Showing papers on "Linear particle accelerator published in 1997"

Accurate characterization of Monte Carlo calculated electron beams for radiotherapy

Abstract: Monte Carlo studies of dose distributions in patients treated with radiotherapyelectron beams would benefit from generalized models of clinical beams if such models introduce little error into the dose calculations. Methodology is presented for the design of beam models, including their evaluation in terms of how well they preserve the character of the clinical beam, and the effect of the beam models on the accuracy of dose distributions calculated with Monte Carlo. This methodology has been used to design beam models for electron beams from two linear accelerators, with either a scanned beam or a scatteredbeam.Monte Carlo simulations of the accelerator heads are done in which a record is kept of the particle phase-space, including the charge, energy, direction, and position of every particle that emerges from the treatment head, along with a tag regarding the details of the particle history. The character of the simulated beams are studied in detail and used to design various beam models from a simple point source to a sophisticated multiple-source model which treats particles from different parts of a linear accelerator as from different sub-sources. Dose distributions calculated using both the phase-space data and the multiple-source model agree within 2%, demonstrating that the model is adequate for the purpose of Monte Carlotreatment planning for the beams studied. Benefits of the beam models over phase-space data for dose calculation are shown to include shorter computation time in the treatment head simulation and a smaller disk space requirement, both of which impact on the clinical utility of Monte Carlotreatment planning.

Cw particle accelerator with low particle injection velocity

Abstract: An RF linear accelerator (120) using CW or low amplitude pulsed RF excitation which can efficiently accelerate charged particles from 0.1 C to relativistic velocities in excess of 0.9 C. A charged particle source (26) feeds charged particles having velocities of about 0.1 C into a first type RF LINAC having a plurality of side coupled resonator cavities (18, 20, 22) each having a drift tube (30) in the middle. The RF length of the cavities is set relative to the velocity of the particles and the RF excitation wavelength such that the particles experience in-phase accelerating E fields in the gaps on either side of the drift tube and are shielded from decelerating E fields while inside the drift tubes. The RF coupling cavities establish sufficient phase change between adjacent resonators such that the particles arrive in the adjacent resonator cavities in synchronization with oscillations in the standing wave therein so as to experience further acceleration. The charged particles are then passed through a conventional RF LINAC with a CW source which is optimized to accelerate the particles from 0.5 C to relativistic velocities. A variable phase change RF coupler (11) couples the RF between the first RF LINAC and the second RF LINAC such that a variable degree of synchronization can be achieved.

A Primer on Theory and Operation of Linear Accelerators in Radiation Therapy

Abstract: Preface Acknowledgments 1. Introduction 2. Energy Designation in Accelerators 3. An Elementary Linear Accelerator 4. A Comparison of Linacs with Diagnostic X-ray Generators 5. Major Linac Modules and Components 6. Microwave Power Sources 6a. Microwave Cavities 6b. The Klystron 6c. The Magnetron 7. The Waveguide and Circulator 8. Accelerator Structures 8a. Traveling-wave Accelerator Structures 8b. Standing-wave Accelerator Structures 9. Multiple X-ray Energy Mode Accelerators 9a. Traveling-wave Accelerator Structures 9b. Standing-wave Accelerator Structures 10. Bending Magnet 11. Treatment Head 12. Image-guided Radiotherapy 13. Physiologic Beam Gating 14. Functional Block Diagram and Auxiliary Systems 15. Operational Review

Radioactive ion beams facility at triumf

Abstract: A radioactive ion beam (RIB) facility is being built at TRIUMF. A novel design for the target/ion source station will allow us to bombard a thick target with TRIUMF's 100 μA, 500 MeV proton bam, producing a variety of very intense beams of nuclei far from stability. After mass separation the beams can be sent to two different experimental areas. One uses the 60 keV energy beam and the second one will use the 0.15 to 1.50 MeV/u post-accelerated beam. Singly charged ion beams, with A ≤ 30 delivered from the on line mass separator, with an energy of 2 keV/u, will be accelerated in a two stage linac consisting of an RFQ and a post-stripper drift-tube linac up to 1.5 MeV/u. CW operation mode is required to preserve beam intensity. As a consequence of the low q/A ions a low operating frequency for the RFQ is required to achieve adequate transverse focusing. The main features of this accelerator are: 35 MHz RFQ, stripping at 150 keV/u, beam energy continuously variable from 0.15 to 1.50 MeV/u and CW operation.

