Showing papers on "Linear particle accelerator published in 1988"

Design of the laser-driven RF electron gun for the BNL accelerator test facility

Abstract: The BNL electron gun will incorporate a laser-driven photocathode in the wall of a 1/sup 1///sub 2/ cell RF cavity operated at a peak field of 100 MV/m. Pulses of 4.5-MeV energy, 5-ps width, and 1-nC charge will be produced with very little emittance growth due to the effects of space-charge and nonlinear RF fields. The design of the gun was aided by extensive computer simulation. >

Synchrotron-radiation limit on the focusing of electron beams.

Abstract: It is shown that there is an essential limit on the focusing of electron beams due to synchrotron radiation in the final focusing lens of a linear collider. The minimum possible beam size is determined almost only by an invariant emittance of a beam which is given at the entrance of a linear accelerator.

PARMTEQ: A beam-dynamics code fo the RFQ linear accelerator

Abstract: The PARMTEQ code is used for generating the complete cell design of a radio‐frequency quadrupole linear accelerator and for multiparticle simulation of the beam dynamics. We present a review of the code, with an emphasis on the physics used to describe the particle motion and the cell generation.

Heavy-ion linear induction accelerators as drivers for inertial fusion power plants

Abstract: A linear induction accelerator that produces a beam of energetic heavy ions (T -- 10 GeV, A -- 200 amu) is a prime candidate as a driver for an inertial fusion power plant. Some early perceptions were that heavy-ion drive fusion would not be cost-competitive with other power sources because of the high cost of the accelerators. However, improved understanding of the physics of heavy-ion transport and acceleration (supported by experimental results), combined with advances in accelerator technology, have resulted in accelerator design costs -- 50% of previous estimates. As a result, heavy-ion drive fusion power plants are now projected to be cost-competitive with other conceptual fusion power plants. A brief formulation of transport and acceleration physics is presented here, along with a description of the induction Linac cost optimization code LIACEP. Cost trends are presented and discussed, along with specific cost estimates for several accelerator designs matched to specific inertial fusion target yields. Finally, a cost-effective strategy using heavy-ion induction Linacs in a development scenario for inertial fusion is presented.

Heavy-ion linear induction accelerators as drivers for inertial fusion power plants

Abstract: A linear induction accelerator that produces a beam of energetic heavy ions (T approx. = 10 GeV, A approx. = 200 am..mu..) is a prime candidate as a driver for an inertial fusion power plant. Some early perceptions were that heavy-ion driven fusion would not be cost-competitive with other power sources because of the high cost of the accelerators. However, improved understanding of the physics of heavy-ion transport and acceleration (supported by experimental results), combined with advances in accelerator technology, have resulted in accelerator design costs -- 50% of previous estimates. As a result, heavy-ion driven fusion power plants conceptual fusion power plants. A brief formulation of transport and acceleration physics is presented here, along with a description of the induction Linac cost optimization code LIACEP. Cost trends are presented and discussed, along with specific cost estimates for several accelerator designs matched to specific inertial fusion target yields. Finally, a cost-effective strategy using heavy-ion induction Linacs in a development scenario for inertial fusion is presented.

Dosimetric characteristics of a 6 MV photon beam from a linear accelerator with asymmetric collimator jaws

Abstract: Dosimetric measurements have been made of a 6 MV photon beam from a linear accelerator equipped with asymmetric jaws. The field size factors for asymmetrically set fields are compared to those for symmetrically set fields. The change of beam quality has been measured as a function of off-axis position of the asymmetric fields to assess its effect on depth dose. Additional measurements include beam penumbra and shape of isodose curves for open and wedge fields as the field opening is moved asymmetrically from the central ray.

Induced activity in a high-energy linear accelerator.

Abstract: Activation products which contribute significantly to the exposure of the staff operating the accelerator were found in the accelerator head in the transparent holder for the lead blocks and in the 60 degrees wedge filter made of lead. A proper choice of material in these parts of the accelerator could easily reduce this exposure without excessive changes in the construction. The absorbed dose-rate level should always be checked before maintenance is carried out inside the accelerator head.

A compact x-ray free electron laser

Abstract: We present a design concept and simulation of the performance of a compact x-ray, free electron laser driven by ultra-high gradient rf-linacs. The accelerator design is based on recent advances in high gradient technology by a LLNL/SLAC/LBL collaboration and on the development of bright, high current electron sources by BNL and LANL. The GeV electron beams generated with such accelerators can be concerted to soft x-rays in the range from 2--10 nm by passage through short period, high fields strength wigglers as are being designed at Rocketdyne. Linear light sources of this type can produce trains of picosecond (or shorter) pulses of extremely high spectral brilliance suitable for flash holography of biological specimens in vivo and for studies of fast chemical reactions. 12 refs., 8 figs., 4 tabs.

