K. Prelec

Extraction of highly charged Au ions from a multiampere electron beam EBIS at BNL

Excellent progress has been made in the operation of the BNL Electron Beam Ion Source (EBIS), which is a prototype for an EBIS that could meet requirements for a RHIC preinjector. We have achieved very stable operation of the electron beam at 10 A through the EBIS trap. Ion injection of low charge gold ions from a LEVA [1] ion source and subsequent extraction of these ions with most probable charge state AU{sup 34+} has been demonstrated with electron beams up to 8A. The total ion charge for gold measured on current transformer at the EBIS exit was 55nC after a 30ms confinement period. This corresponds to {approx}85% of the theoretical ion trap capacity and exceeds our goal of 50% neutralization. The collected ion charge is proportional to the electron current and the gold charge state scales with the electron current density. Details of the EBIS configuration, total charge measurements, and TOF spectra are given.

EBTS: Design and experimental study

Experimental study of the BNL Electron Beam Test Stand (EBTS), which is a prototype of the Relativistic Heavy Ion Collider (RHIC) Electron Beam Ion Source (EBIS), is currently underway. The basic physics and engineering aspects of a high current EBIS implemented in EBTS are outlined and construction of its main systems is presented. Efficient transmission of a 10 A electron beam through the ion trap has been achieved. Experimental results on generation of multiply charged ions with both continuous gas and external ion injection confirm stable operation of the ion trap.

TEST EBIS Operation and Component Development for the RHIC EBIS

Most design goals of the BNL Test EBIS Project have been exceeded and we are confident that an EBIS meeting RHIC requirements can be built. Achieved parameters include 10 A electron beam current, ion charge state above Au32+, and greater than 55 nC total extracted ion charge. The Test EBIS utilizes the full electron beam power but has only half the trap length and operates at a reduced duty factor compared with an EBIS for RHIC, which would produce at least 85 nC total ion charge in 10–40 microsecond pulses, containing ~3 × 109 particles/pulse of Au32+ ions. Normalized rms emittance values for 1–3 mA extracted ion beams have been in the range of 0.08–0.1 pi mm mrad. Present development of the source is focused on establishing operational reliability and facilitating future upgrades in ion intensity and species, since the major emphasis is now on integrating the EBIS into a pre-injector facility, including an RFQ and linac. Recent progress towards this goal includes the following: (1) An IrCe electron gun cathode and modified anode have been installed in an electron gun chamber separable from the source ionization region by a gate valve. A very low loss 10 A, electron beam has been propagated with the new configuration, with 100 kW peak power dissipation at the electron collector. (2) A new electron collector power supply configuration has been tested which can lower the cost compared to our present setup, while improving the stability of the electron beam launch. This is an important first step towards placing the EBIS on a nominal 50 kV platform, necessary for efficient highly charged ion transport to the RFQ. (3) A hollow cathode ion source obtained from CEA Saclay, has been tested and is being installed. This will allow us to provide a variety of ion species to the RHIC and NASA Space Radiation Laboratory facilities, and is valuable at the present project stage for beamline development and emittance studies of heavy and light ion beams of highly charged ions from the EBIS. (4) An electron collector for RHIC has been designed which would allow operation exceeding 10 A electron beams at 100% duty factor. The RHIC collector design could allow upgrades to 300 kW electron beam power. (5) Controls for pulse to pulse switching and diagnostics for charge state and charge fraction verification have been developed.

Development of an electron‐beam ion source for a relativistic heavy‐ion collider preinjector

At Brookhaven National Laboratory (BNL), an electron‐beam ion source (EBIS) is operational as a test bed for development of a high current EBIS for relativistic heavy‐ion collider (RHIC). Previously, the goal of most EBIS research has been to produce bare or nearly bare nuclei. At BNL, the EBIS is required to produce only medium charge states of heavy ions, e.g., Au35+, since there is further stripping at higher energies. The BNL effort is directed at reaching intensities of interest to RHIC, approximately 3×109 particles/pulse, which will require an EBIS electron beam on the order of 10 A. Initial tests using a 1 mm LaB6 cathode have produced electron beam currents up to the design value of 110 mA. A 2 mm LaB6 cathode has been installed and in a first run has produced currents up to 350 mA. This source has so far produced charge states up to Ar16+ using neutral gas injection, and up to Tl50+ using external ion injection. Results of these studies and ion injection trials are presented.

