John S. Moenich

Transport Experiments with Neutralized and Space Charge Dominated Deneutralized 2 mA 80 keV Xe Beams

The Argonne National Laboratory Ion Beam Fusion group is presently studying the transport and charge neutralization of beams of heavy ions using a small PDPE (Penning Discharge Pierce Extraction) ion source. This source is a scaled down version of the high current high brightness source of the 1.5 MeV Heavy Ion Preaccelerator. Both sources were developed by Hughes Research Laboratories. This report gives results obtained with a low vacuum system (up to 5 × 10-7 torr static vacuum) and an 80 keV dc Xe+1 beam. The emphasis of these measurements was on neutralization times and space charge blow up of the beam.

The Proton Diagnostic Accelerator

The advantage of proton radiography for early cancer detection in soft human tissue has been demonstrated. 1-4 In order for this technique to become a practical medical tool for early detection of cancer, however, a proton source suitable for use in hospitals and clinics is required. An initial concept of such an accelerator has been discussed.5 It would meet the requirements considerably better than any existing accelerator and be simple, reliable, and economical.

Design and Performance Characteristics of the Zero Gradient Synchrotron (ZGS) H- Ion Source and Related Systems

An expression for the maximum H- current obtainable from an H+ beam by charge exchange in hydrogen has served as a guide in the design and development of a source of H- ions for booster injection into the ZGS. Here it is used as a criterion in the evaluation of testbench results obtained with the present test source. Space and power limitations in the 750-keV terminal of the preinjector have led to the use of titanium sublimation pumping to handle large instantaneous gas loads. Power limitations and the need for high pumping conductance have led to the substitution of electrostatic deflection for magnetic deflection in the beam separator.

Conceptual Design of the Argonne 6-GeV Synchrotron Light Source

The Argonne National Laboratory Synchrotron Light Source Storage Ring is designed to have a natural emittance of 6.5 × 10-9 m for circulating 6-GeV positrons. Thirty of the 32 long straight sections, each 6.5-m long, will be available for synchrotron light insertion devices. A circulating positron current of 300 mA can be injected in about 8 min. from a booster synchrotron operating with a repetition time of 1.2 sec. The booster synchrotron will contain two different rf systems. The lower frequency system (38.97 MHz) will accept positrons from a 360-MeV linac and will accelerate them to 2.25 GeV. The higher frequency system (350.76 MHz) will accelerate the positrons to 6 GeV. The positrons will be produced from a 300-MeV electron beam on a tungsten target. A conceptual layout is shown in Fig. 1. Related papers on the Argonne Synchrotron Light Source may be found in references 1-3.

A 12.5 MHz Heavy Ion Linac for Ion Beam Fusion

Argonne National Laboratory (ANL) is currently developing the injector of a heavy ion beam driver for the inertial confinement fusion program. The first phase of the program is to accelerate about 20 mA of Xe/sup +1/ from a 1.5 MV preaccelerator 11.4 MeV in a low-beta RF linac. The first section of the linac utilizes a single harmonic buncher and independently-phased short linac resonators with a FODO magnetic quadrupole focusing lattice. These are followed by two double-stub Wideroee linacs. A layout of the linac up to 6.4 MeV is shown. The operating parameters of the low-beta linac are given. This paper gives details of the low-beta linac design and results of low power measurements on the first accelerating cavity.

A Cold-Bore Vacuum System Design for POPAE

We have made a conceptual design of a cold-bore vacuum system for the Fermilab 1000 GeV × 1000 GeV colliding beam facility (POPAE). A double wall vacuum system is used between magnets and cryopumped molecular traps between the cold-bore and warm straight section regions. The beam-induced pressure rise phenomena has been taken into account as well as the liquid helium leak rate between the cold magnets and the vacuum bore. Since beam for POPAE will be injected at the desired energy, there are no heat loads from accelerated beam or eddy currents and the cold-bore system appears very attractive. This design is based on the best experimental evidence available today.

Rapid Cycling Valve for 30-HZ Pulsed H- Ion Source

This valve is used to reduce the gas loading on the vacuum system of a multipulsing H- ion source. It is a self-aligning chopper type. A mechanism of this construction assures the reilability required for an ion source of this nature. The reliability of this mechanism is due to the fact that the disc of the chopper is rotated at a relatively slow constant velocity and no wearing parts of the assembly are subjected to the extreme vacuum atmosphere. The entire valve assembly is very simple in construction. It is driven with a synchronous motor to keep it in step with the accelerating frequency. Vacuum integrity is maintained with the use of a ferromagnetic fluid coupling as part of the drive system. All bearings, motors, and drive mechanisms are external to the vacuum cavity.

Design and Operating Characteristics of the Developmental H- Ion Source for 30-HZ Injection into the Argonne National Laboratory (ANL) Booster

A tandem-acceleration extended stationary arc duoplasmatron used for 1-Hz injection into the ANL booster is undergoing further development for 30-Hz operation. A 200-?s, 50-MeV H- beam of at least 4 mA at 30 Hz will be required by the booster in its final development phase. To meet this requirement and to offset losses occurring in the linac and in the 750-keV and 50-MeV beam lines, the source must provide about 10 mA of H-ions. The present source produces negative ion currents of this order but the H-component is typically only 50% of the total beam; the remainder of the beam consists of ions with mass numbers in the neighborhood of 17. Source design will be discussed and data will be presented for typical operating conditions on the test bench and in the 75-keV terminal of the preaccelerator. Physical and chemical properties of materials which affect their suitability for use in pulsed ion sources as load-bearing structural materials, as functional components, and as vacuum walls will also be discussed.

A Vacuum System for the Argonne 6 GeV Synchrotron Light Source

The ANL vacuum system for the 6 GeV light source storage ring features non-evaporable strip getter pumps for uniform pumping around the ring within a gas desorption antechamber, and it also features lumped getter pumping directly under and above crotch radiation absorbers that are positioned after each bending magnet. Based on experiments at ANL in 1980 and by others, the technical and economical advantages have been established for the use of the distributed NeG pumps of non-magnetic strips coated with a nonevaporable Zr Al getter matrix. The NeG strip pump lifetime approaches ten years. The antechamber improves the isolation of the gas desorption process from the main beam chamber and beam. The combination oE these vacuum techniques; the NeG strip getter pumps, the gas desorption antechambers, and the lumped ion and lumped getter pumping provide a unique and reliable system for maintaining long beam lifetime.

A Vacuum Chamber System for High Radiation Environment

As the radiation environment in the proximity of high energy beams becomes an ever increasing problem, the need for radiation resistant vacuum chambers and seals of inorganic materials has become apparent. The long range plans for the ZGS have been in this direction. A three-year development program has resulted in a design which will withstand radiation levels several orders of magnitude greater than at present. Such a chamber will be installed early in 1968?five years after original machine startup.