high-energy ions and hence a stronger radial redistribution of the high-energy α-particles by the AEs. Renewal of the distribution function by thermonuclear reactions and losses of α-particles to the wall lead to a continuous drive of the AEs and a radial redistribution of the α-particles. The condition for excitation of AEs is shown to depend on the heating scenario where heating at the low field side creates a significant population of high-energy non-standard orbits which drive the modes. The redistribution results in a reduction in the averaged α-particle energy and a degradation of the heating efficiency. The effect on the distribution function in the presence of several unstable modes is not additive and the particle redistribution is found to saturate with an increasing number of modes.

  • 6.
    Bergkvist, Tommy
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Hellsten, Torbjörn
    KTH, Superseded Departments, Alfvén Laboratory.
    Johnson, T
    Laxåback, Martin
    KTH, Superseded Departments, Alfvén Laboratory.
    Nonlinear interaction between RF-heated high-energy ions and MHD-modes2003In: RADIO FREQUENCY POWER IN PLASMAS / [ed] Forest C.B., 2003, Vol. 694, 459-462 p.Conference paper (Refereed)
    Abstract [en]

    Excitation of global Alfven eigenmodes by fast ions during ICRH is frequently observed in tokamaks. The importance of the phasing of the ICRH antennae for the excitation of these modes have been seen in experiments. The Alfven eigenmodes will drive the distribution function of the fast ions towards a state where the gradient in phase space is reduced. In general, the fast ions are displaced outwards, which can have a significant effect on the ICRH power deposition and lead to reduced heating efficiency. To calculate the effect on the heating profiles by the excitation of Alfven eigenmodes and the, effect on the resonating ions the Monte Carlo code FIDO, used for ICRH, has been upgraded to include particle interactions with MHD-waves. This allows self-consistent calculations of the mode amplitude and the distribution function during RF heating.

  • 7.
    Bergkvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, T.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Non-linear study of fast particle excitation of global Alfvén eigenmodes during ICRH2005In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, 485-493 p.Article in journal (Refereed)
    Abstract [en]

    High-power ion–cyclotron resonance heating (ICRH) can produce centrally peaked fast ion distributions with wide non-standard drift orbits exciting Alfvén eigenmodes (AEs). The dynamics of the AE excitation depends not only on the anisotropy and the peaking of the fast ion distribution but also on the decorrelation of the AE interactions and the renewal of the fast ions resonant with the AE by ion–cyclotron interactions. A method of self-consistently including the evolution of the distribution function of fast ions during excitation of AEs and ICRH has been developed and implemented in the SELFO code. Numerical simulations of the AE dynamics and ICRH give a variation of the AE amplitude consistent with the experimentally observed splitting of the mode frequency. The experimentally observed fast damping of the mode as the ICRH is switched off is also evident in the simulations.

  • 8.
    Bergkvist, Tommy
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Self-consistent study of fast particle redistribution by Alfvén eigenmodes during Ion cyclotron resonance heating2005In: Proceedings of the 9th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems, 2005, 14-20 p.Conference paper (Refereed)
  • 9. Campbell, D. J.
    et al.
    Barabaschi, P.
    Becoulet, M.
    Federici, G.
    Hellsten, Torbjörn
    Loarte, A.
    Pautasso, G.
    Wilson, H.
    Report on the 9th European fusion physics workshop2003In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, Vol. 45, no 4, 505-520 p.Article in journal (Refereed)
    Abstract [en]

    The 9th EFPW took place in December 2001 at Saariselka in Finland, hosted by the Technical Research Centre of Finland (VTT) and the Helsinki University, and sponsored by the European Commission. Within an overall theme of 'transient events, their mitigation and their implications for plasma facing components in ITER', four topics of importance to the future development of magnetically confined fusion were discussed in detail. In addition, the key issues for the ITER design which are associated with transient events and a review of the JET scientific and technical programme under EFDA were presented. The main issues discussed and the areas identified as requiring further study are summarized here.

  • 10. Eriksson, J.
    et al.
    Nocente, M.
    Binda, F.
    Cazzaniga, C.
    Conroy, S.
    Ericsson, G.
    Giacomelli, L.
    Gorini, G.
    Hellesen, C.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hjalmarsson, A.
    Jacobsen, A. S.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Kiptily, V.
    Koskela, T.
    Mantsinen, M.
    Salewski, M.
    Schneider, M.
    Sharapov, S.
    Skiba, M.
    Tardocchi, M.
    Weiszflog, M.
    Dual sightline measurements of MeV range deuterons with neutron and gamma-ray spectroscopy at JET2015In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 12, 123026Article in journal (Refereed)
    Abstract [en]

