D.L. Haynes

Selection and design of the Oak Ridge radioactive ion beam facility target/ion source

Abstract The high-temperature version of the CERN ISOLDE source has been selected as the first source to be used for the generation of radioactive ion beams at the Oak Ridge Radioactive Ion Beam Facility (ORRIBF) because of its low emittance, relatively high ionization efficiency, and capability for producing a broad range of radioactive species. Of equal importance, the source has been cleverly engineered for remote installation, removal and servicing as required for safe handling of highly radioactive contaminated sources, source components, and ancillary equipment. The source design also permits easy modification to lower-temperature versions and conversion from electron impact ionization to either thermal or positive and negative surface ionization sources. The reasons for choosing the CERN ISOLDE source and design features of the source are discussed in this paper.

Design aspects of a compact, single-frequency, permanent-magnet electron cyclotron resonance ion source with a large uniformly distributed resonant plasma volume

A compact, all-permanent-magnet, single-frequency electron cyclotron resonance (ECR) ion source with a large uniformly distributed ECR plasma volume has been designed and is presently under construction at the Oak Ridge National Laboratory. The central region of the field is designed to achieve a flat field (constant mod-B) which extends over the length of the central field region along the axis of symmetry and radially outward to form a uniformly distributed ECR plasma “volume.” The magnetic field design strongly contrasts with those used in conventional ECR ion sources where the central field regions are approximately parabolic and the resulting ECR zones are “surfaces.” The plasma confinement magnetic field mirror has a mirror ratio Bmax/BECR of slightly greater than 2. The source is designed to operate at a nominal rf frequency of 6 GHz. The central flat magnetic field region can be easily adjusted by mechanical means to tune the source to the resonant conditions within the limits of 5.5–6.8 GHz. The ...

A new beam intensity monitoring system with wide dynamic range for the Holifield Radioactive Ion Beam Facility

A new beam intensity monitoring system with a wide dynamic range has been designed, fabricated and tested for use at the Holifield Radioactive Ion Beam Facility (HRIBF). Radioactive ion beams produced with this first generation facility will have intensities much lower than those of stable ions previously injected into the 25 URC tandem accelerator and the existing beam current monitoring systems, which have a lower limit of approximately 100 pA, will not be adequate to tune the injection line or accelerator. This paper describes a new system which combines a Faraday cup and a continuous dynode electron multiplier (CDEM) to yield a dynamic range from a few particles per second to greater than a microampere. The CDEM can be biased to count either secondary electrons or Rutherford backscattered ions.

A simple, inexpensive voltage grading resistor for large electrostatic accelerators

Abstract A simple, inexpensive voltage grading resistor installation for electrostatic accelerators is described. Functional tests in the Holifield Heavy Ion Research Facility 25-MV tandem accelerator indicate that this system is insensitive to spark-induced damage at operating potentials up to 24 MV.

Improved voltage performance of the Oak Ridge 25URC tandem accelerator

Abstract Installation of compressed geometry acceleration tubes and associated changes in the corona voltage grading system have resulted in significant improvement in voltage performance of the Oak Ridge 25URC tandem accelerator. Details of the final phase of this work and initial tests on the modified accelerator are provided.

Development of the HRIBF 25-MV tandem accelerator as a RIB accelerator

The Holifield Facility 25URC tandem accelerator will begin accelerating radioactive ion beams (RIBs) for nuclear structure and astrophysics research in 1996. This paper addresses the development of the accelerator to allow optimum operation with the particular challenges associated with RIBs. New diagnostics for ultra-low-intensity beams are being installed and the terminal potential stabilization system is being studied to optimize control with these low beam intensities. A new resistor-based voltage-grading system has resulted in more stable operation as well as allowing operation at the very low terminal potentials which are required for some astrophysics experiments. Also addressed is beam transmission optimization, particularly at low terminal potentials, and operation of the accelerator at high terminal potentials.

Tests of compressed geometry acceleration tubes in the Oak Ridge 25URC tandem accelerator

Abstract In an effort to improve further the voltage performance of the Oak Ridge 25URC accelerator, the original acceleration tubes will be replaced with NEC compressed geometry acceleration tubes. In this paper, we report on tests in the 25URC accelerator of two prototype compressed geometry acceleration tube designs. One of the designs utilizes a novel aperture which provides enhanced electron and ion trapping.

The Holifield Heavy Ion Research Facility

The Holifield Heavy Ion Research Facility has been in routine operation since July 1982. Beams have been provided using both the tandem accelerator alone and a coupled mode in which the Oak Ridge Isochronous Cyclotron is used as an energy booster for tandem beams. The coupled mode has proved to be especially effective and has allowed us to provide a wide range of energetic beams for scheduled experiments. In this report we discuss our operational experience and recent development activities.

Selection and design of ion sources for use at the Holifield radioactive ion beam facilitya)

The Holifield Radioactive Ion Beam Facility now under construction at the Oak Ridge National Laboratory will use the 25 MV tandem accelerator for the acceleration of radioactive ion beams to energies appropriate for research in nuclear physics; negative ion beams are, therefore, required for injection into the tandem accelerator. Because charge exchange is an efficient means for converting initially positive ion beams to negative ion beams, both positive and negative ion sources are viable options for use at the facility. The choice of the type of ion source will depend on the overall efficiency for generating the radioactive species of interest. Although direct‐extraction negative ion sources are clearly desirable, the ion formation efficiencies are often too low for practical consideration; for this situation, positive ion sources, in combination with charge exchange, are the logical choice. The high‐temperature version of the CERN‐ISOLDE positive ion source has been selected and a modified version of t...

Progress, status, and plans for the HRIBF project☆

Abstract Over the last three years, the Holifield accelerator system has been reconfigured into a first-generation radioactive ion beam facility, the HRIBF, a national user facility for RIB research. The construction and reconfiguration have been completed and the equipment commissioning and beam development phases have started. The progress to date, the present status, and future plans will be given. The special problems connected with the production and acceleration of RIBs will be discussed.