Electrodes

1. Pull Merging R=0.15-0.22m , R/a=1.6 B ~.5kG , T =10-100eV , i 0 T =20-30eV , e Push Merging j' 20 t n =0.5-1. 1 0 m - 3  e j t j t Impulsive and Transient Magnetic Reconnection in TS-3 and TS-4 Merging ExperimentsY. Ono, T. Hayashi, M. Inomoto, C. Z. Frank Cheng Graduate School of Frontier Sciences, University of Tokyo, Tokyo E F Coils Separation Coils 2- D Magnetic Probe Array Electrostatic Probe Torus/OH coil r z CO2 Laser Interferometer PF Coils Electrodes Polychromator

2. "Close d Current , Open Flux" "Close d Current , Close d Flux" Close MRX('95~) VTF('00~) Sheet Current Electrode Sheet Current hole Merging Experiments for Magnetic Reconnection Open Flux d Flux Internal Coil Sheet Current Close d Current TS-3('86~) , TS-4('00~), , SSX, Swift-FR C ('01~) , TS-5(UTST ‘05?) Open Current "Open " Exp. Type Caltech Exp.('98~) SS X ('96~) "Open Current , Close d Flux" Electrode

3. Pull Merging Experiment Push Merging Experiment Impulsive and Transient Magnetic Reconnection in TS-3 and TS-4 Merging ExperimentsY. Ono, T. Hayashi, M. Inomoto, C. Z. Frank Cheng Graduate School of Frontier Sciences, University of Tokyo, Tokyo Operation: Magnetic Reconnection Exp. High-ß FRC/ ST Formation Boundary Exp. of CT/ST/RFP

4. Theory& Simulation Major four researches have advantages and disadvantagesCollaboration among four fields Magnetosphere Observation Solar Observation Laboratory Experiment

5. CONTENTS ● High-power reconnection heating for fusion plasma startup (for Fusion Application) TS-3/4 ● Transition from steady rec. through transient one to sheet ejection (for Space/ Solar Study) [1] Impulsive sheet ejection: Push Merging:TS-3/4, in low resistivity/ high inflow. exp MAST from private to common flux, pileup & ejection [2]Mass pileup in high inflow exp. [3] Quasi-steady rec. in low inflow merging exp. [1’] Impulsive plasmoid ejection:Pull Merging:TS-4 from common to private flux, pileup & ejection

6. High-power reconnection heating for startup of fusion plasmas Most of ion heating energy is confined by thick closed flux around X-point.

7. Second-Stable ST with Absolute Minimum-B High-ß ST by merging Low-ß ST w/o merging Comparison with Troyon ScalingST merging :ßN<10C: 1st stableD: unstableCounterhelicity Merging: ßN<20A: 2nd stableB: unstable

8. Question Can the reconnection heat plasmas under high guide field Bt? = How can we have high reconnection (outflow) speed when >>i?

9. jt [MA/m2] Effective resistivity (E/j) of current sheet increases significantlywhen  is compressed shorter than ri. (no correlation with c/pi). • : thickness

10. Sheet Ejection 3 150 Sheet Ejection B /B =0.5 B /B =2.2 //0 t t //0 V 2 B /B =1.0 B /B =2.7 B r //0 //0 t t z m] B /B =1.6 B /B =3.2 t //0 t //0 100 W 1 [m before (b) (t) reconnection 0 50 0 1 2 3 4 5 6 h X [ / ](t) d r i Large Bt B 0 z -1 0 1 2 3 4 5 6 Ejection .3 Anomalous Resistivity(d<ri) g´10[sec-1] Transition to intermittent reconnection increases averaged rec. speed as well as Ti significantly. .2 (a) .1 after reconnection Ti [eV] Bt0/B// large ri Reconnection rate as a function of Bx

11. Current-Sheet Ejection (a) High inflow reconnection (b) Low inflow reconnection Compression

12. Compression Multiple current-sheet ejections are composed of pileup and ejection. Inward Compression Reconnected flux ratio [%] ejection [1] Rec. from private flux to common flux

13. jt [MA/m ] 2 [A] Quasi-Steady Reconnection [B] Transient Reconnection [C] Intermittent Reconnection Slow inflow causes the quasi-steady reconnection. Quasi-Steady Phase Formation Phase Quasi-Steady Decay Formation Inflow Outflow 0 2 4 6 8 10 12 Time[µsec]

14. jt [MA/m ] 2 [A] Quasi-Steady Reconnection [B] Transient Reconnection [C] Intermittent Reconnection Fast inflow causes the mass pile-up inside the sheet, transforming the steady rec. to the transient rec. Transient (Formation) Pileup VinL, Voutd [m2sec-1]