    Observations made in a JET experiment aimed at accelerating deuterons to the MeV range by third harmonic radio-frequency (RF) heating coupled into a deuterium beam are reported. Measurements are based on a set of advanced neutron and gamma-ray spectrometers that, for the first time, observe the plasma simultaneously along vertical and oblique lines of sight. Parameters of the fast ion energy distribution, such as the high energy cut-off of the deuteron distribution function and the RF coupling constant, are determined from data within a uniform analysis framework for neutron and gamma-ray spectroscopy based on a one-dimensional model and by a consistency check among the individual measurement techniques. A systematic difference is seen between the two lines of sight and is interpreted to originate from the sensitivity of the oblique detectors to the pitch-angle structure of the distribution around the resonance, which is not correctly portrayed within the adopted one dimensional model. A framework to calculate neutron and gamma-ray emission from a spatially resolved, two-dimensional deuteron distribution specified by energy/pitch is thus developed and used for a first comparison with predictions from ab initio models of RF heating at multiple harmonics. The results presented in this paper are of relevance for the development of advanced diagnostic techniques for MeV range ions in high performance fusion plasmas, with applications to the experimental validation of RF heating codes and, more generally, to studies of the energy distribution of ions in the MeV range in high performance deuterium and deuterium-tritium plasmas.

  • 11. Eriksson, L. G.
    et al.
    Bergeaud, V.
    Basiuk, V.
    Hellsten, Torbjörn A. K.
    KTH, Superseded Departments, Alfvén Laboratory.
    Modelling of ripple losses in tokamak plasmas heated by ICRF waves2001In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 43, no 10, 1291-1302 p.Article in journal (Refereed)
    Abstract [en]

    A model for treating ripple induced fast ion losses during ion cyclotron resonance frequency heating is presented. It is suitable for codes solving an orbit averaged three-dimensional Fokker-Planck equation with a Monte Carlo method, and has been implemented in such a code. The resulting code has been used for a comparison with experimental data form Tore Supra and for assessing the ripple induced losses in different ICRF heating scenarios.

  • 12. Eriksson, L. -G
    et al.
    Hellsten, Torbjörn A K
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas Joe
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brzozowski, Jerzy H.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Nave, F.
    Ongena, J.
    Zastrow, K. -D
    Simulation of fast ion contribution to toroidal rotation in ICRF heated jet plasmas2008In: EPS Conf. Plasma Phys., EPS - Europhys. Conf. Abstr., 2008, no 3, 1679-1682 p.Conference paper (Refereed)
  • 13. Eriksson, L. G.
    et al.
    Hellsten, Torbjörn A. K.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Nave, M. F. F.
    Brzozowski, Jerzy H.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ongena, J.
    Zastrow, K. D.
    Holmström, K.
    Toroidal rotation in RF heated JET plasmas2009In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, no 4Article in journal (Refereed)
    Abstract [en]

    Observations of bulk plasma rotation in radio frequency (RF) heated JET discharges are reported. This study is concentrated on RF heated L-mode plasmas. In particular, the toroidal rotation profiles in plasmas heated by ion cyclotron resonance frequency (ICRF) waves and lower hybrid (LH) waves have been analysed. It is the first time that rotation profiles in JET plasmas with LH waves have been measured in dedicated discharges. It is found that the toroidal plasma rotation in the outer region of the plasmas is in the co-current direction irrespective of the heating scenario. An interesting feature is that the toroidal rotation profile appears to be hollow in many discharges at low plasma current, but a low current in itself does not seem to be a sufficient condition for finding such profiles. Fast ion transport and finite orbit width effects are mechanisms that could explain hollow rotation profiles. This possibility has been investigated by numerical simulations of the torque on the bulk plasma due to fast ICRF accelerated ions. The obtained torque is used in a transport equation for the toroidal momentum density to estimate the effect on the thermal bulk plasma rotation profile.

  • 14. Eriksson, L. -G
    et al.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Nave, F.
    Brzozowski, Jerzy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ongena, J.
    Zastrow, K. -D
    Toroidal rotation in RF heated JET plasmas2007In: RADIO FREQUENCY POWER IN PLASMAS, 2007, Vol. 933, 59-62 p.Conference paper (Refereed)
    Abstract [en]

    Experiments have been carried out on JET aimed at studying rotation in RF heated plasmas with low external momentum input. Both plasmas with Ion Cyclotron Resonance Frequency (ICRF) heating and Lower Hybrid Current Drive (LHCD) have been investigated. The rotation profiles are measured by Charge Exchange recombination spectroscopy, using short diagnostic Neutral Beam Injection (NBI) pulses. Moreover, the temporal evolution of the central rotation could in some cases be deduced from MHD activity. While most of the measurements were focussed on ICRF heating, the profiles measured in plasmas with LHCD are interesting since they are the first reported from JET in such plasmas. In particular, they allowed for studies of rotation in RF heated plasmas with q>1. The experimental results are presented together with an analysis of the torque from ICRF heated fast ions.

