Showing papers on "Linear particle accelerator published in 1993"

Particle accelerator physics

Abstract: Tools We Need.- Of Fields and Forces.- Particle Dynamics in Electromagnetic Fields.- Electromagnetic Fields.- Beam Dynamics.- Single Particle Dynamics.- Particle Beams and Phase Space.- Longitudinal Beam Dynamics.- Periodic Focusing Systems.- Beam Parameters.- Particle Beam Parameters.- Vlasov and Fokker-Planck Equations.- Equilibrium Particle Distribution.- Beam Emittance and Lattice Design.- Perturbations.- Perturbations in Beam Dynamics.- Hamiltonian Resonance Theory.- Hamiltonian Nonlinear Beam Dynamics.- Acceleration.- Charged Particle Acceleration.- Beam-Cavity Interaction.- Coupled Motion.- Dynamics of Coupled Motion.- Intense Beams.- Statistical and Collective Effects.- Wake Fields and Instabilities.- Synchrotron Radiation.- Fundamental Processes.- Overview of Synchrotron Radiation.- Theory of Synchrotron Radiation.- Insertion Device Radiation.- Free Electron Lasers.

Enhanced acceleration in a self-modulated-laser wake-field accelerator

Abstract: An alternative configuration of the laser wake-field accelerator is proposed in which enhanced acceleration is achieved via resonant self-modulation of the laser pulse. This requires laser power in excess of the critical power for relativistic guiding and a plasma wavelength short compared to the laser pulse length. Relativistic and density wake effects strongly modulate the laser pulse at the plasma wavelength, resonantly exciting the plasma wave and leading to enhanced acceleration.

The Next Linear Collider Test Accelerator

Abstract: During the past several years, there has been tremendous progress on the development of the RF system and accelerating structures for a Next Linear Collider (NLC). Developments include high-power klystrons, RF pulse compression systems and damped/detuned accelerator structures to reduce wakefields. In order to integrate these separate development efforts into an actual X-band accelerator capable of accelerating the electron beams necessary for an NLC, we are building an NLC Test Accelerator (NLCTA). The goal of the NLCTA is to bring together all elements of the entire accelerating system by constructing and reliably operating an engineered model of a high-gradient linac suitable for the NLC. The NLCTA will serve as a testbed as the design of the NLC evolves. In addition to testing the RF acceleration system, the NLCTA is designed to address many questions related to the dynamics of the beam during acceleration. In this paper, we will report on the status of the design, component development, and construction of the NLC Test Accelerator. >

Optical performance of the CLIO infrared FEL

Abstract: First laser oscillation on the CLIO infrared FEL was obtained in January 1992. This paper describes the layouts of the optical devices used for CLIO, and discusses the optical performances. This machine consists of an rf linear accelerator, described in a companion paper, providing a 30/70 MeV electron beam through a 48 period planar undulator ( K = 0 to 2). The optical cavity is 4.8 m long and uses broadband metal mirrors. The optical beam is extracted with an intracavity CaF 2 or ZnSe plate. Laser oscillation has been obtained thus far in the range of λ =2.5 to 15 μ m at accelerator energies of 32, 40 and 50 MeV. The average power of the laser is about 65 mW for the low duty cycle (6.25 Hz/32 ns) and up to 0.5 W for a duty cycle of 50 Hz/32 ns and should be 5–10 W at maximum repetition rate. The peak power extracted for 8 ps micropulses is 2.5 MW corresponding to 0.4% efficiency. Laser oscillation on the third harmonic of 10 μm has also been achieved (at λ = 3.3 μ m). Application experiments have already been done with CLIO infrared laser (companion paper on nonlinear absorption in InSb), showing the good reliability and overall quality of the laser. The programme now is to operate the accelerator at other energies so as to cover the rest of the designed wavelength range (2–20 μm).

Electron transport of a linac coherent light source (LCLS) using the SLAC linac

Abstract: A linac configuration providing a low emittance high peak current electron beam is under study for a potential Linac Coherent Light Source (LCLS) based on the SLAC accelerator. The parameters of the final electron bunch are nearing the technological limits of present accelerators in both transverse and longitudinal phase space. In this note we describe a layout of the RF gun, linac, and bunch compressors to deliver the required bunch properties. >

Probing Dense Nuclear Matter in the Laboratory

Abstract: A 150‐meter‐long outdoor beam line wanders through eucalyptus trees down the 45‐meter slope connecting the SuperHILAC and the Bevatron at the Lawrence Berkeley Laboratory. The SuperHILAC is a linear accelerator designed to accelerate heavy nuclei at high intensities to energies of up to 8 MeV/nucleon for the purpose of studying heavy and superheavy elements. The Bevatron is a weak focusing synchrotron born in 1954 with the mission of discovering the antiproton and exploring the riddle of the hadrons using beams of 6.2‐GeV protons. In 1974 these two machines were coupled to create the Bevalac, and with it a new field of research: relativistic heavy‐ion reactions.

