Showing papers on "Linear particle accelerator published in 1999"

The time-of-flight system for CLAS

Abstract: The time-of-flight system for the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility is described. The system, covering an area of 206-square-meters, is composed of scintillation counters 5.08 cm thick, 15 and 22 cm wide, and lengths which vary from 32 cm at the most forward angle to 450 cm at larger angles. All of the components of the system have been designed to optimize the time resolution. Event timing, achieved by leading-edge discrimination with time-walk correction, has been measured with cosmic rays, a laser pulser, and known particle interactions. The intrinsic time resolution varies from about 80 ps for the short counters to 160 ps for the longer counters. Reconstruction of interacting particles during the first period of operation yields an average time resolution for electrons of 163 ps.

Calibration of Super-Kamiokande using an electron LINAC

Abstract: In order to calibrate the Super-Kamiokande experiment for solar neutrino measurements, a linear accelerator (LINAC) for electrons was installed at the detector. LINAC data were taken at various positions in the detector volume, tracking the detector response in the variables relevant to solar neutrino analysis. In particular, the absolute energy scale is now known with less than 1% uncertainty.

Monte Carlo investigation of electron beam output factors versus size of square cutout.

Abstract: A major task in commissioning an electron accelerator is to measure relative output factors versus cutout size (i.e., cutout factors) for various electron beam energies and applicator sizes. We use the BEAM Monte Carlo code [Med Phys. 22, 503-524 (1995)] to stimulate clinical electron beams and to calculate the relative output factors for square cutouts. Calculations are performed for a Siemens MD2 linear accelerator with beam energies, 6, 9, 11, and 13 MeV. The calculated cutout factors for square cutouts in 10 X 10 cm2, 15 X 15 cm2, and 20 X 20 cm2 applicators at SSDs of 100 and 115 cm agree with the measurements made using a silicon diode within about 1% except for the smallest cutouts at SSD= 115 cm where they agree within 0.015. The details of each component of the dose, such as the dose from particles scattered off the jaws and the applicator, the dose from contaminant photons, the dose from direct electrons, etc., are also analyzed. The calculations show that inphantom side-scatter equilibrium is a major factor for the contribution from the direct component which usually dominates the output of a beam. It takes about 6 h of CPU time on a Pentium Pro 200 MHz computer to simulate an accelerator and additional 2 h to calculate the relative output factor for each cutout with a statistical uncertainty of 1%.

Fixed field circular accelerator designs

Abstract: The rapid rate and cycle time required to efficiently accelerate muons precludes conventional circular accelerators. Recirculating linacs provide one option, but the separate return arcs per acceleration pass may prove costly. Recent work on muon acceleration schemes has concentrated on designing fixed-field circular accelerators whose strong superconducting fields can sustain a factor of 4 increase in energy from injection to extraction. A 4 to 16 GeV fixed-field circular accelerator has been designed which allows large orbit excursions and the tune to vary as a function of momentum. Acceleration is 0.6 GeV per turn so the entire cycle consists of only 20 turns. In addition a 16 to 64 GeV fixed-field circular accelerator has been designed which is more in keeping with the traditional Fixed Field Alternating Gradient machines. In this work all three machine designs are described.

An MCNP-based model of a linear accelerator x-ray beam.

Abstract: The Monte Carlo N-Particle radiation transport computer code (MCNP) has been employed on a personal computer to develop a simple model simulating the major components within the beam path of a linear accelerator radiation head, namely the electron target, primary conical collimator, beam flattening filter, wedge filter and the secondary collimators. The model was initially used to calculate the energy spectra and angular distributions of the x-ray beam for the Philips SL 75/5 linear accelerator, in a plane immediately beneath the flattening filter. These data were subsequently used as a `source' of x-rays at the target position, to assess the emergent beam from the secondary collimators. The depth dose distributions and dose profiles at constant depth for various field sizes have been calculated for a nominal operating potential of 4 MV and found to be within acceptable limits. It is concluded that the technique may be used to calculate the energy spectra of any linear accelerator upon specification of the component dimensions, materials and nominal accelerating potential. It is anticipated that this work will serve as the basis of a quality control tool for linear accelerators and treatment planning systems.

