Forty years of surface plasma source development

Abstract

The cesiation effect, a significant enhancement of negative ion emission from a gas discharge with decrease of co-extracted electron current below negative ion current, was observed for the first time on July 1, 1971 by placing into the discharge a compound with 1 mg of cesium. Subsequent developments of surface plasma sources (SPS) for highly efficient negative ion production caused by the interaction of plasma particles with electrodes on which the adsorbed cesium reduced the surface work function are described. In the last 40 years, the intensity of negative ion beams has increased by cesiation up to 10(4) times from 3 mA to tens of amperes. Here, the main attention is concentrated on earlier SPS developments because recent results are well known and widely available.

Ion extraction from a saddle antenna RF surface plasma source

“…(In the existing RF SPS the Spe~2-3 mA/cm 2 kW [7,8]; in the TRUIMF filament arc discharge negative ion source [17,18] the best Spe is about 4 mA/cm 2 kW; in a compact Penning discharge SPS [12][13][14][15]19,20] the Spe is ~150 mA/cm 2 kW). During H -beam extraction from an external antenna with RF discharges in the AlN discharge chamber, a slow degradation of H -beam intensity after cesiation was observed [7].…”

Development of versatile multiaperture negative ion sources

“…Plasma cools by expansion and for the effect of a transverse magnetic filter while diffusing to a second region (with T e < 2) eV near the plasma grid (PG), where negative ions are efficiently generated and extracted. Typical beam current densities j H− of H − at the extraction holes of PG are up to 340 A/m 2 for cesiated PG [1,3,12] and are an order of magnitude less ( j vol H− ∼ = 10 1.5 A/m 2 ) with no cesium. Cesium may have adverse effect on long term NBI operation, so alternatives are being researched.…”

“…Negative ion sources [1,2,3] are a fundamental component of Neutral Beam Injectors (NBI) [4,5,6,7,8,9], which contribute most of the additional plasma heating and current drive to the International Tokamak Experimental Reactor (ITER) project and which need to be strongly optimized in the perspective of the more demanding DEMO reactor [10]. A relatively compact radiofrequency (rf) ion source, named NIO1 (Negative Ion Optimization phase 1) is being developed and tested in Padua, Italy, in collaboration bewteen Consorzio RFX and INFN [11], in the framework of the accompanying activities in support to the ITER NBI test facility and to the Megavolt ITer Injector Concept Advancement (MITICA) [8], to provide a test bench for source optimizations.…”

CW/Pulsed H− ion beam generation with PKU Cs-free 2.45 GHz microwave driven ion source

“…Source with Cs makes its construction more complicated and its operation is more difficult compared with a non-Cs one. Up to now, many H -ion sources with/without Cs are successfully delivering H -ion beam current up to several tens milliamperes with duty factor lower than 6% and they are used as "working sources" for gigantic accelerator complexes even with cesium added 070005-1 [5] . Until now, there is no prototype H -source that has the capability of producing very intense H -beams of arbitrary duty factor in a very large scale [1] .…”

“…Volume production source is a tandem type source where filaments, radio frequency (rf) or microwave (2.45 GHz) are used to ignite and maintain the magnetically confined plasmas [4] . Cesium (Cs) is commonly used in surface-produced ion sources and surface-enhance volume-produced sources because of its significant ability of work function reducing when being desorbed on certain metal surfaces [5] . Source with Cs makes its construction more complicated and its operation is more difficult compared with a non-Cs one.…”