Plasma current start-up experiments using outboard- and top-launch lower hybrid wave on the TST-2 spherical tokamak

Abstract

Non-inductive plasma current start-up experiments were performed using the lower hybrid wave (LHW) on the TST-2 spherical tokamak. The density limit, observed in previous experiments using the outboard-launch antenna, disappeared after changing the plasma condition in the scrape-off layer, and the plasma current reached about 20 kA. In order to improve the LHW power deposition in the plasma core through an up-shift of the parallel wavenumber during the first pass through the plasma, a new top-launch antenna was designed, fabricated and installed. The plasma current ramp-up to 12 kA was achieved using the top-launch antenna alone in a preliminary experiment. Ray-tracing calculations using the measured plasma parameters showed a large up-shift during the first pass, satisfying the strong electron Landau damping condition in the plasma core.

On the breakdown modes and parameter space of ohmic tokamak start-up

“…1987) and low hybrid wave heating (LHWH) (Yoshino & Seki 1997; Shinya et al. 2017) started being employed to help initiate the discharge. Experiments (Gilgenbach et al.…”

A simulation environment to simulate lower-hybrid-wave-driven plasmas efficiently

“…In the past, on the one hand the coupled GENRAY/CQL3D simulation has been proven useful [26,16] to evaluate LH-wave-driven plasmas in spherical Tokamaks. On the other hand, the MHD-kinetic particle code MEGA [22,21,29,23] has been successfully applied to investigate the interaction between energetic particles and the bulk plasma.…”

“…Conventional ratio tokamaks are favorable for LH current drive since the plasma dielectric constant is lower because of the higher magnetic fields compared to ST devices [12]. In TST-2, an ST device with major radius R 0 =0.36 m, minor radius a=0.23 m, aspect ratio A = R 0 /a ≥ 1.6, toroidal magnetic field B t ≤ 0.3 T, and plasma current I p ≤ 0.14 MA [19], non-inductive plasma current start-up using LH waves has been investigated thoroughly [18,28,25,15,16]. A recently installed capacitively coupled combline (CCC) antenna [16] has a coupling efficiency of nearly 100% and can be applied at high power.…”

“…In TST-2, an ST device with major radius R 0 =0.36 m, minor radius a=0.23 m, aspect ratio A = R 0 /a ≥ 1.6, toroidal magnetic field B t ≤ 0.3 T, and plasma current I p ≤ 0.14 MA [19], non-inductive plasma current start-up using LH waves has been investigated thoroughly [18,28,25,15,16]. A recently installed capacitively coupled combline (CCC) antenna [16] has a coupling efficiency of nearly 100% and can be applied at high power. Recently, plasma current ramp-up to 25 kA has been achieved injecting 74 kW of net RF power at 200 MHz.…”

Reconstruction of plasma shape and eddy current profile based on modified cauchy condition surface method in merging spherical tokamak

“…Thus, establishment of CS-free start-up scheme is strongly required. Various types of start-up methods, such as introductions of the electron cyclotron waves, the electron Bernstein waves [2,3], the lower hybrid wave [4], the coaxial helicity injection [5][6][7][8], the induction by vertical field [9][10][11], and the merging technique [12,13], are being developed in many experimental devices.…”