Integrated normal-conducting/superconducting high-power proton linac for the APT project

Abstract: The baseline accelerator design for the APT (Accelerator Production of Tritium) Project is a normalconducting-superconducting proton linac that produces a CW beam power of 170 MW at 1700 MeV. Compared with the previous all-NC linac design, the NC/SC linac provides significant power savings and lower operating and capital costs. It allows a much larger aperture at high energies, and permits greater operational flexibility. The design has been approved by high-level technical panels and is published in a Conceptual Design Report. The high-energy portion is a superconducting (SC) RF linac employing elliptical-type niobium cavities, while the low-energy portion is a normal-conducting (NC) linac constructed from copper cavities. This provides an integrated accelerator design that makes optimum use of the two technologies in their appropriate regions of application. The NC linac, which consists of an injector, RFQ, CCDTL, and CCL, accelerates a 100-mA beam to 217 MeV. The SC linac is built in two sections optimized for different beam velocity spans, with each section made up of cryomodules containing 5-cell cavities and SC singlet quads in a FODO focusing lattice. Alternate SC linac designs are being studied that employ a doublet focusing lattice using conventional quadrupoles located between cryomodules.

Pencil-like mm-size electron beams produced with linear inductive voltage adders

Abstract: We present the design, analysis, and results of the high brightness electron beam experiments currently under investigation at Sandia National Laboratories. The anticipated beam parameters are the following: energy 12 MeV, current 35–40 kA, rms radius 0.5 mm, and pulse duration 40 ns full width at half-maximum. The accelerator is SABRE, a pulsed linear inductive voltage adder modified to higher impedance, and the electron source is a magnetically immersed foilless electron diode. 20–30 T solenoidal magnets are required to insulate the diode and contain the beam to its extremely small-sized (1 mm) envelope. These experiments are designed to push the technology to produce the highest possible electron current in a submillimeter radius beam. Design, numerical simulations, and experimental results are presented.

Performance and design concepts of a free electron laser operating in the x-ray region

Abstract: We report on the Design Study of a Free-Electron-Laser experiment designed to produce coherent radiation at the wavelength of 1.5 {Angstrom} and longer. The proposed experiment utilizes 1/3 of the SLAC linac to accelerate electrons to 15 GeV. The high brightness electron beam interacts with the magnetic field of a long undulator and generates coherent radiation by self-amplified spontaneous emission (SASE). The projected output peak power is about, 10 GW. The project presents several challenges in the realization of a high brightness electron beam, in the construction and tolerances of the undulator and in the transport, of the x-ray radiation. The technical solutions adopted for the design are discussed. Numerical simulations are used to show the performance as a function of system parameters.

Beam dynamics studies with the heavy-ion linear induction accelerator MBE-4

Abstract: Current amplification of heavy-ion beams is an integral feature of the induction linac approach to heavy-ion fusion (HIF). In this paper we report on amplification experiments conducted on a single beam of the Multiple Beam Experiment (MBE-4), a heavy-ion (Cs+) induction linac. Earlier MBE-4 experiments [H. Meuth et al., Nucl. Instrum. Methods Phys. Res. A 278, 153 (1989)] had demonstrated up-to-9× current amplification but had been accompanied by an up-to-2× increase of normalized transverse emittance. Experiments to pinpoint the causes of this emittance growth indicated various factors were responsible, including focusing aberrations and mismatch difficulties between the injector diode and the accelerator transport lattice, a localized quadrupole misalignment problem, and the interaction of transversely large beams with the nonlinear elements of the focusing lattice. Following ameliorative measures, new current amplification experiments, both with and without acceleration, showed that current amplifications of up to 3× and line charge density increases of up to ≈2× could be achieved without increasing the beam’s normalized transverse emittance. Finally, both the transverse beam dynamics, and beam current and energy measurements were accurately modeled by numerical particle-in-cell simulations and longitudinal dynamics codes, respectively.

