Speaker
Dr
Ivan Chernoshtanov
(Budker Institute of Nuclear Physics)
Description
Alfvén ion-cyclotron (AIC) instability is an electromagnetic instability which leads to excitation of elliptically-polarized waves rotating in the direction of ion gyro-rotation and propagating along external magnetic field. The instability causes anomalous ions scattering and can influences on particles and energy losses. For example, confinement in the central cell of TMX device was limited by AIC instability which was excited in end cells and heats up central cell ions [1]. The hot ions anisotropy in the central cell of GAMMA-10 device is limited by AIC instability which causes hot ion angle scattering [2]. Insignificant increasing of fast ions axial losses caused by AIC instability is observed in the central cell of GDT device [3].
The ion motion in an axisymmetric mirror trap with electric and magnetic field perturbations is investigated analytically and numerically in present work. The most intense interaction between wave and ions occurs near minimum of mirror field where cyclotron resonant condition $v_\|=v_r\equiv(\omega-\Omega_{ci})/k_\|$ can be satisfied, here $\Omega_{ci}$ is the ion cyclotron frequency and $\omega$ and $k_\|$ are wave frequency and wave vector. Particle energy can changes over many bounce-periods essentially if changing of phase difference between ion gyro-rotation and wave field rotation during bounce-period equals integer number [4]. In other words, ion energy changes essentially when the following resonant condition takes place: $\omega-\langle\Omega_{ci}\rangle=n\Omega_b$, here $\langle\Omega_{ci}\rangle$ is the ion-cyclotron frequency averaged over bounce period and $\Omega_b$ is the bounce frequency. As well as in the case of electron cyclotron resonance heating [4, 5], the interaction between bounce-oscillations and AIC wave leads to chaotic dynamic of ions having relatively low transversal energy and $v_\|\sim v_r$. Thus the diffusion on magnet momentum arises which results in anomalous axial losses of ions.
The distribution of fields perturbations are calculates from linear WKB analysis of instability threshold [6], fields distributions found from the Pearlstein-Berk approximation are used for analytical calculations. The margin of chaos area and diffusion coefficient is estimated analytically and ions losses caused by AIC instability are calculated. Also transversal ion diffusion is considered. The analytical calculations are compared with numerical simulation of ion dynamic.
This work has been supported by Russian Science Foundation (Project No. 14-50-00080).
References:
[1] R.P. Drake, et. al., Nucl. Fusion, Vol. 21, No 3, 359-364 (1981)
[2] H. Hojo, M. Nakamura, S. Tanaka, M. Ichimura and A. Mase, J. Plasma Fusion Res., Vol 75 No 9, 1089-1094 (1999)
[3] A.V. Anikeev et al., Plasma Physics Reports, Vol. 41, Issue 10, 773–782 (2015)
[4] F. Jaeger, A.J. Lichtenberg and M.A. Lieberman, Plasma Phys., Vol. 14, No 12, 1073-1100 (1972)
[5] M.A. Lieberman and A.J. Lichtenberg, Plasma Phys., Vol. 15, No 2, 125-150 (1973)
[6] D.C. Watson, Phys. Fluids, Vol. 23, No 12, 2485-2492 (1980)
Primary author
Dr
Ivan Chernoshtanov
(Budker Institute of Nuclear Physics)
