High Power Heating of Magnetic Reconnection for High-Beta ST Formation in TS-3 and UTST ST Merging Experiments Y. Ono, H. Tanabe, Y. Kamino, K. Yamasaki, K. Kadowaki, Y. Hayashi, T. Yamada, C. Z. Cheng Univ. Tokyo, Japan, National Cheng Kung Univ. Tw. UTST TS-3 TS-4 PF Pair Coils PF Pair Coils 0.7m
Magnetic reconnection of two merging toroidal plasmas B field lines and j t measured by 2-D magnetic probe array. B t I Z B p B p T e
ST Merging for Reconnection Heating t Vou t j t Vou
2011 RSI by Tanabe et al. 2-D fiber bundle 1-D fiber bundle line-of-sight at the toroidal plane Relay lens Slit Realignment (from 2-D to 1-D) 2-D fiber array Polychromator ICCD 2-D Optical fiber position R [mm]: radius (tangential view) 280 245 210 175 140 105 70-48 -29-10 9 28 Z[mm]:Axial Position
λ 1. Extract each code spectrum from ICCD Image Imin Imax ICCD Image λ Fiber Code Number Intensity 0 Imax Inversion emission profile I(r,λ)dx λ I (r,λ) λ
70 T i [ev] R [mm] 0 Z [mm]
First 2-D T i measurement of reconnection Clear evidence of ion heating by outflow! Fast Shock V out j t V out Fast Shock High Guide Field 50µs 55µs 60µs
At down-stream, hot T i spot, steep increase in n e and dumping of ion flow appear, indicating fast shock formation. 0.28 R[m] 80 Ion Velocity [kms -1 ] 40 (c) 0 current sheet thickness PF/Acc. Coils 0 Sep. Coils Z[m] PF/Acc. Coils T i [ev] v r [kms -1 ] 60 40 20 40 0-40 (d) (e) flow flow current sheet length I Z (a) B t B p B p (b) B t 0.06-0.2 0 0.2 Center Coil T e Z[m] T i n/ B 10 17 [G -1 m -3 ] 2 1 0 n 1 /B 1 ~n 2 /B 2 R [m] I tfc n e [ 10 19 m -3 ] B [G] 5 4 3 2 1 300 200 100 (f) (g) Shock Shock R [m]
2D profiles of reconnection inflow and outflow fast shock? 29µs 30µs 32µs fast shock 20 R [cm] 15 fast shock : 50km/sec -2 2-2 2-2 2 Z [cm] Z [cm] Z [cm]
Significant ion heating in downstream and localized electron heating inside the current sheet. High power heating suppresses paramag. B t, increasing plasma beta. Shock? Shock? I Z B t B p j t B p High Guide-Field Outflow B t 0 T i (b) R[m] PF/Acc. Coils Sep. Coils -0.2 0 Z[m] 0.2 Center Coil 55µsec 75µsec 50 µsec 70 0 15 I tfc 1 Bt [kg] 0.1 R [m].3.1.2.3.1.2.3 T e
Energy Flow during Reconnection High Guide-Field Magnetic Energy Dissipation 145J Outflow Energy Large ion heating Current Sheet Heating E JdVdt 13J Small electron heating Increment of Ion thermal Energy 128J Smaller reconnecting B field than that of counterhelicity merging.
1) Rec. rate and ΔT i decrease with B t before plasmoid ejection. 2) Rec. rate and ΔT i increase significantly after plasmoid ejection. Rec. Rate 10 6 [sec -1 ].3.2.1 150 (a) Anomalous Resistivity(δ<ρ i ) Sheet Ejection B z Ejection V r B z T i [ev] 100 after reconnection Sheet Ejection 50 before (b) reconnection 0-1 0 1 2 3 4 5 6 large B ρi t0 /B //
Plasmoid Ejection increases rec. speed and T i. (a) Fast inflow reconnection (b) Slow inflow reconnection Compression High Guide-Field
Formation of Absolute Min.-B The rec. heating transforms paramagnectic merging STs to diamag. ST with abs min-b. High-Beta ST B p ST B p B p I Z B t B t B t ST Low-Beta ST 0 [kg]. 3 B (a) (b) Ψ q Averaged Beta.2 B [T] (c) 0 0 R[m].3 10 (d) 0 0 Ψ/Ψ 1 1 0 1.8 (e).8.6.4.2 1 B B t0 2 ε 3 Min-B Area Ratio.6.4.2 T i [ev] V r [kms -1 ] B [G] n e [ 10 19 m -3 ] 60 40 20 40 0-40 5 4 3 2 1 300 200 100 (a ) (b ) (c ) (d ) t=60µsec Abs. Min-B.07.14.21.28 R [m]
Comparison with Troyon Scaling Merging Formation of Ultra-High ß ST with ß N <20 A: 2nd stable B: unstable C: 1st stable D: unstable Reconnection Time < Growth Time of Instabilities TS-3, 4
B //2 -scaling for ion heating of reconnection ITER Regime ITER Regime high B t rec. (tokamak plasma) low B t rec. (spheromak) Δ W m /W m ~100% zero B t rec. (counter) MAST (R~.9m) Δ W m /W m =1% TS-4 (R~.5m)
MAST-TS Collaboration M. Gryaznevich, R. Scannel The reconnection startup heats ions and electrons much higher than the conventional CS startup. Y. Ono et al. to be published in PPCF MAST Rec. startup CS startup Rec. startup CS startup T e [kev] Merging T i [kev] Merging MAST
Summary and Conclusions 1) Reconnection outflow heats ions by fast shock in two downstream regions where T i peaks. 2) Electron heating occurs inside current sheet and T e peaks at X-point. 3) Ion heating power >> Electron heating power 4) Ion heating energy and T i increase with B //2. 5) The high-power rec. heating forms high-ß ST with absolute minimum B profile. Reconnection heating power in MAST is much higher (> kev) than TS-3 and 4 due to its higher reconnecting field B // and better energy confinement. Direct ion heating by rec. is a promising method for heating ions > 10keV for fusion plasmas.