  • 15. Eriksson, L. G.
    et al.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Mayoral, M. L.
    Coda, S.
    Sauter, O.
    Buttery, R. J.
    McDonald, D.
    Hellsten, Torbjörn A. K.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Mantsinen, M. J.
    Mueck, A.
    Noterdaeme, J. M.
    Santala, M.
    Westerhor, E.
    de Vries, P.
    On ion cyclotron current drive for sawtooth control2006In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, no 10, S951-S964 p.Article in journal (Refereed)
    Abstract [en]

    Experiments using ion cyclotron current drive (ICCD) to control sawteeth are presented. In particular, discharges demonstrating shortening of fast ion induced long sawteeth reported in (Eriksson et al 2004 Phys. Rev. Lett. 92 235004) by ICCD have been analysed in detail. Numerical simulations of the ICCD driven currents are shown to be consistent with the experimental observations. They support the hypothesis that an increase in the magnetic shear, due to the driven current, at the surface where the safety factor is unity was the critical factor for the shortening of the sawteeth. In view of the potential utility of ICCD, the mechanisms for the current drive have been further investigated experimentally. This includes the influence of the averaged energy of the resonating ions carrying the current and the spectrum of the launched waves. The results of these experiments are discussed in the light of theoretical considerations.

  • 16. Eriksson, L-G
    et al.
    Johnson, Thomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Hellsten, Torbjörn
    KTH, Superseded Departments, Alfvén Laboratory.
    Giroud, C
    Kiptily, G
    Kirov, K
    Brzozowski, Jerzy H.
    KTH, Superseded Departments, Alfvén Laboratory.
    DeBaar, M
    DeGrassie, J
    Mantsinen, M
    Meigs, A
    Noterdaeme, M
    Staebler, A
    Testa, D
    Tuccillo, A
    Zastrow, D
    Plasma rotation induced by directed waves in the ion-cyclotron range of frequencies2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, no 23Article in journal (Refereed)
    Abstract [en]

    Changes of the toroidal plasma rotation induced by directed waves in the ion-cyclotron range of frequencies (ICRF) have been identified experimentally for the first time on the JET tokamak. The momentum carried by the waves is initially absorbed by fast resonating ions, which subsequently transfer it to the bulk plasma. Thus, the results provide evidence for the influence of ICRF heated fast ions on plasma rotation.

  • 17.
    Hannan, Abdul
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    A Fokker-Planck Code for Fast Self-Consistent Calculations of ICRH2010In: 37th EPS Conference on Plasma Physics, 2010Conference paper (Other academic)
    Abstract [en]

    Modeling of ion cyclotron resonant heating, ICRH, requires self-consistent modeling of the distribution function of the resonant ion species and the wave field. A method has been devised for fast self-consistent calculation of the distribution function and the wave field for ICRH modeling. The distribution function is obtained by solving a pitch angle averaged 1D time dependent Fokker Planck equation that includes the Coulomb collision and quasi-linear operators. The quasi-linear operators describing the wave-particle interactions are obtained from the LION code [1]. The time dependent 1D Fokker-Planck equation solved with a cubic finite element method will be presented in this report. The modifications of the susceptibility tensors of the resonant ion species due to changes of the distribution functions caused by heating are calculated by the Fokker-Planck solver and then used in the LION code for calculating the modified wave field

  • 18.
    Hannan, Abdul
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Fast wave current drive scenarios for DEMO2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 4, 043005- p.Article in journal (Refereed)
    Abstract [en]

    Scenarios for non-inductive current drive using the fast magnetosonic wave in the ion cyclotron range of frequencies in DEMO have been studied. The strong ion cyclotron damping and large Doppler broadening of the alpha particles are shown to limit the possible current drive scenarios to four frequency bands. However, these scenarios may be compromised in the presence of impurities with unfavourable charge to mass ratio. For each frequency the current drive efficiency is optimized with respect to the parallel wave number. The optimized current drive efficiencies are comparable to that from neutral beam injection and electron cyclotron heating, and thus the ion cyclotron range of frequencies should remain a candidate for driving the non-inductive current in DEMO.

  • 19.
    Hannan, Abdul
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    On fast wave current drive at higher cyclotron harmonics2011In: 38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts: Volume 35 1, 2011, 889-892 p.Conference paper (Other academic)
  • 20.
    Hannan, Abdul
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Self-consistent Ion Cyclotron Resonant Heating and Fast Wave Current Drive for DEMOArticle in journal (Other academic)
  • 21. Hedin, J.
    et al.
    Hellsten, Torbjörn A. K.
    KTH, Superseded Departments, Alfvén Laboratory.
    Eriksson, L. G.
    The influence of non-standard orbits on ICRH power deposition in tokamaks2000In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 40, no 11, 1819-1824 p.Article in journal (Refereed)
    Abstract [en]

    The distribution function and power deposition during ICRH in a tokamak plasma are analysed. The importance of self-consistent calculations and the formation of son-standard drift orbits are addressed. It is found that for high power ICRH, the presence of non-standard orbits are crucial for describing the distribution function. For a standard minority heating scenario with the ion cyclotron resonance located at the high field side, the absorption of the wave power is shifted to the low field side (LFS) because of the orbit topology and the evolving wave field profile. The high energy tail of the distribution function of the resonating ions is found to be dominated by ions in passing orbits, of which some reside completely on the LFS of the tokamak.

