Abstract. Two-dimensional (2-D) particle-in-cell (PIC) simulations are performed to investigate the evolution of the electron current sheet (ECS) in guide field reconnection. The ECS is formed by electrons accelerated by the inductive electric field in the vicinity of the X line, which is then extended along the x direction due to the imbalance between the electric field force and Ampere force. The tearing instability is unstable when the ECS becomes sufficiently long and thin, and several seed islands are formed in the ECS. These tiny islands may coalesce and form a larger secondary island in the center of the diffusion region.

Rayleigh–Taylor instability (RTI) is a primary hurdle for many different fusion approaches, most of which rely on external pressure to stabilize the plasma by impeding plasma displacement. In this paper, we report a novel method that utilizes a rotating magnetic field (RMF) to drive an azimuthal electron current to reduce the charge separation caused by RTI. The fluctuation measured in the central cell of the mirror device, approximately half a device length away from the RMF, is identified as the m=1 mode and is suppressed by the RMF in the plug cell. The azimuthal electric fields of the fluctuation are found to decrease to almost zero, and the radial confinement is improved by more than a factor of ten. The separation of the RMF region from the central cell makes this stabilization method unique because the RMF, which can complicate the local magnetic field lines, has little influence on the magnetic field configuration in the central cell. This study may shed light on the use of resonant magnetic perturbations in tokamaks as well as on stabilization methods for many other fusion experiments.

We report a novel method to control plasma rotation speed, namely, using the rotating magnetic field (RMF), which is a mature technique to form field reversed configuration, to drive the electron rotation and then the ion rotation via electron–ion collisions in a magnetic mirror plasma. It can be observed that the plasma starts rotating if the RMF strength exceeds a threshold value, corresponding to which the value of the magnetization parameter becomes larger than the value of the penetration parameter. The flow speed achieved in this experiment is approximately 0.14 Mach. The rotation is found to start from outside to inside with the propagating time almost equal to the penetration time of the RMFs. Also, a clear sheared flow is observed to have developed in the region of core plasma. It has been further identified that the electron–ion friction is the dominant force to drive the ion spinning up. The rotation speed is primarily determined by the RMF strength, instead of background magnetic field strength, which may offer a method to study the effect of rotation on the confinement in different magnetic field strengths while keeping the rotation profile intact.

In this paper, we report the results of ion cyclotron resonance frequency (ICRF) heating in the central cell of a fully axisymmetric tandem mirror. With a total power of 100 kW radiated by double half-turn and half-turn antennas, the plasma diamagnetism increases by 15-fold, with a corresponding peak β⊥ ∼2%, density ∼1.5×1018m−3, and total temperature ∼60 eV. The effects of the magnetic configuration on resonance heating and wave emission are studied by varying the magnetic fields at the midplane and at the location of the antennas, respectively; the results confirm that the magnetic beach configuration is key to successful ICRF heating. The axial phase speed measurements suggest that the excited wave is a slow wave in the plasma core and a fast wave at the edge.

A new medium-sized washer gun is developed for a plasma start-up in a fully axisymmetric mirror. The gun is positioned at the east end of the Keda Mirror with AXisymmetricity facility and operated in the pulsed mode with an arc discharging time of 1.2 ms and a typical arc current of 8.5 kA with 1.5 kV discharge voltage. To optimize the operation, a systematic scan of the neutral pressure, the arc voltage, the bias voltage on a mesh grid 6 cm in front of the gun and an end electrode located on the west end of mirror, and the mirror ratio was performed. The streaming plasma was measured with triple probes in the three mirror cells and a diamagnetic loop in the central cell. Floating potential measurements suggest that the plasma could be divided into streaming and mirror-confined plasmas. The floating potential for the streaming plasma is negative, with an electric field pointing inwards. The mirror-confined plasma has a typical lifetime of 0.5 ms.