Overview of the recent experimental research on the J-TEXT tokamak

Abstract

Recent J-TEXT research has highlighted the significance of the role that non-axisymmetric magnetic perturbations, so called three-dimensional (3D) magnetic perturbation (MP) fields, play in a fundamentally 2D concept, i.e. tokamaks. This paper presents the J-TEXT results achieved over the last two years, especially on the impacts of 3D MP fields on magnetohydrodynamic instabilities, plasma disruptions and plasma turbulence transport. On J-TEXT, the resonant MP (RMP) system, capable of providing either a static or a high frequency (up to 8 kHz) rotating RMP field, has been upgraded by adding a new set of 12 in-vessel saddle coils. The shattered pellet injection system was built in J-TEXT in the spring of 2018. The new capabilities advance J-TEXT to be at the forefront of international magnetic fusion facilities, allowing flexible study of 3D effects and disruption mitigation in a tokamak. The fast rotating RMP field has been successfully applied for avoidance of mode locking and the prevention of plasma disruption. A new control strategy, which applies pulsed RMP to the tearing mode only during the accelerating phase region, was proved by nonlinear numerical modelling to be efficient in accelerating mode rotation and even completely suppresses the mode. Remarkably, the rotating tearing mode was completely suppressed by the electrode biasing. The impacts of 3D magnetic topology on the turbulence has been investigated on J-TEXT. It is found that the fluctuations of electron density, electron temperature and plasma potential can be significantly modulated by the island structure, and a larger fluctuation level appears at the X-point of islands. The suppression of runaway electrons during disruptions is essential to the operation of ITER, and it has been reached by utilizing the 3D magnetic perturbations on J-TEXT. This may provide an alternative mechanism of runaway suppression for large-scale tokamaks and ITER.

Disruption prevention using rotating resonant magnetic perturbation on J-TEXT

“…J-TEXT [27] is a circular cross-section tokamak with the major radius R0 = 105 cm (at magnetic axis) and minor radius a = 25.5 cm in our experiments. The m/n = 2/1 tearing mode usually appears in the operation regime with a sufficiently large plasma current Ip.…”

The development of 1 MW ECRH system on J-TEXT

“…The J-TEXT tokamak is a conventional iron core tokamak reconstructed from the Texas Experimental Tokamak Upgrade (TEXT-U) [5][6][7]. The basic operation parameters of J-TEXT are listed in Table 1.…”

Disruption prediction based on fusion feature extractor on J-TEXT

“…[19] J-TEXT is a mid-sized limiter configuration tokamak with a minor radius a = 0.25 m and a typical plasma I p of around 200 kA, a toroidal field B t of around 2.0 T, a pulse length of 800 ms, a plasma densities n e of 1-7 × 10 19 m −3 , and an electron temperature T e of about 1 keV. [20] The J-TEXT tokamak has a complete diagnostic system. The three-wave FIR laser polarimeter-interferometer system (POLARIS) is provided to obtain electron density and current profiles with high temporal and spatial resolution.…”