  • 22. Hedin, J.
    et al.
    Hellsten, Torbjörn A. K.
    KTH, Superseded Departments, Alfvén Laboratory.
    Eriksson, L. G.
    Johnson, Thomas J.
    KTH, Superseded Departments, Alfvén Laboratory.
    The influence of finite drift orbit width on ICRF heating in toroidal plasmas2002In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 42, no 5, 527-540 p.Article in journal (Refereed)
    Abstract [en]

    Ion cyclotron resonance heating in a toroidal plasma not only increases the perpendicular energy of the resonating ions but also results in their spatial transport. Depending on the direction of propagation of the waves, the ions will either drift inwards or outwards giving rise to an RF induced rotation with the toroidal torque component in the co-current or counter-current directions, respectively. It is found that the spatial transport induced by the RF field, the topology of the ion drift orbits and a wave field consistent with ion absorption are important for determining the distribution function of the heated species. Studies of ICRF heating with the self-consistent code SELFO reveal new features such as the formation of non-standard passing orbits residing on the low field side of the magnetic axis. For a symmetric spectrum the drift terms will in general not cancel. Some classes of orbit will be subjected only to an inward drift and others only to an outward drift. The lack of cancellation of the drift terms is further enhanced by the self-consistent coupling, increasing the absorption for waves propagating parallel to the plasma current, but not for waves propagating in the antiparallel direction. This results in a strong inward pinch also for symmetric wave spectra as well as for typical experimental spectra, with the dominant peak in the counter-plasma-direction.

  • 23.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    A statistical model of the wave field in a bounded domain2017In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 24, no 2, 022122Article in journal (Refereed)
    Abstract [en]

    Numerical simulations of plasma heating with radiofrequency waves often require repetitive calculations of wave fields as the plasma evolves. To enable effective simulations, bench marked formulas of the power deposition have been developed. Here, a statistical model applicable to waves with short wavelengths is presented, which gives the expected amplitude of the wave field as a superposition of four wave fields with weight coefficients depending on the single pass damping, as. The weight coefficient for the wave field coherent with that calculated in the absence of reflection agrees with the coefficient for strong single pass damping of an earlier developed heuristic model, for which the weight coefficients were obtained empirically using a full wave code to calculate the wave field and power deposition. Antennas launching electromagnetic waves into bounded domains are often designed to produce localised wave fields and power depositions in the limit of strong single pass damping. The reflection of the waves changes the coupling that partly destroys the localisation of the wave field, which explains the apparent paradox arising from the earlier developed heuristic formula that only a fraction a(s)(2)(2-a(s)) and not as of the power is absorbed with a profile corresponding to the power deposition for the first pass of the rays. A method to account for the change in the coupling spectrum caused by reflection for modelling the wave field with ray tracing in bounded media is proposed, which should be applicable to wave propagation in non-uniform media in more general geometries.

  • 24.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Integrated Modelling of Heating, Current Drive and Fast Particle Physics2007In: IAEA Technical Meeting on Fast Particles, 2007Conference paper (Other academic)
  • 25.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Momentum transport by wave-particle interaction2011In: PLASMA PHYS CONTROL FUSION, 2011, Vol. 53, no 5, 054007- p.Conference paper (Refereed)
    Abstract [en]

    Energy and momentum can be transported across the plasma by waves emitted at one place and absorbed at another. Exchange of momentum and energy between the particles and the waves change the drift orbits, which may give rise to a non-ambipolar particle transport. The main effect of the non-ambipolar transport and quasi-neutrality is a toroidal precession of the trapped particles, which together with the changes in the parallel velocities of the passing resonant particles conserve the toroidal momentum. Non-resonant interactions can give rise to a net change of the local wave number in spatial inhomogeneous plasmas with a resulting force on the medium. Both resonant and non-resonant interactions have to be taken into account in order to have a consistent description of the momentum transported by the waves. The momentum transfer is, in particular, important for waves with short wave length and low frequency, and may explain the enhanced rotation seen in some mode conversion experiments, when the fast magnetosonic wave is converted to an ion-cyclotron wave. The apparent contradiction that the wave momentum may change due to non-resonant wave-particle interactions without changing the energy in geometric optics is explained.

  • 26.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    On self-consistent modelling of energetic particles generated by auxiliary heating and associated instabilities2006Conference paper (Other academic)
  • 27.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rotation Driven by Rectified RF-sheath Potentials and Spatial Dispersion2009In: RADIO FREQUENCY POWER IN PLASMAS, 2009, Vol. 1187, 625-628 p.Conference paper (Refereed)
    Abstract [en]

    Plasma rotation is of interest for improving confinement and stabilising plasma. Effects from fast particles with broad orbits can only partly explain the changes in the rotation profiles during ICRH. The effect on wave-particle interaction of a finite poloidal mode number is discussed and two new RF-mechanisms are proposed: Co-current torque caused by sputtering by rectified RF-sheath potentials and transport of momentum due to spatial dispersion. The latter effect affects the RF-current drive, in particular, in conjunction with mode conversion.

