23P110-P
Flow measurement in double-pulsing CHI experiment on HISTHIST装置におけるダブルパルスCHI実験でのフロー計測
Mitsuru Ishihara, Kengo Ito, Takafumi Hanao, Keisuke Matsumoto, Tiki Higashi, Yusuke Kikuchi
Naoyuki Fukumoto, Masayoshi Nagata
石原 充, 伊藤兼吾, 花尾隆史, 松本圭祐, 東 大樹, 菊池祐介, 福本直之, 永田正義
Graduate School of Engineering, University of Hyogo
2167 Syosya, Himeji City, Hyogo 671-2280, Japan
兵庫県立大学大学院工学研究科 〒671-2280 兵庫県姫路市書写2167
Flux amplification and sustainment of the spherical torus (ST) configurations by operating in Multi-pulsing
Coaxial Helicity Injection (M-CHI) method have been demonstrated in the Helicity Injected Spherical
Torus (HIST) device. We have measured the radial profiles of the flow velocities by using Ion Doppler
Spectrometer and Mach probes. The result shows that poloidal shear flow exists between the open flux
column and the most outer closed flux surface.

1. Introduction
The new CHI method, so called multi-pulsing
CHI (M-CHI) [1] was applied for a hightemperature spheromak on SSPX at LLNL [2]. It is
important to investigate plasma flow, dynamo andmode structures between the spheromak and STplasma configurations. Thus, we have tested double
pulsing operations on the HIST device in order toexplore the usefulness of the M-CHI for the ST
configurations. In this experiment, we haveinvestigated the plasma flow profile and ion heating
due to dynamo in the double-CHI driven ST plasma
by using Ion Doppler Spectrometer (IDS) and Machprobes.
2. Experimental setup and results
The HIST device is a low aspect ratio torus withmajor radius R=0.30 m, minor radius a=0.24 m, andaspect ratio A=1.25 [3] (see Fig.1). The capacitorbanks (Vmax=10 kV, C=0.6-2.6 mF) are used for ST
formation. The two sustainment banks (Vmax= 900 V,
C=195 mF and 335 mF) have been prepared for the
double gun pulsing experiment. The HIST device
can sustain the ST by utilizing the variation of theexternal toroidal field (TF) coil current Itf.
Figure 2 illustrates temporal evolutions of the (a)toroidal plasma current It, (b) the line averaged
electron density <ne> in the core, (c), (d) the edge
poloidal magnetic field Bp.in, Bp.out at the inboardside (R=0.15 m) and the outboard side (R=0.45 m)
and the ion Doppler temperature TiD (OII: 441.5nm) in the comparison of single and double pulsed
discharges. By secondly pulsing the MCPG at t =1.5 or 2.5 ms during the partially decay phase, total
plasma current is effectively amplified against theresistive decay. The core current density isgenerated due to dynamo. By secondly pulsing theMCPG at t = 1.5 or 2.5 ms during the partiallydecay phase, the total plasma current is effectively
amplified against the resistive decay. The corecurrent density is generated due to dynamo. Theedge λ in the OFC is larger than the core λ, causing
helicity transport from the edge to the core. Ion
Doppler temperature TiD increases from 20 eV up to30 eV after the second CHI pulse, suggesting theion heating due to dynamo.

Fig.2. Time evolution of (a) It, (b) <ne>, (c) Bp.in(R=0.15 m), (d) Bp.out (R=0.45 m), (e) TiD in thecomparison of single (#14162) and double pulsed
discharges (#14160).
Fig.1. HISTFigure 3 displays comparison of a radial profileof poloidal and toroidal flows (a)(b), electron
density (c) and radial electric field Er (d) between
before and after the second CHI pulse. The result
from the measurement shows that poloidal flow
velocity shear exists between the OFC and the lastclosed flux surface, i.e., at the separatrix. As seen inFig.3 (a), there is a large poloidal flow in the ion
diamagnetic direction at the OFC with the peak at R
= 0.15 m. The poloidal flow shear may be causedby the diamagnetic drift of ions vpol=-∇p×Bt/ZenB2
that being larger than the Er×Bt drift because of asteep density gradient there as shown in Fig.3 (c).
This is consistent with the observation that the OFC
has a diamagnetic toroidal magnetic field structure.
The negative Er ~∇pi/en − (v×B) (the inward way
to the magnetic axis) may be produced by the crossfield flow rather than the ion pressure gradient. It
should be noted that the direction of the toroidal ion
flow in the OFC is anti-parallel to that of theelectron flow. The second CHI pulse tends toincrease the poloidal flow shear and decrease thetoroidal flow shear which suggests that the ion flow
is driven in the poloidal direction by the CHI pulse.
Figure 4 shows the poloidal flow profile of theimpurity and neural particles obtained by the IDS
measurement of OII and Hβspectral lines. Although
this is not a local flow, the shear profile of the OII
impurity flow is similar to the Mach probe data, but
the direction in the OFC (R< 0.1 m) is not reversed.
On the other hand, we can see that the Hβpoloidal
flow is reversed in this region. This reason isunclear at present. According to the formulavpol=Er×Bt − ∇ p×Bt/ZenB2, the diamagnetic drift
velocity of impurity particles is decreased by afactor of Z as compared to the Er×Bt drift so that thediamagnetic poloidal flow velocity of the OII
impurity particles is slower than that of the ion.

FIG. 3. Radial profiles of (a) vpol,(b)vtor, (c) ne, (d) Er.

3. Summary
We have successfully demonstrated theflux/current amplification and sustainment of theplasmas in the double gun pulse experiment. Machprobe and IDS measurements have shown that thereis the strong poloidal flow shear due to the ion
diamagnetic drift around the separatrix.
References[1] E.B. Hooper, Plasma Phys. Control. Fusion 53,085008 (2011).
[2] S. Woodruff, et al., Phys. Rev. Lett. 90,205002-1 (2004).
[3] M. Nagata, et al., Phys. Plasmas 10, 2932
(2003).

FIG. 4. Radial profiles of (a)Vpol of OII,(b)Vpol of Hβ.