Measurements of Neutron Spectra at the Stanford Linear Accelerator Center

Abstract: The purpose of the present measurements was to determine neutron spectra outside the shielding of high energy electron accelerators, with a special emphasis on the high energy (>20 MeV) portion of the spectra. The spectrometer system used consists of a standard set of Bonner spheres augmented by a custom made 30.48 cm (12) sphere with a 1 cm inner layer of lead, which increases its response in the high energy region. The system was further complemented by a plastic scintillator used for the measurement of 11 C activation. A pair of rem meters was also used: one standard Anderson-Braun, and one with an inner layer of lead which has an extended high energy response. Measured spectra and relevant dosimetric quantities outside shielding at three different electron beam energies are presented.

Simulations of the LEDA RFQ 6.7-MeV accelerator

Abstract: The codes PARMTEQM and RFQTRAK simulate the beam transport through the radio-frequency-quadrupole (RFQ) accelerator for the low-energy-demonstration accelerator (LEDA). They predict 95% transmission for a matched 110-mA proton beam with a normalized-RMS emittance of 0.02 mm mrad. RFQTRAK simulates the effects of arbitrary vane-tip misalignments. This RFQ includes some new features in its design. It consists of four resonantly coupled 2-m-long segments that make up its 8-m length. It has higher vane-gap voltages at the high-energy end than the low-energy end. The entrance end of the RFQ has lower transverse focusing strength to facilitate beam matching. The exit of the RFQ has a transition cell and a radial-matching section. The exit radial-matching section matches the beam into the following accelerator.

Design, commissioning and operational results of wide dynamic range BPM switched electrode electronics

Abstract: The Continuous Electron Beam Accelerator Facility (CEBAF) is a high-intensity, continuous-wave electron accelerator for nuclear physics. Total acceleration of 4 GeV is achieved by recirculating the beam through two 400-MeV linacs. The operating currents over which the linac beam position monitoring system must meet specifications are 1 μA to 1000 μA. A system was developed in 1994 and installed in the spring of 1995 that switches four electrode signals at 120 kHz through two signal-conditioning chains that use computer-controlled variable gain amplifiers with a dynamic range greater than 80 dB. The system timing was tuned to the machine recirculation period of 4.2 μs so that components of the multipass beam could be resolved in the linacs. Other features of this VME-based system include long-term stability and high-speed data acquisition, which make it suitable for use as both a time-domain diagnostic tool and as part of a variety of beam feedback systems. The computer interface has enough control over th...

Improvement of the operational performance of SRF cavities via in situ helium processing and waveguide vacuum processing

Abstract: The useful performance range of the superconducting RF cavities in the CEBAF accelerator at Jefferson Lab is frequently limited by electron field emission and derived phenomena. Improvements are required to support future operation of the accelerator at higher than 5 GeV. Twelve operational cryomodules have been successfully processed to higher useful operating gradients via RF-helium processing. Progress against field emission was evidenced by improved high-field Q, reduced X-ray production and greatly reduced incidence of arcing at the cold ceramic window. There was no difficulty reestablishing beamline vacuum following the processing. Cavities previously limited to 4-6 MV/m are now operating stably at 6-9 MV/m. By applying a pulsed-RF processing technique, we have also improved the pressure stability of the thermal transition region of the input waveguide for several cavities.

Upgrades to the LLNL flash X-ray induction linear accelerator (FXR)

Abstract: The FXR is an induction linear accelerator used for flash radiography at the Lawrence Livermore National Laboratory's Site 300 Test Facility. The FXR was originally completed in 1982 and has been in continuous use as a radiographic tool. At that time the FXR produced a 17 MeV, 2.2 kA burst of electrons for a duration of 65 ns. An upgrade of the FXR was recently completed. The purpose of this upgrade was to improve the performance of the FXR by increasing the energy of the electron injector from 1.2 MeV to 2.5 MeV and the beam current from 2.2 kA to 3 kA, improving the magnetic transport system by redesigning the solenoidal transport focus coils, reducing the RF coupling of the electron beam to the accelerator cells, and by adding additional beam diagnostics. The authors describe the injector upgrades and performance, as well as their efforts to tune the accelerator by minimizing beam corkscrew motion and the impact of beam breakup instability on beam centroid motion throughout the beam line as the current is increased to 3 kA.