  • 28.
    Hellsten, Torbjörn A. K.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergkvist, Tommy
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    On ion cyclotron emission in toroidal plasmas2006In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, no 7, S442-S454 p.Article in journal (Refereed)
    Abstract [en]

    A detailed study of ion cyclotron interactions in a toroidal plasma has been carried out in order to elucidate the role of toroidal effects on ion cyclotron emission. It is well known that non-relaxed distribution functions can give rise to excitation of magnetosonic waves by ion cyclotron interactions when the distribution function increases with respect to the perpendicular velocity. We have extended and clarified the conditions under which even collisionally relaxed distribution function can destabilize magnetosonic eigenmodes. In a toroidal plasma, cyclotron interactions at the plasma boundary with ions having barely co-current passing orbits and marginally trapped orbits can cause destabilisation by the strong inversion of the distribution function along the characteristics of cyclotron interaction by neo-classical effects. The unstable interactions can further be enhanced by tangential interactions, which can also prevent the interactions from reaching the stable part of the characteristics, where they interact with trapped orbits. Conditions on the localization of the magnetosonic eigenmodes for unstable excitation are analysed by studying the anti-Hermitian part of the susceptibility tensor of thermonuclear alpha-particles. The pattern of positive and negative regions of the anti-Hermitian part of the susceptibility tensor of thermonuclear alpha-particles is, in general, consistent with the excitation of edge localized magnetosonic eigenmodes, even though the eigenmodes are usually not localized in the major radius and for distribution functions that have relaxed to steady state.

  • 29.
    Hellsten, Torbjörn A K
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Johnson, Thomas Joe
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    A model collision operator for orbit averaged Monte Carlo codes2006In: AIP Conf. Proc., 2006, 362-367 p.Conference paper (Refereed)
    Abstract [en]

    Modelling of fast ion populations, e.g. during ion cyclotron resonance heating, requires accurate treatment of both the fast ions and the thermal populations, while retaining the effects of wide guiding centre orbits. Often the ion-ion collisions are modelled as test particles colliding against a Maxwellian background. However, this type of operator generates a transport of thermal ions on the time scale of ion-ion collisions, and not on the ion-electron time scale as suggested by neoclassical theory. Various approaches have been made to correct this defect. Here we introduce a radial electric field so that the friction between the trapped and passing ions balances the diffusion due to ion-ion collisions.

  • 30.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergkvist, Tommy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Effects of Finite Orbit Width and RF-Induced Spatial Diffusion on Ion Cyclotron Emission2005In: Radio Frequency Power in Plasmas: 16th Topical Conference on Radio Frequency Power in Plasmas / [ed] S. J. Wukitch and P. T. Bonoli, Melville, New York: AIP Conference Proceedings , 2005, 50-53 p.Conference paper (Refereed)
    Abstract [en]

    The theory of ion cyclotron emission, ICE, in tokamak plasmas has been revised by including the effects of finite orbit width and RF-induced spatial transport in the wave-particle interactions. Two mechanisms for excitation of edge localised magnetosonic modes are discussed. An inverted distribution function of suprathermal ions near the plasma edge is driving the modes. Counter current propagating waves can be excited by interacting with barely co passing ions. Co current propagating waves interacting at the inner leg only can drive the modes unstable by throwing the fast ions out of the plasma.

  • 31.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergkvist, Tommy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Integrated Modelling of ICRH and AE Dynamics2005In: IEA Burning Plasma Workshop, 2005Conference paper (Other academic)
  • 32.
    Hellsten, Torbjörn
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Bergkvist, Tommy
    KTH, Superseded Departments, Alfvén Laboratory.
    Johnson, Thomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Laxåback, Martin
    KTH, Superseded Departments, Alfvén Laboratory.
    Non-linear study of fast particle excitation of global Alfvén eigenmodes during ICRH2004In: Proceedings 20th IAEA Fusion Energy Conference, 2004Conference paper (Refereed)
  • 33.
    Hellsten, Torbjörn
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Bergkvist, Tommy
    Johnson, Thomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Laxåback, Martin
    KTH, Superseded Departments, Alfvén Laboratory.
    Self-consistent calculations of ion distribution function during ICRH in the presence of AE2004In: European Fusion Workshop, 2004Conference paper (Refereed)
  • 34.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hannan, Abdul
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Eriksson, L. -G
    Höök, Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Villard, L.
    On Self-Consistent ICRH ModellingArticle in journal (Other academic)
  • 35.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hannan, Abdul
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Eriksson, L. -G
    Höök, Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Villard, L.
    Self-consistent ICRH modelling2012In: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 2, 2012, 2012, 1106-1109 p.Conference paper (Refereed)
  • 36.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hannan, Abdul
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Eriksson, L. -G
    Höök, Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Villard, L.
    Self-Consistent ICRH Modelling2011In: RADIO FREQUENCY POWER IN PLASMAS: PROCEEDINGS OF THE 19TH TOPICAL CONFERENCE, 2011, 365-368 p.Conference paper (Refereed)
    Abstract [en]

    A new code for self-consistent modelling of ion cyclotron heating suitable for routine calculations has been developed.