15. Uniform Compression [A] Quasi-Steady Rec. [B] Transient Rec. [C] Intermittent Rec. 500 400 300 V L in 200 V d out 100 0 0 2 4 6 8 10 12 jt [MA/m ] 2 Further increase in inflow causes significant pileup in the sheet and the mass ejection. Compression Quasi-Steady Phase Transient (Formation) ejection Inflow Pileup /sec] /sec] 2 2 Outflow [m L [m d out in V V Time [µsec]

16. 5 -3 4 10 [m ] 19 3 ｴ 2 n 1 5 -3 4 10 [m ] 19 3 ｴ 2 n 1 5 -3 4 10 [m ] 19 3 ｴ 2 n 1 0.2 0.1 0.3 R [m] Evidence of density pileup and mass ejection t=194µsec t=196µsec t=174ｵsec t=176ｵsec 0 t=195µsec t=175ｵsec t=177ｵsec t=197µsec n (density) V r 0 Double-peaked profile! t=196µsec t=198µsec t=178ｵsec t=176ｵsec 0 0.2 0.1 0.3 Ejection V R [m] r

17. L u u d Pile-up Pile-up v v v v eject eject A A The combination of mass pileup and ejection explain effective mass ejection. Ejection where pileup factor Ejection For simplicity, Ejection

18. 1 ) Reconnection of private flux to common flux 2 ) Reconnection of common flux to private flux j' t j j' j t t t j t j t Mass ejection j j t t AP J Yokoyama Shibata et al. 1996 AP J Yokoyama Shibata et al. 1995

19. Merging from Private Flux to Common Flux?

20. Merging from Common Flux to Private Flux

21. Plasmoid Ejection (closed flux) formation ejection 40 .43 -.43 .1 0 -.1 Small-size Large-size J [MAm-2] Z[m] Et [Vm-1] 20 20µsec 40µsec 0µsec.09 R[m] .72 60µsec 80µsec Push Merging 0 0 100 200 Time [µsec] Current Sheet Ejection (No closed flux) The high inflow causes ejection of plasmoid with closed flux in the pull merging experiment with high guide field. Pull Merging

22. Max Et & dV/dt 40 Et [Vm-1] 20 Z [cm] dV/dt [102kms-2] V [kms-1] 0 100 50 Time [µsec] The maximum reconnection speed Et is obtained, when the plasmoid acceleration is maximized. Time evolutions of reconnection electric field Et, position Z, velocity V and acceleration dV/dt of ejecting plasmoid

23. 8 6 4 2 190 195 200 205 Ejection Push Merging Mode Large increase in h occurs 1-2µsec after that in inflow speed.Large increase in inflow speed can not be explained sorely by sheet ejection.  [km/sec] High speed rec.  at X-point [mm] Delay Uniform Compression 0

24. How does the sheet ejection cause large increase in? Thinning of sheet?----NO Ejection Ejection Ejection <ri Ejection Really d <ri? Fractal Sheet? New Effect? The ejection induces the inflow =Br increases Sheet d comp. <ri causes the large increase in h.

25. Ejection 3 B /B =0.5 B /B =2.2 //0 t t //0 2 B /B =1.0 B /B =2.7 //0 //0 t t m] B /B =1.6 B /B =3.2 t //0 t //0 W 1 Ejection [m (t) 0 0 1 2 3 4 5 6 h X [ / ](t) d r i Large Bt Fine structures of current sheet were observed during the sheet ejection, possibly causing increase in . Each <ri total ri Fractal Sheet? New fine scale probe array in TS-4

26. CONCLUSIONS ● Huge reconnection heating for fusion plasma startup. ●Large increase in CS resistivity when CS () < i. ●Quasi-steady rec. was transformed to impulsive rec. with comp. force (inflow) in Push Merging exp. • Pileup of density and flux / their ejection. • Pileups of mass increase the rec. speed. 3) The current sheet ejection also causes the high rec. speed due to large mass ejections from X-point region. ●Similar impulsive reconnection in high inflow Pull Merging exp. • Pileup of density &plasmoid ejection cause impulsive rec. in high inflow case. ●Extension of rec. heating to the new UTST exp.

27. Smal l ST RF NBI Coils ST Washer-gun plasma ST ST Coils Smal l ST Mer gin g Startu p o f High-Bet a S T usin g Null-Points U. Tokyo UTST Experiment for High-ß ST Startup and RF Sustainment UTST with NBI (0.5MW) PF Coils