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  • 151.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    Electron Temperature Determination from the He I 3889Å and 5016Å Line Intensities1979Rapport (Övrigt vetenskapligt)
  • 152.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    Electron Temperature Measurements in Low Density Plasmas by Helium Spectroscopy1977Rapport (Övrigt vetenskapligt)
  • 153.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    Electron temperature measurements in low density plasmas by helium spectroscopy II - parameter limits for validity of different methods1978Rapport (Övrigt vetenskapligt)
  • 154.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    Experiments on the Critical Ionization Velocity Interaction in Weak Magnetic Fields1980Rapport (Övrigt vetenskapligt)
  • 155.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    "Horizontal" Thermal Equilibrium due to Excitation Transfer Between Excited States of Neutral He in Transient Plasma1978Rapport (Övrigt vetenskapligt)
  • 156.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    On the Role of the Ionization Frequency to Gyrofrequency Ratio in the Critical Ionization Velocity Interaction1986Rapport (Övrigt vetenskapligt)
  • 157.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    On the Role of the Magnetic Field Strength in Critical Ionization Velocity Interaction1985Rapport (Övrigt vetenskapligt)
  • 158.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    On the Spoke Structure in Critical Velocity Rotating Plasmas1989Rapport (Övrigt vetenskapligt)
  • 159.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    Review of Impact Experiments on the Critical Ionization Velocity1982Rapport (Övrigt vetenskapligt)
  • 160.
    Brenning, Nils
    KTH, Tidigare Institutioner.
    Testing a Very Good Microwave Interferometer1986Rapport (Övrigt vetenskapligt)
  • 161.
    Brenning, Nils
    et al.
    KTH, Tidigare Institutioner.
    Bohm, Martin
    KTH, Tidigare Institutioner.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner.
    Dynamic Trapping of Electrons in Space Plasmas1989Rapport (Övrigt vetenskapligt)
  • 162.
    Brenning, Nils
    et al.
    KTH, Tidigare Institutioner.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner.
    Bohm, Martin
    KTH, Tidigare Institutioner.
    An Extension of the Boltzmann Relation to Collisionless Magnetized Plasma1990Rapport (Övrigt vetenskapligt)
  • 163.
    Brenning, Nils
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Haerendel, G.
    Kelley, M.C.
    Marklund, Göran
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Pfaff, R.
    Providakes, J.
    Stenbaek-Nielsen, H.C.
    Swenson, C.
    Torbert, R.
    Wescott, E.M.
    Interpretation of the Electric Fields Measured in an Ionospheric Critical Ionization Velocity Experiment1991Ingår i: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 96, s. 9719-9733Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper deals with the quasi-dc electric fields measured in the CRIT I ionospheric release experiment, which was launched from Wallops Island on May 13, 1986. The purpose of the experiment was to study the critical ionization velocity (CIV) mechanism in the ionosphere. Two identical barium shaped charges were fired from distances of 1.99 km and 4.34 km towards a main payload, which made full three-dimensional measurements of the electric field inside the streams. There was also a subpayload separated from the main payload by a couple of kilometers along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in CIV is investigated in the light of the CRIT I results. It is concluded that both the “homogeneous” and the “ionizing front” models probably apply, but in different parts of the stream. It is also possible that electrons are directly accelerated by a magnetic-field-aligned component of the electric field; the quasi-dc electric field observed within the streams had a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. The coupling between the ambient ionosphere and the ionized barium stream in CRIT I was more complicated than is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes. One interpretation of the quasi-dc electric field data is that the internal electric fields of the streams were not greatly modified by magnetic-field-aligned currents, i.e., a state was established where the transverse currents were to a first approximation divergence-free. It is argued that this interpretation can explain both a reversal of the strong explosion-directed electric field in burst 1 and the absence of such a reversal in burst 2.

  • 164.
    Brenning, Nils
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Haerendel, G.
    Kelley, M.C.
    Marklund, Göran
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Pfaff, R.
    Providakes, J.
    Stenbaek-Nielsen, H.C.
    Swenson, C.
    Torbert, R.B.
    Wescott, E.M.
    Critical ionization velocity interaction in the CRIT I rocket experiment1990Ingår i: Advances in Space Research, ISSN 02731177, Vol. 10, s. 63-66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the rocket experiment CRIT I, launched from Wallops Island on 13 May 1986, two identical Barium shaped charges were fired from distances of 1.3 km and 3.6 km towards the main experiment payload, which was separated from a sub-payload by a couple of km along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in ionospheric critical velocity experiments is investigated in the light of the CRIT I results. It is concluded that both the "homogeneous" and the "ionizing front" models can be applied, in different parts of the stream. It is also possible that a third, entirely different, mechanism may contribute to the electron heating. This mechanism involves direct energization of electrons in the magnetic-field-aligned component of the DC electric field. © 1989.