  • 37.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hannan, Abdul
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Eriksson, L-G
    Höök, Lars Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Villard, L.
    A model for self-consistent simulation of ICRH suitable for integrating modelling2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 9, 093004- p.Article in journal (Refereed)
    Abstract [en]

    A self-consistent modelling of ion cyclotron resonance heating (ICRH) is reviewed with the aim of obtaining a fast robust scheme suitable for routine simulation for transport codes and data analysis. Due to the complexity of calculating the wave field and the distribution function self-consistently simplifications are necessary. To improve modelling of the wave field, methods are developed to include higher order finite Larmor radius terms, up-and downshifts of the parallel wave number and to improve calculations of damping due to the transit time magnetic pumping in finite element wave codes without decomposing the wave locally into planar waves. A new code, SELFO-light, for self-consistent modelling of ion cyclotron heating suitable for routine calculations is developed. The code is based on coupling the global wave code LION with a simple one-dimensional time-dependent Fokker-Planck code. Both the wave and the Fokker-Planck codes use finite element representations. The importance of self-consistent modelling of ion cyclotron heating is illustrated by studying the effect on the power partition for a fast wave current drive scenario at lower harmonic resonances in a deuterium plasma. It is found that the fraction of the power absorbed on the deuterium and the time to reach the steady state vary strongly depending on the position of the resonances. It is found that the deuterium absorption becomes strongly localized to regions where the resonances are tangential to the magnetic flux surfaces.

  • 38.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hannan, Abdul
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Höök, Lars Josef
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Villard, L.
    A dielectric response model for FEM solutions of ICRF wave fields2012In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 401, no 1, 012009- p.Article in journal (Refereed)
    Abstract [en]

    Modelling of fast wave ICRF heating in large machines with high density such as DEMO is challenging because of the short wave lengths. Therefore, fast, efficient global wave solvers are necessary. A major difficulty with calculating the wave field in a spatial dispersive medium is that the dielectric tensor becomes a function of the local wave vector, which in its turn depends on the solution. Furthermore, the solution may consist of several waves co-existing at the same location subjected to separate response functions. In order to model upshift of the parallel wave vector, higher order FLR-effects on the cyclotron absorption and TTMP damping for the electron absorption methods based on iteration, suitable for FEM codes, are proposed.

  • 39.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Holmström, Kerstin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Tomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergkvist, Tommy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    ICE in toroidal plasmas2005In: IAEA Technical Meeting on Fast Particles, 2005Conference paper (Other academic)
  • 40.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Neoclassical Electric Field in Presence of Large Gradients and Particle Losses2008In: 35th EPS Conference on Plasma Physics 2008, EPS 2008 - Europhysics Conference Abstracts: Volume 32, Issue 3, 2008, 1847-1850 p.Conference paper (Other academic)
  • 41.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    On Current Drive and Wave Induced Bootstrap Current in Toroidal Plasmas2008In: Theory of Fusion Plasmas: Joint Varenna - Lausanne International Workshop, Melville, New York, USA: AMER INST PHYSICS , 2008, 88-99 p.Conference paper (Other academic)
    Abstract [en]

    A comprehensive treatment of wave-particle interactions in toroidal plasmas including collisional relaxation. applicable to heating or anomalous wave induced transport, has been obtained by using Monte Carlo operators satisfying quasi-neutrality. This approach enables a self-consistent treatment of wave-particle interactions applicable to the banana regime in the neoclassical theory. It allows an extension into a regime with large temperature and density gradients, losses and transport of particles by wave-particle interactions making the method applicable to transport barriers. It is found that at large gradients the relationship between radial electric field, parallel velocity, temperature and density gradient in the neoclassical theory is modified such that coefficient in front of the logarithmic ion temperature gradient, which in the standard neoclassical theory is small and counteracts the electric field caused by the density gradient, now changes sign and contributes to the built up of the radial electric field. The Possibility to drive current by absorbing the waves on trapped particles has been studied and flow the wave-particle interactions affect the bootstrap current. Two new current drive mechanisms are studied: current drive by wave induced bootstrap current and selective detrapping into passing orbits by directed waves.

  • 42.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Self-Consistent ICRH Modelling2014In: Radiofrequency power in plasmas, 2014, Vol. 1580, 295-297 p.Conference paper (Refereed)
    Abstract [en]

    Self-consistent modelling of ICRH requires calculations of the wave field consistent with the distribution function of the resonant species. Because of the difference in time scales for wave propagation and the evolution of distribution functions this is commonly done by iterations. A robust code SELFO-light, suitable for routine calculations was recently developed, based on coupling a 1D time dependent Fokker-Planck code with the global wave solver LION using a FEM. Here the structure of an upgraded version of the SELFO-light code is presented calculating the distribution function with a 2D Fokker-Planck code. This requires new interfaces calculating the quasi-linear diffusion coefficient from the wave field and the susceptibility tensor from distribution functions.

