Retarding field energy analyzers for the ion temperature measurements in the SOL plasmas of the tokamak ISTTOK and the TJ-II stellarator
Measurements of the ion temperature in the plasma boundary of fusion devices typically employs the Retarding Field Analyzer (RFA) that is based on selective rejecting or retarding the plasma ions by a varying braking electric field. Normally, the RFA comprises an input slit and collector electrode with two or more separately biased fine grids placed in front of it. With an assumption of Maxwellian ion distribution, the exponential decay of the RFA collector currentvoltage characteristic is determined by the ion temperature. This contribution describes 1- and 3channels RFAs for the ion temperature measurements in the scrape-off-layer of the tokamak ISTTOK and the TJ-II stellarator. Selected results of the ion temperature measurements on the ISTTOK and the TJ-II are presented. In addition, limitations related to the RFA operation (including the alignment along magnetic field direction and plasma loading) are considered.
Compact retarding field energy analyzer for the tokamak ISTTOK boundary plasma
The retarding field energy analyzer (RFEA) remains the more reliable diagnostic to measure the ion temperature in the boundary plasmas of magnetic fusion devices. A compact, simple design and inexpensive RFEA has been developed for investigations on the tokamak ISTTOK. It consists of a stainless steel pinhole (with a diameter of 0.6mm), three fine nickel grids with a separation of 1mm, and a collector, all insulated by mica. All the components are placed inside a boron nitride housing with dimensions of 14×14×23mm3. The RFEA has been tested in both ion and electron modes. The conditions of the RFEA operation are discussed, and preliminary measurements of the ion and electron temperature profiles presented.
Measuring impurity ion energy and charge state distributions in the tokamak plasma boundary
Abstract A new diagnostic, combining both electrical and surface collection techniques has been designed in an effort to characterize the SOL with respect to the charge and energy of impurity ions. The probe utilizes the tokamak magnetic field to obtain spatial profiles of impurity deposition due to the gyroradii of particles passing through small apertures. Measurements have been made of the spatial distributions of iron and carbon on high purity aluminium substrates. The deposited profiles are compared with the results of a simple 2-D Monte Carlo model leading to estimates of the impurity ion temperature and the determination of approximate charge state distributions.