Dense Metal Plasma in a Solenoid for Ion Beam Neutralization

Abstract

Abstract-Space-charge neutralization is required to compress and focus a pulsed, high-current ion beam on a target for warm dense matter physics or heavy ion fusion experiments. We described approaches to produce dense plasma in and near the final focusing solenoid through which the ion beam travels, thereby providing an opportunity for the beam to acquire the necessary space-charge compensating electrons. Among the options are plasma injection from pulsed vacuum arc sources located outside the solenoid, and using a high current (> 4 kA) pulsed vacuum arc plasma from a ring cathode near the edge of the solenoid. The plasma distribution is characterized by photographic means, by an array of movable Langmuir probes, by a small single probe, and by evaluating Stark broadening of the Balmer H  spectral line. In the main approach described here, the plasma is produced at several cathode spots distributed azimuthally on the ring cathode. It is shown that the plasma is essentially hollow, as determined by the structure of the magnetic field, though the plasma density exceeds 10 14 cm -3 in practically all zones of the solenoid volume if the ring electrode is placed a few centimeters off the center of the solenoid. The plasma is non-uniform and fluctuating, however, since its density exceeds the ion beam density it is believed that this approach could provide a practical solution to the space charge neutralization challenge.2

Plasma source development for the NDCX-I and NDCX-II neutralized drift compression experiments

“…Plasma generated near the wall inside the solenoid will follow magnetic field lines that pass through the midplane of the solenoid at large radius. A compact cathodic-arc source has been developed that generates plasma around the circumference of a ring (Anders et al, 2011), whereas here a compact ferroelectric plasma source is discussed.…”

Neutralization of ion beam by electron injection: Excitation and propagation of electrostatic solitary waves

“…Neutralization of positive ion beam space-charge by electrons is important in many areas including accelerators [1], ion thrusters [2], heavy ion inertial fusion [3,4], and ion-based surface engineering [5], etc. Neutralizing electrons can originate from direct injection of electrons [6], beam-induced ionization of residual gas [7,8], or plasmas generated by discharge in vacuum [9][10][11][12][13][14][15][16][17][18]. In a companion paper [19], hereafter referred to as Part 1, by using two-dimensional particle-in-cell (PIC) simulations we have studied the process of cold electron accumulation during the neutralization of an ion beam.…”

Excitation of electrostatic solitary waves during neutralization of ion beam pulse by plasma

“…Very-dense volumetric plasma in the beam path is able to provide a minimum space-charge potential and the best option for the charge neutralization of the ion beam pulse, compared with other neutralization schemes such as electron injection, gas ionization by ion beam, etc [27][28][29][30][31][32][33][34][35][36][37][38][39]. For heavy ion fusion applications, the space-charge potential of the ion beam pulse during propagation can be several orders higher than the potential of background plasma [30].…”