Progress in lithium beam power, divergence, and intensity at sandia national laboratories

We have achieved lithium intensities of 1.4±0.4 TW/cm² and have pe/formed target experiments at the ∼1000 TW/g level on PBFA II achieving 58±6 eV radiation temperatures. Our near-term milestone of achieving a 100 eV radiation temperature in an ion-driven hohlraum will require an increase in lithium beam intensity to ∼5±1 TW/cm². Our lithium beam intensity is presently limited by a parasitic load that restricts ion power and by the total beam divergence. Recent experiments indicate that the parasitic load is carried by ions and that the beam divergence is predominately caused by LiF source divergence and possibly by electric field non-uniformities. Visible spectroscopy shows both significant anode and cathode plasmas within the ion diode that could be the source of these parasitic ions and also contribute to the electric field non-uniformities. Diode impedance collapse may also be caused by the parasitic load. Cleaning the electrodes in the ion diode could eliminate the source of these parasitic ions. We plan to combine heating, RF-discharge cleaning, and Ti-gettering to clean the diode and improve the local vacuum. Simulations predict a 2–3 times increase in coupled ion power without the parasitic load. Beam divergence and diode impedance may also be improved as a result of diode cleaning.