Meter-long plasma source for heavy ion beam space charge neutralization

Plasmas are a source of unbound electrons for charge neutralizing intense heavy ion beams to allow them to focus to a small spot size and compress their axial pulse length. The plasma source should be able to operate at low neutral pressures and without strong externally-applied electric or magnetic fields. To produce one-meter-long plasma columns, sources based upon ferroelectric ceramics with large dielectric coefficients have been developed. The source utilizes the ferroelectric ceramic BaTiO₃ to form metal plasma. The drift tube inner surface of the Neutralized Drift Compression Experiment (NDCX) is covered with ceramic material, and high voltage (∼ 8 kV) is applied between the drift tube and the front surface of the ceramics. A lead-zirconium-titanate prototype Ferroelectric Plasma Source (FEPS), 20 cm in length, has produced plasma densities of 5 × 10¹¹ cm^-3. It was integrated into the Neutralized Transport Experiment (NTX), and successfully charge neutralized the K⁺ ion beam. A one-meter-long BaTiO₃ source comprised of five 20-cm-long sources has been tested and characterized, producing relatively uniform plasma over the one-meter length of the source in the mid-10¹⁰ cm^-3 density range. This source has been integrated into the NDCX device for charge neutralization and beam compression experiments. Initial beam compression experiments with this source yielded current compression ratios near 100. Future research will develop longer and higher plasma density sources to support beam compression experiments for high energy density physics applications.