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

Abstract

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.

Volume and surface effects in Cs-free regimes in NIO1

“…Gas mixing is also reported for H − production [12]. Some other important effects of source walls both in Cs-free regimes and Cs-based regimes are discussed elsewhere [13,14].…”

Design improvements to the SNS ion source and diagnostics

“…The system has been described previously [1,3] and overall performs quite well but does have a few disadvantages: (i) It is limited to only 2-3 cesiations (accomplished by briefly heating collar to ~500 o C), (ii) can fail to maintain an optimal Cs coating on the ionization surface leading to slight beam decay and electron loading of power supplies over a run period and (iii) can occasionally cause LEBT sparking due to over cesiation. To improve this, we first set out to design a supplemental rear-feed, elemental Cs system, as is commonly employed in other Hfacilities [11]. Fig.…”

Recent H- ion source research and development at the Oak Ridge National Laboratory*

“…At that time, we left the source outlet aperture diameter fixed ∼7 mm. This year, due to the desire for higher beam current margins, we reconsidered increasing the source outlet aperture diameter by ∼1 mm [10]. The approach of increasing the source outlet aperture diameter was under consideration for some time at the SNS and was motivated by the following factors: (i) potentially increasing beam current due to having a ∼30% larger plasma emission surface, (ii) H 2 flow out of source is restricted by conductance through 2 apertures and a cylindrical Cs collar.…”

“…We will continue to explore this option but, at this time, the simplicity and dramatically higher power efficiency of the pulsed plasma gun seems more attractive and more likely to support lower H 2 flows which will benefit the overall H − ion source performance. Some external antenna RF-sources used in other facilities also employ the plasma gun approach to ignition [10,15,16].…”