  • 43.
    Hellsten, Torbjörn
    et al.
    KTH, Superseded Departments, Alfvén Laboratory.
    Johnson, Thomas
    KTH, Superseded Departments, Alfvén Laboratory.
    Carlsson, J.
    Eriksson, L.-G.
    Hedin, J.
    KTH, Superseded Departments, Alfvén Laboratory.
    Laxåback, Martin
    KTH, Superseded Departments, Alfvén Laboratory.
    Mantsinen, M.
    Effects of finite drift orbit width and RF-induced spatial transport on plasma heated by ICRH2004In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 44, no 8, 892-908 p.Article in journal (Refereed)
    Abstract [en]

    The effects of RF-induced transport and orbit topology of resonant ions are analysed for high power ion cyclotron resonance heating (ICRH). These effects are found to play important roles in the details of the high-energy part of the distribution function, and affect the driven current and momentum transfer to the background plasma. The finite drift orbit width broadens the power deposition and leads to losses of high-energy ions intercepted by the wall. RF-induced transport of resonant ions across magnetic flux surfaces appears due to the toroidal acceleration of resonant ions interacting with waves having a finite toroidal mode number. Heating with waves propagating parallel to the current leads to a drift of the turning points of trapped resonant ions towards the midplane. As the turning points meet, the orbits will de-trap, preferentially into co-current passing orbits, which may ultimately be displaced to the low field side of the magnetic axis. Ions with such orbits are a typical feature in plasmas heated with directed toroidal mode spectra of waves propagating parallel to the plasma current. These ions will be subjected to a strong RF diffusion partly caused by the focusing of the wave field and partly by the Doppler shifted cyclotron resonance, as it approaches tangency with the drift orbit. The resonance condition puts a limitation on the achievable energy for these ions, which is more severe than for corresponding trapped ions. This results in a rather flat tail up to a critical energy, above which the tail rapidly decays. Heating with waves propagating anti-parallel with the plasma current curtails the energy of the trapped ions due to a vertical outward drift of the turning points of the trapped ions. Heating with symmetric spectra, in particular with waves with low magnitude of the toroidal mode numbers, gives rise to high-energy trapped ions with wide orbits, of which the maximum energy is either restricted by the fact that the RF diffusion vanishes due to cancellation of the perpendicular acceleration over a gyro orbit or by the drift orbits being intercepted by the wall. In the steady state the main source for momentum transfer to the bulk plasma comes from the finite momentum of the wave for heating with asymmetric spectra. For heating with symmetric spectra the enhanced losses of high-energy trapped ions can produce a net counter-current torque on the plasma.

  • 44.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Van Eester, D.
    Lerche, E.
    Lin, Y.
    Mayoral, M-L
    Ongena, J.
    Calabro, G.
    Crombe, K.
    Frigione, D.
    Giroud, C.
    Lennholm, M.
    Mantica, P.
    Nave, M. F. F.
    Naulin, V.
    Sozzi, C.
    Studholme, W.
    Tala, T.
    Versloot, T.
    Observations of rotation in JET plasmas with electron heating by ion cyclotron resonance heating2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 7, 074007- p.Article in journal (Refereed)
    Abstract [en]

    The rotation of L-mode plasmas in the JET tokamak heated by waves in the ion cyclotron range of frequencies (ICRF) damped on electrons, is reported. The plasma in the core is found to rotate in the counter-current direction with a high shear and in the outer part of the plasma with an almost constant angular rotation. The core rotation is stronger in magnitude than observed for scenarios with dominating ion cyclotron absorption. Two scenarios are considered: the inverted mode conversion scenarios and heating at the second harmonic He-3 cyclotron resonance in H plasmas. In the latter case, electron absorption of the fast magnetosonic wave by transit time magnetic pumping and electron Landau damping (TTMP/ELD) is the dominating absorption mechanism. Inverted mode conversion is done in (He-3)-H plasmas where the mode converted waves are essentially absorbed by electron Landau damping. Similar rotation profiles are seen when heating at the second harmonic cyclotron frequency of He-3 and with mode conversion at high concentrations of He-3. The magnitude of the counter-rotation is found to decrease with an increasing plasma current. The correlation of the rotation with the electron temperature is better than with coupled power, indicating that for these types of discharges the dominating mechanism for the rotation is related to indirect effects of electron heat transport, rather than to direct effects of ICRF heating. There is no conclusive evidence that mode conversion in itself affects rotation for these discharges.

  • 45.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Sharapov, S. E.
    Kiptily, V.
    Eriksson, J.
    Mantsinen, M.
    Schneider, M.
    Rimini, F.
    Tsalas, M.
    RF Heating for Fusion Product Studies2015In: RADIOFREQUENCY POWER IN PLASMAS, American Institute of Physics (AIP), 2015, UNSP 060007Conference paper (Refereed)
    Abstract [en]

    Third harmonic cyclotron heating is an effective tool for accelerating deuterium (D) beams to the MeV energy range, suitable for studying ITER relevant fast particle physics in plasmas without significant tritium content. Such experiments were recently conducted in JET with an ITER like wall in D plasmas with He-3 concentrations up to 30% in order to boost the fusion reactivity by D-He-3 reactions. The harmonic cyclotron heating produces high-energy tails in the MeV range of D ions by on-axis heating and of He-3 ions by tangential off-axis heating. The discharges are characterized by long sawtooth free periods and a rich spectrum of MHD modes excited by the fast D and He-3 ions. The partitions of the power, which depend on the distribution function of D, vary strongly over several slowing down times. Self-consistent modelling of the distribution function with the SELFO-light code are presented and compared with experimental data from fast particle diagnostics.