  • 165.
    Brenning, Nils
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Fälthammar, Carl-Gunne
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Haerendel, G.
    Kelley, M.C.
    Marklund, Göran
    KTH, Tidigare Institutioner, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Pfaff, R.
    Providakes, J.
    Stenbaek-Nielsen, H.C.
    Swenson, C.
    Wescott, E.M.
    Electrodynamic interaction between the CRIT I ionized barium streams and the ambient ionosphere1990Ingår i: Advances in Space Research, ISSN 02731177, Vol. 10, s. 67-70Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the CRIT I Critical Velocity experiment, launched from Wallops Island on 13 May, 1986, two fast barium streams were ejected by means of shaped charges. Their electrodynamic interaction with the ambient ionosphere is discussed. An outstanding feature of the DC electric field observed within the streams was a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. One interpretation of the DC electric field data is that the internal electric fields of the streams is not greatly modified by Birkeland currents, i.e. a state is established, where the transverse currents are to a first approximation divergence-free. It is argued that this interpretation can explain why a reversal of the strong explosion-directed electric field was observed in the first explosion but not in the second (more distant one). © 1989.

  • 166.
    Brenning, Nils
    et al.
    KTH, Tidigare Institutioner.
    Lindberg, Lennart
    KTH, Tidigare Institutioner.
    Eriksson, A.
    Energization of Electrons in a Plasma Beam Entering a Curved Magnetic Field1980Rapport (Övrigt vetenskapligt)
  • 167.
    Brenning, Nils
    et al.
    KTH, Tidigare Institutioner.
    Swenson, C.
    Kelley, M. C.
    Providakes, J.
    Torbert, R.
    The Collective Gyration of a Heavy Ion Cloud in a Magnetized Plasma1990Rapport (Övrigt vetenskapligt)
  • 168. Brezinsek, S.
    et al.
    Fundamenski, W.
    Eich, T.
    Coad, J. P.
    Giroud, C.
    Huber, A.
    Jachmich, S.
    Joffrin, E.
    Krieger, K.
    McCormick, K.
    Lehnen, M.
    Loarer, T.
    de la Luna, E.
    Maddison, G.
    Matthews, G. F.
    Mertens, Ph.
    Nunes, I.
    Philipps, V.
    Riccardo, V.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stamp, M. F.
    Tsalas, M.
    Overview of experimental preparation for the ITER-Like Wall at JET2011Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, nr 1, s. S936-S942Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments in JET with carbon-based plasma-facing components have been carried out in preparation of the ITER-Like Wall with beryllium main chamber and full tungsten divertor. The preparatory work was twofold: (i) development of techniques, which ensure safe operation with the new wall and (ii) provision of reference plasmas, which allow a comparison of operation with carbon and metallic wall. (i) Compatibility with the W divertor with respect to energy loads could be achieved in N-2 seeded plasmas at high densities and low temperatures, finally approaching partial detachment, with only moderate confinement reduction of 10%. Strike-point sweeping increases the operational space further by re-distributing the load over several components. (ii) Be and C migration to the divertor has been documented with spectroscopy and QMBs under different plasma conditions providing a database which will allow a comparison of the material transport to remote areas with metallic walls. Fuel retention rates of 1.0-2.0 x 10(21) D s(-1) were obtained as references in accompanied gas balance studies.

  • 169. Brezinsek, S.
    et al.
    Widdowson, A.
    Mayer, M.
    Philipps, V.
    Baron-Wiechec, P.
    Coenen, J. W.
    Heinola, K.
    Huber, A.
    Likonen, J.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stamp, M. F.
    Borodin, D.
    Coad, J. P.
    Carrasco, Alvaro Garcia
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kirschner, A.
    Krat, S.
    Krieger, K.
    Lipschultz, B.
    Linsmeier, Ch.
    Matthews, G. F.
    Schmid, K.
    Beryllium migration in JET ITER-like wall plasmas2015Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 6, artikel-id 063021Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    JET is used as a test bed for ITER, to investigate beryllium migration which connects the lifetime of first-wall components under erosion with tokamak safety, in relation to long-term fuel retention. The (i) limiter and the (ii) divertor configurations have been studied in JET-ILW (JET with a Be first wall and W divertor), and compared with those for the former JET-C (JET with carbon-based plasma-facing components (PFCs)). (i) For the limiter configuration, the Be gross erosion at the contact point was determined in situ by spectroscopy as between 4% (E-in = 35 eV) and more than 100%, caused by Be self-sputtering (E-in = 200 eV). Chemically assisted physical sputtering via BeD release has been identified to contribute to the effective Be sputtering yield, i.e. at E-in = 75 eV, erosion was enhanced by about 1/3 with respect to the bare physical sputtering case. An effective gross yield of 10% is on average representative for limiter plasma conditions, whereas a factor of 2 difference between the gross erosion and net erosion, determined by post-mortem analysis, was found. The primary impurity source in the limiter configuration in JET-ILW is only 25% higher (in weight) than that for the JET-C case. The main fraction of eroded Be stays within the main chamber. (ii) For the divertor configuration, neutral Be and BeD from physically and chemically assisted physical sputtering by charge exchange neutrals and residual ion flux at the recessed wall enter the plasma, ionize and are transported by scrape-off layer flows towards the inner divertor where significant net deposition takes place. The amount of Be eroded at the first wall (21 g) and the Be amount deposited in the inner divertor (28 g) are in fair agreement, though the balancing is as yet incomplete due to the limited analysis of PFCs. The primary impurity source in the JET-ILW is a factor of 5.3 less in comparison with that for JET-C, resulting in lower divertor material deposition, by more than one order of magnitude. Within the divertor, Be performs far fewer re-erosion and transport steps than C due to an energetic threshold for Be sputtering, and inhibits as a result of this the transport to the divertor floor and the pump duct entrance. The target plates in the JET-ILW inner divertor represent at the strike line a permanent net erosion zone, in contrast to the net deposition zone in JET-C with thick carbon deposits on the CFC (carbon-fibre composite) plates. The Be migration identified is consistent with the observed low long-term fuel retention and dust production with the JET-ILW.

