E. D. Hudson

Cyclotron Internal Ion Source with DC Extraction

This paper describes a method for increasing the intensities for heavy ion beams accelerated in isochronous cyclotrons at high harmonics (h?5) of the orbit frequency. Normally, only small intensities are obtained at high harmonics because of the low effective accelerating voltage between the ion source and the puller electrode. We have developed and tested a dc ion extraction system for the Oak Ridge Isochronous Cyclotron (ORIC). Use of the dc extraction system has increased beams of 4OAr3+ on the 5th harmonic and 2ONel+ on the 7th harmonic from nanoamperes to microamperes.

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.

High Performance Heavy-Ion Source for Cyclotrons

A cold cathode Penning discharge ion source, power supply, and its performance in the Oak Ridge Isochronous Cyclotron (ORIC) are described. The ion source has operated at power levels as high as 8 kW and has produced a variety of particle beams, ranging from deuterium to xenon and with charge states up to +12. In particular, 20 e?A (electrical microampere) of 05+, 5 × 104 p/sec (particle per second) of 40Ar10+, and 107 p/sec of 132Xe12+ have been extracted from ORIC. From the known intensities of accelerated ions and the calculated total ionization potential, a means of predicting particle intensity for a given charge state has been developed.

Achievement and measurement of the ORIC magnetic field

The magnetic field for ORIC is achieved by means of conventional main coils requiring 1 MW at maximum energy and internal coils with a power capability of another megawatt. The internal coils include ten pairs of circular trimming coils for shaping the radial gradient, a pair of valley coils in each of three sectors for changing the flutter, and three pairs of harmonic coils in each sector for cancelling the first harmonic. All internal coils are sealed in stainless steel containers. The objective of the measuring program was to obtain sufficient information on the effects of currents in all 21 magnet circuits so that current settings for these coils could be computed for any given particle and energy. A half million 5-digit field values were measured and recorded. Nine levels of main field excitation were measured both with and without each of the auxiliary coils. The difference between a composite azimuthally average field calculated from individual coil measurements and a measured field obtained with these same coil current values varied from one to eight gauss in about 14 500 gauss.

Magnetic Field Measuring System for Remapping the ORIC Magnetic Field

The Holifield Heavy Ion Research Facility will integrate a new 25 MV tandem electrostatic accelerator into the existing cyclotron laboratory which includes the Oak Ridge Isochronous Cyclotron (ORIC). 1 Computations of ion paths for beam injection from the new tandem into ORIC require field mapping in the regions traversed by the beam. Additional field data is also desired for the higher levels (~19 kG) now used for most heavy ion beams. The magnetic field measurement system uses 39 flip coil/current integrator sets with computer controlled data scanning. The coils are spaced radially at 1 inch intervals in an arm which can be rotated azimuthally in 2 degree increments. The entire flip coil assembly can be shifted to larger radii to measure fields beyond the pole boundary. Temperature stabilization of electronic circuitry permits a measurement resolution of ±1 gauss over a dynamic range of ±25,000 gauss. The system will process a scan of 8000 points in about one hour.

Production of Positive Ion Beams from Solids

We have recently reported a technique for making metal ions for cyclotrons. Metal and non-metal ions from solids are produced in a Penning ion source by a process that involves ions that are unable to cross the first acceleration gap between the ion source and dee and are accelerated back into the ion source where they sputter charge material into the arc. This material is ionized and extracted from the ion source and accelerated. We have now used this technique for a large variety of ions, both metal and non-metal, including most recently aluminum from the metal and boron from boron nitride charge materials. We have also calculated the efficiency for making iron ions with different ion support gases and have experimentally checked these results. We are presently designing a dual ion source for our dc Penning ion source test stand which we believe will make an excellent source for producing ions from solids for dc extracted Penning ion sources.

An ion source for high-intensity metal ions

Abstract A simple method of producing high-intensity metal ion beams from a high-powered Penning ion source in a cyclotron is described.

Unique features in the Oak Ridge Isochronous Cyclotron

The results of the initial month of operation of the Oak Ridge Isochronous Cyclotron are presented along with a description of the machine. An 8-MeV proton beam was obtained at the full 32-in. radius on 18 March. Beam-phase studies since that time have lowered the threshold voltage from 13 to 8 kV. ORIC is designed as a variable energy, three-sector, 76-inch, fixed-frequency cyclotron to accelerate protons to 75 MeV and nitrogen 4 + to 100 MeV.

The Oak Ridge Isochronous Cyclotron as an Energy Booster for a 25 MV Tandem

The maximum heavy-ion energy available at Oak Ridge will be substantially increased by using ORIC as an energy booster for the 25 MV “folded” tandem now being acquired. Beams of ions with mass up to A=160, with energy sufficient to overcome the Coulomb barrier on lead will be produced. The beams will enter the cyclotron through the dee stem, be directed by a magnet through the fringe and main fields to a stripping foil which lies on the appropriate orbit for acceleration. General orbit and beam transport codes have been used to aid in the design of the injection system.

Performance of a Penning Ion Source in the Oak Ridge Isochronous Cyclotron

One year of operation of a heavy-ion Penning source in the Oak Ridge Isochronous Cyclotron has resulted in the acceleration of a number of isotopes of 17 elements, ranging from boron to tantalum. The method of positive identification of these beams and the operational techniques used to develop certain beams are described. Comparison of the extracted particle current for a given charge state with the calculated ionization potential has resulted in a systematic understanding of particle currents to be expected for undeveloped beams. In particular, shell effects and total ionization potential must both be considered in predicting beam intensities. The particle currents of ArR8+ Ar9+ and Ar10+ provide a sensitive test for the comparison of multiple and single impact calculations. The data are in agreement with multiple impact calculations. Also, low energy x-rays emitted from the Penning source have been detected and the observed spectra characterize the two modes of source operation.