HEAVY ION FUSION SCIENCE VIRTUAL NATIONAL LABORATORY 4th QUARTER 2008 MILESTONE REPORT

Abstract

This milestone has been met. In the previous quarter (3rd quarter FY2008), the Heavy Ion Fusion Science Virtual National Laboratory (HIFS-VNL) completed the new experimental target chamber facility for future Warm Dense Matter (WDM) experiments [1]. The target chamber is operational and target experiments are now underway, using beams focused by a final focus solenoid and compressed by an improved bunching waveform. Initial experiments have demonstrated the capability of the Neutralized Drift Compression Experiment (NDCX) beam to heat bulk matter in target foils. The experiments have focused on tuning and characterizing the NDCX beam in the target chamber, implementing the target assembly, and implementing target diagnostics in the target chamber environment. We have completed a characterization and initial optimization of the compressed and uncompressed NDCX beam entering the target chamber. The neutralizing plasma has been significantly improved to increase the beam neutralization in the target chamber. Preliminary results from recent beam tests of a gold cone for concentrating beam energy on target are encouraging and indicate the potential to double beam intensity on target. Other advantages of the cone include the large amount of neutralizing secondary electrons expected from the grazing incidence at the cone walls, and the shielding of the target from the edges of the beam pulse. The first target temperature measurements with the fast optical pyrometer were made on Sep. 12, 2008. The fast optical pyrometer is a unique and significant new diagnostic. These new results demonstrate for the first time beam heating of the target to a temperature well over 2000 K. The initial experimental results are suggestive of potentially interesting physics. The rapid initial rise and subsequent decay of the target temperature during the beam pulse indicate changes in the balance of beam heating and target evaporative cooling, a behavior which may be affected by phenomena such as droplet formation and rapid changes in the optical properties of the hot target material. NDCX, possibly uniquely, is capable of studying these changes because of its wide range of diagnostic capabilities. These capabilities include target diagnostics already in place such as the fast pyrometer and streak camera, as well as the ability to measure both ion beam transmission and optical transmission through the foil. Measurements with these diagnostic techniques can help determine the rate at which the target is breaking up into droplets and the rate at which its bulk optical properties are changing.