Emittance studies at the Los Alamos national laboratory free electron laser

Abstract: Recent emittance studies at the Los Alamos FEL have indicated several areas of concern in the linac and beamline feeding the wiggler. These studies included both experimental measurements and computer simulations. The beamline starts with a 5 A micropulse from the thermionic cathode in the gun. After bunching by velocity modulation and acceleration to 20 MeV in a 1300 MHz standing wave accelerator, the beam current is roughly 250 A. Final bunching to 800 A is performed in the nonisochronous bend that rotates the electrons onto the axis of the wiggler and the optical cavity. Four emittance growth mechanisms of special importance have been studied. First, a rapid growth of the electron beam's emittance immediately after the spherical gridded Pierce gun resulted, in part, from the long time required for our pulsing electronics to ramp the grid voltage up at the start and down at the end of the pulse, which created a pulse with a cosine-like current distribution as a function of time. The growth was compounded by the extremely small radial beam size (almost a waist) leaving the gun. In addition, we saw evidence of electrostatic charging of the insulators in the gun, reducing the quality of the electron beam further. Second the action of the solenoidal focusing fields in the low-voltage bunching region was studied, and criteria for a minimum emittance growth were established. Third, maximum misalignment angles and displacements for various elements of the beamline were calculated for the desired low emittance growth. Finally, emittance growth in the horizontal dimensions through the nonisochronous bend caused by varying energy depression on the particles due to longitudinal wake fields was both calculated and observed. In addition, we measured energy depressions caused by the wake fields generated by various other elements in the beamline. Strategies were developed to relieve the magnitude of these wake-field effects.

An introduction to acceleration mechanisms

Abstract: This paper discusses the acceleration of charged particles by electromagnetic fields, i.e., by fields that are produced by the motion of other charged particles driven by some power source. The mechanisms that are discussed include: Ponderamotive Forces, Acceleration, Plasma Beat Wave Acceleration, Inverse Free Electron Laser Acceleration, Inverse Cerenkov Acceleration, Gravity Acceleration, 2D Linac Acceleration and Conventional Iris Loaded Linac Structure Acceleration. (LSP)

PARMTEQ-A beam dynamics code for the RFQ linear accelerator

Abstract: The PARMTEQ code is used for generating the complete cell design of a radio‐frequency quadrupole linear accelerator and for multiparticle simulation of the beam dynamics. We present a review of the code, with an emphasis on the physics used to describe the particle motion and the cell generation.

Disk and washer linac and method of manufacture

Abstract: A coupled-cavity linear accelerator for accelerating charged particles to velocities greater than about one-third the speed of light. The accelerator includes a first tank for accelerating charged particles at a first velocity to a second velocity and a second tank for accelerating the particles to a higher third velocity. A bridge coupler for focusing a beam formed by the charged particles joins the first and second tanks. Each tank is substantially symmetrical about an axis and includes a generally cylindrical tank outer wall having an inner surface and an outer surface. A series of axially spaced disks are positioned inside the tank and bear on the inside tank surface. Each disk has an outer diameter greater than the as-manufactured inside diameter of the tank wall so that each disk causes an annular indentation in the inner surface of the outer wall. At least one washer is supported by each of alternating disks. These washers have central apertures which together define a particle beam acceleration path through the tank. Methods of fabricating the linear accelerator and of tuning it are also disclosed.

Application of Fermi scattering theory to a magnetically scanned electron linear accelerator.

Abstract: This paper uses a solution to the Fermi electron transport equation for an isotropic point source to characterize the magnetically scanned broad electron beams from the Sagittaire Therac 40 accelerator in the air space above patients. Thick leadcollimation is shown to be adequately modeled by an infinitely thin absorbing plate when used to predict penumbra shape. A relationship between broad beam penumbra width and the value of the root‐mean‐square spatial Gaussian spread σ(z) of an elementary pencil beam is derived. This relationship is applicable for any rectangular field size.Measurement of the variation in broad beam penumbra width with source–surface distance (SSD) for a 7‐MeV beam locates the isotropic source to be coincident with the exit window of the accelerator and indicates that the scattering effect of the monitor chamber may be considered negligibly small. Using this source location accurate predictions of beam profile shape for any clinically used beam energy, SSD, or field size are made in the presence of lead trimmer collimation. Field penumbra beyond the photoncollimation system is formed in each lateral direction by two lead blocks whose faces are aligned along a diverging ray emanating from the source. The photoncollimator closest to the source restricts the field size causing a variation of both fluence and the mean square angle spread of the electrons across the plane at the level of the lower collimator. This variation is accounted for by introducing an empirical perturbation factor into the mathematical formalism. An interesting feature of this perturbation factor is that it is field size dependent and its effect on penumbra width may be scaled for both beam energy and SSD to accurately predict beam profile shape.

