M. L. Mallory

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.

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.

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.

A Diagnostic System for Optimization of the External Beam Quality of the Oak Ridge Isochronous Cyclotron

The parameters of the external beam that are of prime importance to the experimenter are the emittance, energy spread, intensity of analyzed beam, and time structure. Diagnostic equipment has been developed for routine measurement and optimization of these parameters.

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.

A Penning Multiply Charged Heavy Ion Source Test Facility

An ion source test facility has been constructed at Oak Ridge National Laboratory for making fundamental measurements of the properties of Penning ion sources. The extracted ion energies from the source can be up to 36 × q (keV), where q is the ion charge. Both negative and multiply charged positive ions have been extracted from the source. The facility has high current capabilities for acceleration and for the arc power supply. These low-energy, multiply charged ions are currently being used for measurements of charge exchange cross sections, x-ray production, and electron impact excitation and ionization.

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.

Separated-sector cyclotron post-accelerator for the Oak Ridge Heavy Ion Laboratory

A separated sector cyclotron post-accelerator is proposed for the Oak Ridge Heavy Ion Laboratory. The SSC accepts beams from either ORIC or the 25 MV tandem electrostatic accelerator and extends the maximum particle energy to 75 MeV/u for A less than 40 and to at least 10 MeV/u for A greater than 40. The SSC has a field-radius product of 2540 kG-cm, a 4-sector configuration, and azimuthal pole width of 52°. RF acceleration of up to 1 MV per turn is obtained with two resonators in opposite valleys. An RF tuning range of 6 to 14 MHz accommodates acceleration on harmonics 2 through 11. Concentric second harmonic resonators are provided for optimizing phase acceptance.