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 a n intense lithium beam is being developed to drive inertial confinemen t fusion targets. An important issue is the purity of the beam. To ass ess this concern, direct nuclear activation diagnostics based on the r eactions Li-7(p,n)Be-7, B-10(p,alpha)Be-7, and F-19(7Li,d)Na-24 Were f ielded 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 a node shots taken and was always less than 10%. The total hydrogen ener gy in the beam ranged from only 0.5-10 W. Over this shot series increa sing efforts were made to clean the anode prior to each shot. In gener al, 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 locatio n was also measured and found to typically vary by factors of 1.5-4 ov er the diode. (C) 1997 American Institute of Physics.