Negative-Ion Capture by Vortex Lines in Helium II

Abstract

We have studied negative-ion absorption by rotating He II from 0.98°K to 1.7°K. Measurements of vortex-line capture cross sections are reported as a function of temperature (0.98°K to 1.7°K at three electric fields (16.3, 49.0, and 97.9 V/cm) and as a function of electric field (10 to 200 V/cm) at two temperatures. Great care was taken to insure that the reported cross-section values were not affected by space-charge effects. The results are found in good agreement with the ion-capture theories developed by Donnelly and Roberts. The decrease in cross section above 1.6°K is in agreement with the escape calculation of Parks and Donnely and supports their value of 15.96 Å for the negative-ion radius.