J. A. Martin

The histrap proposal: Heavy-ion storage ring for atomic physics

Abstract HISTRAP, Heavy-Ion Storage Ring for Atomic Physics, is a proposed 46.8-m-circumference synchrotron-cooling-storage ring optimized to accelerate, decelerate, and store beams of highly charged very-heavy ions at energies appropriate for advanced atomic physics research. The ring is designed to allow studies of electron-ion, photon-ion, ion-atom, and ion-ion interactions. An electron cooling system will provide ion beams with small angular divergence and energy spread for precision spectroscopic studies and also is necessary to allow the deceleration of heavy ions to low energies. HISTRAP will have a maximum bending power of 2.0 T m and will be injected with ions from either the existing Holifield Heavy Ion Research Facility 25-MV tandem accelerator or from a dedicated ECR source and 250 keV/nucleon RFQ linac.

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.

Charge-state distributions of 100, 175, 275 and 352 MeV gold ions emerging from thin carbon foils

Abstract Ion charge-state distributions were measured for 100, 175, 275 and 352 MeV gold ions emerging from thin carbon foils. The 90° double-focusing energy analyzing magnet of the Holifield Heavy Ion Research Facility 25 MV tandem accelerator was used to separate the charge-states. Carbon foil thicknesses of 10, 20, 40 and 80 μg/cm 2 were used depending on the beam energy. At least two different foil thicknesses were used at each energy to insure that equilibrium distributions were measured. The measured mean charge was compared with the predictions of the Sayer, Nikolaev-Dmitriev, and Shima et al. semi-empirical charge-distribution formulas. The measurements are in general agreement with the semi-empirical predictions at 100 MeV but were systematically lower at the higher energies. The largest discrepancy was −4.9 charge-states at 352 MeV. These results are especially significant for the design of booster accelerators for large tandem accelerators and for the design of coupled cyclotron systems.

Status of the Holifield Heavy Ion Research Facility

The Holifield Heavy Ion Research Facility presently operates the Oak Ridge Isochronous Cyclotron (ORIC). This accelerator provides heavy ions up to argon with energies useful for nuclear physics. The Phase I expansion of this facility, now a year away from completion, includes a 25-MV vertical folded tandem accelerator, beam transport and injection systems to use the ORIC as an energy booster, and additional experiment areas for the beams directly from the tandem. The tandem-cyclotron combination will provide heavy ions with energies up to 25 MeV/A for A < 35 and above 6 MeV/A up to A = 160, with intensities ¿ 1011 particles/sec. Building construction for the project is essentially complete. The accelerator manufacturer, National Electrostatics Corporation, has completed installation and testing of the 10-m-diam by 30-m-high accelerator pressure vessel and has begun installation of the accelerator system. The column structure and injector have previously been assembled at the NEC plant and the digital control system operated without voltage on the column. It is expected that voltage tests will begin at Oak Ridge in January 1979 and beam tests in April. Completion of the project, including acceptance tests of the tandem and the beam injection system for ORIC, is presently scheduled for November 15, 1979. Construction of Phase II for the facility, which will include a much larger booster cyclotron and additional research areas, is expected to begin in 1982.

Recent Advances in Design for Low- and Medium-Energy Heavy Ion Accelerators

Recent developments in the technology of electrostatic accelerators, linear accelerators, and cyclotrons for the acceleration of heavy ions are reviewed. (GHT)

Design Status of a Separated-Sector Cyclotron Booster Accelerator for the Holifield Heavy Ion Research Facility

A separated-sector cyclotron booster accelerator is being designed for the Holifield Heavy Ion Research Facility as a Phase II project to be started in 1978. Phase I of the HHIRF, now under construction, includes a 25 MV tandem electrostatic accelerator, a beam transport and injection system to enable use of the Oak Ridge Isochronous Cyclotron as an energy booster for tandem beams, and some additional experiment areas and associated beam transport systems. The Phase I facility using the ORIC-25 MV tandem combination will provide energies up to about 25 MeV/amu for light ions such as oxygen and more than 5 MeV/amu up to the region of mass 160. The new Phase II separated-sector cyclotron will provide energies up to 100 MeV/amu for light ions and up to 12 MeV/amu for the heaviest ions such as uranium.

Increased Intensity Heavy Ion Beams at ORIC with Cryopumping

Previously reported measurements of heavy ion beam attenuation with pressure have demonstrated the need for additional pumping in the circulating beam region of the Oak Ridge Isochronous Cyclotron (ORIC). Two specially designed 20°K cryopumps, located on the magnet poles, have increased the pumping speed in the circulating beam region by about a factor of 3. This has led to increased intensity for beams of heavy ions of elements that can be condensed by the cryopumps (e. g., oxygen, nitrogen, etc.). The improved vacuum has led to an increased understanding of a beam loss in the internal region of the cyclotron. Measured cross sections for beam loss and the cross section energy dependence have been determined.

A Multi-Accelerator System for Heavy Ions

The accelerators for the new National Heavy-Ion Laboratory (NHL) being planned at Oak Ridge will provide beams of all ions from helium to uranium with energies ranging from 100 MeV/u for light ions to 10 MeV/u for the heaviest ions accelerated. The heart of the proposed accelerator system is a large 4 sector isochronous cyclotron of the separated sector type with an energy rating of 440 q2/A MeV. Ions are to be injected into the large cyclotron from either a large tandem electrostatic acclerator or from the Oak Ridge Isochronous Cyclotron (ORIC). The ORIC will generally suffice as the injector up to the mass 160-180 range, beyond which use of the tandem is necessary. Beam intensities will range from 1013 ions/sec for 100 MeV/u oxygen to ~2 × 1012/sec for 10 MeV/u uranium ions. The beam emittance is expected to be less than 10 mm-mrad and the energy spread less than 0.1%. The large cyclotron uses auxiliary RF accelerating cavities operating at twice the main RF frequency to flattop the effective accelerating voltage waveform to thus increase the phase acceptance and reduce the energy spread of the beams.

The 4-MeV Separated-Orbit Cyclotron

The Separated-Orbit Cyclotron Experiment (SOCE) will extend and complement earlier theoretical and experimental studies and will provide a unique facility for the evaluation of an operating SOC system. The six-sector, fourturn accelerator will provide maximum energies of 4 MeV for protons and deuterons and 8 MeV for 3He++ and 4He++ ions. The output energy is variable over a 2:1 range by adjustment of the magnetic field and acceleration of the ions at the appropriate harmonic of the ion frequency. Ions are injected into the SOC at one quarter the final energy. The injection system consists of a duoplasmatron ion source, a 500-kV dc accelerator, and a three-cavity linear accelerator. Proton currents in the 10-to 20-mA range are predicted. The principal characteristics of the accelerator are given in Table I. All of the major components have been fabricated and delivered on site except the injectors linac cavities, which are expected shortly. The photograph in Fig. 1 shows the accelerator as seen from the control area on a mezzanine about 40 feet away. The SOC sector magnets and rf cavities are in the approximate location, with the dc injector components in the background. The tops of the magnet yokes have been temporarily removed to permit completion of pole tip alignment. An rf power amplifier will be mounted on the outer wall of each cavity. One of the PA units can be seen in the background (Fig. 1) on a test stand with a water-cooled dummy load.

A 4-MeV Experimental Separated-Orbit Cyclotron

A small experimental Separated-Orbit Cyclotron is being built to provide experience in the design and operation of this new type of accelerator. It will permit examination of the sensitivity of the SOC design to methods of construction and to errors in alignment. Some features are variable so that the flexibility of this class of machines for the acceleration of various particles and the applicability to high beam intensities can be evaluated.