Advances Of Accelerator Physics And Technologies

Abstract: Part 1 Introduction: what we can learn from experiments with accelerators and storage rings, C. Jarlskog. Part 2 Circular accelerators and storage rings: beam optics and lattice design, P. Bryant collective phenomena and instabilities, J. Gareyte acceleration and storage of heavy ions, Ozaki bottom- and charm-tau factories, Y. Baconnier. Part 3 Linear accelerators: general aspects of linear accelerators, P. Lapostolle RF quadrupoles as accelerators, A. Schempp results from the Stanford linear collider and plans for the final focus test beam facility, J. Seeman the road to TeV electron-positron colliders, Y. Kimura. Part 4 New methods and technologies: SC magnets, G. Brianti SC cavities, H. Lengeler beam cooling, D. Moehl acceleration of polarized particles, J. Buon ion sources, H. Haseroth and H. Hora a good idea at the time, B. Montague new methods of Geodesy, J. Gervais. Part 5 Applications: synchrotron radiation sources, S. Tazzari spallation neutron sources, J.L. Finey inertial fusion by heavy ions, R. Bock accelerators in medicine, P. Mandrillon industrial applications of accelerators, K. Bethge.

How is photon head scatter in a linear accelerator related to the concept of a virtual source

Abstract: The virtual source in a photon linear accelerator is a familiar concept which arises from head scatter, and which accounts for small but detectable deviations of photon energy fluence from the inverse-square law. The authors present a simple method for calculating the position of the virtual source using the geometry of the flattening filter, which acts as the main photon scatterer. The authors also show that, for unwedged beams, the position of the virtual source is relatively insensitive to collimator size. This means that the same head-scatter factor which is measured at the isocentre can also be used at other distances from the source. However, wedges may scatter so much radiation that the position of the virtual source depends upon collimator size.

3-Dimensional optimization of multiple arcs for stereotactic radiosurgery

Abstract: Purpose: During linear accelerator-based radiosurgery, the physicians and physicists need to determine which combination of treatment arcs are "best" with regard to target coverage and incidental dose to adjacent structures. This is a complex problem, especially when targets are geometrically close to critical structures. The purpose of this article is to present a method to mathematically determine a set of arcs to produce desired target and normal structure dose distributions in linear accelerator radiosurgery. Methods and Materials: Nonlinear least squares regression was used to determine the table angles and gantry angle arc ranges and their associated beam weights appropriate to linear accelerator radiosurgery. Results: Three cases are presented: (a) critical structure close to target volume; (b) target volume too large for the largest collimator to cover the volume with one isocenter and a standard plan; (c) target volume located within one critical structure and close to another critical structure. The optimized treatment plans are all shown to be superior to a defined standard plan. Conclusion: The method successfully enables one to determine nonstandard arcs which achieve the desired results. In particular, the method enables one to find clinical treatment solutions, even when the desired results cannot be a priori defined.

Design considerations for a 60-meter pure permanent magnet undulator for the SLAC linac coherent light source (LCLS)

Abstract: In this paper we describe design, fabrication, and measurement aspects of a pure permanent magnet (PM) insertion device designed to operate as an FEL at a 1st harmonic energy of 300 eV and an electron energy of 7 GeV in the self-amplified spontaneous emission regime.<>

Measurement of longitudinal phase space in an accelerated H− beam using a laser-induced neutralization method☆

Abstract: Laser-induced neutralization of H − ions is a process that can be used to measure the longitudinal phase space of accelerated H − beams. The laser-induced neutralization diagnostic approach (LINDA) measures the longitudinal emittance of an H − beam by photoneutralizing different phase slices of beam microbunches and analyzing the energy distribution of the neutral slices. A LINDA system utilizing a pulsed laser and time-of-flight analysis has successfully measured longitudinal emittance of the 5 MeV H − beam exiting the drift-tube linac of the Los Alamos Accelerator Test Stand. Design considerations associated with the LINDA laser-based emittance measuring system are given. The present LINDA system is described and its limitations are discussed. Experimental results are given from an application of the LINDA system to the measurement of longitudinal emittance growth in a drift space and following insertion into the beamline of beam transport elements comprising a single-arm funnel. A new system is proposed which uses a mode-locked laser and spectrometer to improve resolution and shorten measurement time.

