[en] 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 beta 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 10¹⁴ 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.

[en] A ring cathode for a pulsed, high-current, multi-spot cathodic arc discharge was placed inside a pulsed magnetic solenoid. Photography is used to evaluate the plasma distribution. The plasma appears hollow for cathode positions close the center of the solenoid, and it is guided closer to the axis when the cathode is away from the center.

[en] The NDCX-II accelerator for target heating experiments has been designed to use a large diameter (≅ 10.9 cm) Li⁺ doped alumino-silicate source with a pulse duration of 0.5 (micro)s, and beam current of ≅ 93 mA. Characterization of a prototype lithium alumino-silicate sources is presented. Using 6.35mm diameter prototype emitters (coated on a ≅ 75% porous tungsten substrate), at a temperature of ≅ 1275 C, a space-charge limited Li⁺ beam current density of ≅ 1 mA/cm² was measured. At higher extraction voltage, the source is emission limited at around ≅ 1.5 mA/cm², weakly dependent on the applied voltage. The lifetime of the ion source is ≅ 50 hours while pulsing the extraction voltage at 2 to 3 times per minute. Measurements show that the life time of the ion source does not depend only on beam current extraction, and lithium loss may be dominated by neutral loss or by evaporation. The life time of a source is around (ge) 10 hours in a DC mode extraction, and the extracted charge is ≅ 75% of the available Li in the sample. It is inferred that pulsed heating may increase the life time of a source.

[en] We report results on lithium alumino-silicate ion source development in preparation for warm-dense-matter heating experiments on the new Neutralized Drift Compression Experiment (NDCX-II). The practical limit to the current density for a lithium alumino-silicate source is determined by the maximum operating temperature that the ion source can withstand before running into problems of heat transfer, melting of the alumino-silicate material, and emission lifetime. Using small prototype emitters, at a temperature of ∼1275 C, a space-charge-limited Li⁺ beam current density of J ∼1 mA/cm² was obtained. The lifetime of the ion source was ∼50 hours while pulsing at a rate of 0.033 Hz with a pulse duration of 5-6 (micro) s.

[en] A space-charge-limited beam with current densities (J) exceeding 1 mA/cm² have been measured from lithium alumino-silicate ion sources at a temperature of ∼1275 deg. C. At higher extraction voltages, the source appears to become emission limited with J≥ 1.5 mA/cm², and J increases weakly with the applied voltage. A 6.35 mm diameter source with an alumino-silicate coating, ≤0.25 mm thick, has a measured lifetime of ∼40 h at ∼1275 deg. C, when pulsed at 0.05 Hz and with pulse length of ∼6 μs each. At this rate, the source lifetime was independent of the actual beam charge extracted due to the loss of neutral atoms at high temperature. The source lifetime increases with the amount of alumino-silicate coated on the emitting surface, and may also be further extended if the temperature is reduced between pulses.

[en] Low-frequency (such as 16.77 MHz) RF bunchers are widely used in RF accelerator systems for longitudinal compression of pulses into a single RF bucket, which increases instantaneous beam intensity for time-dependent studies. In this study, the dependency of capture into a 201.25 MHz Drift Tube Linac (DTL) was measured as a function of gap voltage for a 16.77 MHz buncher on chopped H^- beam (approximately 25 ns at 750 keV, 10 mA peak current). The multiparticle code PARMILA was used to simulate the phase-space distribution of the 10 mA, 750 keV, H^- beam at the entrance to DTL with a wide range of the Low-Frequency Buncher (LFB) field (10 kV to 35 kV). The measurement and simulation indicated that the DTL capture could be dilute (reduced) for a non-optimized buncher field to a pre-configured beamline geometry. The data shows that changing the bunch field while keeping the incoming beam current and energy constant does not significantly alter the beam’s emittance. However, downstream beam capture into the DTL is changed for a non-optimized phase-space bunching distance with the buncher field.

[en] Here we report a comparison between the simulation of beam phase-space and profile distributions with diagnostic measurements. TRANSPORT, a particle transport code, was used for the prediction of a 800 MeV proton beam envelope from the end of the linac to the proton radiography (pRad) facility (a total length of 80 meters). The beam profile was measured at key positions along the beamline using wire scanners and gated CCD camera systems. These measurements were compared to their respective points along the simulated beamline. The predicted beam envelope and measured data correspond within expected errors. (paper)

[en] We report results on lithium alumino-silicate ion source development in preparation for warm dense matter heating experiments on the new neutralized drift compression experiment II. The practical limit to the current density for a lithium alumino-silicate source is determined by the maximum operating temperature that the ion source can withstand before running into problems of heat transfer, melting of the alumino-silicate material, and emission lifetime. Using small prototype emitters, at a temperature of ≅1275 deg. C, a space-charge limited Li⁺ beam current density of J ≅1 mA/cm² was obtained. The lifetime of the ion source was ≅50 h while pulsing at a rate of 0.033 Hz with a pulse duration of 5-6 μs.

[en] As an alternative to conventional scintillator-based beam profile diagnostics in ion accelerators, with the Beam Induced Fluorescence (BIF) Monitor, transverse beam profiles can be determined by observation of single fluorescence photons emitted by residual gas molecules. With this instrument we recorded profiles of a 10¹² particles per pulse K⁺ beam of 7.7 keV/u in 10^-5 Torr N₂ gas. Single photon counting was performed using an image intensified digital CCD camera. Moreover the applicability of this method has been successfully demonstrated at GSI for various ion beams in the energy range of 5 to 750 MeV/u. Secondly this method can be applied to the study of plasma properties. For a cathodic-arc Al-plasma spatial distribution and plasma density have been investigated. Time resolved spectra were recorded with a streak-spectrometer camera. Results are presented for a typical parameter space, profile distortions and feasibility is discussed

[en] A nonperturbing electron-beam diagnostic system for measuring the charge distribution of an ion beam is developed for heavy ion fusion beam physics studies. Conventional diagnostics require temporary insertion of sensors into the beam, but such diagnostics stop the beam, or significantly alter its properties. In this diagnostic a low energy, low current electron beam is swept transversely across the ion beam; the measured electron-beam deflection is used to infer the charge density profile of the ion beam. The initial application of this diagnostic is to the neutralized transport experiment (NTX), which is exploring the physics of space-charge-dominated beam focusing onto a small spot using a neutralizing plasma. Design and development of this diagnostic and performance with the NTX ion beamline is presented