| 1. |
- Bergkvist, Tommy, et al.
(författare)
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Effects of ICRH on the dynamics of fast particle excited alfven eigenmodes
- 2007
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Ingår i: Radio Frequency Power in Plasmas. - : American Institute of Physics (AIP). - 9780735404441 - 0735404445 ; , s. 455-458
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 2. |
- Bergkvist, Tommy, et al.
(författare)
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Non-linear Alfvén eigenmode dynamics of a burning plasma in the presence of ion cyclotron resonance heating
- 2006
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Ingår i: EPS Conf. Plasma Phys., EPS. - 9781622763337 ; , s. 1792-1795
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Bergkvist, Tommy, et al.
(författare)
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Nonlinear interaction between RF-heated high-energy ions and MHD-modes
- 2003
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Ingår i: RADIO FREQUENCY POWER IN PLASMAS. - 0735401586 ; , s. 459-462
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Eriksson, L. -G, et al.
(författare)
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Toroidal rotation in RF heated JET plasmas
- 2007
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Ingår i: RADIO FREQUENCY POWER IN PLASMAS. - : AIP. - 9780735404441 ; , s. 59-62
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Hannan, Abdul, et al.
(författare)
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A Fokker-Planck Code for Fast Self-Consistent Calculations of ICRH
- 2010
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Ingår i: 37th EPS Conference on Plasma Physics.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- 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
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| 9. |
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| 10. |
- Hellsten, Torbjörn A K, et al.
(författare)
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A model collision operator for orbit averaged Monte Carlo codes
- 2006
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Ingår i: AIP Conf. Proc.. - : AIP. - 0735403767 - 9780735403765 ; , s. 362-367
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Konferensbidrag (refereegranskat)abstract
- 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.
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