Axial symmetric open magnetic traps with depressed transversal losses of plasmas A. Sidorov, S. Golubev, I. Izotov, S. Razin, V. Skalyga and A. Vodopyanov Institute of Applied Physics, RAS, 603950 Nizhny Novgorod, Russian Federation
Outline Introduction Cusp Systems with shear flow control Non-paraxial systems
Experimental investigations of plasma MHD stabilization in open mirror trap of the ECR ion source R time 200 µs 1 projection of the streak camera slit Puller current Image from streak-camera (positive image, time goes from left to right, the duration of the entire scan is 200 µs), obtained at the same time with the puller current waveform and N 3+ ions. Rectangle on the waveforms corresponds to the duration of streak-camera scan.
Theoretical model plasma convection in axisymmetric or effectively symmetrized shearless magnetic systems; magnetic field can be presented as: stability of flute-like mode : Marginally stable (MS) profile U < 0 - sufficient condition for the reasonable density profiles BUT not required
MHD stabilization: Cusp-type magnetic configuration SMIS 37 setup L eff =30 cm Quasi gas dynamic confinement regime τ c =1/ν ei << τ g =L eff /V s MW 100 kw @ 37.5 GHz Ion beam Ø 1mm N e =10 13 cm -3 T e =50 100 ev Magnetic trap N e g g 10 s 10 8 [ cm 3 s]
Analyzer signal, a. u. MHD stabilization: Cusp-type magnetic configuration 600 400 N2+ g 10 s 200 N3+ N+ 8 n 10 0 120 160 200 240 280 320 Magnet current, A N: <Z>=2 Ag: <Z>=3.5 Losses trough the axial slit is too high!
Conditions of the vortex creation v g View of the plasma core in the transversal plane v E r 0 B v g - velocity transversal flow caused by flute instability If v E >>v g then the closed streamlines appears and the existence of the vortex like structures is possible
Conditions of the vortex creation φ Δφ r 0 r v g View of the plasma core in the transversal plane v E r 0 B v g - velocity transversal flow caused by flute instability If v E >>v g then the closed streamlines appears and the existence of the vortex like structures is possible
Conditions of the vortex creation φ Δφ r 0 r v g View of the plasma core in the transversal plane v E r 0 B v g - velocity transversal flow caused by flute instability If v E >>v g then the closed streamlines appears and the existence of the vortex like structures is possible
Conditions of the vortex creation φ E Δφ r 0 r r 0 r v g View of the plasma core in the transversal plane v E r 0 B v g - velocity transversal flow caused by flute instability If v E >>v g then the closed streamlines appears and the existence of the vortex like structures is possible
Conditions of the vortex creation φ E Δφ r 0 r r 0 r v g View of the plasma core in the transversal plane v E r 0 B v g - velocity transversal flow caused by flute instability If v E >>v g then the closed streamlines appears and the existence of the vortex like structures is possible
Conditions of the vortex creation φ E Δφ v E =c (E B)/B 2 velocity of the rotation r 0 r r 0 r v g View of the plasma core in the transversal plane v E r 0 B v g - velocity transversal flow caused by flute instability If v E >>v g then the closed streamlines appears and the existence of the vortex like structures is possible
The threshold of the vortex confinement: analytical estimations e 10 T e Te M Z c ebl According to the SMIS 37 parameters (L=30 cm, B=0.5 T, κ=6, Te=100 ev) one can get: e 0.45 T e A Z For the helium and nitrogen ions: So, the value of the limiter Voltage has to be in order of 100 V according to the estimations e 1. 2T e Beklemishev, A. D. Shear Flow Effects in Open Traps. Theory of Fusion Plasmas, AIP Conference Proceedings. V. 1069. P. 14 25 (2008)
Scheme of the experiments (SMIS 37) Magnetic field coils MW 100 kw@ 37.5 GHz Limiter Probes Disk-mask 22.5 0 Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe
Scheme of the experiments (SMIS 37) Magnetic field coils MW 100 kw@ 37.5 GHz Limiter Probes Disk-mask 22.5 0 Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe
Scheme of the experiments (SMIS 37) Magnetic field coils MW 100 kw@ 37.5 GHz Limiter Probes Disk-mask 22.5 0 Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe
Scheme of the experiments (SMIS 37) Magnetic field coils MW 100 kw@ 37.5 GHz Limiter Probes Disk-mask 22.5 0 Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe
Scheme of the experiments (shear flow drive) Magnetic field coils Vacuum chamber walls Limiter Δφ Shear flow layer Insulator
Q (a.u.) Total charge registered by probes #1-3, Helium Magnetic field at the plug: 1.7 T 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 20 40 60 80 100 U, limiter (V) 1 2 3 probes #1-3
Q (a.u.) Total charge registered by probes #1-3, Helium Magnetic field at the plug: 1.7 T 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0 20 40 60 80 100 U, limiter (V) 1 2 3 probes #1-3
Current (a.u.) Current (a.u.) Decay experiment: microwave pulse-length 400μs Limiter voltage U lim =150 V Limiter voltage U lim =0 V 2.5 1.6 1.4 2.0 1.2 1.5 1.0 ( s 1.0 0.8 0.6 ( s 0.5 0.4 0.2 0.0 13700 13800 13900 14000 14100 Time ( s) 0.0-0.2 13700 13800 13900 14000 14100 Time ( s) End of the microwave pulse Ion saturation current on the center probe (#1)
current (a.u.) Results of the recent experiments: ion current density profiles, B=1.7 T 0,60 0,55 0,50 0,45 0 14 30 60 110 138 0,40 0,35 0,30 0,25 0,20 0,15 0,10 1,0 1,5 2,0 2,5 3,0 3,5 4,0 1 st probe radial radius coordinate 2 nd probe 3 rd probe 4 th probe
Results of the experiments with streak camera: photos, B=1.7 T R Limiter potential 0 V 100 µs time Limiter potential 120 V
75 GHz plasma heating - Total current increase with the shift of limiter potential - Shift of the plasma density profile maximum - Bias of the plasma potential in radial direction with no external potential on limiter
Divertor (DS) stabilization in mirrors Contrary to min B principle realization of DS is based on maintenance of the MS pressure profile p ~ U -γ separatrix Optimal divertor r s ~ L Plasma compressibility is the main stabilizing effect in the nonparaxial magnetic field with unfavorable curvature. Under influence of this effect sufficiently gradually decreasing pressure profiles become stable for all interchange flute-like modes. grad(b)/b>grad(p)/p Presence of the divertor-like separtrix with magnetic field nulls essentially enhances the effect of compressibility and leads to existance of MS pressure profiles with the vanishing pressure value at separatrix p(ψ s )=0
Magnetic field, T Магнитное поле (Тл) Divertor magnetic system 2,0 1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 Coils current 1.4 ka 0,2 0,0-30 -20-10 0 10 20 30 Длина (см) Length, cm
Plasma confinement in open magnetic trap with divertor τ = 61 μs τ 1 = 58 μs τ 2 = 190 μs τ = 57 μs τ 1 = 71 μs τ 2 = 220 μs Plasma decay. Waveforms of the probe ion currents in semilog scale. The forms start from the end of MW pulse. Left side trap w/o divertor. right with divertor.
Plasma confinement in open magnetic trap with divertor а.) b.) a trap w/o divertor, b with divertor
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