Measuring MeV ions from fusion reactions in magnetic-mirror experiments

Abstract

Successful initial testing has been completed on a different approach to determining plasma characteristics in magnetic-confinement fusion experiments. Ions produced in fusion reactions, with energies in the low-MeV range, were detected in real time. A well-collimated silicon surface-barrier detector was used, along with particle-counting equipment and pulse-height analysis. This type of compact detector can readily observe the fusion ions and can function under conditions often encountered in magnetic-fusion experiments: high magnetic field, good vacuum, and cryogenic temperature. This measuring technique was tested on the 2XIIB magnetic-mirror experiment, with a detector placed outside the mirror region. All three ions produced in D-D fusion reactions (3.02-MeV H, 1.01-MeV T, and 0.82-MeV 3He) were observed. These measurements provide data on the spatial distribution of the 2XIIB plasma, on the fusion-reaction rate, and on the energy resolution obtainable (resolution found satisfactory for possible future measurements of the plasma-ion temperature). The results show that the equipment functioned well in a harsh experimental environment and performed as expected. This measuring technique appears promising for obtaining further and more detailed information on plasma parameters in magnetic-confinement fusion experiments.