Experimental study of non-inductive current in Heliotron J

It is important to control non-inductive current for generation and steady-state operation of highperformance plasmas in toroidal fusion devices. Helical devices allow dynamic control of non-inductivecurrent through a wide variety of magnetic configurations. The reversal of non-inductive current consisting of bootstrap current and electron cyclotron driven current in electron cyclotron heating plasmas has been observed in a specific configuration at low density in Heliotron J device. By analyzing thenon-inductive current for normal and reversed magnetic fields, we present experimental evidence for the reversal of bootstrap current. Our experiments and calculations suggest that the reversal is caused bya positive radial electric field of about 10 kV/m. Moreover, we show that the typical electron cyclotron current drive efficiency in Heliotron J plasma is about 1.0 × 1017 AW?1m?2, which is comparable to other helical devices. We have found that the value is about 10 times lower than that of tokamak devices. This might be due to an enhanced Ohkawa effect by trapped particles

Present Status of the Nd:YAG Thomson Scattering System Development for Time Evolution Measurement of Plasma Profile on Heliotron J

A new high repetition rate Nd:YAG Thomson scattering system is developed for the Heliotron J helical device. A main purpose of installing the new system is the temporal evolution measurement of a plasma profile for improved confinement physics such as the edge transport barrier (H-mode) or the internal transport barrier of the helical plasma. The system has 25 spatial points with ~10 mm resolution. Two high repetition Nd:YAG lasers (> 550 mJ@50 Hz) realize the measurement of the time evolution of the plasma profile with ~10 ms time intervals. Scattered light is collected by a large concave mirror (D = 800 mm, f/2.25) with a solid angle of ~100 mstr and transferred to interference filter polychromators by optical fiber bundles in a staircase form. The signal is amplified by newly designed fast preamplifiers with DC and AC output, which reduces the low frequency background noise. The signals are digitized with a multi-event QDC, fast gated integrators. The data acquisition is performed by a VME-based system operated by the CINOS

Recent Progress in Plasma Control Studies on the Improvement of Plasma Performance in Heliotron J

Recent progress in plasma control studies on the improvement of plasma performance in Heliotron J is reviewed. The supersonic molecular beam injection (SMBI) fueling is successfully applied to Heliotron J plasma. A supersonic H2-beam is effectively injected to increase fueling efficiency and generate a peaked density profile. Local fueling with a short-pulsed SMBI can increase the core plasma density and avoid the degradation arising from edge cooling. Second harmonic electron cyclotron current drive (ECCD) experiments were conducted by launching a focused Gaussian beam with a parallel refractive index of −0.05 ≤ N‖ ≤ 0.6. Results show that the electron cyclotron (EC) driven current is determined not only by N‖ but also by local magnetic field (B) structure where the EC power is deposited. Detailed analysis of the observed N‖ and B dependences is in progress with a ray-tracing simulation using the TRAVIS code. Fast ion velocity distribution was investigated using fast protons generated by ion cyclotron resonant frequency (ICRF) minority heating. For the standard configuration in Heliotron J, charge exchange neutral particle analysis (CX-NPA) measurements show higher effective temperature of fast minority protons in the on-axis resonance case compared to that in the HFS (high field side) off-axis resonance case. However, the increase in bulk ion temperature in the HFS resonance case is larger than that in the on-axis resonance

ECCD Experiments Using the Upgraded Launching System in Heliotron J

Electron cyclotron current drive (ECCD) experiments have been made in Heliotron J by using an upgraded EC launching system. A focused Gaussian beam is injected with the parallel refractive index, N, ranging from -0.05 to 0.6. Ray tracing calculation shows that the EC power is more localized than that in the previous launching system. In the initial ECCD experiment, the EC injection angle has been successfully scanned as designed. Comparison between perpendicular and oblique launching experiments shows that for standard configuration, the EC current of 1 kA is driven at N~ 0.3 in the Fisch-Boozer direction, and the bootstrap current flows up to 1 kA. A large increase in electron cyclotron emission (ECE) signals has been observed when the EC current was driven