Sensitivity of heavy ion beam probe to hot electrons in EBT

This paper discusses a method of studying the radial position of locally heated hot electrons in EBT. The heavy ion beam probe on EBT is sensitive to all three electron components - those of the cold surface plasma, the warm core plasma, and the hot electron ring. The total detected signal is proportional to the local electron density at the point of ionization and to the beam ionization rate, which is in turn a function of the local electron temperature. Use of the total detected signal enables qualitative profile measurements of this product known as nf(T/sub e/). The function f(T/sub e/) peaks at several hundred eV, and falls slowly for electron temperatures up to several hundred keV. Especially useful in studies of the hot electrons are the triply ionized Cs3+ ionization products. Observations of Cs3+ signals with and without 18 GHz microwave power input to the beam probe cavity in EBT-I show a sensitivity to a locally heated hot electron component. Measurements of this component show that it is spatially localized near the 18 GHz second harmonic resonance surface. The hot component is observed at both the upper and lower edges of the plasma and its radial position is observed to vary as the toroidal magnetic field is changed