  • 170. Brezinsek, Sebastijan
    et al.
    Wirtz, Marius
    Dorrow-Gesprach, Daniel
    Loewenhoff, Thorsten
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    16th International Conference on Plasma-Facing Materials and Components for Fusion Applications2017Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikel-id 010201Artikel i tidskrift (Refereegranskat)
  • 171.
    Brunsell, P
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Cecconello, M
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Drake, J R
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, J-A
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Franz, P
    Martin, P
    Marrelli, L
    Piovesan, P
    Spizzo, G
    Quasi Single Helicity in EXTRAP-T2R2003Ingår i: Europhysics Conf. Abstracts Vol. 27A, 2003, s. P-1.211-Konferensbidrag (Refereegranskat)
  • 172.
    Brunsell, P R
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Bergsåker, H
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brzozowski, J H
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Cecconello, M
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Drake, J R
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, J-A
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Scheffel, J
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Schnack, D D
    Mode dynamics and confinement in the reversed-field pinch2000Ingår i: IAEA-CN-77: Fusion Energy 2000, 2000, s. Paper EXP3/14-Konferensbidrag (Refereegranskat)
  • 173.
    Brunsell, P R
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Malmberg, J-A
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yadikin, D
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Resistive wall mode studies in the EXTRAP T2R reversed-field pinch2002Ingår i: Europhysics Conf. Abstracts 26B, 2002, s. P-1.107-Konferensbidrag (Refereegranskat)
  • 174.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive Wall Mode Studies utilizing External Magnetic Perturbations2014Ingår i: Proceeding of the 25th IAEA Fusion Energy Conference, 2014, artikel-id Paper EX/P4-20Konferensbidrag (Övrigt vetenskapligt)
  • 175.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Volpe, Francesco
    Columbia University, New York, NY, USA.
    Olofsson, Erik
    Columbia University, New York, NY, USA.
    Fridström, Rickard
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Setiadi, Agung Chris
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Resistive Wall Mode Studies utilizing External Magnetic PerturbationsManuskript (preprint) (Övrigt vetenskapligt)
  • 176.
    Brunsell, Per
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Olofsson, K. Erik J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Yadikin, D.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabethth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Resistive wall mode feedback control experiments in EXTRAP T2R2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, s. 544-547Konferensbidrag (Refereegranskat)
    Abstract [en]

    Experiments in EXTRAP T2R on RWM stabilization using intelligent shell feedback with a P-controller showed that mode suppression improves with increasing gain up to the system stability limit. A PD-controller gives faster response and allows operation with higher gain. The PI-controller is useful for suppression of modes driven by external resonant field error. Best mode suppression was in the present study achieved with a PID-controller.

  • 177.
    Brunsell, Per R.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Kuldkepp, Mattias
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Menmuir, Sheena
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Hedqvist, Anders
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Yadikin, Dimitry
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Reversed field pinch operation with intelligent shell feedback control in EXTRAP T2R2006Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, nr 11, s. 904-913Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Discharges in the thin shell reversed field pinch (RFP) device EXTRAP T2R without active feedback control are characterized by growth of non-resonant m = 1 unstable resistive wall modes (RWMs) in agreement with linear MHD theory. Resonant m = 1 tearing modes (TMs) exhibit initially fast rotation and the associated perturbed radial fields at the shell are small, but eventually TMs wall-lock and give rise to a growing radial field. The increase in the radial field at the wall due to growing RWMs and wall-locked TMs is correlated with an increase in the toroidal loop voltage, which leads to discharge termination after 3-4 wall times. An active magnetic feedback control system has been installed in EXTRAP T2R. A two-dimensional array of 128 active saddle coils (pair-connected into 64 independent m = 1 coils) is used with intelligent shell feedback control to suppress the m = 1 radial field at the shell. With feedback control, active stabilization of the full toroidal spectrum of 16 unstable m = 1 non-resonant RWMs is achieved, and TM wall locking is avoided. A three-fold extension of the pulse length, up to the power supply limit, is observed. Intelligent shell feedback control is able to maintain the plasma equilibrium for 10 wall times, with plasma confinement parameters sustained at values comparable to those obtained in thick shell devices of similar size.

