Cesiated surface H⁻ ion source: optimization studies

Abstract

The H − ion beam intensity required for high-energy and high-intensity proton accelerators is continuously increasing. The required 95%-beam transverse normalized root mean square emittance (ε 95%rnmsx/y ) of the beam is around 0.25 πmm mrad for all accelerators. The Japan Proton Accelerator Complex (J-PARC) 400 MeV linear accelerator (LINAC) succeeded in accelerating the world's highest-class H − ion beam of 50 mA with a cesiated RF-driven H − ion source. This was achieved by increasing the beam brightness through the following measures

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

“…Also, the excellent transverse emittances suitable for the J-PARC RFQ, which were measured on the test stand, enabled the excellent J-PARC RFQ transmission efficiency of 94.3% (67.9 mA acceleration for the injected 72 mA Hˉ beam) [12]. This source performance was enabled by the following improvements [8]; (1) 45 º tapered Plasma Electrode (PE) with 16 mm thickness to significantly increase I H-, (2) continuous-wave igniter plasma driven by 50 W, 30 MHz RF to reduce hydrogen pressure in plasma-chamber by 50 % and beam loss in the Low Energy Beam-Transport (LEBT) by 12 % compared with that by popularly used 300 W 13.56 MHz-RF, (3) operation with low PE temperature of ~60 ºC to significantly reduce the transverse normalized rms emittances (ε 95% ) and (4) slight water (H 2 O) feed in hydrogen line to avoid ε 95% growth and divergence angle expansion. It should also be noted that during beam development periods on the J-PARC accelerator and on the test stand the ion source was shown to be capable of meeting the near-term, J-PARC RCS upgrade LINAC beam current requirement of ~60mA, 0.6 ms, 25 Hz for 1.44 MW of beam power on target.…”

“…The J-PARC RF ion source routinely produces ~60 mA Hion pulses, 0.8 ms in duration with a 25 Hz repetition rate [8]. Fig.…”

Impurities Reduction Conditionings to Recover Best Beam Quality of J-PARC Cesiated RF-Driven H- Ion Source with New Parts Exposed to Plasma

“…An internal-RF-antenna, a cesium (Cs) injector composed of a Cs-reservoir, a remotely controlled Cs-valve and a Cs-tube, each of which is temperature controlled by using a thermocouple and a heating mantle attached to it, the PE made of molybdenum, a PETCP made of oxygen free copper (OFC) attached to the PE and an axial magnetic field (AMF) correction (AMFC) coil located around the downstream flange are installed to #4PCH. The AMFC coil was operated with coil currents between -14.25 A (-1311 AT) and 14.25 A (1311 AT) for the IRCs and of 0 A (0 AT) for all beam measurements presented in this paper to maximize the RF efficiency [4]. The PE temperature (T PE ) is controlled by air temperature control heater power.…”

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

“…The H − ion beam is deflected a small amount by the edump magnets. Instead of correcting the beam with anti-dipole magnets 13 or adjustable ion source bellows, 14 the entire vessel is tilted relative to the LEBT. This is a nontrivial exercise because the ion source will be adjusted depending on the facility requirements.…”