Bongard, M W | Engineering Papers

DOE OSTI2011

Full-wave modeling of the O-X mode conversion in the Pegasus toroidal experiment

The ordinary-extraordinary (O-X) mode conversion is modeled with the aid of a 2D full-wave code in the Pegasus toroidal experiment as a function of the launch angles. It is shown how the shape of the plasma density profile in front of the antenna can significantly influence the mode conversion efficiency and, thus, the generation of electron Bernstein waves (EBWs). It is therefore desirable to control the density profile in front of the antenna for successful operation of an EBW heating and current drive system. On the other hand, the conversion efficiency is shown to be resilient to vertical displacements of the plasma as large as {+-}10 cm.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2010

A Hall sensor array for internal current profile constraint

Measurements of the internal distribution of B in magnetically confined plasmas are required to obtain current profiles via equilibrium reconstruction with sufficient accuracy to challenge stability theory. A 16-channel linear array of InSb Hall effect sensors with 7.5 mm spatial resolution has been constructed to directly measure internal B{sub z}(R,t) for determination of J({psi},t) associated with edge-localized peeling mode instabilities in the Pegasus Toroidal Experiment. The diagnostic is mounted in an electrically isolated vacuum assembly which presents a slim, cylindrical profile ({approx}1 cm outside diameter) to the plasma using graphite as a low-Z plasma facing component. Absolute calibration of the sensors is determined via in situ cross-calibration against existing magnetic pickup coils. Present channel sensitivities are of order of 0.25 mT. Internal measurements with bandwidth of {<=}25 kHz have been obtained without measurable plasma perturbation. They resolve n=1 internal magnetohydrodynamics and indicate systematic variation in J({psi}) under different stability conditions.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