  • 178.
    Brunsell, Per R.
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Yadikin, Dmitriy
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gregoratto, D.
    Bolzonella, T.
    Cecconello, Marco
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Luchetta, A.
    Malmberg, Jenny-Ann
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Manduchi, G.
    Marchiori, G.
    Liu, Y.
    Ortolani, S.
    Paccagnella, R.
    First results from intelligent shell experiments with partial coil coverage in the EXTRAP T2R reversed field pinch2004Ingår i: Europhysics Conf. Abstracts Vol 29C, 2004, s. P-5.190-Konferensbidrag (Refereegranskat)
  • 179.
    Brändström, B. U. E.
    et al.
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Enell, C. F.
    Widell, O.
    Hansson, T.
    Whiter, N.
    Mäkinen, S.
    Mikhaylova, D.
    Axelsson, K.
    Sigernes, F.
    Gulbrandsen, N.
    Schlatter, N. M.
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Gjendem, A. G.
    Cai, L.
    Reistad, J. P.
    Daae, M.
    Demissie, T. D.
    Andalsvik, Y. L.
    Roberts, O.
    Poluyanov, S.
    Chernouss, S.
    Results from the intercalibration of optical low-light calibration sources 20112012Ingår i: Geoscientific Instrumentation, Methods and Data Systems, ISSN 2193-0856, E-ISSN 2193-0864, Vol. 1, s. 43-51Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Following the 38th Annual European Meeting on Atmospheric Studies by Optical Methods in Siuntio in Finland, an intercalibration workshop for optical low light calibration sources was held in Sodankylä, Finland. The main purpose of this workshop was to provide a comparable scale for absolute measurements of aurora and airglow. All sources brought to the intercalibration workshop were compared to the Fritz Peak reference source using the Lindau Calibration Photometer built by Wilhelm Barke and Hans Lauche in 1984. The results were compared to several earlier intercalibration workshops. It was found that most sources were fairly stable over time, with errors in the range of 5–25%. To further validate the results, two sources were also intercalibrated at UNIS, Longyearbyen, Svalbard. Preliminary analysis indicates agreement with the intercalibration in Sodankylä within about 15–25%.

  • 180. Bucalossi, J.
    et al.
    Neu, R.
    Joffrin, E.
    Lomas, P.
    Nunes, I.
    Rimini, F.
    Beurskens, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Baruzzo, M.
    Bourdelle, C.
    Challis, C.
    Coenen, J.
    De Vries, P.
    Dux, R.
    Giroud, C.
    Giruzzi, G.
    Maddison, G.
    Mayoral, M.
    Characterization of the ELMy H-mode regime with the ITER-like wall in JET2012Ingår i: 39th EPS Conference on Plasma Physics 2012, EPS 2012 and the 16th International Congress on Plasma Physics: Volume 1, 2012, 2012, s. 45-48Konferensbidrag (Refereegranskat)
  • 181.
    Burch, J. L.
    et al.
    Southwest Res Inst, San Antonio, TX 78238 USA..
    Ergun, R. E.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Cassak, P. A.
    Univ Virginia, Dept Phys & Astron, Morgantown, WV USA..
    Webster, J. M.
    Rice Univ, Dept Phys & Astron, Houston, TX USA..
    Torbert, R. B.
    Southwest Res Inst, San Antonio, TX 78238 USA.;Univ New Hampshire, Dept Phys, Durham, NH 03824 USA..
    Giles, B. L.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Dorelli, J. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Rager, A. C.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA.;Catholic Univ Amer, Dept Phys, Washington, DC 20064 USA..
    Hwang, K. -J
    Phan, T. D.
    Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA..
    Genestreti, K. J.
    Austrian Acad Sci, Space Res Inst, Graz, Austria..
    Allen, R. C.
    Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA..
    Chen, L. -J
    Wang, S.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Gershman, D.
    NASA, Goddard Space Flight Ctr, Greenbelt, MD USA..
    Le Contel, O.
    Univ Paris Sud, Observ Paris, Lab Phys Plasmas, CNRS,Ecole Polytech,UPMC Univ Paris 06, Paris, France..
    Russell, C. T.
    Univ Calif Los Angeles, Dept Earth & Planetary Sci, Los Angeles, CA USA..
    Strangeway, R. J.
    Univ Calif Los Angeles, Dept Earth & Planetary Sci, Los Angeles, CA USA..
    Wilder, F. D.
    Graham, D. B.
    Swedish Inst Space Phys, Uppsala, Sweden..
    Hesse, M.
    Univ Bergen, Dept Phys & Technol, Bergen, Norway..
    Drake, J. F.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Swisdak, M.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Price, L. M.
    Univ Maryland, Dept Astron, College Pk, MD 20742 USA..
    Shay, M. A.
    Univ Delaware, Dept Phys & Astron, Newark, DE 19716 USA..
    Lindqvist, Per-Arne
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Pollock, C. J.
    Denali Sci, Healy, AK USA..
    Denton, R. E.
    Dartmouth Coll, Dept Phys & Astron, Hanover, NH 03755 USA..
    Newman, D. L.
    Univ Colorado, LASP, Boulder, CO 80309 USA..
    Localized Oscillatory Energy Conversion in Magnetopause Reconnection2018Ingår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, nr 3, s. 1237-1245Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Data from the NASA Magnetospheric Multiscale mission are used to investigate asymmetric magnetic reconnection at the dayside boundary between the Earth's magnetosphere and the solar wind. High-resolution measurements of plasmas and fields are used to identify highly localized (similar to 15 electron Debye lengths) standing wave structures with large electric field amplitudes (up to 100 mV/m). These wave structures are associated with spatially oscillatory energy conversion, which appears as alternatingly positive and negative values of J . E. For small guide magnetic fields the wave structures occur in the electron stagnation region at the magnetosphere edge of the electron diffusion region. For larger guide fields the structures also occur near the reconnection X-line. This difference is explained in terms of channels for the out-of-plane current (agyrotropic electrons at the stagnation point and guide field-aligned electrons at the X-line).

