Axial symmetric open magnetic traps with depressed transversal losses of plasmas

Transcription

1 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, Nizhny Novgorod, Russian Federation

2 Outline Introduction Cusp Systems with shear flow control Non-paraxial systems

3 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.

4 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

5 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 GHz Ion beam Ø 1mm N e =10 13 cm -3 T e = ev Magnetic trap N e g g 10 s 10 8 [ cm 3 s]

6 Analyzer signal, a. u. MHD stabilization: Cusp-type magnetic configuration N2+ g 10 s 200 N3+ N+ 8 n Magnet current, A N: <Z>=2 Ag: <Z>=3.5 Losses trough the axial slit is too high!

7 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

8 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

9 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

10 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

11 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

12 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

13 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 P (2008)

14 Scheme of the experiments (SMIS 37) Magnetic field coils MW GHz Limiter Probes Disk-mask Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe

15 Scheme of the experiments (SMIS 37) Magnetic field coils MW GHz Limiter Probes Disk-mask Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe

16 Scheme of the experiments (SMIS 37) Magnetic field coils MW GHz Limiter Probes Disk-mask Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe

17 Scheme of the experiments (SMIS 37) Magnetic field coils MW GHz Limiter Probes Disk-mask Discharge vacuum chamber 45 0 Isolators Edge magnetic force line Expanding chamber 12 mm Ø 12 mm Ø 84 mm Probe

18 Scheme of the experiments (shear flow drive) Magnetic field coils Vacuum chamber walls Limiter Δφ Shear flow layer Insulator

19 Q (a.u.) Total charge registered by probes #1-3, Helium Magnetic field at the plug: 1.7 T U, limiter (V) probes #1-3

20 Q (a.u.) Total charge registered by probes #1-3, Helium Magnetic field at the plug: 1.7 T U, limiter (V) probes #1-3

21 Current (a.u.) Current (a.u.) Decay experiment: microwave pulse-length 400μs Limiter voltage U lim =150 V Limiter voltage U lim =0 V ( s ( s Time ( s) Time ( s) End of the microwave pulse Ion saturation current on the center probe (#1)

22 current (a.u.) Results of the recent experiments: ion current density profiles, B=1.7 T 0,60 0,55 0,50 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

23 Results of the experiments with streak camera: photos, B=1.7 T R Limiter potential 0 V 100 µs time Limiter potential 120 V

24 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

25 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

26 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, Длина (см) Length, cm

27 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.

28 Plasma confinement in open magnetic trap with divertor а.) b.) a trap w/o divertor, b with divertor

29 Thank you for your attention!