Linear induction accelerator approach for advanced radiography

Abstract: Recent advances in induction accelerator technology make it possible to envision a single accelerator that can serve as an intense, precision multiple pulse x-ray source for advanced radiography Through the use of solid-state modulator technology repetition rates on the order of 1 MHz can be achieved with beam pulse lengths ranging from 200 ns to 2 /spl mu/secs By using fast kickers, these pulses may be sectioned into pieces which are directed to different beamlines so as to interrogate the object under study from multiple lines of sight The ultimate aim is to do a time dependent tomographic reconstruction of a dynamic object The technology to accomplish these objectives along with a brief discussion of the experimental plans to verify it will be presented

Recirculating Accelerator Driver for a High-Power Free-Electron Laser: A Design Overview

Abstract: Jefferson Lab is building a free-electron laser (FEL) to produce continuous-wave (cw), kW-level light at 3-6 /spl mu/m wavelength. A superconducting linac will drive the laser, generating a 5 mA average current, 42 MeV energy electron beam. A transport lattice will recirculate the beam back to the linac for deceleration and conversion of about 75% of its power into rf power. Bunch charge will range up to 135 pC, and bunch lengths will range down to 1 ps in parts of the transport lattice. Accordingly, the space charge in the injector and coherent synchrotron radiation in magnetic bends come into play. The machine will thus enable studying these phenomena as a precursor to designing compact accelerators of high-brightness beams. The FEL is scheduled to be installed in its own facility by 1 October 1997. Given the short schedule, the machine design is conservative, based on modifications of the CEBAF cryomodule and MIT-Bates transport lattice. This paper surveys the machine design.

On using the coherent far IR radiation produced by a charged particle bunch to determine its shape — II Measurement with synchrotron and transition radiation

Abstract: The coherent radiation spectrum from mm long relativistic electron bunches perturbed in different ways is investigated with a large aperture Michelson spectrometer. From these data we are able to determine the structure and asymmetric shape of the longitudinal electron density of short relativistic electron bunches on a submillimeter length scale by utilizing the Kramers-Kronig analysis technique described previously. Both synchrotron and transition radiation have been used successfully to determine the bunch shape. We further demonstrate how the influence of the LINAC tuning on bunch width and bunch asymmetry can be determined by using this technique.

Experimental confirmation of transverse focusing and adiabatic damping in a standing wave linear accelerator

Abstract: The measurement of the transverse phase-space map, or transport matrix, of a relativistic electron in a high-gradient, radio-frequency linear accelerator (rf linac) at the UCLA photoinjector is reported. This matrix, which indicates the effects of acceleration (adiabatic damping), first-order transient focusing, and ponderomotive second-order focusing, is measured as a function of both rf field amplitude and phase in the linac. The elements of the matrix, determined by observation of centroid motion at a set of downstream diagnostics due to deflections induced by a set of upstream steering magnets, compare well with previously developed analytical theory [J. Rosenzweig and L. Serafini, Phys. Rev. E {bold 49}, 1599 (1994)]. The determinant of the matrix is obtained, yielding a direct confirmation of trace space adiabatic damping. Implications of these results on beam optics at moderate energy in high-gradient linear accelerators such as rf photoinjectors are discussed. {copyright} {ital 1997} {ital The American Physical Society}

Lattice design for a high-power infrared FEL

Abstract: A 1 kW infrared FEL for industrial, defense, and related scientific applications, is being built at Jefferson Lab. It will be driven by a compact energy-recovering CW superconducting radio-frequency (SRF) linear accelerator. Stringent phase space requirements at the wiggler, low beam energy, and high beam current subject the design to numerous constraints. This report addresses these issues and presents a design solution for an accelerator transport lattice meeting the requirements imposed by physical phenomena and operational necessities.

Recirculating accelerator driver for a high-power free-electron laser: a design overview

Abstract: Jefferson Lab is building a free-electron laser (FEL) to produce continuous-wave (cw), kW-level light at 3-6 /spl mu/m wavelength. A superconducting linac will drive the laser, generating a 5 mA average current, 42 MeV energy electron beam. A transport lattice will recirculate the beam back to the linac for deceleration and conversion of about 75% of its power into rf power. Bunch charge will range up to 135 pC, and bunch lengths will range down to 1 ps in parts of the transport lattice. Accordingly, the space charge in the injector and coherent synchrotron radiation in magnetic bends come into play. The machine will thus enable studying these phenomena as a precursor to designing compact accelerators of high-brightness beams. The FEL is scheduled to be installed in its own facility by 1 October 1997. Given the short schedule, the machine design is conservative, based on modifications of the CEBAF cryomodule and MIT-Bates transport lattice. This paper surveys the machine design.

