SLOWING DOWN OF NEUTRAL INJECTED PARTICLES AND HEATING EFFICIENCY IN WENDELSTEIN VII-A
The excitation of ion cyclotron modes by the perpendicular neutral beam injection has been investigated by means of linear stability analysis. Strong instability was found for the switching on phase of the NI. The stationary slowing down distribution by Coulomb collisions, however, is expected to be mainly stable. The nonlinear Fokker-Planck equation for Coulomb interaction has been solved by Monte Carlo technique for H**0 injection in a H**+/D**+ plasma mixture. The high density NI results in a strong pressure anisotropy, but the D**+ distribution is nearly undistorted by the NI (isotropic Maxwellian). By means of Monte Carlo simulation, the ion confinement time is estimated as a function of the ambipolar potential. For the thermal ion component in the plateau regime, the transport properties are strongly reduced by the ambipolar electric field. In a similar way, the orbit losses of the high energy ions (ripple regime) are decreased. This results in an improved heating efficiency. For small ambipolar potential, the particle confinement time becomes less than the average slowing down time. Then, the loss cone dominates the slowing down distribution function leading to ion cyclotron instabilities. Finally, the bounce averaged drift kinetic equation and the basic principles of the corresponding Monte Carlo simulation are discussed shortly.
Bibliographic Reference: 5TH INTERNATIONAL WORKSHOP ON STELLARATORS, SCHLOSS RINGBERG, BAVARIA (GERMANY), SEPT. 24-28, 1984 VOL. II, PP. 507-523, EUR 9618 EN (1985) FS, VOL. I AND VOL. II, 787 P., BFR 3500 (BOTH VOLUMES), EUROFFICE, LUXEMBOURG, POB 1003
Record Number: 1989124120100 / Last updated on: 1987-01-01
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