E. Beebe

The Stockholm electron beam ion source

The electron beam ion source, CRYSIS, produces highly charged ions for injection into the heavy ion storage ring - CRYRING at the Manne Siegbahn Institute, and for low energy atomic physics experiments. It will also provide highly charged ions for the Stockholm-Mainz Penning trap scheduled for installation at MSI in early 1993. CRYSIS has produced ions up to Ar18+ and 136Xe49+ using electron beam currents of typically Ie = 200-300 mA and current density je = 100-200 A/cm2. Continuous electron beams of energy E = 19 keV and current Ie = 600 mA have been propagated through the source with transmission greater than 99.9%. Test beams of He2+ and N7+ extracted from the source in 50-100 ?s pulses have been injected into CRYRING with the entire CRYSIS platform raised to 20 kV. Ions of charge up to 136Xe44+ extracted in extended 50-100 ms pulses have been used in coincidence-type atomic physics experiments. The status of CRYSIS as of March 15, 1992 is reported. Improvements, modes of operation, and results are discussed.

The Brookhaven National Laboratory electron beam ion source for RHIC

As part of a new heavy ion preinjector that will supply beams for the Relativistic Heavy Ion Collider and the National Aeronautics and Space Administration Space Radiation Laboratory, construction of a new electron beam ion source (EBIS) is now being completed. This source, based on the successful prototype Brookhaven National Laboratory Test EBIS, is designed to produce milliampere level currents of all ion species, with q/m=(1/6)-(1/2). Among the major components of this source are a 5 T, 2-m-long, 204 mm diameter warm bore superconducting solenoid, an electron gun designed to operate at a nominal current of 10 A, and an electron collector designed to dissipate approximately 300 kW of peak power. Careful attention has been paid to the design of the vacuum system, since a pressure of 10(-10) Torr is required in the trap region. The source includes several differential pumping stages, the trap can be baked to 400 C, and there are non-evaporable getter strips in the trap region. Power supplies include a 15 A, 15 kV electron collector power supply, and fast switchable power supplies for most of the 16 electrodes used for varying the trap potential distribution for ion injection, confinement, and extraction. The EBIS source and all EBIS power supplies sit on an isolated platform, which is pulsed up to a maximum of 100 kV during ion extraction. The EBIS is now fully assembled, and operation will be beginning following final vacuum and power supply tests. Details of the EBIS components are presented.

RHIC EBIS: basics of design and status of commissioning

RHIC EBIS will be used for producing multicharged ions from helium to uranium using primary ions from various external ion sources. The EBIS is followed by an RFQ and short linac, forming the new preinjector which will produce beams used for physics at RHIC and the NASA Space Radiation Laboratory, The design of RHIC EBIS is based on the BNL Test EBIS, which was a successful 10A electron current prototype. Improvements have been made in the RHIC EBIS design to increase the capacity of the ion trap, repetition frequency of operation, electron current, acceptance for injected ions, and improve vacuum conditions in the ionization region. RHIC EBIS has been assembled and installed in its final position. Commissioning is now underway to reach its project parameters. The results of this commissioning stage are presented.

Simulation of 10 A electron-beam formation and collection for a high current electron-beam ion source

Presented is a report on the development of an electron-beam ion source (EBIS) for the relativistic heavy ion collider at Brookhaven National Laboratory (BNL) which requires operating with a 10 A electron beam. This is approximately an order of magnitude higher current than in any existing EBIS device. A test stand is presently being designed and constructed where EBIS components will be tested. It will be reported in a separate paper at this conference. The design of the 10 A electron gun, drift tubes, and electron collector requires extensive computer simulations. Calculations have been performed at Novosibirsk and BNL using two different programs, SAM and EGUN. Results of these simulations will be presented.

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.

Development of electron beam ion source charge breeder for rare isotopes at Californium Rare Isotope Breeder Upgrade.

Recently, the Californium Rare Isotope Breeder Upgrade (CARIBU) to the Argonne Tandem Linac Accelerator System (ATLAS) was commissioned and became available for production of rare isotopes. Currently, an electron cyclotron resonance ion source is used as a charge breeder for CARIBU beams. To further increase the intensity and improve the purity of neutron-rich ion beams accelerated by ATLAS, we are developing a high-efficiency charge breeder for CARIBU based on an electron beam ion source (EBIS). The CARIBU EBIS charge breeder will utilize the state-of-the-art EBIS technology recently developed at Brookhaven National Laboratory (BNL). The electron beam current density in the CARIBU EBIS trap will be significantly higher than that in existing operational charge-state breeders based on the EBIS concept. The design of the CARIBU EBIS charge breeder is nearly complete. Long-lead components of the EBIS such as a 6-T superconducting solenoid and an electron gun have been ordered with the delivery schedule in the fall of 2011. Measurements of expected breeding efficiency using the BNL Test EBIS have been performed using a Cs(+) surface ionization ion source for external injection in pulsed mode. In these experiments we have achieved ∼70% injection∕extraction efficiency and breeding efficiency into the most abundant charge state of ∼17%.

High performance EBIS for RHIC

An electron beam ion source (EBIS), capable of producing high charge states and high beam currents of any heavy ion species in short pulses, is ideally suited for injection into a synchrotron. An EBIS-based, high current, heavy ion preinjector is now being built at Brookhaven to provide increased capabilities for the Relativistic Heavy Ion Collider (RHIC), and the NASA Space Radiation Laboratory (NSRL). Benefits of the new preinjector include the ability to produce ions of any species, fast switching between species to serve the simultaneous needs of multiple programs, and lower operating and maintenance costs. A state-of-the-art EBIS, operating with an electron beam current of up to 10 A, and producing multi-milliamperes of high charge state heavy ions, has been developed at Brookhaven, and has been operating very successfully on a test bench for several years. The present performance of this high- current EBIS is presented, along with details of the design of the scaled-up EBIS for RHIC, and the status of its construction. Other aspects of the project, including design and construction of the heavy ion RFQ, Linac, and matching beamlines, are also mentioned.

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.

Status report on studies of EBIS in the string mode of operation

A short description of an EBIS apparatus in the reflex mode of operation, resulting in electron string formation, and recent experimental results are presented. The focus is on experimental studies of electron energy distribution in strings, for which a long tail to high energy was observed and about 30% half width was confirmed by means of spectrometry using the radiative recombination of Ar17+. We have obtained considerable information about the dependency of the number of string electrons versus solenoid magnetic field strength using different EBIS sources and found that it has about 3 in power of B in the region 0–3.5 T. Preparations for the first experiments on the BNL EBIS Test Stand in the reflex mode of operation and for the first test of the JINR Krion-2 source in the string mode at the Nuclotron injector on acceleration of Ar16+ are also described briefly.