Ultraviolet free-electron laser driven by a high-brightness 45-MeV electron beam

Abstract: We report on experimental studies of an ultraviolet (UV) free-electron laser (FEL) oscillator driven by low-energy electrons from a radio-frequency linear accelerator. Previous UV FELs have been driven by 350--800-MeV electrons from storage rings. We verify the concept of driving an UV FEL with a low-energy, but high-current, low-emittance electron beam. This and other innovations allowed the FEL to lase at wavelengths from 369 to 380 nm using 45.9--45.2-MeV electrons, and to achieve a peak optical output power of 270 kW. The experimental results are in good agreement with simulations.

The LRT/TUM small caliber electrothermal accelerator

Abstract: A small electrothermal particle accelerator has been developed for the purpose of simulating micrometeoroid and space debris impacts. The test range with the energy storage system, the experimental setup with all diagnostics, and the configuration of the accelerator are described. Emphasis is placed on the design of the discharge chamber. Experimental results for two designs and various geometries of the chamber are presented. The maximum particle velocity obtained is 5.2 km/s for a projectile with a mass of 28 mg. >

High-power RF pulse compression with SLED-II at SLAC

Abstract: Increasing the peak RF power available from X-band microwave tubes by means of RF pulse compression is envisioned as a way of achieving the few-hundred-megawatt power levels needed to drive a next-generation linear collider with 50-100 MW klystrons. SLED-II is a method of pulse compression similar in principal to the SLED method currently in use on the SLC and the LEP injector linac. It utilizes low-loss resonant delay lines in place of the storage cavities of the latter. This produces the added benefit of a flat-topped output pulse. At SLAC, we have designed and constructed a prototype SLED-II pulse-compression system which operates in the circular TE/sub 01/ mode. It includes a circular guide 3-dB coupler and other novel components. Low-power and initial high-power tests have been made, yielding a peak power multiplication of 4.8 at an efficiency of 40%. The system will be used in providing power for structure tests in the ASTA (Accelerator Structures Test Area) bunker. An upgraded second prototype will have improved efficiency and will serve as a model for the pulse compression system of the NLCTA (Next Linear Collider Test Accelerator). >

Performance of the APEX free-electron laser at Los Alamos National Laboratory

Abstract: The APEX (APLE Prototype Experiment) FEL (free-electron laser) is an advanced technology test-bed for the Average Power Laser Experiment (APLE). APEX is a photoinjector-driven FEL that is currently operated as an oscillator with untapered wigglers. Photocathodes are rapidly becoming the source of choice for high-brightness electron beams to drive high-efficiency FELs. The electron accelerator is a 40-MeV L-band rf linac with a 6-MeV photoinjector. Since the commissioning of the FEL in 1991, we have been engaged in accelerator and laser experiments. We have demonstrated that the accelerator is capable of providing a high-brightness electron beam at high current. Initial lasing has been at wavelengths near 3 μm, and our electron-beam brightness is such that harmonic lasing at much shorter wavelengths is possible. We have recently lased on the third harmonic at 0.83 μm. In this paper, we report the results of the accelerator and FEL performance in the oscillator mode. The results show that a photoinjector can be integrated into an FEL system to produce stable and reliable operation.

Operation of the CLIO accelerator

Abstract: CLIO (Collaboration for an Infrared Laser at Orsay) is a FEL users facility at LURE Laboratory, Orsay, France. The first laser oscillation has been obtained in January 1992 at 5 μm wavelength with an electron beam of 40 MeV from a S-band linac. The first user experiment was performed in April at a wavelength between 7 and 10 μm. Presently, the spectral range spans from 2.5 to 15 μm with beam energies from 50 to 30 MeV. The 2 m undulator, within a 4.8 m long optical cavity, is fed by the S-band linac (3 GHz) designed for 50 MeV ± 20 MeV with a beam current of 0.6 nC charge per bunch of 8 ps duration. We present several measurements of the accelerator performances such as rf stability, beam phase stability, bunch length, beam emittance and energy spectrum with and without laser.