High gradient, compact, standing wave linear accelerator structure

Abstract: A standing wave accelerator structure that has both inline coupling cavities and side coupling cavities combined into one structure. Additionally, the invention uses a prebunching (re-entrant) cavity, excited electrically or magnetically, through apertures between a first accelerating cavity and the prebunching cavity.

DAHRT accelerators update and plans for initial operation

Abstract: The Dual-Axis Radiographic Hydrodynamics Test (DARHT) facility will use two perpendicular electron linear induction accelerators to produce intense, bremsstrahlung X-ray pulses for flash radiography. We intend to produce measurements containing 3D information with sub-millimeter spatial of the interior features of very dense explosively driven objects. The facility will be completed in two phases with the first operational by June 1999 utilizing a single-pulse, 19.8-MeV, 2 to 4-kA, 60-ns accelerator (activated in March 1999), a high-resolution electro-optical X-ray imaging system, and other hydrodynamics testing systems. The second phase will be operational by Sept. 2002 and features the addition of a 20-MeV, 2 to 4-kA, 2-microsecond accelerator. Four short electron micropulses of variable pulse-width and spacing will be chopped out of the original, long accelerator pulse for producing time-resolved X-ray images. The second phase also features an extended, high-resolution electro-optical X-ray system with a framing speed of about 2-MHz. In this paper we present a Figure-Of-Merit for a X-ray based flash radiography system to motivate the selection of accelerator parameters. We will then present sub-system performance measurements from Phase 1, the physics of the interaction of our high-intensity beams with the X-ray conversion target, initial Phase 1 accelerator measurements (if available), and plans for operation. We will also discuss designs and prototype testing results for the 2-microsecond Phase 2 accelerator, including prototype induction cells and pulsed power, prototype kicker magnet performance to chop the beam, and design considerations for a multipulse X-ray conversion target.

Detailed dynamics of electron beams self-trapped and accelerated in a self-modulated laser wakefield

Abstract: The electron beam generated in a self-modulated laser-wakefield accelerator is characterized in detail. A transverse normalized emittance of 0.06 π mm mrad, the lowest ever for an electron injector, was measured for 2 MeV electrons. The electron beam was observed to have a multicomponent beam profile and energy distribution. The latter also undergoes discrete transitions as the laser power or plasma density is varied. In addition, dark spots that form regular modes were observed in the electron beam profile. These features are explained by analysis and test particle simulations of electron dynamics during acceleration in a three-dimensional plasma wakefield.

Photoneutron target development for the RPI linear accelerator

Abstract: Two new photoneutron targets have been developed for neutron time-of-flight experiments, the axial water-moderated target (AWMT) and the bare bounce target (BBT). These targets operate without any lead shielding nearby and both have superior neutron resolution compared to the older bounce target. The BBT has been selected over the AWMT for general time-of-flight measurements because it exhibited lower neutron background in the keV energy region.

Generation of periodic accelerating structures in plasma by colliding laser pulses.

Abstract: A mechanism for generating large (>1 GeV/m) accelerating wakes in a plasma is proposed. Two slightly detuned counterpropagating laser beams, an ultrashort timing pulse and a long pump, exchange photons and deposit the recoil momentum in plasma electrons. This produces a localized region of electron current, which acts as a virtual electron beam, inducing intense plasma wakes with phase velocity equal to the group velocity of the short pulse. Modulating the pumping beam generates periodic accelerating structures in the plasma ("plasma linac") which can be used for particle acceleration unlimited by the dephasing between the particles and the wake. An important difference between this type of plasma accelerator and the conventional wakefield accelerators is that this type can be achieved with laser intensities I<<10(18) W/cm(2).

Beam Test of Gamma-ray Large Area Space Telescope Components

Abstract: A beam test of GLAST (Gamma-ray Large Area Space Telescope) components was performed at the Stanford Linear Accelerator Center in October, 1997. These beam test components were simple versions of the planned flight hardware. Results on the performance of the tracker, calorimeter, and anti-coincidence charged particle veto are presented.