  • 182. Burch, J. L.
    et al.
    Torbert, R. B.
    Phan, T. D.
    Chen, L. -J
    Moore, T. E.
    Ergun, R. E.
    Eastwood, J. P.
    Gershman, D. J.
    Cassak, P. A.
    Argall, M. R.
    Wang, S.
    Hesse, M.
    Pollock, C. J.
    Giles, B. L.
    Nakamura, R.
    Mauk, B. H.
    Fuselier, S. A.
    Russell, C. T.
    Strangeway, R. J.
    Drake, J. F.
    Shay, M. A.
    Khotyaintsev, Yu. V.
    Lindqvist, Per-Arne
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Marklund, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Wilder, F. D.
    Young, D. T.
    Torkar, K.
    Goldstein, J.
    Dorelli, J. C.
    Avanov, L. A.
    Oka, M.
    Baker, D. N.
    Jaynes, A. N.
    Goodrich, K. A.
    Cohen, I. J.
    Turner, D. L.
    Fennell, J. F.
    Blake, J. B.
    Clemmons, J.
    Goldman, M.
    Newman, D.
    Petrinec, S. M.
    Trattner, K. J.
    Lavraud, B.
    Reiff, P. H.
    Baumjohann, W.
    Magnes, W.
    Steller, M.
    Lewis, W.
    Saito, Y.
    Coffey, V.
    Chandler, M.
    Electron-scale measurements of magnetic reconnection in space2016Ingår i: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 352, nr 6290, s. 1189-+Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Magnetic reconnection is a fundamental physical process in plasmas whereby stored magnetic energy is converted into heat and kinetic energy of charged particles. Reconnection occurs in many astrophysical plasma environments and in laboratory plasmas. Using measurements with very high time resolution, NASA's Magnetospheric Multiscale (MMS) mission has found direct evidence for electron demagnetization and acceleration at sites along the sunward boundary of Earth's magnetosphere where the interplanetary magnetic field reconnects with the terrestrial magnetic field. We have (i) observed the conversion of magnetic energy to particle energy; (ii) measured the electric field and current, which together cause the dissipation of magnetic energy; and (iii) identified the electron population that carries the current as a result of demagnetization and acceleration within the reconnection diffusion/dissipation region.

  • 183.
    Bushby, P. J.
    et al.
    Newcastle Univ, Sch Math Stat & Phys, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England..
    Käpylä, P. J.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Masada, Y.
    Aichi Univ Educ, Dept Phys & Astron, Kariya, Aichi 4468501, Japan..
    Brandenburg, Axel
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Favier, B.
    Aix Marseille Univ, CNRS, Cent Marseille, IRPHE UMR 7342, Marseille, France..
    Guervilly, C.
    Newcastle Univ, Sch Math Stat & Phys, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England..
    Kaepylae, M. J.
    Large-scale dynamos in rapidly rotating plane layer convection2018Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, artikel-id A97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Convectively driven flows play a crucial role in the dynamo processes that are responsible for producing magnetic activity in stars and planets. It is still not fully understood why many astrophysical magnetic fields have a significant large-scale component. Aims. Our aim is to investigate the dynamo properties of compressible convection in a rapidly rotating Cartesian domain, focusing upon a parameter regime in which the underlying hydrodynamic flow is known to be unstable to a large-scale vortex instability. Methods. The governing equations of three-dimensional non-linear magnetohydrodynamics (MHD) are solved numerically. Different numerical schemes are compared and we propose a possible benchmark case for other similar codes. Results. In keeping with previous related studies, we find that convection in this parameter regime can drive a large-scale dynamo. The components of the mean horizontal magnetic field oscillate, leading to a continuous overall rotation of the mean field. Whilst the large-scale vortex instability dominates the early evolution of the system, the large-scale vortex is suppressed by the magnetic field and makes a negligible contribution to the mean electromotive force that is responsible for driving the large-scale dynamo. The cycle period of the dynamo is comparable to the ohmic decay time, with longer cycles for dynamos in convective systems that are closer to onset. In these particular simulations, large-scale dynamo action is found only when vertical magnetic field boundary conditions are adopted at the upper and lower boundaries. Strongly modulated large-scale dynamos are found at higher Rayleigh numbers, with periods of reduced activity (grand minima-like events) occurring during transient phases in which the large-scale vortex temporarily re-establishes itself, before being suppressed again by the magnetic field.

  • 184. Bykov, I.
    et al.
    Rudakov, D. L.
    Ratynskaia, Svetlana V.
    Tolias, Panagiotis
    De Angeli, M.
    Hollmann, E. M.
    McLean, A. G.
    Lasnier, C. J.
    Riva, G.
    Modification of adhered dust on plasma-facing surfaces due to exposure to ELMy H-mode plasma in DIII-D2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 379-385Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transient heat load tests have been conducted in the lower divertor of DIII-D using DiMES manipulator in order to study the behavior of dust on tungsten Plasma Facing Components (PFCs) during ELMy H-mode discharges. Samples with pre- adhered, pre- characterized dust have been exposed at the outer strike point (OSP) in a series of discharges with varied intra-(inter-) ELM heat fluxes. We used C dust because of its high sublimation temperature and non-metal properties. Al dust as a surrogate for Be and W dust were employed as relevant to that in the ITER divertor. The poor initial thermal contact between the substrate and the particles led to overheating, sublimation and shrinking of the carbon dust, and wetting induced coagulation of Al dust. Little modification of the W dust was observed. An enhanced surface adhesion and improvement of the thermal contact of C and Al dust were the result of exposure. A post mortem "adhesive tape" sampling showed that 70% of Al, <5% of W and C particles could not be removed from the surface owing to the improved adhesion. Al and C but not W particles that could be lifted had W inclusions indicating damage to the substrate. This suggests that non destructive methods may be inefficient for removal of dust in ITER.

