High brightness, negative hydrogen ion sources are used extensively in scientific facilities operating worldwide. Negative hydrogen beams have become the preferred means of filling circular accelerators and storage rings as well as enabling efficient extraction from cyclotrons. Several well-known facilities now have considerable experience with operating a variety of sources such as RF-, filament-, magnetron- and Penning-type H- ion sources. These facilities include the US Spallation Neutron Source (SNS), Japan Proton Accelerator Research Complex (J-PARC), Rutherford Appleton Laboratory (RAL-ISIS), Los Alamos Neutron Science Center (LANSCE), Fermi National Accelerator Laboratory (FNAL), Brookhaven National Laboratory (BNL), numerous installations of D-Pace (licenced by TRIUMF) ion sources used mainly on cyclotrons and, most recently, the CERN-LINAC-1 injector. This report first summarizes the current performance of these ion sources in routine, daily operations with attention toward source service-periods and availability metrics. Sustainability issues encountered at each facility are also reported and categorized to identify areas of common concern and key issues. Recent ion source improvements to address these issues are also discussed as well as plans for meeting future facility upgrade requirements.

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

The ISIS spallation neutron and muon facility is undergoing an upgrade to the negative hydrogen (H−) linac preinjector with the addition of a medium-energy beam transport (MEBT) line. A fast electrostatic sweep chopper is included in the MEBT and will notch the linac bunch train at the synchrotron frequency. The MEBT and chopper will increase the beam transport efficiency significantly, reducing the output H− current requirements from the ion source. As such, a long-lifetime, noncesiated, RF-driven, external-antenna H− ion source based on the successful CERN Linac4 and SNS designs is constructed, which will improve facility uptime and reliability. This paper will highlight the latest developments on the MEBT before focusing on the RF ion source. The RF ion source must deliver 35 mA of H− beam current in pulses 400 μs long at a 50 Hz repetition rate, with transverse normalized 4 rms emittances less than 1.2 π mm mrad. The beam current and emittance are within the reach of a noncesiated H− source, whereas operating at relatively high duty cycles presents challenges in terms of thermal management, which this paper will address.The ISIS spallation neutron and muon facility is undergoing an upgrade to the negative hydrogen (H−) linac preinjector with the addition of a medium-energy beam transport (MEBT) line. A fast electrostatic sweep chopper is included in the MEBT and will notch the linac bunch train at the synchrotron frequency. The MEBT and chopper will increase the beam transport efficiency significantly, reducing the output H− current requirements from the ion source. As such, a long-lifetime, noncesiated, RF-driven, external-antenna H− ion source based on the successful CERN Linac4 and SNS designs is constructed, which will improve facility uptime and reliability. This paper will highlight the latest developments on the MEBT before focusing on the RF ion source. The RF ion source must deliver 35 mA of H− beam current in pulses 400 μs long at a 50 Hz repetition rate, with transverse normalized 4 rms emittances less than 1.2 π mm mrad. The beam current and emittance are within the reach of a noncesiated H− source, whereas o...

/pdf/a-pre-injector-upgrade-for-isis-including-a-medium-energy-2nd414h01t.pdf

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

Surface plasma H− ion sources for accelerators; design of surface plasma H− ion sources for accelerators; formation of H− ion beams in surface plasma sources for accelerators; surface plasma sources with Penning discharge for microlithography; semiplanotrons; geometric focusing; semiplanotrons for accelerators; semiplanotrons with spherical focusing for continuous operation; compact surface plasma sources for heavy negative ion production; development of surface plasma sources world-wide; large volume surface plasma sources with self-extraction; large volume surface plasma sources for accelerators; large volume surface plasma sources for heavy ion production; surface plasma sources for intense neutral beam production for controlled fusion; RF surface plasma sources for ITER; neutral beam injector with RF SPS development at Novosibirsk; RF surface plasma sources for spallation neutron sources; carbon films in RF surface plasma sources with cesiation; poisoning and recovery of converter surfaces; RF surface plasma sources with external antenna; RF surface plasma sources with solenoidal magnetic field; testing RF surface plasma sources with saddle antenna and magnetic field; estimation of H− ion beam generation efficiency; RF surface plasma source operation in continuous mode; RF surface plasma sources at CERN; surface plasma sources at J-PARC, Japan; surface plasma sources for low-energy neutrals.

Surface Plasma Negative Ion Sources

Experimental campaigns were undertaken to understand and improve the coupling efficiency of Radio frequency (RF) power into the plasma in three accelerator-based ion sources. Different matching circuit and mechanical engineering setups were used and the network resistance calculated. The efficiency was then measured for a range of RF frequencies and input gas flows. Coupling efficiencies of around 60% were measured in setups using RF-coils mounted external to the plasma chamber. The efficiency is improved to 80% when the coil is immersed in the plasma, allowing closer coupling. As well as the coil geometry, the isolation transformer required for beam production contributes to the overall losses.

https://iopscience.iop.org/article/10.1088/1361-6463/acb5ac/pdf

RF efficiency measurements of inductively-coupled plasma H− ion sources at accelerator facilities

This work focuses on the production of negative-ions on graphite and diamond surfaces bombarded by positive ions in a low pressure (2 Pa) low power (20 W) capacitively coupled deuterium plasma. A sample is placed opposite a mass spectrometer and negatively biased so that surface produced negative ions can be self-extracted from the plasma and measured by the mass spectrometer. The ratio between negative-ion counts at mass spectrometer and positive ion current at sample surface defines a relative negative-ion yield. Changes in negative-ion production yields versus positive ion energy in the range 10-60 eV are analysed. While the negative-ion production yield is decreasing for diamond surfaces when increasing the positive ion impact energy, it is strongly increasing for graphite. This increase is attributed to the onset of the sputtering mechanisms between 20 and 40 eV which creates negative ions at rather low energy that are efficiently collected by the mass spectrometer. The same mechanism occurs for diamond but is mitigated by a strong decrease of the ionization probability due to defect creation and loss of diamond electronic properties.

Impact of positive ion energy on carbon-surface production of negative ions in deuterium plasmas

/pdf/linac4-h-source-r-d-cusp-free-icp-and-magnetron-discharge-1gp9q7m2or.pdf

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

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