Beam optics design of the REX-ISOLDE /q/m-separator

Abstract: In the radioactive beam experiment (REX) at ISOLDE/CERN radioactive singly charged ions are delivered by the online mass separator ISOLDE and are accelerated up to 2.2 MeV/ u by a new concept, using a linear accelerator consisting of a RFQ accelerator, an IH-structure and three 7-gap-resonators (Habs et al., Nucl. Instr. and Meth. B 126 (1997) 218). The ions coming from ISOLDE are first accumulated, bunched and cooled in a Penning Ion Trap (REXTRAP), which is similar to ISOLTRAP (Bollen et al., Nucl. Instr. and Meth. A 368 (1996) 675). Then, in an electron beam ion source (REXEBIS) charge multiplication takes place. Finally, the highly charged ions are accelerated in the LINAC. As the ions coming out from the EBIS contain impurities coming from residual gas inside the EBIS, an accurate q/m selection is necessary before the beam is injected into the RFQ accelerator. This paper presents the design of the REX-ISOLDE separator.

SC driver linac for a rare isotope facility.

Abstract: An ion linac formed of superconducting rf cavities can provide a multi-beam driver accelerator for the production of nuclei far from stability. A multi-beam driver supports a wide variety of production reactions and methods. This paper outlines a concept for a 1.3 GV linac capable of delivering several hundred kilowatts of uranium beam at an energy of 400 MeV per nucleon. The linac would accelerate the full mass range of ions, and provide higher velocities for the lighter ions, for example 730 MeV for protons. The accelerator will consist of an ECR ion source injecting a normally conducting RFQ and four short IH structures, then feeding an array of more than 400 superconducting cavities of six different types, which range in frequency from 58 to 700 MHz. A novel feature of the linac is the acceleration of beams containing more than one charge state through portions of the linac, in order to maximize beam current for the heavier ions. Such operation is made feasible by the large transverse and longitudinal acceptance provided by the large aperture and high gradient which are characteristic of superconducting rf cavities.

Measurement and correction of accelerator optics

Abstract: This report reviews procedures and techniques for measuring, correcting and controlling various optics parameters of an accelerator, including the betatron tune, beta function, betatron coupling, dispersion, chromaticity, momentum compaction factor, and beam orbit. The techniques described are not only indispensable for the basic set-up of an accelerator, but in addition the same methods can be used to study more esoteric questions as, for instance, dynamic aperture limitations or wakefield effects. The different procedures are illustrated by examples from several accelerators, storage rings, as well as linacs and transport lines.

APF or KONUS drift tube structures for medical synchrotron injectors-a comparison

Abstract: Tumor therapy with light ion beams like carbon out of a synchrotron is a topical accelerator application. In all designs the layout of the injector linac is an important factor with respect to construction and operation costs as well as to the operation performance of such a medical facility. Two alternative linac approaches which keep the number of components and setting parameters as low as possible are discussed. In both cases the interdigital H-type drift tube structure is used for acceleration of C/sup 4+/ ions from 0.3 MeV/u to 7 MeV/u. The "Combined Zero Degree Structure" KONUS is used in one design; the other approach is "Alternating Phase Focusing" APF without any magnetic quadrupoles for transverse focusing. Both designs were investigated with the LORASR code. As the same linac should also provide protons with beam intensities of a few mA, the comparison was extended towards the capability of accelerating intense ion beams.

Inductive voltage adder driven X-ray sources for hydrodynamic radiography

Abstract: Inductive voltage adder (IVA) accelerators were developed to provide high-current (100s of kA) power pulses at high voltage (up to 20 MV) using robust modular components. This architecture simultaneously resolves problems found in conventional pulsed and linear induction accelerators. A variety of high-brightness pulsed X-ray radiographic sources are needed from submegavolt to 16-MeV endpoints with greater source brightness (dose/spot/sup 2/) than presently available. We are applying IVA systems to produce very intense (up to 75 TW/cm/sup 2/) electron beams for these flash radiographic applications. The accelerator electromagnetic pulse is converted to a directed electron beam at the end of a self-magnetically insulated vacuum transmission line. The cantilevered cathode threading the accelerator cavities terminates in a small (l-mm diameter) needle, producing the electron beam which is transported to a grounded Bremsstrahlung converter within a strong (/spl sim/50 T) axial magnetic field. These systems produce mm-sized stable electron beams, yielding very intense X-ray sources. Detailed simulations of the electron beam generation, transport, and target interaction are presented along with scaling laws for the radiation production and X-ray spot size. Experimental studies confirm these simulations and show this reliable, compact, and inexpensive technology scales to 1000-R doses a meter from a mm-diameter source in 50 ns.

