Meter-Long Plasma Source for Heavy Ion Beam Charge Neutralization

Plasmas are a source of unbound electrons for charge neutralizing intense heavy ion beams to focus them to a small spot size and compress their axial length. The source should operate at low neutral pressures and without strong externally-applied electric or magnetic fields. To produce long plasma columns, sources based upon ferroelectric ceramics with large dielectric coefficients have been developed. The source utilizes the ferroelectric ceramic BaTiO$_{3}$ to form metal plasma. The drift tube inner surface of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic material. High voltage ($\sim $ 8 kV) is applied between the drift tube and the front surface of the ceramics. A BaTiO$_{3}$ source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma in the 5x10$^{10}$ cm$^{-3}$ density range. The source has been integrated into the NDCX device for charge neutralization and beam compression experiments. Initial beam compression experiments yielded current compression ratios $\sim $ 120. Future research will develop longer and higher density sources to support beam compression experiments for high energy density physics applications.