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Non-linear dynamics of Alfvén eigenmodes excited by thermonulcear alpha particles in the presence of ion cyclotron resonance heating
KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
2007 (Engelska)Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 9, s. 1131-1141Artikel i tidskrift (Refereegranskat) Published
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.

Ort, förlag, år, upplaga, sidor
2007. Vol. 47, nr 9, s. 1131-1141
Nyckelord [en]
Alpha particles; Cyclotron resonance; Distribution functions; High energy physics; Plasma heating; Thermonuclear reactions; Ion cyclotron resonance heating (ICRH); Magnetosonic waves; Excitation energy
Nationell ämneskategori
Annan elektroteknik och elektronik
Identifikatorer
URN: urn:nbn:se:kth:diva-6937DOI: 10.1088/0029-5515/47/9/009ISI: 000249968800012Scopus ID: 2-s2.0-34548217149OAI: oai:DiVA.org:kth-6937DiVA, id: diva2:11790
Anmärkning
QC 20100628Tillgänglig från: 2007-03-29 Skapad: 2007-03-29 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
Ingår i avhandling
1. Non-linear dynamics of Alfvén eigenmodes excited by fast ions in tokamaks
Öppna denna publikation i ny flik eller fönster >>Non-linear dynamics of Alfvén eigenmodes excited by fast ions in tokamaks
2007 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

The tokamak is so far the most promising magnetic configuration for achieving a net production of fusion energy. The D-T fusion reactions result in 3.5 MeV alpha-particles, which may destabilize Alfvén eigenmodes through wave-particle interaction. These instabilities redistribute the alpha-particles from the central region of the plasma towards the edge, where they are thermalized, and hence result in a reduced heating efficiency. The high-energy alpha-particles may even be thrown out of the plasma and may damage the wall.

To investigate the destabilization of Alfvén eigenmodes by high-energy ions, ion cyclotron resonance heating (ICRH) and neutral beam injection (NBI) are often used to create a high-energy tail on the distribution function. The ICRH does not only produce high-energy anisotropic tails, it also decorrelates the wave-particle interaction with the Alfvén eigenmodes. Without decorrelation of the wave-particle interaction an ion will undergo a superadiabatic oscillation in phase space and there will be no net transfer of energy to the mode. For the thermal ions the decorrelation from collisions dominates while for the high-energy ions the decorrelation from ICRH dominates. As the unstable modes grow up, the gradients in phase space, which drive the mode, are reduced, resulting in a weaker drive. The dynamics of the system becomes non-linear due to a continuous restoration of the gradients by D-T reactions and ICRH.

In this thesis the non-linear dynamics of toroidal Alfvén eigenmodes (TAEs) during ICRH has been investigated using the SELFO code. The SELFO code, which calculates the distribution function during ICRH self-consistently using a Monte-Carlo metod, has been upgraded to include interactions with TAEs. The fast decay of the mode amplitude as the ICRH is switched off, which is seen in experiments, as well as the oscillation of the mode amplitude as the distribution function is repetetively built up by the ICRH and flattened by the TAE has been reproduced using numerical simulations. In the presence of several unstable modes the dynamics become more complicated. The redistribution of an alpha-particle slowing down distribution function as well as the reduced heating efficiency in the presence of several modes has also been investigated.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH, 2007. s. xiv, 61
Serie
Trita-EE, ISSN 1653-5146 ; 2007:001
Nyckelord
fusion plasma, tokamak, MHD, toroidal Alfvén eigenmodes, thermonuclear alpha particles, ion cyclotron resonance heating
Nationell ämneskategori
Annan elektroteknik och elektronik
Identifikatorer
urn:nbn:se:kth:diva-4320 (URN)978-91-7178-564-0 (ISBN)
Disputation
2007-04-23, Sal F3, KTH, Lindstedtsvägen 23, Stockholm, 10:15
Opponent
Handledare
Anmärkning
QC 20100628Tillgänglig från: 2007-03-29 Skapad: 2007-03-29 Senast uppdaterad: 2010-06-28Bibliografiskt granskad

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Bergkvist, TommyHellsten, TorbjörnHolmström, Kerstin
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