Spectroscopic Measurements of Argon Plasma Formation by a High-Intensity Lithium Ion Beam
We describe the first measurements of plasma formation by a 20thinspthinspnsec, 9thinspthinspMeV, 20 kA/cm{sup 2} Li{sup +3} ion beam injected into 2-Torr argon, conditions similar to inertial-fusion ion-beam transport requirements. A new visible-spectroscopy diagnostic exploits ion-beam-excited Ar II transitions to measure the time-resolved plasma electron density (10{sup 15} cm{sup {minus}3}{endash}10{sup 16} cm{sup {minus}3}) and temperature (1{endash}2thinspthinspeV) during the initial breakdown phase. Stark broadening and line intensity ratios are used as diagnostics after the plasma forms. Comparisons with computer simulations examine intense-beam effects important for the transport of light- and heavy-ion beams. {copyright} {ital 1999} {ital The American Physical Society }