The Bevatron/Bevalac main guide field power supply was originally designed to provide a 15250-V DC at 8400-A peak magnet pulse. Protons were accelerated to 6.2 GeV. The 128-MW pulse required two large motor-generator (MG) sets with 67-ton flywheels to store 680 MJ of energy. Ignitron rectifiers are used to rectify the generator outputs. Acceleration of heavy ions results in an operating schedule with a broad range of peak fields. The maximum field of 12.5 kG requires a peak pulse of 80 MW. Acceleration of ions to 1.0 kG requires an 8-MW peak pulse. One MG set can provide pulses below 45 MW. Peak pulses of less than 15 MW are now a large block of the operating schedule. A proposal has been made to replace the existing MG system with eight silicon controlled rectifier (SCR) power supplies for low field operation. The SCR supplies will be powered directly from the Lawrence Berkeley Laboratory's 12.3-kV power distribution system. It is concluded that the implementation of this proposal will benefit Bevaton/Bevalac operations by reducing operating costs and improving beam quality. It is noted that the ability to achieve a requested field without extensive Ignitron warmup would, by itself, be justification for the concept. >

It is noted that demand for relativistic heavy-ion beams at the Bevalac has increased dramatically in the past two years. To keep pace, the Bevalac makes use of five injectors, precise guide field control, present beam transport line tunes, nine nuclear science target areas, and three biology/radiotherapy areas, along with elegant computer control algorithms, to achieve high operating efficiency. Routine operation includes as many as ten ion/energy/beamline changes per day, 15 major nuclear science experiments each year, and radiotherapy on nearly a daily basis, with biology experiments operating biweekly. High operating efficiency and low failure rates combine to produce high annual research hours

The Bevatron/Bevalac main guide field power supply stores 680 MJ in the flywheel-shaft systems of two independent motor-generator sets. During the normal acceleration cycle of various heavy-ion beams, the energies of the rotating shafts are converted to energy stored in the main magnet guide field. At the end of the acceleration cycle, the magnet energy is inverted back to the shafts. Generally, this takes place from 10 to 15 times per minute. The rapid switching of ions, energy, and beam lines at the Bevalac has required various control techniques for fast switching between all operational Bevalac fields within 1 min. The power supply control systems and operating parameters are described

Rapid switching of ion, energy, and beam line has been accomplished on a routine basis; typical transfer time is l-2 minutes in worst case situations. Opera- tional efficiency has been improved by substantial reduction of inter-experiment tune time and improved optics in the external beam area installed in 1985. A comparison of current research efficiency and previous vear efficiencv is qiven.

Rapid changes of ion, intensity, beam line, and output energy between two modes have been achieved. The techniques for switching among the Bevalac's several injectors are described. Energy level limits at the output (for q/A=1/2) are 470-2100 MeV/n (high power) or 50-1050 MeV/n (low power). Depending on specific field value differences, the total time required for a mode change is less than one minute. This mode of operation greatly improves program efficiency in interleaving medical and nuclear science programs at the Bevalac.

Heavy ion radiobiology has been integrated successfully into the research program at the Bevatron/Bevalac for the past several years. During the 1979-1980 year radiotherapy trials have been conducted side-by-side with the demanding program of heavy ion nuclear science research at this national facility. Careful attention is given to the scheduling of research on the SuperHILAC and Bevatron/Bevalac so that the nuclear science and biomedical programs at the Bevatron/Bevalac and the program at the SuperHILAC are served to maximum effect. Efforts to maximize the researchers' time have resulted in hardware, software, and operating improvements that offer a total machine availability of about 90% and a user availability of about 80%. Fast beam switching and beam sharing permit virtually simultaneous use of the Bevatron/Bevalac by two or more users. Current beam delivery systems will be augmented in FY81 to provide two ion energies per Bevatron/Bevalac pulse.

The performance of the Bevalac is reported. The Bevalac uses the LBL SuperHILAC as the heavy ion injector to the Bevatron. Ion species up to 40A have been accelerated to energies of 1.9 GeV/A at modest intensity. Neon has been accelerated to 2.1 GeV/A at an intensity of 4·1010 particles per pulse. The modifications to the SuperHILAC and Bevatron are briefly reviewed and the computer control system is described. Results of the first phase of operation and plans for further improvements are reported.

High Energy Heavy-Ion Beams have become a standard operational feature of the Bevatron. A diver-sified experimental program using these beams complement the traditional proton-physics program, and at present accounts for about one-quarter of the Bevatron operation time. Beams of ion species up to mass number 20 (neon), and with intensities up to 108 particles per pulse for carbon, are available on target in the extracted beam channel. Initial heavy-ion operation began a year-and-one-half ago and for the most part utilized existing Bevatron features and capabilities. Acceleration of ion species heavier than helium-ions, however, required the adaptation of a side-extracted PIG ion-source to the Bevatron pre-injector. The immediate success of this development effort and the concomitant demand for experimental beam time motivated an improvement program to provide higher beam intensities, improved beam control and monitoring, and closed-loop beam control for intensities as low as 106 particles per pulse. Single particle beam dynamics has been invest igated. Predicted operation settings based on these studies are found to be close to actual running parameters. Losses due to recomibination are well explained with existing theories for single electron capture.

The Bevatron has associated with its acceleration cycle many parameters which vary in a dynamic manner throughout that cycle. Control and monitoring of such parameters is now done largely by computer, so that many variables formerly in the analog realm and easily observed on the conventional oscilloscope are now in the digital realm and not easily observed. The Chromonitor is a device which has been developed to accept inputs from computers or the analog realm and display on a TV screen any or all of sixteen different parameters which may be associated with particle acceleration and delivery, or which may be pertinent to monitoring a computer process in progress. Each of the parameters may be displayed in any of seven colors.

Control of the Bevatron acceleration system had been entirely analogue until developments in proton extraction techniques required substantial reduction of hum and noise during the acceleration cycle. The decision was made to employ a digital processor to control the acceleration cycle. An algorithm is developed which allows introduction of radial-feedback data into the digital processor and the real-time error signal is combined with arbitrary field dependent functions for transmission to the existing master. oscillator. A high common-mode rejection digital system is utilized to enter the resultant control data directly into the master-oscillator environment before conversion into the required analog reference for frequency modulation. A comprehensive hardware "calculator" provides a continuous curve of digital representations to be sent along to the oscillator. The paper describes implementation of these facilities and the development of operator-oriented interface to capitalize upon the flexibilities inherent within a digitally oriented system.

Author(s): Allison, Robert W.; Crebbin, Kenneth C.; Everette, William L.; Lothrop, Fred H.G.; Zajec, Emery.