High-Brightness RF Linear Accelerators

Abstract: Soon after electrons and ions were discovered, production of practical generators of particle beams began, and a succession of machines were invented that could produce more energetic and more intense beams. Progress on the energy frontier is often charted from the 1930s in the form of the Livingston Chart, Fig. 1, showing that particle accelerator energy has increased by a factor of about 25 every 10 years. The corresponding cost per million electron volts has decreased by about a factor of 16 per decade (Lawson, 1982). The physics principles on which all of these devices work were deduced long ago; the energy increase were possible because of cost reductions from thorough exploitation of parameters, engineering perfection, systems integration, and advanced manufacturing methods (Voss, 1982).

The Darmstadt near-infrared free electron laser project

Abstract: It is planned to modify the superconducting continuous-wave 130 MeV electron accelerator under construction at the Nuclear Physics Institute of the Technische Hochschule Darmstadt in order to supply an electron beam suitable for FEL experiments. The accelerator consists of an electrostatic preacceleration, superconducting injector and main linac and two recirculating beamlines. The FEL project is planned with the electron beam of the first recirculation in an energy range from 35 to 50 MeV, corresponding to wavelengths from 4.9 to 2.4 μm. In order to achieve higher peak currents, the present design of the injector has to be changed. This redesign, the modifications of the beam transport system of the first recirculation and a preliminary hybrid wiggler design will be presented.

Construction and operating experience with the Tokyo Institute of Technology post accelerators

Abstract: A multipurpose heavy-ion accelerator system has been constructed to generate beams for material science, atomic physics and nuclear solid-state physics. The system consists of a 1.6-MV tandem, a high energy gain ( E out E in = 10 ) and a low energy gain ( E out E in = 1.4 ) Wideroe linear accelerator with an IH structure. The accelerating characteristics have been studied, and operation experiences during the last 18 months are reported.

Propagation of a picosecond‐duration, relativistic electron beam through hydrogen at atmospheric pressures

Abstract: An experiment demonstrating the propagation of a 42‐MeV electron beam from an rf linear accelerator through 1 m of H2 at pressures from 10−3 to 1.25 atm is reported. Measurements were made of the transmitted current and the beam’s radius, transverse position, and angular divergence along the path. The beam current was fully transmitted at all pressures, without the often detrimental plasma interactions (space‐charge neutralization, magnetic neutralization, and various plasma instabilities) seen in previous studies. The observed beam expansion was consistent with calculations of multiple scattering. The propagation can be attributed to the 4‐ps duration of the accelerator’s electron bunches. This time is three to four orders of magnitude shorter than that used in the earlier work and is shorter than the growth times for the beam‐plasma interactions. Such a beam should prove suitable for a gas‐loaded free‐electron laser.

Design and testing of the 5 kHz, 3 MW thyratron modulators for ETA II

Abstract: The Experimental Test Accelerator (ETA) II is a high-average-power linear induction accelerator built to support free-electron-laser research. Magnetic pulse compression and high-power thyratron modulators are used to generate the 125 kV accelerator drive pulses. The authors describe the design and testing of the 5 kHz, 3 MW thyratron modulators for the ETA II. The power conditioning system and the pulse timing requirements are described, and the operation of the ETA II system is discussed. >

A high speed electrostatic kicker for the pulse stretcher ring at Saskatchewan accelerator laboratory

Abstract: The linear accelerator laboratory (SAL) at Saskatoon recently installed and commissioned a pulse stretcher ring for upgrading the performance of the existing SLAC style pulsed linac. Two fast electrostatic kickers were developed to deflect the ring's closed orbit for multiturn injections. The first kicker has been used successfully to inject 200 MeV 300 ns to 1 μs pulses. The second kicker is being assembled and upon completion, it is planned to use the pair to inject 300 MeV 1 μs pulses. The unique features of this style of deflector are its relatively small size, simple operation, and wide range of capabilities.

Pulsed high-power beams

Abstract: The marriage of induction linac technology with nonlinear magnetic modulators has produced some unique capabilities It is now possible to produce short-pulse electron beams with average currents measured in amperes, at gradients approaching 1-MeV/m, and with power efficiencies exceeding 50% A 70-Mev, 3-kA induction accelerator (ETA II) constructed at the Lawrence Livermore National Laboratory incorporates the pulse technology concepts that have evolved over the past several years The ETA II is a linear induction accelerator and provides a test facility for demonstration of the high-average-power components and high-brightness sources used in such accelerators The pulse drive for the accelerator is based on state-of-the-art magnetic pulse compressors with very high peak-power capability, repetition rates exceeding 1 kHz, and excellent reliability 6 figs

Dosimetric aspects of the therapeutic photon beams from a dual-energy linear accelerator.

