NONEQUILIBRIUM HEAVY GASES PLASMA MHDSTABILIZATION IN AXISYMMETRIC MIRROR

NON-EQUILIBRIUM HEAVY GASES PLASMA MHD-STABILIZATION IN AXISYMMETRIC MIRROR MAGNETIC TRAP A. V. Sidorov 2, P. A. Bagryansky 1, A. D. Beklemishev 1, I. V. Izotov 2, V. V. Prikhodko 1, S. V. Razin 2, V. A. Skalyga 2 and V. G. Zorin 2 1 Budker Institute of Nuclear Physics, 630090, Novosibirsk, Russia of Applied Physics, 603950, Nizhny Novgorod, Russia 2 Institute

ECR Multicharged Ion Sources Applications Accelerator injectors Technologies Hadron therapy Beta beam project Heavy Ion Fusion High density energy physics Surface processing Ion implantation (SOI-technologies etc)

Principles of Gas-dynamic ECR Ion Source Operation SMIS 37 Magnetic trap, 2 T, R=5 U~30 k. V Plasma electrode (PE) FC Gyrotron radiation Puller 100 k. W @ 37. 5 GHz ECR discharge beam Np~Ncutoff~1013 cm-3 Te~70 e. V High e-i collision frequency Lp~30 cm L~35 cm Loss cone is filled EDF is isotropic λii<<L Gas-dynamic regime of confinement τc=1/νei << τg=Leff/Vs Plasma lifetime = τg

Minimum-B field Confinement in ECR Ion Source Solenoid Coils Sextupole e- heating µ wave gas ions

MHD stabilization: Cusp-type magnetic configuration MW Ion beam Ø 1 mm Magnetic coils N: <Z>=2 Ag: <Z>=3. 5 Losses trough the axial slit is too high!

GDT experiment parameters (D - beams, Н – plasma) § § § Center magnetic field: D-injection power: Trapped power: 2. 8 3 k. G 3. 5 MW 2 MW § § § Plasma density: Electron temperature: Hot ions density: 1. 5 3 1013 cm-3 140 e. V 4 1013 cm-3

Vortex confinement: potential profile control Limiter (+150 V) Plasma source Injection +150 V Plasma receivers Injection V Potential profile β ~ 0. 6!! V V cm E. I. SOLDATKINA, P. A. BAGRYANSKY and A. L. SOLOMAKHIN. Plasma Physics Reports, 34, 259 (2008).

Finite larmor radius (FLR) effect GDT - ion gyroradius, L – trap length, a – plasma radius. At m=1 mode dominates in spatial spectrum of the flute instability SMIS 37 Ion beam emittance ~ , so in ECR ion sources ion temperature is low, 1÷ 10 e. V and FLR effects are negligible.

Vortex confinement: theory ØCalculation results (A. D. Beklemishev) Calculated energy life-time changing in SMIS 37 setup for helium plasma. Times normalized on the time of external layers turning according to internal layers. Initial unperturbed state of the plasma cord (time=0) was chosen axisymmetric with the symmetry center equal to the magnetic system center. τE=50 correspond to the gas dynamic confinement time. In case of the absence of the shear flow τE=5. A. D. Beklemishev, Shear Flow Effects in Open Traps, Theory of Fusion Plasmas, AIP Conference Proceedings 1069 (2008) pp. 3 -14.

Scheme of the experiments Magnetic field coils Limiter MW 100 k. W@ 37. 5 GHz Discharge vacuum chamber Zonds Isolators Expanding chamber Edge magnetic force line

Total charge registered by zonds #1 -3, Helium Magnetic field at the plug: 1. 7 T 1 2 3 zonds #1 -3

Total charge registered by zonds #1 -3, Nitrogen Magnetic field at the plug: 1. 7 T Critical value of the U limiter in both cases is about of 70 V what is close to electron temperature and it is in good agreement with calculations

Mode structure: calculations and experiment Plasma potential and electron temperature distribution in the plasma cord section. Potential is normalized on the electron temperature; 1 – corresponds to limiter radius projection in central plane of the trap. Calculations show that azimuthal modes m=1, m=2 and m=3 have to dominate in the spatial spectrum under conditions of “vortex” confinement. Experiments show that azimuthal modes m=1 and m=2 dominate in the spatial spectrum under conditions of “vortex” confinement what is in good agreement with calculations.

“Decay” experiment: microwave pulse-length 400μs Limiter voltage Ulim=150 V Limiter voltage Ulim=0 V End of the microwave pulse Ion saturation current on the center zond (#1)

Future plans The experiments demonstrated good agreement with calculation: mode structure, critical value of the limiter potential for “vortex” confinement regime realization In future it is planned to improve electrode-limiter for the opportunity to control the potential profile and to extract the ions from the plasma at the same time. In this case it will be possible to research multicharged ion creation in the plasma of ECR ion source under conditions of “vortex” confinement regime realization.

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