RF models

SNAP's routines [, ] to calculate the energy and pitch angle distribution of the fast minority tail (as a function of radius) driven by radio-frequency heating are modifications of the SHOOT code. They use the Stix model of the tail. In addition to calculating the fast-ion distribution function, these routines calculate the power coupled from the tail population to thermal ions and electrons.

The RF routines generate some 2D arrays which cannot be plotted with the standard SNAP utilities such as CUPLOT. Run program LOOKRF to create a short plot file with these and other RF-relevant plots. This program asks only for a shot-try number.

One of the more important inputs to the RF modeling section doesn't appear in the SNAPIN RF menu: the concentration of the ``minority'' ion species, which is typically ³He or hydrogen. Adjusting the hydrogen concentration is relatively straightforward; use the menu item for the H/(H+D) ratio in the impurities menu. Presumably some estimate of the H/(H+D) ratio can be obtained from the ratio of edge H to D light from HIAFA.

There is no simple measurement of the ³He concentration. Generally, a small puff of ³He is added just before the start of RF; by examining the increase in or in the total electron population (from the MIRI waveform FM-TOTNE), you can estimate how much ³He was added. The standard assumption is that it recycles with 100% efficiency, so that the total population of ³He is constant in time following the puff. Since ³He cannot be treated as one of the main thermal ion species; it must be regarded as an impurity (see Section ).