A transition from low to high radial confinement mode is triggered by biasing a limiter in the HIEI tandem mirror. Positive dc biasing gives rise to reduction of the fluctuation level in density and potential in the periphery, drop of neutral line emission, and bifurcation in limiter current. After the transition, the plasma exhibits density rise in the bulk and steepening of the density gradient. Significant radial rotational shear is observed when the edge turbulence is suppressed by the biasing. The total feature shows similar characteristics of L-to //-mode transition observed in tokamak devices.
The low-frequency instability observed in an axisymmetric mirror is identified as a curvature-driven flute instability for a wide range of densities up to 1014cm−3. It is demonstrated that this flute instability is stabilized by the RF field which is coupled electromagnetically and applied only in the bad-curvature region. Radial plasma loss is significantly reduced by the stabilization. This method of stabilization is revealed to be effective for densities from 1010 to 1014cm−3, indicating the possibility of a purely axisymmetric tandem mirror.
A rotating field antenna set — a pair of two closely spaced dual half-turn antennas — is used to tailor the azimuthal spectrum of the antenna field. It is demonstrated that the azimuthal mode of ICRF waves can be controlled by proper phasing of the antenna set. Ion heating is shown to be strongly dependent on the azimuthal mode number. When the antenna set is operated in the m = −1 (left rotating) mode, the m = −1 modified ion cyclotron wave is selectively excited, resulting in efficient ion heating.
A large-diameter uniform plasma is obtained by microwave discharge without the use of magnetic fields at pressures in the mTorr range. Microwave fields at 2.45 GHz are radiated from a multislotted planar antenna located a short distance above the glass window of a discharge chamber. Overdense plasmas are produced with ± 3-4% uniformity of ion saturation current over 30 cm diameter for wide ranges of microwave power and gas pressure. The discharge can be started up at pressures as low as 0.5 mTorr. The efficient production of overdense plasmas is investigated by measuring microwave field propagation in the system.
For the numerical simulation of electron cyclotron resonance plasma production, a two-dimensional model that describes wave propagation and plasma transport is developed. The modeling code calculates profiles of electromagnetic wave fields, power absorption of electrons, and temporal evolution of plasma densities in a bounded, inhomogeneous, cylindrical system. The calculation of the plasma production in a mirror magnetic field shows that the plasma production property is very sensitive to the antenna location.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.