Blob motion and control. simple magnetized plasmas

Transcription

1 Blob motion and control in simple magnetized plasmas Christian Theiler A. Fasoli, I. Furno, D. Iraji, B. Labit, P. Ricci, M. Spolaore 1, N. Vianello 1 Centre de Recherches en Physique des Plasmas (CRPP) École Polytechnique Fédérale de Lausanne, Switzerland (EPFL) 1 Consorzio RFX, Euratom-ENEA, Padova, Italy 5 nd APS DPP Annual Meeting November , Chicago, IL

2 A blob in TORPEX Torpex geometry cross-section C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

3 Blobs are everywhere in linear machines, in simple toroidal plasmas LAPD TORPEX Carter POP 06 3 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

4 Blobs are everywhere in tokamaks NSTX MAST C-Mod B Zweben et al. POP 04 Kirk et al. PRL 04 Grulke et al. POP 06 and they are important for fusion, they influence Confinement Divertor efficiency Plasma-wall interactions DIII-D Yu et al. POP 08 4 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

5 Motivation Mechanism of blob motion [1] The radial velocity of a filament/blob is a crucial parameter as it governs the fraction of energy and particles that are transported to the wall It is therefore crucial to understand the mechanisms behind blob propagation, the scaling of blob dynamical properties with plasma parameters, and to investigate ways to influence the blob motion [1] Krasheninnikov PLA C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

6 Outline Derivation of blob velocity scaling law In situ measurements of blob motion in a simple geometry Verification of scaling law via a wide scan in (normalized) blob size by varying ion mass Control of blob motion by Reduction of connection length Variation of neutral gas pressure Biased electrodes 6 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

7 Generalized scaling law: derivation Ji n z r ϑ J J pol Fig. from Krasheninnikov et al. JPP 08 I Vorticity equation cs mi n nmi D = RB z B Dt Estimate of terms n ~ z φ φ δn a ~ φ a ~ ne c T L e c s D Dt ~ φ ~ ~ φ + ~ Bv nm B cs Ra blob a i ν in φ + a - 7 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

8 Generalized scaling law: derivation Ji n z r ϑ J J pol Vorticity equation cs mi n nmi D = RB z B Dt φ ne c T L e c s ~ φ + nm B i ν in φ I Fig. from Krasheninnikov et al. JPP 08 He blobs in TORPEX ob [m/s] v blo [1,] a (blob size) [m] [1] Garcia et al. POP 005 [] Myra and D Ippolito POP 005 [3] Krasheninnikov PLA 001 [4] Katz et al. PRL 008 [5] Theiler et al. PRL C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

9 Generalized scaling law: derivation Ji n z r ϑ J J pol Vorticity equation cs mi n nmi D = RB z B Dt φ ne c T L e c s ~ φ + nm B i ν in φ I Fig. from Krasheninnikov et al. JPP 08 He blobs in TORPEX ob [m/s] v blo [1,] a (blob size) [m] [3] [1] Garcia et al. POP 005 [] Myra and D Ippolito POP 005 [3] Krasheninnikov PLA 001 [4] Katz et al. PRL 008 [5] Theiler et al. PRL C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

10 Generalized scaling law: derivation Ji n z r ϑ J J pol Vorticity equation cs mi n nmi D = RB z B Dt φ ne c T L e c s ~ φ + nm B i ν in φ I Fig. from Krasheninnikov et al. JPP 08 He blobs in TORPEX [4] ob [m/s] v blo [1,] a (blob size) [m] [3] [1] Garcia et al. POP 005 [] Myra and D Ippolito POP 005 [3] Krasheninnikov PLA 001 [4] Katz et al. PRL 008 [5] Theiler et al. PRL C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

11 Generalized scaling law: derivation Ji n z r ϑ J J pol Vorticity equation cs mi n nmi D = RB z B Dt φ ne c T L e c s ~ φ + nm B i ν in φ I Fig. from Krasheninnikov et al. JPP 08 He blobs in TORPEX [4] ob [m/s] v blo [1,] a (blob size) [m] [3] [5] [1] Garcia et al. POP 005 [] Myra and D Ippolito POP 005 [3] Krasheninnikov PLA 001 [4] Katz et al. PRL 008 [5] Theiler et al. PRL C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

12 Generalized scaling law: derivation Ji n z r ϑ J J pol Vorticity equation cs mi n nmi D = RB z B Dt φ ne c T L e c s ~ φ + nm B i ν in φ I Fig. from Krasheninnikov et al. JPP 08 v blob = 1+ a cs R 1 R 5/ υin Ra a + ρ L c s c [1,] [3] [4] s δn n [5] [1] Garcia et al. POP 005 [] Myra and D Ippolito POP 005 [3] Krasheninnikov PLA 001 [4] Katz et al. PRL 008 [5] Theiler et al. PRL C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