Use of Ukrainian semiconductor dosimeters in a CERN particle accelerator field

Abstract: The results of the application of p-i-n and MOS dosimeters in the PS-ACOL Irradiation Facility (PSAIF) at CERN for separate measurements of gamma dose and fast neutron fluences are presented. The mixed gamma-neutron field was due to 26 GeV protons hitting an iridium target, yielding an instantaneous dose rate of approximately 3.10/sup 5/ Gy/s. Good agreement with calibration curves is found for MOS in a /sup 60/Co gamma source as well as for p-i-n sensors in a neutron reactor spectrum with mean energy of 1 MeV. Experimental results from PSAIF are presented and pulse current injection annealing of p-i-n diodes is considered. Such sensors are very convenient for on-line separated total dose measurements in mixed gamma-neutron radiation fields, as well as for radiation hardness testing of electronics. Components on irradiation facilities, and could be installed near the detector area of the LHC. >

Performance of the high brightness linac for the Advanced Free Electron Laser Initiative at Los Alamos

Abstract: The AFEL accelerator has produced beams of 1 nC with peak currents greater than 100 A and a normalized, rms emittance less than 2π mm mrad. The 1300 MHz standing-wave accelerator uses on-axis coupling cells. The electron source is a photoinjector with a CsK 2 Sb photocathode. The photoinjector is an integral part of a single 11-cell accelerator structure. The accelerator operates between 12 and 18 MeV. The beam emittance growth in the accelerator is minimized by using a photoinjector, a focusing solenoid to correct the emittance growth due to space charge, and a special design of the coupling slots between accelerator cavities to minimize quadrupole effects. This paper describes the experimental results and compares those results with PARMELA simulation. The simulation code PARMELA was modified for this effort. This modified version uses SUPERFISH files for the accelerator cavity fields, MAFIA files for the fields due to the coupling slots in the accelerator cells, and POISSON files for the solenoid field in the gun region.

Heavy Ion Therapy: Bevalac Epoch

Abstract: An overview of heavy ion therapy at the Bevelac complex (SuperHILac linear accelerator + Bevatron) is given. Treatment planning, clinical results with helium ions on the skull base and uveal melanoma, clinical results with high-LET charged particles, neon radiotherapy of prostate cancer, heavy charged particle irradiation for unfavorable soft tissue sarcoma, preliminary results in heavy charged particle irradiation of bone sarcoma, and irradiation of bile duct carcinoma with charged particles and-or photons are all covered. (GHH)

A new method for the measurement of bremsstrahlung spectra

Abstract: The X-ray energy spectrum from a 15 MeV linear accelerator (Siemens Mevatron 77/20) was determined combining attenuation and photoactivation analysis. The X-ray flux of the therapy linac is produced in a thick target and filtered through several materials. The theoretical expression for a thin-target spectrum was corrected for absorption in the target and materials in the accelerator head. The low-energy part of the spectrum was calculated from attenuation measurements and the high-energy part of the spectrum was determined by photoactivation.

High gradient acceleration in a 17 GHz photocathode RF gun

Abstract: The physics and technological issues involved in high gradient particle acceleration at high microwave (RF) frequencies are under study at MIT. The 17 GHz photocathode RF gun has a 1 1/2 cell room temperature copper cavity with a peak accelerating gradient of about 250 MV/m. The anticipated beam parameters, when operating with a photoemission cathode, are: energy 2 MeV, normalized emittance 0.43 /spl pi/ mm-mrad, energy spread 0.18%, bunch charge 0.1 nC, and bunch length 0.39 ps. The goal is to study particle acceleration at high field gradients and to generate high quality electron beams for potential applications in next generation linear colliders and free electron lasers. The experimental setup and status are described. >

A 50-MeV mm-wave electron linear accelerator system for production of tunable short wavelength synchrotron radiation

Abstract: The Advanced Photon Source (APS) at Argonne in collaboration with the University of Illinois at Chicago and the University of Wisconsin at Madison is developing a new millimeter wavelength, 50-MeV electron linear accelerator system for production of coherent tunable wavelength synchroton radiation. Modern micromachining techniques based on deep etch x-ray lithography, LIGA (Lithografie, Galvanoforming, Abformung), capable of producing high-aspect ratio structures are being considered for the fabrication of the accelerating components. >

Indirectly sensing accelerator beam currents for limiting maximum beam current magnitude

Abstract: A beam current limiter for sensing and limiting the beam current in a particle accelerator, such as a cyclotron or linear accelerator, used in scientific research and medical treatment. A pair of independently operable capacitive electrodes sense the passage of charged particle bunches to develop an RF signal indicative of the beam current magnitude produced at the output of a bunched beam accelerator. The RF signal produced by each sensing electrode is converted to a variable DC voltage indicative of the beam current magnitude. The variable DC voltages thus developed are compared to each other to verify proper system function and are further compared to known references to detect beam currents in excess of pre-established limits. In the event of a system malfunction, or if the detected beam current exceeds pre-established limits, the beam current limiter automatically inhibits further accelerator operation. A high Q tank circuit associated with each sensing electrode provides a narrow system bandwidth to reduce noise and enhance dynamic range. System linearity is provided by injecting, into each sensing electrode, an RF signal that is offset from the bunching frequency by a pre-determined beat frequency to ensure that subsequent rectifying diodes operate in a linear response region. The system thus provides a large dynamic range in combination with good linearity.

