H. Lancaster

Improved Field Stability in RFQ Structures with Vane Coupling Rings

The small apertures common in many RFQ linac designs lead to tuning difficulties, primarily because asymmetries in the quadrant fields can arise as a result of small non-uniformities in the vane to vane capacitances. Sensitivity to such capacitance or other tuning variation in the quadrants is greatly reduced by the introduction of pairs of vane coupling rings that provide periodic electrical connections between diametrically opposite vanes. Results of measurements on a cold model RFQ structure with and without vane coupling rings are presented. The number of rings required for field stabilization and the effect of rings on mode frequencies are discussed.

Vane Coupling Rings: A Simple Technique for Stabilizing a Four-Vane Radiofrequency Quadrupole Structure

The benefits of stabilized accelerating structures, with regard to the manufacture and operation, have been well documented. The four-vane radiofrequency quadrupoles (RFQ) presently being designed and constructed in many laboratories are not stabilized because of the weak electromagnetic coupling between the quadrant resonators. This paper presents a simple technique developed at the Lawrence Berkeley Laboratory using vane coupling rings (VCRs) which azimuthally stabilize the RFQ structure and greatly enhance its use as a practical accelerator. In particular, the VCRs: ¿ Completely eliminate the dipole modes in the frequency range of interest; ¿ Provide adequate quadrant balance with an initial precision mechanical alignment of the vanes; ¿ Enhance axial balance and simplify end tuners. Experimental verification tests on a scale model will be discussed.

RFQ Development at LBL

The radio frequency quadrupole (RFQ) is a structure which can efficiently focus, bunch and accelerate low velocity ion beams. It has many features which make it particularly attractive for applications in the biomedical and nuclear sciences. There are two projects in progress at LBL where the incorporation of heavy ion RFQ technology offers substantial benefits: in the upgrade of the Bevatron local injector, and in the design of a dedicated heavy ion medical accelerator. In order to meet the requirements of these two important applications, a 200 MHz RFQ structure has been designed for ions with charge to mass ratios as low as 0.14, and a low RF power scale model has been built and tested. Construction of the high power model has begun. The status of this project is reviewed and a summary of technical specifications given.

Design of a Dedicated Heavy Ion Accelerator for Radiotherapy

A new heavy ion accelerator facility for radiotherapy is being designed at the Lawrence Berkeley Laboratory. Performance requirements have been established. Ions from helium to argon can be accelerated to a maximum energy of 800 MeV/nucleon with intensities in the range 108-109 particles per second. The accelerator subsystems consist of a linac injector, a synchrotron and a beam delivery system. Specifications have been developed for many of the technical components, and some details of the technical design are presented.

Digital Computer Control of the Bevatron Inflection System

A program is being carried out at the Bevatron, in cooperation with the 200-BeV Design Study,1 to investigate the application of computerized digital control to accelerators. Specifically, a digital-computer control system has been placed in operation at the Bevatron injector for investigation of control and operator interaction between an on-line control computer and an operating accelerator. The system controls transport and inflection of the 19.3 proton beam. The computer, which is remotely located from the accelerator, collects and disseminates control information through time-shared, hybrid (analog -- digital) interface hardware. Data transmission is via twisted pair cable. With this system the beams center of gravity has been maintained at the entrance of the achromatic inflector, in the transverse planes, to ±0.1 mm and ±0.1 mrad2 by closed-loop sampled-data control of steering magnets at three points along the beam-transport channel. Beam-position information is obtained from 200-MHz resonant induction electrodes3 located near each steering magnet. In addition, the inflector deflection and focussing elements may be set by the operator and then regulated automatically by the computer. The operator may request typewritten or cathode-ray-tube (CRT) alphanumeric display or a CRT plot of parameters of interest. Optimization of the circulating charge in the accelerator by automatic adjustment of the inflector magnets and on-line diagnostics of certain injector components during trouble periods are planned.

Advanced Medical Accelerator Design

This report describes the design of an advanced medical facility dedicated to charged particle radiotherapy and other biomedical applications of relativistic heavy ions. Project status is reviewed and some technical aspects discussed. Clinical standards of reliability are regarded as essential features of this facility. Particular emphasis is therefore placed on the control system and on the use of technology which will maximize operational efficiency. The accelerator will produce a variety of heavy ion beams from helium to argon with intensities sufficient to provide delivered dose rates of several hundred rad/minute over large, uniform fields. The technical components consist of a linac injector with multiple PIG ion sources, a synchrotron and a versatile beam delivery system. An overview is given of both design philosophy and selected accelerator subsystems. Finally, a plan of the facility is described.

The LBL Wideroe-Based Heavy Ion Injector Project

The LBL Wideroe-based high-intensity heavy-ion injector for the SuperHILAC will be operational by April 1981. It will provide several emA of low charge state ions up through uranium at high duty factor to the SuperHILAC. Several of the subsystems have already operated to specification and will be described.

A High Performance Control System for a Heavy Ion Medical Accelerator

A high performance control system is being designed as part of a heavy ion medical accelerator. The accelerator will be a synchrotron dedicated to clinical and other biomedical uses of heavy ions, and it will deliver fully stripped ions at energies up to 800 MeV/nucleon. A key element in the design of an accelerator which will operate in a hospital environment is to provide a high performance control system. This control system will provide accelerator modeling to facilitate changes in operating mode, provide automatic beam tuning to simplify accelerator operations, and provide diagnostics to enhance reliability. The control system being designed utilizes many microcomputers operating in parallel to collect and transmit data; complex numerical computations are performed by a powerful minicomputer. In order to provide the maximum operational flexibility, the Medical Accelerator control system will be capable of dealing with pulse-to-pulse changes in beam energy and ion species.

New RF Power System for SuperHILAC

The upgraded rf system for the SuperHILAC is now operational using 9 new tetrode amplifiers. Each amplifier can produce in excess of lMw of 70 Mhz pulsed rf power. Ferrite is used to decouple the screen grid circuit and to absorb parasitic oscillations. This results in a very stable amplifier with reasonable gain. This system uses a common 6 Mw anode power supply and crowbar system. Overall system efficiency has been increased significantly. We project a 3 year payback on the equipment cost, realized from the power savings alone.

The 50-MeV Bevatron Injection Linac

The BNL 50-MeV injection linac has been installed as a new injector for the Bevatron. The preinjector, linac modifications, and beam transfer lines are described. The linac and modulator have been modified to permit longer pulse operation at a higher peak current. Most support equipment was already on hand and modified for use.