Finding mechanisms responsible for the spectral distribution of electron beams produced by a linear accelerator

Abstract: The measured electron spectra of linear accelerators from several manufacturers differ in comparison to the spectral form and width. As part of our investigations of linac performance and stability, we analyzed the electron spectra of our linacs. After building a spectrometer the electron spectra were measured. The measured spectral widths were comparable with the results published in the literature. It appeared that the phase of the recycled radio pulse in combination with the limited bandwidth of the bending magnet are responsible for unusual (multipeak) electron spectra. The scatter filters only have a relatively small widening effect on the spectrum. There was no indication that multipeak or wide spectra are related to linac instabilities.

Applications of X-band technology in medical accelerators

Abstract: Most radiation therapy machines are based on microwave linear accelerators. The majority of medical accelerators use frequencies in the S-band range. Having a compact accelerator allows for a wide range of treatments. The size and weight of the accelerator is substantially reduced if a higher frequency is used. X-band frequencies are suitable for such applications. The X-band accelerator technology has been used in high-energy as well as industrial applications. In the radiation therapy field, it is already implemented in some machines. The Mobetron an Intra-Operative Radiation Therapy (IORT) treatment system is one example. Another example is the Stereotactic Radiosurgery machine, the CyberKnife. The compactness of these machines required the use of an X-band accelerator. The basis for choosing the X-band technology in some of the medical machines is analysed. A review of the exiting medical applications is included. We also discuss the availability of other X-band components in the machine, including high-power RF sources.

704 mhz superconducting cavities for a high intensity proton accelerator

Abstract: The Hybrid program has been recently started in France in order to explore nuclear waste transmutation technology, based on a spallation neutron source driven by a high-intensity proton linear accelerator. The study of the high-energy section of this accelerator (Superconducting Accelerator for Hybrid) has begun : it aims at developing 704 MHz superconducting radiofrequency (SCRF) cavities for the two different beta sections ( β=0.47 and β=0.65). A single-cell (β=0.65) SCRF cavity has been designed by CEA Saclay, and built in industry (CERCA). Mechanical stiffness was analyzed at IPN Orsay. The first cryogenic tests have been performed, showing excellent RF performance. The Qo value was as high as 7.10 10 , indicating extremely low RF losses. The accelerating field went up to 26MV/m, exceeding by more than a factor of two the design point of 10 MV/m.

A study of lithium deuteride as a material for a polarized target

Abstract: Experiment E155 at the Stanford Linear Accelerator Center (SLAC) measured the spin-dependent structure of the proton and neutron, using for the first time 6 LiD as the polarized deuteron target material in a high-energy electron beam. This compound provides a significantly higher dilution factor than any other solid deuteron target material currently used in high-energy physics experiments. Results of the polarization behavior of the 6 LiD target material before and after exposure to the 50 GeV/ c electron beam used in E155 are presented.

A linear accelerator power amplification system for high gradient structure research

Abstract: The ongoing development of linear collider high power RF sources and pulse compression systems has resulted in substantial progress towards a goal of providing a peak RF power level of approximately 250 MW at the input of the accelerator structure. While the immediate development and the high power testing of specialized waveguide components required for power transmission at these high levels have proceeded expeditiously due to the availability of resonant ring systems, the testing of high gradient accelerator structures at very high power levels, and the investigation of coupler cavity RF breakdown problems have, typically, been curtailed due to the unavailability of suitable 200 to 300 MW RF test facilities. We describe herein a compact, high peak power amplification system based on a dual hybrid bridge configuration that avoids the need for power splitters at the accelerator dual feed couplers, and also provides a convenient interface for installing high gradient accelerator test structures. Design pa...