Accelerator structure development for NLC

Abstract: In the program of work directed towards the development of an X-Band Next Linear Collider accelerator structure, two different test accelerator sections have been completed, and a third is being fabricated. The first is a simple 30-cell constant-impedance section in which no special attention was given to surface finish, pumping, and alignment. The second is an 86-cell section in which the cells were precision diamond-turned by Texas Instruments Inc. The structure has internal water-cooling and vacuum pumping manifolds. Some design details are given for the third section, which is a 206-cell structure with cavities dimensioned to give a Gaussian distribution of dipole mode frequencies. It has conventional machining surface finishes and external water and pumping manifolds. Component design, fabrication, and assembly brazing are described for the first two experimental sections. >

Advances in the development of the Nested High Voltage Generator

Abstract: The Nested High Voltage Generator (NHVG) is a high voltage accelerator/power supply topology which can potentially satisfy a variety of requirements for a compact, reliable inexpensive DC accelerator in the 0.25-10 MeV range. Applications for this technology include the generation of high voltage, high current pulsed electron beams for microwave generation, the sterilization of medical products, the curing of polymers, and the sterilization of medical waste. This technology has recently been demonstrated in an accelerator which has operated at 500 kV with an electron beam in a 36 inch long, 17 inch diameter device. >

Calculation of intercavity coupling coefficient for side coupled standing wave linear accelerator

Abstract: Expressions are developed for the main to side cavity coupling coefficient of a side coupled standing wave linac structure and for the shift in cavity resonant frequency produced by the coupling iris. The theoretical predictions show reasonable agreement with the measured values. >

Construction of the CEBAF RF separator

Abstract: The CEBAF accelerator is designed in a multipass racetrack configuration, with two 1497 MHz linear accelerator sections joined by independent magnetic transport arcs. Room temperature subharmonic RF separator cavities will be used on each independent are to extract a portion of the recirculating beam, and one additional cavity will be used to divide the final full-energy beam between CEBAF's three experimental end stations. A single-cell prototype cavity has already been built and tested at low power levels. The next stage of the design process is the construction of a cavity capable of operation at full power, i.e. at a gradient sufficient to provide the required 100 /spl mu/rad bend to a 6 GeV beam. The paper will discuss both the electrical and mechanical design of the cavity, construction techniques employed, and preliminary test results. >

The IH structure—a new approach to the fusion RF linac

Abstract: Short zero degree synchronous particle structures and magnetic focusing lenses can be combined in such a way that the emittance of each section is well adapted to the acceptance of the following section. By that way drift tube linacs can do the particle acceleration more close to the crest of the RF wave, the transverse RF defocusing effect can be minimized and the emittance growth of the beam is kept low. Specific problems of the heavy-ion fusion linacs are the acceleration of 1+charged ions with mass numbers around 200 and beam currents around 100 mA. This paper investigates the suitability of theInterdigitalH-type structure for that application. Technical as well as beam-dynamical aspects and the beam-cavity interaction are discussed.

Quality control and monitoring of radiation damage in charge coupled devices at the Stanford Linear Collider

Abstract: The radiation testing of CCDs (charge coupled devices) for the vertex detector now installed at the SLAC (Stanford Linear Accelerator Center) Linear Collider is described. In addition to data from the batch qualification, results are also presented on the effect of biasing the CCDs during irradiation. A comparison between Co/sup 60/ and Sr/sup 90/ irradiation is made, and initial results for radiation effects in the vertex detector during operations are presented. It has been shown that commercial CCDs can be used as silicon tracking arrays in the radiation environment close to the interaction point at the SLC (SLAC Linear Collider). Measurements of reset FET turn-on potentials on the vertex detector in situ indicate an accumulated dose consistent with that extrapolated from remote dosimetry. Given the well-defined beam conditions that SLC now routinely maintains, these measurements indicate that the detector operation will not be significantly degraded during its lifetime. >