The BNL volume H− ion source

This paper is a progress report on the studies of the BNL volume H− ion source. We have measured the H− yield, IH−, and the ratio Ie/IH− as function of the size of the extraction aperture, strength of the conical filter field, size and position of the filament, and of the phase of the filament heating current. The H− current density in the extraction aperture was lower for the largest aperture, while there was a broad maximum when the conical field varied. Position of the filament and the phase of the filament heating current are very important parameters.

Experimental results from the Brookhaven National Laboratory test electron beam ion source

At Brookhaven National Laboratory, an Electron Beam Ion Source (EBIS) is operational and has produced charge states such as N7+, Ar16+, and Xe26+ using neutral gas injection. Ions such as Na7+ and Tl41+ have been produced using external ion injection. The BNL EBIS effort is directed at reaching intensities of interest to RHIC, approximately 3×109 particles/pulse which will require EBIS electron beams on the order of 10 A. Pulsed electron beams up to 1.14 A have been produced using a 3 mm LaB6 cathode. Ion yields corresponding to 50% of the maximum trap capacity for electron beams up to 0.5 A have been obtained. The goal for the TestEBIS is to produce a uranium ion charge state distribution peaked at U45+ with 50% of the trap capacity for a 1 A electron beam.

Experimental study of electron- and ion-beam properties on the BNL electron-beam ion source and comparison with theoretical models

The maximum achievable perveance of the electron beam in the ion trap region and in the electron collector of the BNL Test electron-beam ion source (EBIS) has been measured for different electron-beam currents. These perveances determine the maximum degree of electron-beam retardation in these areas, which limits for the first case the maximum capacity of the ion trap, and for the second case the minimum dissipated power on the electron collector, for a given electron current. The results are compared with the results of optical simulations of the electron beam. In another set of experiments, data on Test EBIS ionization efficiency for different experimental conditions were obtained. These results are presented and compared with calculations based on stepwise ionization assuming 100% ion confinement in the trap. Finally, a series of experimentally measured longitudinal-energy spectra of the extracted ion beam are presented, and will be compared with the calculated energy spread.

Status of the Brookhaven National Laboratory high current electron beam ion source test stand

As part of a new, compact heavy ion injector for the AGS/RHIC complex at Brookhaven National Laboratory we are developing an electron beam ion source (EBIS) that would satisfy present and future requirements. Such a source should be capable of producing intensities of, e.g., Au35+ ions of about 3×109 particles/pulse or U45+ of about 2×109 particles/pulse. To achieve this, the required e-beam intensity is 10 A, at a pulse length of 100 ms. An EBIS test stand has been constructed, designed for the full electron beam power and having close to 1/2 of the trap length of an EBIS for RHIC. Initial electron beam tests have resulted in a 50 μs, 13 A electron beam. Ion production and extraction has been shown with a 3.1 A, 50 ms electron beam, achieving an ion yield of 19 nC/pulse (neutralization degree of 61%); fast extraction trials have yielded extracted ion pulses of 1 mA peak current and 18 μs at FWHM. Details of the test stand construction, results of the electron beam studies, and properties of the extracted...

Design of an EBIS for RHIC

An Electron Beam Ion Source (EBIS) can be used to produce beams of high charge state heavy ions, and is an excellent choice for injection into a synchrotron, since short pulses of high intensity can be produced for single-or few-turn injection into the ring. As a result of successful experiments on a test EBIS at BNL, we are now confident that an EBIS meeting RHIC requirements can be built. This EBIS would be part of a new linac-based preinjector which would serve as a modern alternative to the existing Tandem preinjectors, offering improvements in performance and operational simplicity. The BNL test EBIS, which is a 1/2 trap-length prototype of the RHIC EBIS, has produced > 10/sup 9/ ions per pulse of Au/sup 32+/, in 10-20 microsecond pulses, and has exceeded our design goals. Performance of the test EBIS is summarized and the design of the RHIC EBIS presented.

Experimental study of ion injection into an extended trap of the Brookhaven National Laboratory EBIS

Experiments on the Brookhaven National Laboratory EBIS electron beam test stand (EBTS) with the ion trap extending beyond the edges of the superconducting solenoid had the main goal to study ion trap operation with a trap length exceeding that of the normal EBTS trap. Preliminary results indicate that the ion trap with a length of 107 cm is stable and controllable in the same fashion as our normal 70 cm trap with a multiampere electron beam. EBTS operation with ion trap 145 cm long and with electron current up to 3 A in earlier experiments also was stable and yielded more ions than from the basic “short” trap. These results increased our confidence in operation of the proposed RHIC in a stable mode and in the correctness of linear scaling of ion intensity with the length of the ion trap.