  • 46.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    An iterative method for including Doppler shift in global wave solvers using FEM decomposition2014In: Journal of Physics: Conference series, ISSN 1742-6596, Vol. 561Article in journal (Refereed)
    Abstract [en]

    A method for calculating the wave field for spatial dispersive media is proposed suitable for FEM. The method is based on operator splitting by separating the induced current and wave field calculations, and solving the system by means of iterations. In order to take into account several coexisting waves with different poloidal mode numbers when calculating the induced current the wave field is decomposed into wavelets, for which the current is calculated assuming the plasma to be weakly non-uniform.

  • 47.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Influence of coupling to spectra of weakly damped eigenmodes in the ion cyclotron range of frequencies on parasitic absorption in rectified radio frequency sheaths2005In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 12, no 3Article in journal (Refereed)
  • 48. Hellsten, Torbjörn
    et al.
    Laxåback, Martin
    Bergkvist, T.
    Johnson, Thomas J.
    Mantsinen, M.
    Matthews, G.
    Meo, F.
    Nguyen, F.
    Noterdaeme, J. -M
    Petty, C. C.
    Tala, T.
    Van Eester, D.
    Andrew, P.
    Beaumont, P.
    Bobkov, V.
    Brix, M.
    Brzozowski, J.
    Eriksson, L. -G
    Giroud, C.
    Joffrin, E.
    Kiptily, V.
    Mailloux, J.
    Mayoral, M. -L
    Monakhov, I.
    Sartori, R.
    Staebler, A.
    Rachlew, E.
    Tennfors, E.
    Tuccillo, A.
    Walden, A.
    Zastrow, K. -D
    Fast wave current drive in JET ITB-plasma2005In: AIP Conference Proceedings, 2005, Vol. 787, 273-278 p.Conference paper (Refereed)
    Abstract [en]

    Fast wave current drive has been performed in JET plasmas with internal transport barriers, ITBs, and strongly reversed magnetic shear. Although the current drive efficiency of the power absorbed on the electrons is fairly high, only small effects are seen in the central current density. The main reasons are the parasitic absorption of RF power, the strongly inductive nature of the plasma and the interplay between the fast wave driven current and bootstrap current. The direct electron heating in the FWCD experiments is found to be strongly degraded compared to that with the dipole phasing.

  • 49.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergkvist, Thomas
    KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Johnson, T
    Meo, F
    Nguyen, F
    Petty, C
    Mantsinen, M
    Matthews, G
    Noterdaeme, M
    Tala, T
    Van Eester, D
    Andrew, P
    Beaumont, P
    Bobkov, V
    Brix, M
    Brzozowski, J
    Eriksson, G
    Giroud, C
    Joffrin, E
    Kiptily, V
    Mailloux, J
    Mayoral, L
    Monakhov, I
    Sartori, R
    Staebler, A
    Rachlew, E
    Tennfors, E
    Tuccillo, A
    Walden, A
    Zastrow, D
    On the parasitic absorption in FWCD experiments in JET ITB plasmas2005In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, no 7, 706-720 p.Article in journal (Refereed)
  • 50.
    Hellsten, Torbjörn
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Laxåback, Martin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergkvist, Tommy
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zastrow, K.-D.
    et, al
    Fast Wave Current Drive and Direct Electron Heating in JET ITB Plasmas2006In: Proc 21st IAEA Fusion Energy Conference, 2006Conference paper (Refereed)
    Abstract [en]

    Experiments with Fast Wave Current Drive, FWCD, and heating have been carried out in JET Internal Transport Barrier (ITB) discharges with strongly reversed magnetic shear. In order to maximize the current drive efficiency and increase the electron damping, and at the same time modifying the current profile in the transport barrier, hot low density ITB plasmas with strongly reversed magnetic shear, close to current hole, were created with Lower Hybrid Current Drive. It was difficult to strongly modify the central plasma current, even though the calculated current drive efficiency in terms of ampere per watts absorbed by the electrons was fairly high, 0.07A/W, because of: the strongly inductive nature of the plasma current due to the high electric conductivity; the interplay between the fast wave driven current and the bootstrap current, which, due to the dependence of the bootstrap current on the poloidal magnetic field, decreases the bootstrap current as the driven current increases; and parasitic absorption of the waves that decreased the power absorbed by the electrons. The power absorbed by the electrons was measured with a power modulation technique and the associated fast wave current drive calculated. Current diffusion simulations using the JETTO transport code, assuming neoclassical resistivity, were then carried out to calculate what changes to the plasma current profile could be expected from the current drive. The simulations showed a much slower response to the current drive compared to the measured central current densities suggesting a faster current penetration in the experiments than expected from neoclassical theory. Whereas the direct electron heating by fast magnetosonic waves using dipole spectra has proven to be an effective method to heat electrons in high-temperature ITB plasmas, even for a single pass damping of only a few percent, the heating in FWCD experiments with + 90o and - 90o antenna phasings were, for similar single pass damping as for the dipole, strongly degraded by parasitic losses, and with a heating efficiency of about half that of the dipole. Observations supporting that the losses are primarily caused by the presence of rectified RF-sheath potentials come from the large differences in performance and in Beryllium-II and Carbon-IV line radiation intensities between the dipole and ±90o phasings.

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