J. Alessi

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.

The Algebraic Reconstruction Technique (ART)

Projections of charged particle beam current density (profiles) are frequently used as a measure of beam position and size. In conventional practice only two projections, usually horizontal and vertical, are measured. This puts a severe limit on the detail of information that can be achieved. A third projection provides a significant improvement. The Algebraic Reconstruction Technique (ART) uses three or more projections to reconstruct 3-dimensional density profiles. At the 200 MeV H/sup -/ linac, we have used this technique to measure beam density, and it has proved very helpful, especially in helping determine if there is any coupling present in x-y phase space. We will present examples of measurements of current densities using this technique.

Optically pumped polarized H− ion source for RHIC spin physics

A new optically pumped polarized H− ion source (OPPIS) was developed for the RHIC polarization program and successfully used for the first polarized beam commissioning at RHIC. The OPPIS produces in excess of 1.0 mA H− ion current at about 80% polarization. An ECR primary proton source development and a new 29 GHz microwave power supply are described. A new type sodium-jet ionizer cell is biased to −32 kV to produce a 35 keV polarized beam ready for injection to the RFQ. Higher current and higher polarization were also obtained with the biased jet-cell in comparison with an old oven-type ionizer cell.

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.

Linac4 H⁻ ion sources.

CERNs 160 MeV H(-) linear accelerator (Linac4) is a key constituent of the injector chain upgrade of the Large Hadron Collider that is being installed and commissioned. A cesiated surface ion source prototype is being tested and has delivered a beam intensity of 45 mA within an emittance of 0.3 π ⋅ mm ⋅ mrad. The optimum ratio of the co-extracted electron- to ion-current is below 1 and the best production efficiency, defined as the ratio of the beam current to the 2 MHz RF-power transmitted to the plasma, reached 1.1 mA/kW. The H(-) source prototype and the first tests of the new ion source optics, electron-dump, and front end developed to minimize the beam emittance are presented. A temperature regulated magnetron H(-) source developed by the Brookhaven National Laboratory was built at CERN. The first tests of the magnetron operated at 0.8 Hz repetition rate are described.

Regular and asymmetric negative ion magnetron sources with grooved cathodes

A significant improvement in the performance of the BNL Mark III magnetron negative ion sources has been achieved by putting cylindrical grooves on the cathode to geometrically focus surface produced H− and D− ions into the emission slit in the anode. The addition of these grooves has allowed us to reach desired negative ion emission current densities with an order of magnitude lower arc current than was previously required. An additional improvement in the operation of the magnetron has resulted from increasing the anode‐to‐cathode spacing in the back of the source, which facilitates ignition of the discharge at low pressures. The net result of these modifications has been an improvement in the gas and power efficiencies by at least a factor of three, and a reduction in the emittance of the beam.

Performance of the Magnetron H− Source on the BNL 200 MeV Linac

A magnetron surface plasma H− ion source has been used at Brookhaven since 1982 for injection into the 200 MeV linac. Since 1989, this source has operated with a circular aperture, injecting into an RFQ. The source typically produces 90–100 mA of H− at 35 keV, in 700 μs pulses at up to 10 Hz. The arc parameters are −15 A, 150 V, and the extracted e/H− ratio is 1/2. Ions are extracted from a 2.8 mm diameter aperture (J=1.6 A/cm2). The emittance is approximately en, rms = 0.4 π mm mrad. The performance is very reliable, operating continuously for −6 months, with essentially no parameter adjustments required once the source is stabilized.

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.

H− source and low energy transport for an RFQ preinjector

A radio‐frequency quadrupole (RFQ) accelerator has replaced a 750‐keV Cockcroft‐Walton as the H− preinjector for the Brookhaven alternating gradient synchrotron. A magnetron surface‐plasma source with a circular aperture is used to produce 65–100 mA of H− at 35 keV with a discharge current of less than 20 A. The symmetry of the beam is maintained in the 2‐m transport to the RFQ via the use of magnetic solenoids for focusing. Currents up to 60 mA have been obtained out of the RFQ. A traveling‐wave electrostatic chopper in the 35‐keV transport line leads to a distortion of the emittance due to space‐charge effects.

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.