Performance of the accelerator driver of Jefferson Laboratory's free-electron laser

Abstract: The driver for Jefferson Lab's kW-level infrared free-electron laser (FEL) is a superconducting, recirculating accelerator that recovers about 75% of the electron-beam power and converts it to radiofrequency power. In achieving first lasing, the accelerator operated "straight-ahead" to deliver 38 MeV, 1.1 mA cw current through the wiggler for lasing at wavelengths in the vicinity of 5 /spl mu/m. Just prior to first lasing, measured rms beam properties at the wiggler were 7.5/spl plusmn/1.5 mm-mr normalized transverse emittance, 26/spl plusmn/7 keV-deg longitudinal emittance, and 0.4/spl plusmn/0.1 ps bunch length which yielded a peak current of 60/spl plusmn/15 A. The waste beam was then sent directly to a dump, bypassing the recirculation loop. Stable operation at up to 311 W cw was achieved in this mode. Commissioning the recirculation loop then proceeded. As of this Conference, the machine has recirculated cw average current up to 4 mA, and has lased cw with energy recovery up to 710 W.

Photocathode rf gun emittance measurements using variable-length laser pulses

Abstract: The Gun Test Facility (GTF) at the Stanford Linear Accelerator Center (SLAC) was created to develop an appropriate injector for the proposed Linac Coherent Light Source (LCLS) at SLAC The LCLS design requires the injector to produce a beam with at least 1 nC of charge in a 10 ps or shorter pulse with no greater than 1 (pi) mm-mrad normalized rms emittance The first photoinjector under study at the GTF is a 16 cell S-band symmetrized gun with an emittance compensation solenoid Emittance measurements, reported here, were made as function of the transverse laser pulse shape and the Gaussian longitudinal laser pulse length The lowest achieved emittance to data with 1 nC of charge is 56 (pi) mm-mrad and was obtained with both a Gaussian longitudinal and transverse pulse shape with 5 ps FWHM and 24 mm FWHM respectively The measurement is in agreement with a PARMELA simulation using measured beam parameters There are indications that the accelerator settings used in the results presented here were not optimal Simulations indicate that a normalized emittance meeting the LCLS requirement can be obtained using appropriately shaped transverse and temporal laser/electron beam pulses Work has begun on producing temporal flat top laser pulses which combined with transverse clipping of the laser is expected to lower the emittance to approximately 1 (pi) mm-mrad for 1 nC beams with optimal accelerator settings© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Wakefield and beam centering measurements of a damped and detuned X-band accelerator structure

Abstract: We present wakefield measurements of a prototype Next Linear Collider (NLC) accelerator structure that was built with dipole mode damping and detuning to suppress the long-range transverse wakefield induced by a beam. In addition, we describe beam centering tests that use as a guide the dipole power coupled out of the structure for damping purposes.

Stopping-power ratios for clinical electron beams from a scatter-foil linear accelerator

Abstract: Restricted mass collision stopping-power ratios for electron beams from a scatter-foil medical linear accelerator (Varian Clinac 2100C) were calculated for various combinations of beams, phantoms and detector materials using the Monte Carlo method. The beams were of nominal energy 6, 12 or 20 MeV, with square dimensions 1 × 1 cm2 to 10 × 10 cm2. They were incident at nominal SSDs of 100 or 120 cm and inclined at 90° or 30° to the surface of homogeneous water phantoms or water phantoms interspersed with layered lung or bone-like materials. The broad beam water-to-air stopping-power ratios were within 1.3% of the AAPM TG21 protocol values and consistent with the results of Ding et al to within 0.2%. On the central axis the stopping-power ratio variations for narrow beams compared with normally incident broad beams were 0.1% or less for water-to-LiF-100, graphite, ferrous sulfate dosimeter solution, polystyrene and PMMA, 0.5% for water-to-silicon and 1% for water-to-air and water-to-photographic-film materials. The transverse variations of the stopping-power ratios were up to 4% for water-to-silicon, 7% for water-to-photographic-film materials and 10% for water-to-air in the penumbral regions (where the dose was 10% of the global dose maximum) at shallow depths compared with the values at the same depths on the central axis. In the inhomogeneous phantoms studied, the stopping-power ratio correction factors varied more significantly for air, followed by photographic materials and silicon, at various depths on the central axis in the heterogeneous regions. For the simple layered phantoms studied, the estimation of the stopping-power ratio correction factors based on the relative electron-density derived effective depth approach yielded results that were within 0.5% of the Monte Carlo derived values for all the detector materials studied.