  • 185.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Experimental studies of materials migration in magnetic confinement fusion devices: Novel methods for measurement of macro particle migration, transport of atomic impurities and characterization of exposed surfaces2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    During several decades of research and development in the field of Magnetically Confined Fusion (MCF) the preferred selection of materials for Plasma Facing Components (PFC) has changed repeatedly. Without doubt, endurance of the first wall will decide research availability and lifespan of the first International Thermonuclear Research Reactor (ITER). Materials erosion, redeposition and mixing in the reactor are the critical processes responsible for modification of materials properties under plasma impact. This thesis presents several diagnostic techniques and their applications for studies of materials transport in fusion devices. The measurements were made at the EXTRAP T2R Reversed Field Pinch operated in Alfvén laboratory at KTH (Sweden), the TEXTOR tokamak, recently shut down at Forschungszentrum Jülich (Germany) and in the JET tokamak at CCFE (UK). The main outcomes of the work are:

    • Development and application of a method for non-destructive capture and characterization of fast dust particles moving in the edge plasma of fusion devices, as well as particles generated upon laser-assisted cleaning of plasma exposed surfaces. 
    • Advancement of conventional broad beam and micro ion beam techniques to include measurement of tritium in the surfaces exposed in future D-T experiments. 
    • Adaption of the micro ion beam method for precision mapping of non uniform elements concentrations on irregular surfaces. 
    • Implementation of an isotopic marker to study the large scale materials migration in a tokamak and development of a method for fast non destructive sampling of the marker on surfaces of PFCs.
  • 186.
    Bykov, Igor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsaker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Zhou, Y.
    Heinola, K.
    Pettersson, J.
    Conroy, S.
    Likonen, J.
    Petersson, Per
    Widdowson, A.
    Studies of Be migration in the JET tokamak using AMS with Be-10 marker2016Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 371, s. 370-375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The JET tokamak is operated with beryllium limiter tiles in the main chamber and tungsten coated carbon fiber composite tiles and solid W tiles in the divertor. One important issue is how wall materials are migrating during plasma operation. To study beryllium redistribution in the main chamber and in the divertor, a Be-10 enriched limiter tile was installed prior to plasma operations in 2011-2012. Methods to take surface samples have been developed, an abrasive method for bulk Be tiles in the main chamber, which permits reuse of the tiles, and leaching with hot HCl to remove all Be deposited at W coated surfaces in the divertor. Quantitative analysis of the total amount of Be in cm(2) sized samples was made with inductively coupled plasma atomic emission spectroscopy (ICP-AES). The Be-10/Be-9 ratio in the samples was measured with accelerator mass spectrometry (AMS). The experimental setup and methods are described in detail, including sample preparation, measures to eliminate contributions in AMS from the B-10 isobar, possible activation due to plasma generated neutrons and effects of diffusive isotope mixing. For the first time marker concentrations are measured in the divertor deposits. They are in the range 0.4-1.2% of the source concentration, with moderate poloidal variation. (C) 2015 Elsevier B.V. All rights reserved.

  • 187.
    Bykov, Igor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Likonen, Jari
    Possnert, Göran
    Quantitative plasma-fuel and impurity profiling in thick plasma-deposited layers by means of micro ion beam analysis and SIMS2014Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 332, s. 280-285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The operation of the Joint European Torus (JET) with full-carbon wall during the last decades has proven the importance of material re-deposition processes in remote areas of the tokamak. The thickness of the deposits in shadowed areas can reach 1 mm. The main constituent is carbon, with little inclusion of Inconel components. Atomic fractions Be/C and D/C can locally reach 1. Three methods were used to study thick deposits on JET divertor surfaces: (i) NRA analysis with a 15 mu m wide, 3 MeV He-3 ion microbeam on a polished cross section of the layer to determine the concentration distribution of D, Be and C and the distribution of Ni by particle induced X-ray emission; (ii) elastic proton scattering (EPS) from the top of the layers with a broad proton beam at 3.5 and 4.6 MeV. These methods were absolutely calibrated using thick elemental targets. (iii) Depth profiling of D, Be and Ni was done with secondary ion mass spectrometry (SIMS), sputtering the layers from the surface. The three methods are complementary. The thickest layers are accessible only by microbeam mapping of the cross sections, albeit with limited spatial resolution. The SIMS has the best depth resolution, but is difficult for absolute quantification and is limited in accessible depth. The probed depth with proton backscattering is limited to about 30 mu m. The combination of all three methods provided a coherent picture of the layer composition. It was possible to correlate the SIMS profiling results to quantitative data obtained by the microbeam method.

  • 188.
    Bykov, Igor
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Litnovsky, A.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Time resolved collection and characterization of dust particles moving in the TEXTOR scrape-off layer2013Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, nr Suppl., s. S681-S685Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Moving dust has been collected in the SOL of TEXTOR in a time-resolved way with silica aerogel collectors [1-3]. The collectors were exposed to the toroidal particle flux in NBI heated discharges during the startup and flat top phase. Intrinsic dust was collected in several discharges. Other discharges were accompanied with injection of known amounts of pre-characterized dust (W, C flakes and C microspheres) from a position toroidally 120° away from the collector. Particle flux, composition and dust size distribution have been determined with SEM and EDX. Calibration allowed particle velocity estimates to be made. Upper limits for the deuterium content of individual dust grains have been determined by NRA.

