Robert M. Main

Invited Paper-The Omnitron: A Versatile Medium-Energy Synchrotron for the Acceleration of Light and Heavy Ions

A novel guide-magnet configuration has been devised which makes possible the acceleration of all charge-to-mass ratios from 0.04 to 1. A concentric storage ring, with the associated beam-switching equipment, allows for the extension of beam duty factor to essentially 100%. The storage ring can also be used in a bootstrap acceleration of heavy ions in which the ions are injected at low e/m, accelerated to a moderate velocity, stored while the accelerating ring returns to minimum field, stripped to maximum e/m, and re-injected for further acceleration. With a pressurized 2.5 MV Cockcroft-Walton injector, the proposed system is capable of accelerating all ions from protons to uranium--to energies up to 1.5 BeV for protons and 0.3 to 0.5 BeV/nucleon for the heavier ions. Intensities of 1012 to 1013 nucleons/sec for the lighter ions (M ? 128) are anticipated. The heavy-ion charge-exchange probabilities determine the vacuum requirements of this system. To minimize these requirements and to increase beam intensity, a 60/sec cycling rate has been chosen. The vacuum requirements and the special rf resonator and beam-switching problems attendant with the high cycling rate are discussed.

MODIFICATION OF THE BERKELEY HILAC.

Abstract A program is presently in progress for the modification of the Hilac to make possible the acceleration of ions of all masses to a maximum energy of 8.5 MeV/N. Present scheduling calls for the shut down of the existing Hilac in January 1971 and first beams from the modified system in August 1971. The improved accelerator will consist of a pressurized 2.5 MV Cockcroft-Walton injecting ions of minimum charge-to-mass ratio ϵ=0.045, at 0.112 MeV/N into an Alvarez linac. The linac will be separated at 1.2 MeV/N where particles will be stripped to a minimum ϵ=0.16. The second linac section will be partitioned into individual cavities of approximately equal velocity increments. Adjustment of rf phase and gradient in these cavities will provide variable energy from 2.6 to 8.5 MeV/N. All cavities will operate at 70.2 MHz and magnetic quadrupole focusing will be used throughout.

Review of Linear Accelerators for Heavy Ions

During the past 5 years there has been a considerable increased interest in ions heavier than were available from existing accelerators (M ? 40, Argon). The requirements for this new generation of accelerators are: ions of all masses through uranium at maximum energies of 8-10 MeV/A with completely variable energies above 2 MeV/A and with energy resolution better than l/2%. Intensities of up to 1012 ions per second are required. There are presently three heavy ion accelerators in various stages of planning, design and construction, all of which use linear accelerators as a portion of the system. These are the Unilac at Darmstadt, the Helac at Heidelberg, and the SuperHilac in Berkeley. A brief discussion of these proposed accelerators is presented as well as the present status of these projects.

PEP Insertion Quadrupole Design Features

The insertion quadrupoles for the PEP storage ring must have a very uniform gradient to focus the circulating beams to a very small size at the interaction point for high luminosity. Quads have been built which achieve the desired field within the full pole aperture radius to approximately one part in 104. The design features which permitted this achievement are described.

Proposed Modifications of the Berkeley Hilac

Improvements are planned for the Berkeley Heavy Ion Linear Accelerator which will make possible the acceleration of all elements from hydrogen to uranium to 7.5 MeV/nucleon. The improved system will consist of a 2.7 MV dc injector, a new 11 meter-long prestripper linac and the existing 27 meter long poststripper linac which will be extended to 37 meters. Baffles in the latter portion of this cavity will separate it into individually excited segments to provide completely variable energy from 3 to 7.5 MeV/nucleon. To provide the lighter heavy ion beams, at energies acceptable for biological research and medical therapy, a 25 meter diameter rapid cycling alternating gradient synchrotron is proposed. With this machine fully stripped ions from the Hilac with M?20 can be accelerated to energies up to 500 MeV/nucleon. Details of the synchrotron design will closely follow those developed for the Omnitron and a prototype of the Omnitron accelerating resonator will be used.

A Small Helium-3 Cyclotron

A 27-inch AVF cyclotron of fourfold symmetry designed specifically for use in helium-3 activation analysis is now in operation at the Lawrence Radiation Laboratory in Berkeley. The fixed energy and modest beam quality requirements have resulted in an instrument of minimum size, weight, power consumption, and fabrication costs. New techniques were developed to construct edge-cooled tape-wound magnet coils which are housed inside the vacuum chamber. Other unusual design features include: unit construction dee liners hydraulically pressed to the pole tip contours; two 55° dees-in-valleys operating in pushpull; a removable top yoke assembly which allows complete access to the pole area; a narrow gap with an average spacing of 1.5 inches making possible maximum utilization of the pole diameter for stable orbits. In conjunction with the tape coils, the use of this small gap also results in a magnet of very high efficiency. The cyclotron operates with an average field of 16.6 kG and a grounded-grid triode provides 40 kV dee-to-ground (150 keV/turn). Power is supplied by 220 V, 3-phase service. The magnet requires 17 kW, the HF system uses 17 kW, and the remaining instruments, pumps, and controls use an additional 6 kW. The complete system, including vacuum pumps and power supplies, weighs 10.7 tons and occupies a floor space of 37 × 64 inches.