Neutron-irradiation apparatus for treatment and method therefor

Abstract: PROBLEM TO BE SOLVED: To enable uniform control of the quantity of neutrons irradiated to an affected part by a method wherein accelerated particles radiated from a particle accelerator are branched to apply an impact to a target while irradiating the affected part of a person to be treated at the optimum ratio from a plurality of directions to reduce a heating value at the target. SOLUTION: Numerous protons accelerated by a linear accelerator 1 travel as a flux through a vacuum conduit 21 under the action of a deflection magnet 7 and distributed to branch conduits 23a and 23b by a distribution magnet 25 at a proper ratio, for example, 5:5. The branched flux of protons is made to impacted onto each target 31 by a focusing magnet 9 to generate fast neutrons. The fast neutrons are decelerated to the level of thermal neutrons, for instance, by a moderator 29 as neutron filter provided in a shielded concrete wall 27, and then, focused by a collimator 35 to irradiate an irradiation field 37 in the body of a patient 19 from two directions. B injected into the body emits α rays to treat the affected part.

X-ray optics design studies for the 1.5 to 15-A Linac Coherent Light Source (LCLS) at Stanford Linear Accelerator Laboratory

Abstract: In recent years, comprehensive design studies have been initiated on angstrom-wavelength free-electron laser (FEL) schemes based on driving highly compressed electron bunches from a multi-GeV linac through long undulators. The output parameters of these sources, when operated in the so-called self-amplified spontaneous emission mode, include lasing powers in the 10-100 GW range, full transverse and low-to- moderate longitudinal coherence, pulse durations in the 50- 500 fs range, broad spontaneous spectra with total power comparable to the coherent output, and flexible polarization parameters. In this paper we summarize the status of design studies of the x-ray optics system and components to be utilized in the SLAC linac coherent light source, a 1.5-15 angstrom FEL driven by the last kilometer of the SLAC three kilometer S-band linac. Various aspects of the overall optical system, selected instrumentation and individual components, radiation modeling, and issues related to the interaction of intense sub-picosecond x-ray pulses with matter, are discussed.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Theory of longitudinal beam halo in RF linacs. I. Core/test-particle formulation

Abstract: For intense beams, the analysis of tenuous halo components of the particle distribution that surround the main core of the beam can be challenging. So-called core/test-particle models in which a test-particle is evolved in the applied and space-charge forces of the beam core have been instrumental in understanding the structure and extent of transverse beam halo produced by resonant particle interactions with the oscillating space-charge forces of a mismatched beam core. Here we present a core/test-particle model developed for the analysis of longitudinal beam halo in intense, ion-beam rf linacs. Equations of motion are derived for a test-particle moving interior to, and exterior to, a uniform density ellipsoidal beam bunch. Coupled transverse-longitudinal mismatch modes of the ellipsoidal beam envelope are analyzed. Typical parameters suggest the possibility of a low-order resonant interaction between longitudinal particle oscillations and a low-frequency envelope mode. Properties of this resonance are analyzed in an accompanying paper by the authors in these proceedings.

High peak power test of S-band waveguide switches

Abstract: The injector and source of particles for the Advanced Photon Source (APS) is a 2856-MHz S-band electron-positron linear accelerator (linac) which produces electrons with energies up to 650 MeV or positrons with energies up to 450 MeV. To improve the linac RF system availability, an additional modulator-klystron subsystem is being constructed to provide a switchable hot spare unit for each of the five existing S-band transmitters. The switching of the transmitters will require the use of SF6-pressurized waveguide switches at a peak operating power of 35 MW. A test stand was set up at the Stanford Linear Accelerator Center (SLAC) Klystron-Microwave laboratory to conduct tests characterizing the power handling capability of these waveguide switches. Test results are presented.

