J. Timberlake

Vertical high-resolution Bragg x-ray spectrometer for the tokamak fusion test reactor

A Bragg x‐ray spectrometer of high spectral resolution (λ/Δλ=10u2009000–20u2009000) which accommodates three crystals and position‐sensitive detectors in the Johann configuration has been installed in the diagnostic basement of the tokamak fusion test reactor (TFTR) for the measurement of radial ion temperature profiles. The ion temperature is derived from the Doppler broadening of Kα‐resonance lines of metal impurity ions, e.g., Ti, Cr, Fe, and Ni, in the helium‐like and hydrogen‐like charge states. The x‐ray diffraction plane is almost perpendicular to the magnetic axis, but slightly tilted by an angle of 3.8°, which makes it possible to measure poloidal and toroidal plasma rotation velocities of vΘ>5×103 m/s and vΦ>1×105 m/s, from the Doppler shift of spectral lines. Results obtained from the observation of TiXXl Kα‐line spectra with a 220‐silicon crystal of a 2d spacing of 3.8400 A and a curvature radius of 11.05 m are reported.

CHANGES IN TOKAMAK PLASMA PROPERTIES DURING IMPURITY INJECTION.

Certain applications of laser blow‐off impurity injection, such as ion temperature measurement and spectral line identification, may require the ratio of injected ions‐to‐plasma electron density to exceed 0.001. To achieve these concentrations we have relied on injection of micron‐sized clusters as well as monatomic species. In these cases the injected impurity can no longer be regarded as a nonperturbing trace sourced at the plasma edge. We therefore have studied the variation of plasma parameters in PLT and PDX as a function of the amount of injected impurities, the species mix, and the type of impurity. We find that for ohmically‐heated plasmas, impurity injection can increase ?e more than 4×1012 cm−3 without causing disruptions. During Ge‐injection experiments where Δne/ne ∠0.05, Te initially rises ∠5% on axis and decreases ∠20% at the edge. The plasma current drops 1–3u2009% and the loop voltage and radiated power both double. Varying the amount of injected impurities changes the peaking and decay times ...

Photography of impurity injection into PLT plasmas

Using still color photography with submillisecond time resolution, observations of impurities injected into the PLT tokamak by laser blowoff have been made. These clearly show the existence of atomic vapor and particulates with abundances depending on laser fluence, material, and film thickness. Velocity determinations for each component have been made: for atomic vapor v≂2×105 cm/s; and for particulates v≂5×104 cm/s. Their penetration depths into plasmas of different electron densities have also been measured. Models of penetration are compared with the data.

Performance of the PBX-M passive plate stabilization system

The PBX-M passive plate stabilization system provides significant stabilization of long-wavelength external kink modes, the slowing of vertical instability growth rates, and the amelioration of disruption characteristics. The passive plate stabilization system has allowed the use of LHCD and IBW to induce current density and pressure profile modifications, and m=1 divertor biasing for modifying edge plasma transport. Improvements in the passive plate system insulators and support structures have provided reliable operation. Impurity influxes with the close-fitting passive plates are low. Solid target boronization is applied routinely to reduce conditioning time and maintain clean conditions.

K{beta} spectra of heliumlike iron from TFTR plasmas

K{beta} spectra of helium-like iron, Fe XXV, have been observed from TFTR plasmas with a high-resolution crystal spectrometer. The wavelength range of the Fe K{beta} spectrum partially overlaps the spectrum of helium-like nickel (Ni XXVII), which is used on TFTR and JET for ion temperature measurements. The experimental arrangement made it possible to observe the Fe XXV K{beta} lines and their satellite transitions of the type 1s2l{prime}31{double_prime} {yields} 1s{sup 2}21{prime}, as well as the entire satellite spectrum of the Ni XXVII K {alpha} line simultaneously. In order to identify the features of the K{beta} spectra and to study their possible interference with the Ni XXVII spectrum, the intensity of the K{beta} spectrum was enhanced by injection of iron into the plasma. Accurate wavelengths and intensities have been obtained and compared with different theoretical calculations.