Measurement of hydrogen and lithium ion energy densities on PBFA II using direct nuclear activation diagnostics

In the light-ion-beam fusion program at Sandia National Laboratories an intense lithium beam is being developed to drive inertial confinement fusion targets. An important issue is the purity of the beam. To assess this concern, direct nuclear activation diagnostics based on the reactions 7 Li (p,n) 7 Be , 10 B (p,α) 7 Be , and 19 F( 7 Li ,d) 24 Na were fielded to measure the energy densities of hydrogen and lithium in the beam. The hydrogen beam energy density was measured to be less than 2% of the lithium beam energy density on a majority (10) of the 19 LiF anode shots taken and was always less than 10%. The total hydrogen energy in the beam ranged from only 0.5–10 kJ. Over this shot series increasing efforts were made to clean the anode prior to each shot. In general, there was a modest reduction in the hydrogen energy fraction with improved cleaning, but no corresponding increase in the lithium energy density was seen. The lithium energy density as a function of location was also measured and found to typically vary by factors of 1.5–4 over the diode.