28E12P
RELAXプラズマのパラメータ領域
Plasma Parameter Regimes in RELAX
田中裕之1，出口和明1，中木聖也1，西村香苗1，三瓶明希夫1，比村治彦1，政宗貞男1，江尻晶2，川端一男3，秋山毅志3，D. J. Den Hartog4，小口治久5
Hiroyuki Tanaka，Kazuaki Deguchi, Seiya Nakaki, Kanae Nishimura，Akio Sanpei, Haruhiko Himura and Sadao Masamune et al.
1

京都工芸繊維大学，2東京大学，3NIFS，4ウィスコンシン大学，5産総研
1
Kyoto Institute of Technology, 2The Univ. Tokyo, 3National Institute for Fusion Science,4
Univ. Wosconsin , 5National Institute of Advanced Industrial Science and Technology
１．Introduction
The reversed field pinch (RFP) is one of themagnetic confinement systems for fusion energy
research. The RFP, high beta plasmas can be
confined with weak external magnetic fields;
magnetic pressure at the toroidal field coils is
about 1/10 of that in tokamaks. The RFP thus
has a potential for commercially attractive
fusion reactor.
Some theories have predicted that pressure
driven bootstrap current fraction increases as
the aspect ratio A is lowered; an equilibrium
analysis has shown that the bootstrap fraction
higher than 90% is expected, if the beta value of~60% could be achieved in reactor-relevantplasmas. Thus, the aspect ratio is an importantparameter for optimization of the RFP
configuration.
２．RELAX machine and diagnostics
RELAX is a RFP machine at Kyoto Institute ofTechnology. It uses a SS vacuum vessel withmajor radius R of 0.5m, and minor radius a,0.25m. Major objectives of RELAX includes theMHD studies in low-A RFP configuration,
experimental verification of the bootstrap
current in the RFP configuration by achieving
the beta values of 20-30%. For the latter
experiments, the target (achieved) plasma
parameters are as follows: pasma current
Ip~100kA(125kA), entral electron temperature
Te(0)~200-300eV (150eV), with line-averaged
electron density ne ~ 2-4×1019m-3 (2×1019m-3).
Equilibrium and MHD stability control systems
characterizing the RELAX machine are as
follows: passive equilibrium control with
distributed poloidal windings for Ohmic heating,feedback controlled saddle coils at the insulated
poloidal gaps to compensate for the m=1 fielderrors localized at the gaps, and saddle coilarray (×16 toroidally , ×4 poloidally) for feedback

control of MHD instabilities.
Thomson scattering system using a Nd:YAG laser canmeasure the central electron temperature, and a
104GHz interferometer provides the line-averaged
electron density. Some soft-X ray (SXR) diagnostics
such as a high-speed SXR pin-hole camera and 20
chord photo-diode arrays with thin-foil filters, haveprovided electron pressure profile information.

３．Results
Figure 1 shows an example of 100kA discharge. The
feedback control of a single MHD mode (m=1/n=2
RWM in this case) is inevitable in achieving discharges
longer than ~2ms. Figure 2 shows the central electrontemperature measured at 1ms into the discharge vs.
plasma current. The electron temperature increases withplasma current, and ~150eV at Ip~100kA. The achieved
parameter regimes are as follows: Ip~125kA,
ne~0/2-2.0 × 1019m-3, Te(0)~150eV, and discharge
duration ~3ms. Further optimization of the discharge isin progress for improving the plasma performance
particularly at high current (Ip>100kA) regime.

Fig.1：feedback control effect(red：without control, blue: with control)

Fig.2：Electron temperature obtained by Thomson scatteringsystem