13 Generalized scaling law and possible blob control Normalization: [1,] Variation of ã to test scaling law by Ion mass scan [3] Possibilities of blob control reduce connection length increase neutral gas pressure [4] [1] O. E. Garcia et al., POP 005 [] J. R. Myra and D. A. D Ippolito, POP 005 [3] S. I. Krasheninnikov, PLA 001 [4] N. Katz et al., PRL C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

14 The TORPEX device Toroidal device: R=1 m, a=0. m Open field lines, B and curvature Helical field lines Limiter Microwaves Parameters 14 A. Fasoli et al., POP B 76mT n 10 m B T z / B T 5% C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL T e e 15eV T << i T e

15 Target plasma A simplified model of the tokamak k far edge (SOL) z [m] r [m] 15 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

16 Blob formation Instability characterization: Poli et al. POP 06, POP 08 Ricci et al. PRL 10 Blob formation, propagation, transport, universal statistical properties of turbulence: Furno et al. PRL 08, POP 08 Müller et al. POP 07, PPCF 09 Theiler et al. POP 08, PRL 09 Diallo et al. PRL 08 Podestà et al. PRL 08 Labit et al. PRL 07, PPCF C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

17 Diagnostics and blob analysis Conditional sampling I sat Pattern recognition δi sat 17 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

18 Verification of velocity scaling law: ion mass scan Ion mass scan: 1 0. m i a~ [ a. m. u.] C. Theiler et al., PRL C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

19 Direct measurement of parallel current Blob parallel current at limiter: Single sided LP. Array of B-coils Current measurement at 3cm from limiter 19 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

20 Direct measurement of parallel current Blob parallel current at limiter: j cs m RB i n z L / = J // sheath Furno et al. TTG-TTF 010 Current dipole is asymmetric Parallel current significant to damp blob propagation in H More on parallel currents in filaments on RFX, ASDEX, and TORPEX: N. Vianello,Poster XP , Friday 0 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

21 Short summary Blob motion Different regimes of blob propagation (damping by parallel or cross-field currents) achieved by ion mass scan Good agreement between measured blob velocity and generalized scaling law D structure of parallel current is dipolar with a more pronounced negative pole Next: Attempts of blob control by Reduction of connection length Increase of neutral gas pressure Biased electrodes 1 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

22 Blob control: reduction of connection length Analysis with pattern recognition Data from several experimental sessions L c ~ 6m L c ~ 3m C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

23 Blob control: reduction of connection length Analysis with pattern recognition Data from several experimental sessions L c ( ) L c / ( ) 3 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

24 Blob control: reduction of connection length Analysis with conditional sampling Data from one single experimental session Determination of blob velocity, size, temperature L c ~ 6m 4 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

25 Blob control: reduction of connection length Analysis with conditional sampling Data from one single experimental session Determination of blob velocity, size, temperature L c ~ 6m L c ~ 3m 5 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

26 Blob control: variation of neutral gas pressure Analysis with pattern recognition, 4 different neutral pressures Analysis with cond. sampling, 3 different neutral pressures neutral pressure 6 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

27 Variation of boundary conditions: biased electrodes Idea [1] Induce poloidal electric fields to produce convective cells and thus broadening of SOL and reduction of heat loads on divertor Use of toroidally asym. divertor: wavy nd e - bias gas puff [] Tests in NSTX Local increase of SOL-width No significant effect 1m downstream [1] R. H. Cohen, D. D. Ryutov NF 1997 [] S. J. Zweben et al., PPCF C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

28 Biased electrodes: setup in TORPEX Array of 4 electrodes Each can be biased individually id and the current can be measured Some possible setups: 8 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

29 Biased electrodes: effect on profile and wave biasing no biasing Power spectral density 9 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

30 Biased electrodes: effect on blob m] z [m r [m] r [m] Next questions On what perpendicular scale can potential be varied What is the parallel penetration length of the bias potential What is the magnitude of potential variations that can be achieved 30 C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL

31 Summary Blob motion Different regimes of blob propagation (damping by parallel or cross-field currents) achieved by ion mass scan Good agreement between measured blob velocity and 31 generalized scaling law D structure of parallel current is dipolar with a more pronounced negative pole Blob control As expected, a reduction of connection length reduces blob b velocity in H and He and shows little effect in Ne and Ar As expected, blob velocity decreases eases with neutral gas pressure (shown for He) A D array of biased electrodes has been described and first effects on profiles, mode, and blobs b have been presented C. Theiler, 5 nd APS - DPP, Nov 8-1, 010, Chicago, IL