Robert T. Avery

The ERA 4 MeV Injector

A pulsed electron accelerator has been constructed and is now in operation at the Lawrence Radiation Laboratory, Berkeley. It was designed specifically for and is used as an injector for ERA (electron ring accelerator) studies. Electron bursts of 1200 amperes and 40 nanoseconds duration can be produced at energies of 1.0 MeV to 4.25 MeV. The present repetition rate is approximately one per second. Acceleration is accomplished by means of ferrite loaded accelerating sections, each of which is capable of maintaining a 250 kV voltage pulse across the accelerating gap for a period of 40 ns. The voltage pulse has a rise time of 12 ns and the total timing jitter is of the order of one nanosecond. Five sections stacked together and operated as a unit function as the electron gun. The gun employs a field emission cathode and is operated at approximately 1 MV. Additional acceleration is achieved by means of an iterated system of accelerator sections and solenoidal magnetic lenses.

Thermal problems on high flux beam lines

Abstract Wiggler and undulator magnets can provide very intense photon flux densities to beam line components. This paper addresses some thermal/materials consequences due to such impingement. The LBL/Exxon/SSRL hybrid-wiggler beam line VI [1] now nearing operation will be able to provide up to ∼ 7 kW of total photon power at planned SPEAR operating conditions. The first masks are located at 6.5 m from the source and may receive a peak power density (transverse to the beam) exceeding 20 kW/cm 2 . Significantly, this heat transfer rate exceeds that radiated from the suns surface (7 kW/cm 2 ) and is comparable to that if welding torches. Clearly, cooling and configuration are of critical importance. Configurations for the first mask, the movable mask and the pivot mask on this beam line are presented together with considerations of thermal stress fatigue and of heat transfer by conduction to water-cooling circuits. Some preliminary information on the heating of crystals and mirrors is also presented. For the future, many additional intense wiggler/undulator beam lines are contemplated at several storage rings. The design of these beamlines would be enhanced by faster and more accurate computational techniques. LBL is developing a computer code which will be capable of giving photon power densities onto impinged surfaces for a wide range of source and beam line parameters. These include electron beam energy, current, emittance and orbit deviations; wiggler/undulator length, period and magnetic field; photon energy and angular distribution; reflection/absorption at intermediate impinged surfaces; defining apertures and focusing by mirrors. Three-dimensional computer programs for temperature, stress and strain have been available for some years, but “user friendly” versions are being sought. Other items to pursue are also suggested.

Non-Intercepting Monitor of Beam Current and Position

A compact monitor has been developed which measures beam current and beam position without intercepting or appreciably affecting the particle beam being measured. It is a broad band device which prevents the development of beam disturbing resonant modes. Although developed specifically for use on a short-pulse electron induction accelerator, it might be applied to other accelerator beams of pulsed or rf-bunched nature. The monitor consists of a resistive band inserted in the beam pipe wall with connections for reading the voltage across the band at each vertical and horizontal axis intercept. For pulsed or rf beams, return current equal in magnitude to the beam current flows on the beam pipe inside wall and through the resistive band. If the beam is centered, equal voltage appears on all four monitor connections. If the beam is off-center, the return currents are unsymmetrical and unequal voltages appear at the monitor connections. Beam current is proportional to the sum of all monitor voltages, while beam position is approximately proportional to the difference in voltage at opposing monitors. Tests and operating experience confirm its operation.

Shattering Rock with Intense Bursts of Energetic Electrons

It has been successfully demonstrated that intense bursts of energetic electrons cause significant rock spalling for modest energy inputs. The corresponding temperature rise per pulse in the bombarded volume of rock is only ~ 200° C, or so. Some analytical predictions and experimental evidence of this novel accelerator application are presented. The promise of this technique for more rapid and economical tunneling through rock is also examined.

The Bevalac Beam Tranport System

The Bevalac consists of, in part, a 200 meter long transfer line between the SuperHILAC and the Bevatron, which are at differing elevation. Unique features in the construction of the transfer line are described. The line, located largely outside, must cope with a natural environment. Part of the line passes through a hillside, requiring some unique support and alignment techniques. The dipoles are of the tape-wound variety and the steering magnets use printed circuit conductors. The vacuum system and an inexpensive and effective destructive monitoring sysstem are described.

MBE-4, a Heavy Ion Multiple-Beam Experiment

MBE-4, a heavy-ion multiple beam induction linac being built at LBL in FY85/86, will model many features of a much longer device. It will accelerate four spacecharge-dominated Cesium ion beams from, for example, 0.2 MeV, 5 mA/beam, 3.0 ¿sec, 1.6 m length at injection to ~0.8 MeV, 15 mA/beam, 1.0 ¿sec, 1.1 m length at the exit. It will permit study of simultaneous focussing, acceleration, current amplification and emittance growth of multiple space-charge-dominated ion beams. Some features of this accelerator are described.

Performance of the New Cryogenic Vacuum System at the Bevatron

A cryogenically cooled liner has been installed within the Bevatron to achieve 10-10 Torr vacuum. Features and performance of this liner are described including achieved pressures, residual gas composition, cryo heat loads, leak rates through moving and static seals, and cool-down and warm-up times.

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.

Hard-Rock Tunneling Using Pulsed Electron Beams

It has been demonstrated that intense sub-microsecond bursts of energetic electrons cause significant pulverization and surface spalling of a variety of rock types. The spall debris generally consists of sand, dust, and small flakes. If carried out at rapid repetition rate this can lead to a promising technique for increasing the speed and reducing the cost of underground excavation of tunnels, mines, and storage spaces. The conceptual design features of a Pulsed Electron Tunnel Excavator capable of tunneling approximately ten times faster than conventional drill/blast methods is presented.

Mechanical Design of Compressor Test Apparatus for Electron Ring Accelerator Research

The mechanical and vacuum features of the Compressor II apparatus used in the Fall 1968 Electron Ring Accelerator (ERA) experiment are described. Included are the injection beam transport system, the coils and their support structure, the ceramic vacuum chamber and its pumping system, the gas injection system, and diagnostic probes. The coil arrangement for the upcoming Compressor III experimental apparatus is briefly presented.