The LEDA beam-position measurement system

Abstract: This paper describes the beam-position measurement system being developed for the Low Energy Demonstration Accelerator (LEDA) and the Accelerator Production of Tritium (APT) projects at Los Alamos National Laboratory. The system consists of a beam-position monitor (BPM) probe, cabling, down-converter module, position/intensity module, on-line error-correction system, and the necessary control system interfaces. The modules are built on the VXI-interface standard and are capable of duplex data transfer with the control system. Some of the key, system parameters are: position-measurement bandwidth of at least 180 kHz, the ability to measure beam intensity, a beam-position measurement accuracy of less than 1.25 percent of the bore radius, a beam-current dynamic range of 46 dB, a total system dynamic range in excess of 75 dB, and built-in on-line digital-system-error correction.

Progress Update on the Low-Energy Demonstration Accelerator (LEDA)

Abstract: As part of the linac design for the accelerator production of tritium (APT) project, we are assembling the first approximately 20 MeV portion of this cw proton accelerator. Primary objective of this low-energy demonstration accelerator (LEDA) is to verify the design codes, gain fabrication knowledge, understand LEDA's beam operation, and be able to better predict costs and operational availability for the full 1700 MeV APT accelerator. This paper provides an updated report on this past year's progress that includes beam tests of the 75 keV injector, fabrication of the 6.7 MeV radio-frequency quadrupole (RFQ), preparation of the facility, procurement and assembly of the RF system, and detailed design and documentation of many pieces of support equipment. First tests with the 6.7 MeV, 100 mA, cw beam from the RFQ are scheduled for late 1998. References are given to many detailed papers on LEDA at this conference.

Superconducting cavities for the APT accelerator

Abstract: The design of an Accelerator Production of Tritium (APT) facility being investigated at Los Alamos includes a linear accelerator using superconducting RF-cavities for the acceleration of a high-current cw proton beam. For electron accelerators with particles moving at the speed of light (/spl beta//spl ap/1.0), resonators with a rounded shape, consisting of ellipsoidal and cylindrical sections, are well established. They are referred to as "elliptical" cavities. For the APT-design, this shape has been adapted for much slower proton beams with /spl beta/ ranging from 0.60 to 0.94. This is a new energy range, in which resonators of an elliptical type have never been used before. Simulations with the well-proven electromagnetic modeling tools MAFIA and SUPERFISH were performed. The structures have been optimized for their RF and mechanical properties as well as for beam dynamics requirements. The TRAK.RF simulation code is used to investigate potential multipacting in these structures. All the simulations will be put to a final test in experiments performed on single cell cavities that have started in our structures laboratory.

The computer program LIAR for the simulation and modeling of high performance linacs

Abstract: High performance linear accelerators are the central components of the proposed next generation of linear colliders. They must provide acceleration of up to 750 GeV per beam while maintaining small normalized emittances. Standard simulation programs, mainly developed for storage rings, do not meet the specific requirements for high performance linacs with high bunch charges and strong wakefields. We present the program LIAR ("Linear Accelerator Research code") that includes single and multi-bunch wakefield effects, a 6D coupled beam description, specific optimization algorithms and other advanced features. LIAR has been applied to and checked against the existing Stanford Linear Collider (SLC), the linacs of the proposed Next Linear Collider (NLC) and the proposed Linac Coherent Light Source (LCLS) at SLAC.

Progress update on the Low-Energy Demonstration Accelerator (LEDA)

Abstract: As part of the linac design for the accelerator production of tritium (APT) project, we are assembling the first approximately 20 MeV portion of this cw proton accelerator. Primary objective of this low-energy demonstration accelerator (LEDA) is to verify the design codes, gain fabrication knowledge, understand LEDA's beam operation, and be able to better predict costs and operational availability for the full 1700 MeV APT accelerator. This paper provides an updated report on this past year's progress that includes beam tests of the 75 keV injector, fabrication of the 6.7 MeV radio-frequency quadrupole (RFQ), preparation of the facility, procurement and assembly of the RF system, and detailed design and documentation of many pieces of support equipment. First tests with the 6.7 MeV, 100 mA, cw beam from the RFQ are scheduled for late 1998. References are given to many detailed papers on LEDA at this conference.