Impurity ion transport studies on the PLT tokamak during neutral-beam injection

Abstract

Radial transport of medium- and high-Z ions during co- and counter-neutral-beam heating in the PLT tokamak is studied, using molybdenum and scandium ions as tracer elements. The time evolution of the radial profiles of several ionization stages of both elements, injected by laser blowoff during the neutral-beam heating, is measured under three significantly different beam-plasma combinations. No noticeable differences in the radial profiles attributable to the beam direction are observed. However, a given injected amount resulted in considerably larger interior concentrations of the tracer element in the counter-beam heating cases, suggesting larger penetration of the plasma periphery. Computer simulation with the MIST code suggests a net inward drift of the order 103 cm·s−1 superposed to a diffusion coefficient of the order 104 cm2·s−1 for both scandium and molybdenum ions. Injection of larger amounts of the tracer element, sufficient to cause measurable central electron temperature changes, resulted in dramatic changes in ion-state distributions, making some appear peaked in the centre while others disappeared. This effect could be produced with both co- and counter-beam heating, but with lesser amounts in the latter case. It is interpreted as rearrangement of the ionization balance, rather than any preferential accumulation of the injected element.

Observation of Visible and uv Magnetic Dipole Transitions in Highly Charged Xenon and Barium

“…Long wavelength forbidden transitions have been seen in the solar corona [2,3] and in tokamaks [4 -7], and they have been used extensively to probe a variety of properties for both kinds of plasmas. For example, local ion temperatures and bulk plasma velocities can be inferred from the substantial Doppler widths and shifts of these lines [5,6,8]. It is also possible to determine the direction and magnitude of internal magnetic fields from polarization measurements or from Zeeman shifting or broadening of the line profiles [9 -11].…”

Neoclassical theory for rotation and impurity transport in tokamaks with neutral beam injection

“…In the meantime, a number of experiments were performed in ISX-B 11,12 ͑Impurity Studies Experiment B͒ and Princeton Large Torus 13,14 to investigate the effect of NBI direction on central impurity accumulation. These experimental results confirmed the qualitative theoretical prediction that accumulation of impurities in the center of these plasmas was substantially smaller when the magnetic field, beam, and plasma current were parallel than when one was antiparallel to the other two.…”

Nonlinear Problems of Equilibrium Charge State Transport in Hot Plasmas

“…then from Equation (13) and (38)(39)(40) we get the relations of the HL and EC values [27] (A1 for C), JT-60 [28] (A2 for C) and JET [29,30,32] (A1, A2, F, H for Ar) tokamaks; (b) reduced velocity profiles n w  (dashed) and n u  (dotted) calculated using Formulas (33).…”

“…In the practice of modeling medium and heavy impurities, that is, with an increase in the rates of ionization-recombination, it was found that the DCM sensitivity to the empirical transport coefficients remains extremely low [7][8][9][10][11][12][13] and just unacceptable for W impurity [14,15].…”