Fast digital feedback system for energy and beam position stabilization

Abstract: A digital fast feedback system for beam energy and position stabilization at the target of the CEBAF accelerator is capable of suppressing beam motion in the frequency band from 0 to 80 Hz and also performs narrow band suppression at the first twelve power line harmonics. The system utilizes two VME computers and runs at a 2.4 kHz sampling rate. The numerical algorithm is based on a recursive digital filter with an additional feedforward loop for suppression of high power line harmonics. The system suppresses beam motion by a factor greater than ten, thus achieving the stabilization of relative beam energy fluctuations to better than 10/sup -5/ and stabilization of beam position on the target to better than 20 /spl mu/m.

Charged particle irradiation apparatus

Abstract: PROBLEM TO BE SOLVED: To miniaturize a deflecting electric magnet in a beam transport system, reduce a power capacity, and reduce manufacturing cost and running cost by disposing a circular accelerator and the beam transport system at their upper and lower stages, and forming the shape of beams taken out from the circular accelerator so that vertical emittance is more significant than horizontal emittance. SOLUTION: An irradiation chamber 8 is disposed underground, a circular accelerator 7 is placed vertically, and a linear accelerator 6 is installed on a first floor. In the shape of beams taken out from the circular accelerator 7 by beam taking out means, the beam vertical emittance is smaller than horizontal emittance. Next, these beams are transported to each irradiation chamber 8 on the first ground floor by means of a beam transport system 2 installed in a horizontal face of the ground first ground floor. Thereby, a distance between magnetic electrodes opposed vertically of the defecting electric magnet 3 constituting the beam transport system 2 is reduced, and thus, the whole deflecting electric magnet 3 can be miniaturized.

Experimental results from a microwave cavity beam position monitor

Abstract: Future linear colliders have hard requirements for the beam transverse position stability in the accelerator. A beam position monitor (BPM) with the resolution better than 0.1 micron in the single bunch regime is needed to control the stability of the beam position along the linac. Proposed BPM is based on the measurement of the asymmetrical mode excited by a single bunch in the cavity. Four stages of signal processing (space-, time-, frequency- and phase-filtering providing the required signal-to-noise ratio) are used to obtain extremely high resolution. The measurement set-up was designed by BINP and installed at ATF/BNL to test experimentally this concept. The setup includes three two-coordinates BPM's at the frequency of 13.566 GHz, and reference intensity/phase cavity. BPM's were mounted on a support table.

Improved ETA-II accelerator performance

Abstract: Improvements have been made in the performance of the ETA-II accelerator that allow a nominal 2 kA, 6 MeV beam to be focused to a spot size less that 1 mm in diameter. The improvements include reducing the energy sweep to less than /spl plusmn/0.5% over 40 ns of the pulse using a real time energy diagnostic and improving the magnetic tune of the accelerator to reduce the emittance to 8 cm-mrad. Finally, an automated tuning system (MAESTRO) was run to minimize the time dependent centroid motion (corkscrew) by adjusting the steering dipoles over the focusing solenoids. The corkscrew motion was reduced to less than /spl plusmn/0.5 mm at the output of the accelerator.

Beam-target interaction experiments for bremsstrahlung converter applications

Abstract: For multi-pulse radiography facilities, we are investigating the possible adverse effects of (1) backstreaming ion emission from the bremsstrahlung converter target and (2) the interaction of the resultant plasma with the electron beam during subsequent pulses. These effects would primarily manifest themselves in a static focusing system as a rapidly varying X-ray spot. To study these effects, we are conducting beam-target interaction experiments on the ETA-II accelerator (a 6.0 MeV, 2.5 kA, 70 ns FWHM pulsed, electron accelerator) by measuring spot dynamics and characterizing the resultant plasma for various configurations.