  • 189.
    Bäbler, Matthäus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Energiprocesser.
    Biferale, Luca
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Feudel, Ulrike
    Guseva, Ksenia
    Lanotte, Alessandra S.
    Marchioli, Cristian
    Picano, Francesco
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre. University of Padua, Italy.
    Sardina, Gaetano
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Soldati, Alfredo
    Toschi, Federico
    Numerical simulations of aggregate breakup in bounded and unbounded turbulent flows2015Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 766Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Breakup of small aggregates in fully developed turbulence is studied by means of direct numerical simulations in a series of typical bounded and unbounded flow configurations, such as a turbulent channel flow, a developing boundary layer and homogeneous isotropic turbulence. The simplest criterion for breakup is adopted, whereby aggregate breakup occurs when the local hydrodynamic stress sigma similar to epsilon(1/2), with epsilon being the energy dissipation at the position of the aggregate, overcomes a given threshold sigma(cr), which is characteristic for a given type of aggregate. Results show that the breakup rate decreases with increasing threshold. For small thresholds, it develops a scaling behaviour among the different flows. For high thresholds, the breakup rates show strong differences between the different flow configurations, highlighting the importance of non-universal mean-flow properties. To further assess the effects of flow inhomogeneity and turbulent fluctuations, the results are compared with those obtained in a smooth stochastic flow. Furthermore, we discuss the limitations and applicability of a set of independent proxies.

  • 190.
    Bäbler, Matthäus U.
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Teknisk strömningslära.
    Biferale, Luca
    Lanotte, Alessandra S.
    Breakup of small aggregates driven by turbulent hydrodynamical stress2012Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 85, nr 2, s. 025301-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The breakup of small solid aggregates in homogeneous and isotropic turbulence is studied theoretically and by using direct numerical simulations at high Reynolds number, Re-lambda similar or equal to 400. We show that turbulent fluctuations of the hydrodynamic stress along the aggregate trajectory play a key role in determining the aggregate mass distribution function. The differences between turbulent and laminar flows are discussed. A definition of the fragmentation rate is proposed in terms of the typical frequency at which the hydrodynamic stress becomes sufficiently high to cause breakup along each Lagrangian path. We also define an Eulerian proxy of the real fragmentation rate, based on the joint statistics of the stress and its time derivative, which should be easier to measure in any experimental setup. Both our Eulerian and Lagrangian formulations define a clear procedure for the computation of the mass distribution function due to fragmentation. Contrary, previous estimates based only on single point statistics of the hydrodynamic stress exhibit some deficiencies. These are discussed by investigating the evolution of an ensemble of aggregates undergoing breakup and aggregation.

  • 191. Bílková, P.
    et al.
    Böhm, P.
    Komm, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Peterka, M.
    Šos, M.
    Seidl, J.
    Grover, O.
    Havlíček, J.
    Mitošinková, K.
    Varju, J.
    Vondráček, P.
    Urban, J.
    Imríšek, M.
    Markovič, T.
    Weinzettl, V.
    Hron, M.
    Pánek, R.
    Relative shift in position of temperature and density pedestals at the COMPASS tokamak2017Ingår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferensbidrag (Refereegranskat)
  • 192. Cameron, R. H.
    et al.
    Dikpati, M.
    Brandenburg, Axel
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    The Global Solar Dynamo2016Ingår i: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, s. 1-29Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A brief summary of the various observations and constraints that underlie solar dynamo research are presented. The arguments that indicate that the solar dynamo is an alpha-omega dynamo of the Babcock-Leighton type are then shortly reviewed. The main open questions that remain are concerned with the subsurface dynamics, including why sunspots emerge at preferred latitudes as seen in the familiar butterfly wings, why the cycle is about 11 years long, and why the sunspot groups emerge tilted with respect to the equator (Joy’s law). Next, we turn to magnetic helicity, whose conservation property has been identified with the decline of large-scale magnetic fields found in direct numerical simulations at large magnetic Reynolds numbers. However, magnetic helicity fluxes through the solar surface can alleviate this problem and connect theory with observations, as will be discussed.

  • 193.
    Caputa, Pawet
    et al.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Kyoto University, Kyoto, Japan .
    Simon, Joan
    Stikonas, Andrius
    Takayanagi, Tadashi
    Quantum entanglement of localized excited states at finite temperature2015Ingår i: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work we study the time evolutions of (Renyi) entanglement entropy of locally excited states in two dimensional conformal field theories (CFTs) at finite temperature. We consider excited states created by acting with local operators on thermal states and give both field theoretic and holographic calculations. In free field CFTs, we find that the growth of Renyi entanglement entropy at finite temperature is reduced compared to the zero temperature result by a small quantity proportional to the width of the localized excitations. On the other hand, in finite temperature CFTs with classical gravity duals, we find that the entanglement entropy approaches a characteristic value at late time. This behaviour does not occur at zero temperature. We also study the mutual information between the two CFTs in the thermofield double (TFD) formulation and give physical interpretations of our results.

