Linac4 H− source R&D: Cusp free ICP and magnetron discharge

Abstract

The 2MHz radio-frequency inductively coupled plasma heating (ICP RF) of Linac4's IS03 Hsource is more efficient without its octupole cusp in offset hallbach configuration. This was shown by Particle in cell Monte-Carlo (PIC-MC) simulation using the NINJA software [1] and confirmed by plasma characterization via optical emission spectroscopy [2,3], an easier plasma ignition is also anticipated. In this paper, we present preliminary results of an Alumina plasma chamber IS03 Hsource [4] operated without magnetic cusp. Operation under monthly cesiation induces a slow evolution of the molybdenum cesiated surface correlated with an increase of the co-extracted electron yield. An improved stability of the extracted Hbeam is achieved by compensating the Cs-losses. The high intensity option for Linac4 features an adaptation of BNL's Magnetron. Simulation of this complex H2-Cs arc discharge plasma, where electrons are emitted from a cesiated molybdenum cathode, requires characterization of the plasma impedance and knowledge of hydrogen and cesium densities. We present a measurement of plasma impedance over the range of discharge current, hydrogen and cesium-densities.

Negative hydrogen ion sources for particle accelerators: Sustainability issues and recent improvements in long-term operations

“…Multicusp magnetic plasma confinement is well known to improve plasma densities in small laboratory plasmas for a given amount of input power. However, in our case, simulation and experiment showed that our external antenna inductive coupling is more than twice as efficient without cusp [29,30]. Therefore, the source is now operated without the cusp which halves the RF-power and avoids the e-loss lines that were visible on the inner surface of the ceramic plasma chamber.…”

“…A fail-safe control system ensures a constant, very low flux of cesium that stabilizes operational parameters while keeping the oven at low temperature (60˚C). The source now operates under cesium loss compensation [30] and a simple RF-driven, Hcurrent regulation feedback control system ensures the required stability over time. Every beam interruption is recorded, its origin identified and attributed to subsystems; the analysis of these failure statistics is the key to prioritize improvement.…”

A pre-injector upgrade for ISIS, including a medium energy beam transport line and an RF-driven H− ion source

“…The RF ion source 6 is based on the designs using external RF antennas at CERN's linac4 7 and the ORNL's SNS. 8 Recent studies have shown that noncesiated RF ion sources with 7.5 mm outlet apertures can produce over 40 mA of beam current, 6 provided that no restriction occurs between the filter magnet and aperture.…”

Simulation of Beam Formation in the CERN Negative Ion Source for the Linac4 Accelerator

“…The filter and dump fields are generated by pairs of permanent magnets located around the Plasma Electrode (PE) and in the puller dump electrode. A detailed information of the IS03b ion source and operation are given in [2,4].…”