磁力管合体における磁気ヘリシティー保存性に関する 実験的検証 小野靖, 河森栄一郎 TS-3 & 4 グループ 東京大学・高温プラズマ研究センター

1.Ion particle effect on rec. speed 2. Anomalos ion heating High-ß ST ramp-up 3. Plasmoid ejection Progress in TS-3/4 Merging ST Exp.

Clear evidence of ion heating by outflow! Masuda et al Shibata et al Loop top hard X-ray sources

CONTENTS Helicity effect of two colliding force-free toroids Helicity control by co / counter-helicity merging. 1) Global Helicity Effect ----Global bifurcated relaxations ( Nucl. Fusion ‘99) ● Taylor relxation to low-ß force-free state. ● New kinetic relaxations to high-ß state ● Helicity conservation / annihilation /energy release Yokoyama, Shibata Nature ‘95 Shimizu, Tsuneta, Astrophys. J. 93

What will the merging spheromaks with varied K relax to ? The counterheilcity merging varied K from zero to K Taylor. Large K Total helicity K=0 K=K Taylor

K ／ W Scan Experiment ヘリシティーのバランスしない２個のスフェロマックの合体を用いると（ＭＨＤ 不安定の問題なく）プラズマ全体の磁気ヘリシティーＫ／磁気エネルギーＷを （０付近でも）自由に設定できる。 スフェロマック＃１（ Taylor 状態） K 1 ／ W 1 = a スフェロマック＃２（ Taylor 状態） K 2 ／ W 2 = a 合体プラズマの磁気ヘリシティー K = K 1 - K 2 （ Counter-helicity Merging のため ) 合体プラズマの磁気エネルギー W = W 1 + W 2 （ Merging のタイプに無関係） ２個の初期スフェロマックの磁気ヘリシティー比 K2/ K1 （磁束比  2/  1=  ）を０から１まで変化させれば、 K/W 値は ０から Taylor 状態の値 = a の範囲で自由に設定することができる。

Global Effect : How do the merging toroids relax? Force-Free Loop (Spheromak) vs. High-ß Loop (FRC) Spheromak Taylor State low-ß state FRC High-ß state

Bifurcated Relaxations to Non-Tayor State (FRC) and to Taylor State: Spheromak a)Merging spheromaks with K c >K>0 relax to a Non-Taylor state: high-ß FRC.

Bifurcated Relaxations to Non-Tayor State (FRC) and to Taylor State: Spheromak b) Merging spheromaks with K Taylor >K>K c relax to a Taylor state: spheromak

K Taylor >K>K c ⇨ K/W approaches (K/W) Taylor Tayor Relaxation K c >K>0 ⇨ K/W approaches Non-Tayor Relaxation Non-Taylor Relaxation (Annihilation of helicity) Taylor Relaxation to another spheromak Taylor State (spheromak)

Large Increase in T i ⇨ Relax to High-ß FRC No Increase in T i ⇨ Relax to Taylor State Spheromak Relaxation to an FRCRelaxation to another spheromak

The largest magnetic energy release of counterhelicity reconnection. If toroidally symmetric and kinetic (fusion plasma), relaxation to an FRC. If not (solar coronas etc.), the most violent energy release to space. See Y. Ono et al. Phys. Rev. Lett. 76, 3328, ‘99. Spheromak (ß=0-0.1) toroidal magnetic energy Energy Loss Flux conversion

How does the merging causes large energy-release? If merging toroids have K norm >0.4, relaxation to min. energy state causes energy loss W(const.)- K. However, if K norm <0.2, they relax to another stable state. W=const., K is varied. If  Bt >>  i, Taylor relxation loses huge energy because K:conserved, W: relax to K. K norm W loss Relaxation to Spheromak? huge energy loss Magnetic energy of produced spheromak

Possible Mechanism for the Bifurcated Relaxations: Poloidal current I p was maintained or annihilated depending on I p loop radius  B t >  i or  B t <  i. Relaxation to spheromak (force-free) Relaxation to FRC (high-ß) K norm =(K/W) /(K/W) Taylor

Mechanisms for Taylor and new high-ß relaxations Low-ß relaxation High-ß relaxation

TS-4 large  i (~ i ) exp.: R TS-4 ≈3R TS-3 The regime for FRC relaxation is wider in Ar discharge with larger i, while that for the Taylor relxation is wider in H discharge with smaller i. Taylor relaxation FRC relaxation Time evolutions of normalized eigenvalues K/K Taylor of merging spheromaks with varied initial helicities (K/K Taylor =1: Taylor state) Small i Large i K/K Taylor

テーラー状態へ緩和する限 界となる境界値  /  は S* が大きいほど広範囲. 回転が止まる範囲と Taylor 緩和する範囲が一致  ：緩和前の固有値 (j/B)  y  ：緩和前の固有値 ( =j p /B p ) S* ： プラズマ径 / イオンスキン長 Taylor 状態へ緩和 FRC へ 緩和 K/K Taylor

CONCLUSIONS Helicity Effects on Reconnection/Merging were studied using co/ counterhelicity merging with varied K but equal W Global Effect Bifurcated relaxations 1) Two merging force-free plasmas relax either to another force-free plasmas or to high-ß FRC, depending on whether initial K>K c or K<K c. 2) The threshold value K c is dermined by that where  i =  Bt, indicating the high-ß relaxation is caused by some kinetic effect. 3) The largest energy release was observed in counterhelicity reconnection with  i <  <  Bt.

TS-4 ST/ FRC Merging Device R= m, A= , B t0 <3-5kG, I p ≈300kA Operation: 1) FRC merging formation 2) High-ß ST formation by FRC 3) Boundary study of CTs/STs