  • 194.
    Carlqvist, Per
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Multicomponent Double Layers and Selective Acceleration of Charged Particles1994Rapport (Övrigt vetenskapligt)
  • 195.
    Carlqvist, Per
    KTH, Tidigare Institutioner.
    Plasma Drift Towards a Plane Equipotential Surface1984Rapport (Övrigt vetenskapligt)
  • 196.
    Carlqvist, Per
    et al.
    KTH, Tidigare Institutioner, Alfvénlaboratoriet.
    Gahm, G.
    Manifestations of Electric Currents in Interstellar Molecular Clouds1991Rapport (Övrigt vetenskapligt)
  • 197.
    Carlström, Ola
    et al.
    KTH, Tidigare Institutioner.
    Bylander, Lars
    KTH, Tidigare Institutioner.
    Rapport om införandet av ytmonteringsteknik i raket- och satellitburna experiment1987Rapport (Övrigt vetenskapligt)
  • 198. Catarino, N.
    et al.
    Barradas, N. P.
    Corregidor, V.
    Widdowson, A.
    Baron-Wiechec, A.
    Coad, J. P.
    Heinola, K.
    Rubel, Marek
    KTH. EUROfusion Consortium, JET, Culham Science Centre, Abingdon OX14 3DB, UK.
    Alves, E.
    Assessment of erosion, deposition and fuel retention in the JET-ILW divertor from ion beam analysis data2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 559-563Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Post-mortem analyses of individual components provide relevant information on plasma-surface interactions like tungsten erosion, beryllium deposition and plasma fuel retention with divertor tiles via implantation or co-deposition. Ion Beam techniques are ideal tools for such purposes and have been extensively used for post-mortem analyses of selected tiles from JET following each campaign. In this contribution results from tiles removed from the JET ITER-Like Wall (JET-ILW) divertor following the 2013-2014 campaign are presented. The results summarize erosion, deposition and fuel retention along the poloidal cross section of the divertor surface and provide data for comparison with the first JET-ILW campaign, showing a similar pattern of material migration with the exception of Tile 6 where the strike point time on the tile was similar to 4 times longer in 2013-2014 than in 2011-2012, which is likely to account for more material migration to this region. The W deposition on top of the Mo marker coating of Tile 4 shows that the enrichment takes place at the strike point location.

  • 199. Catarino, N.
    et al.
    Widdowson, A.
    Baron-Wiechec, A.
    Coad, J. P.
    Heinola, K.
    Rubel, Marek
    KTH.
    Alves, E.
    Time-resolved deposition in the remote region of the JET-ILW divertor: measurements and modelling2017Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikel-id 014059Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One crucial requirement for the development of fusion power is to know where, and how much, impurities collect in the machine, and how much of the fuelling isotope tritium will be trapped therein. The most relevant information on this issue comes from the operation of the Joint European Tokamak (JET), which is the world's largest operating tokamak and has the same interior plasma-facing materials as the next step machine, ITER. Much of the information gained so far has been from post-mortem analysis of samples collected after whole campaigns involving varied types of operation. This paper describes time-resolved measurements of the deposition rate using rotating collectors (RC) placed in remote areas of the JET divertor during the 2013-2014 campaign with the ITER-like Wall (ILW). These techniques allow the effects of different types of operation to be distinguished. Rotating collectors made of silicon discs housed behind an aperture are exposed to the plasma. Each time the magnetic field coils are ramped up for a discharge the disc rotates, providing a linear relationship between the exposed region and the discharge number. Post-mortem ion beam analyses provide information on the deposit composition as a function of the discharge number. The results show that the Be deposition average for the RC in the corners of the inner and outer divertor are 4.9 x 10(16) cm(-2) and 1.8 x 10(17) cm(-2), respectively, accumulated over an average of similar to 25 pulses. Data from the rotating collector below Tile 5 in the central region of divertor indicate a Be deposition rate of 9.3 x 10(15) cm(-2), per similar to 25 pulses.

  • 200.
    Causa, F.
    et al.
    CNR, Ist Fis Plasma Piero Caldirola, Via R Cozzi 53, I-20125 Milan, Italy.;CNR, Ist Fis Plasma, Via R Cozzi 53, I-20125 Milan, Italy..
    Ratynskaia, Svetlana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Zito, P.
    ENEA, Fus & Nucl Safety Dept, CR Frascati, Via E Fermi 45, I-00044 Rome, Italy..
    Analysis of runaway electron expulsion during tokamak instabilities detected by a single-channel Cherenkov probe in FTU2019Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 4, artikel-id 046013Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The expulsion of runaway electrons (REs) during different types of tokamak instabilities is analysed by means of a Cherenkov probe inserted into the scrape-off layer of the FTU tokamak. One such type of instability, the well-known tearing mode, is involved in disruptive plasma termination events, during which the risk of RE avalanche multiplication is highest. The second type, known as anomalous Doppler instability, influences RE dynamics by enhancing pitch angle scattering. Three scenarios are analysed here, characterised by different RE generation rates and mechanisms. The main conclusions are drawn from correlations between the Cherenkov probe and other diagnostics. In particular, the Cherenkov probe permits the detection of fast electron expulsion with a high level of detail, presenting peaks with 100% signal contrast during tearing mode growth and rotation, and sub-peak structures reflecting the interplay between the magnetic island formed by the tearing mode, RE diffusion during island rotation and the geometry of obstacles in the vessel. Correlations between the Cherenkov signal, hard x-ray emission and electron cyclotron emission reveal the impulsive development of the anomalous Doppler instability with instability rise time in the microsecond scale resolved by the high time-resolution of the Cherenkov probe.

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