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We describe a magnetic mirror device, namely, the Keda Mirror with AXisymmetricity (KMAX), which aims to study new approaches to confine and stabilize the mirror plasma as well as basic plasma research. KMAX consists of one central cell, two side cells, and two end chambers at two ends of the device. For the central cell, the mirror-to-mirror distance is 5.2 m, while the central cylinder is 2.5 m in length and 1.2 m in diameter. The plasmas are generated by two washer guns located in the end chambers, which subsequently flow into the central cell and merge there. The density in the central cell is usually adjusted by changing the magnetic field strength inside the side cell, and it ranges from 1017 to 1019 m−3, depending on the experimental requirement. Ion cyclotron frequency heating with two 100 kW transmitters is routinely used to heat up the ions. Plasma controls mainly rely on configuring the magnetic geometry and rotating magnetic fields to improve the confinement and suppress instability. Routine diagnostics, such as probes, interferometers, spectrometers, diamagnetic loops, and bolometers, are also reported in this paper. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We show experimentally that Alfvénic fluctuations can spontaneously decay into a fast and a slow magnetosonic wave in an inhomogeneous plasma. The fast wave of higher frequency propagates in the same direction, while the slow wave of lower frequency propagates in the opposite direction with the pump wave. Both of the daughter waves are characterized by strong parallel but modest perpendicular fluctuations. The measured frequencies and wavenumbers are found to satisfy the energy and momentum conservation conditions for a nonlinear three wave interaction. The evidence of energy flowing from pump fluctuations into daughter waves is also presented in this paper. The results may shed light on the origin of inward Alfvén waves observed in the solar corona and chromosphere and how shear Alfvén waves deposit its energy by driving compressional perturbations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 × 10 18 m − 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. [ABSTRACT FROM AUTHOR]