Recent results with Au ions from a multiampere electron beam ion source at Brookhaven National Laboratory (invited abstract)

Abstract

An electron beam ion source (EBIS) that would satisfy Relativistic Heavy Ion Collider (at Brookhaven National Laboratory) (RHIC) requirements should be capable of producing intensities of, e.g., Au32+ ions of about 3×109 particles/pulse in 10–40 μs pulses. The total charge extracted (all charge states) would be 85 nC, assuming 20% in the peak charge state. To achieve this at Brookhaven National Laboratory, pulsed-electron beam currents up to 10 A, 100 ms are being used. A test EBIS has been constructed, designed for the full electron beam power and having close to half of the trap length of an EBIS for RHIC. As a result of successful experiments on the test EBIS, we are confident that an EBIS meeting RHIC requirements can be built. Initial electron beam tests have demonstrated a 100 ms, 8.6 A electron beam through the EBIS trap. The stable operation of 10 A, 50 ms electron beams through the EBIS trap has also been achieved. Gold spectra with a dominant charge state 34+ and total ion charge 55 nC measured on a current transformer have been obtained at the EBIS exit after a 30 ms confinement period. Recent studies with an in-line time-of-flight spectrometer with measurement of charge on a Faraday cup have shown 83% of the >28 nC extracted charge to be Au ions peaked at Au25+, for a 7 A electron beam and 10 ms confinement period. Typical normalized rms emittance values using a 6.8 A electron beam, 20–40 nC total ion charge, and 1–3 mA extracted ion current have been in the range of 0.08–0.1 π mm mrad. An energy analysis of the total extracted ion pulses >35 nC has indicated a longitudinal energy spread of <2 kV full width at half maximum after a 35 ms confinement period using a 7 A electron beam. Most design goals have been exceeded and much of the present work is geared toward improving reliability and providing larger safety margins. These include upgrading the electron gun, decoupling the electron beam launch energy from the electron collection energy, and tailoring the magnetic fields to reduce electron beam losses. Details of these measurements, tests in progress to improve performance, and plans for optimizing the design of the RHIC EBIS will be presented.