Abstract: Parameters of the photon beams (6 and 20 MV) from a dual‐energy linear accelerator (Mevatron‐KD, Siemens Medical Laboratories, CA) are presented. The depth dose characteristics of the photon beams are d max of 1.8 and 3.8 cm and percentage depth dose of 68% and 80% at 10‐cm depth and 100‐cm source–surface distance for a field size of 10×10 cm2 for 6 and 20 MV, respectively. The 6 and 20 MV beams were found to correspond to nominal accelerating potentials of 4.7 and 17 MV, respectively. The stability of output is within ±1% and flatness and symmetry are within ±3%. These figures compare favorably with the manufacturer’s specifications.

Frontiers of particle beams : proceedings of a topical course, held by the Joint US-CERN School on Particle Accelerators at South Padre Island, Texas, October 23-29, 1986

Abstract: Phase space dynamics- Equations for multiparticle dynamics- Electromagnetic fields and instabilities in accelerators- Physics of beam instabilities- Iteration and accelerator dynamics- Electron storage rings for the production of synchrotron radiation- to the physics of the free electron laser- Space charge dominated beams- Intense electron beams- Correlations and beam noise- Advanced cooling techniques: Stochastic cooling of bunches in high-energy colliders- Intra-beam scattering- Crystallization of particle beams- to the next generation of linear colliders- Low emittance storage ring design- Emittance preservation in linear colliders- High energy electron linear accelerators, fields and structures- A conceptual design of final Focus Systems for linear colliders- An introduction to beamstrahlung and disruption- RF frequency scaling and gyroklystron sources for linear supercolliders- An introduction to acceleration mechanisms- Particle beams and Twentieth Century science and technology- Introductory talk Particle accelerators have a history, do they have a future?- Accelerators and the scientific frontier- Frontiers in particle accelerator research and development- Superconducting radio-frequency technology: Expanding the horizons of physics and accelerators

Free-Electron Laser Results from the Advanced Test Accelerator

Abstract: PALADIN is a 106-mum FEL amplifier experiment operating at the Lawrence Livermore National Laboratory's Advanced Test Accelerator, an induction linear accelerator designed to produce a 45-MeV, 10-kA electron beam With a 15-m long wiggler, PALADIN demonstrated 27 dB of exponential gain from a 14-kW input signal With a 5-MW input signal, the amplifier saturated after 10 dB of gain The exponentially growing signal in the unsaturated amplifier was clearly seen to be gain guided by the electron beam 7 refs, 8 figs

The Use of Electromagnetic Particle-in-Cell Codes in Accelerator Applications

Abstract: The techniques developed for the numerical simulation of plasmas have numerous applications relevant to accelerators. The operation of many accelerator components involves transients, interactions between beams and rf fields, and internal plasma oscillations. These effects produce non-linear behavior which can be represented accurately by particle in cell (PIC) simulations. We will give a very brief overview of the algorithms used in PIC Codes. We will examine the range of parameters over which they are useful. We will discuss the factors which determine whether a two or three dimensional simulation is most appropriate. PIC codes have been applied to a wide variety of diverse problems, spanning many of the systems in a linear accelerator. We will present a number of practical examples of the application of these codes to areas such as guns, bunchers, rf sources, beam transport, emittance growth and final focus. 8 refs., 8 figs., 2 tabs.

A temperature- and humidity-stabilized beam bunch phase detector

Abstract: The University of Washington has recently completed a linear accelerator which is injected with the beam from the FN tandem Van de Graaff. A helical-loaded quarter-wave rf resonant cavity which is excited by the beam is located at the entrance of the linac to provide a phase-locking signal to the pretandem buncher. The resonator is similar to the phase-locking resonator used at Stony Brook. To eliminate phase drifts, the temperature of the cavity is maintained within a range of 0.05°C by continuously flowing heated nitrogen gas through it.

On the horizon: New RF power sources for linear accelerators

Abstract: In the past, linear accelerators at frequencies below 3 GHz have been driven by klystrons or gridded tubes, with most of the small electron accelerators using conventional magnetrons. During the past few years, there have been several new rf amplifier developments that could be advantageous to the linear accelerator designer. Among these new devices are the cathode-driven crossed-field amplifier, Klystrode, high-power solid-state amplifier, lasertron, multiple-beam klystron, phase-locked magnetron, and a depressed collector for a high-power klystron. All of these devices are being worked on at this time. Each can contribute to a linear accelerator system by supplying better efficiency, lower cost, higher power, or longer life. This paper will review the present status of each device and, where current test data are available, they will be reviewed. 19 refs., 13 figs.