Showing papers on "Linear particle accelerator published in 2000"

Sustained Kilowatt Lasing in a Free-Electron Laser with Same-Cell Energy Recovery

Abstract: TJNAF recently commissioned its high-average-power infrared free-electron laser (FEL). It incorporates a superconducting accelerator that recovers about 75% of the electron-beam power and converts it to radio-frequency power. In achieving first lasing, the accelerator operated straight-ahead to deliver 38 MeV, 1.1 mA cw average current through the wiggler for lasing at wavelengths near 5 {micro}m. The waste beam was then sent directly to a dump. Stable operation at up to 311 W cw was achieved in this mode. Using a transport loop to send the waste electron beam back to the linac for energy recovery, the machine recently lased cw at up to 1720 W average power at 3.1 {micro}m, for which the electron-beam energy and average current were 48 MeV and 4.4 mA, respectively.

The REX-ISOLDE project

Abstract: The Radioactive Beam Experiment REX-ISOLDE [1-3] is a pilot experiment at ISOLDE (CERN) testing the new concept of post acceleration of radioactive ion beams by using charge breeding of the ions in a high charge state ion source and the efficient acceleration of the highly charged ions in a short LINAC using modern ion accelerator structures In order to prepare the ions for the experiments singly charged radioactive ions from the on-line mass separator ISOLDE will be cooled and bunched in a Penning trap, charge bred in an electron beam ion source (EBIS) and finally accelerated in the LINAC The LINAC consists of a radiofrequency quadrupole (RFQ) accelerator, which accelerates the ions up to 03 MeV/u, an interdigital H-type (IH) structure with a final energy between 11 and 12 MeV/u and three seven gap resonators, which allow the variation of the final energy With an energy of the radioactive beams between 08 MeV/u and 22 MeV/u a wide range of experiments in the field of nuclear spectroscopy, astrophysics and solid state physics will be addressed by REX-ISOLDE

A virtual source model for Monte Carlo modeling of arbitrary intensity distributions.

Abstract: A photon virtual source model was developed for simulating arbitrary, external beam, intensity distributions using the Monte Carlo method The source model consists of a photon fluence grid composed of a matrix of square elements, located 25-cm downstream from the linear accelerator target Each particle originating from the fluence map is characterized by the seven phase space parameters, position (x, y, z), direction (u, v, w), and energy The map was reconstructed from fluence and energy spectra acquired by modeling components of the linear accelerator treatment head using the Monte Carlo code MCNP4B The effect of contaminant electrons is accounted for by the use of a sub-source derived from a phase-space simulation of a 25-MV linac treatment head using the code BEAM The BEAM sub-source was incorporated into the MCNP4B phase-space model and is sampled using a field-size dependent sampling ratio A Gaussian blurring kernel is convolved with the photon fluence map to account for the finite focal spot size and scattering effects from structures such as the flattening filter and MLC leaves Depth dose and profile source calculations for 6-MV and 25-MV photon beams, for 5 x 5 cm2, 10 x 10 cm2, and 15 x 15 cm2 field sizes, are in good agreement with measurement and are well within acceptability criteria suggested by the AAPM Task Group Report No 53 Irregular field calculations compared with film measurement and with a 3-D pencil beam algorithm show that the source model is capable of accurately simulating arbitrary MLC fields

Particle-in-cell modeling of plasma-based accelerators in two and three dimensions

Abstract: In this dissertation, a fully object-oriented, fully relativistic, multidimensional Particle-In-Cell code was developed and applied to answer key questions in plasma-based accelerator research. The simulations increase the understanding of the processes in laser plasma and beam-plasma interaction, allow for comparison with experiments, and motivate the development of theoretical models. The simulations support the idea that the injection of electrons in a plasma wave by using a transversely propagating laser pulse is possible. The beam parameters of the injected electrons found in the simulations compare reasonably with beams produced by conventional methods and therefore laser injection is an interesting concept for future plasma-based accelerators. Simulations of long laser pulses, such as the ones used in self- modulated laser wakefield acceleration, predict the existence of a hosing instability with a wavelength longer than the plasma wavelength. It is found that this effect might increase the emittance of electron beams produced by this acceleration method. Simulations of the optical guiding of a laser wakefield driver in a parabolic plasma channel support the idea that electrons can be accelerated over distances much longer than the Rayleigh length in a channel. Simulations of plasma wakefield acceleration in the nonlinear blowout regime give a detailed picture of the highly nonlinear processes involved. Using OSIRIS, we have also been able to perform full scale simulations of the E-157 experiment at the Stanford Linear Accelerator Center. These simulations have aided the experimentalists and they have assisted in the development of a theoretical model that is able to reproduce some important aspects of the full PIC simulations.

Backscatter towards the monitor ion chamber in high-energy photon and electron beams: charge integration versus Monte Carlo simulation.

Abstract: In some linear accelerators, the charge collected by the monitor ion chamber is partly caused by backscattered particles from accelerator components downstream from the chamber. This influences the output of the accelerator and also has to be taken into account when output factors are derived from Monte Carlo simulations. In this work, the contribution of backscattered particles to the monitor ion chamber response of a Varian 2100C linac was determined for photon beams (6, 10 MV) and for electron beams (6, 12, 20 MeV). The experimental procedure consisted of charge integration from the target in a photon beam or from the monitor ion chamber in electron beams. The Monte Carlo code EGS4/BEAM was used to study the contribution of backscattered particles to the dose deposited in the monitor ion chamber. Both measurements and simulations showed a linear increase in backscatter fraction with decreasing field size for photon and electron beams. For 6 MV and 10 MV photon beams, a 2-3% increase in backscatter was obtained for a 0.5×0.5 cm2 field compared to a 40×40 cm2 field. The results for the 6 MV beam were slightly higher than for the 10 MV beam. For electron beams (6, 12, 20 MeV), an increase of similar magnitude was obtained from measurements and simulations for 6 MeV electrons. For higher energy electron beams a smaller increase in backscatter fraction was found. The problem is of less importance for electron beams since large variations of field size for a single electron energy usually do not occur.

E-157: A 1.4-m-long plasma wake field acceleration experiment using a 30 GeV electron beam from the Stanford Linear Accelerator Center Linac

Abstract: In the E-157 experiment now being conducted at the Stanford Linear Accelerator Center, a 30 GeV electron beam of 2×1010 electrons in a 0.65-mm-long bunch is propagated through a 1.4-m-long lithium plasma of density up to 2×1014 e−/cm3. The initial beam density is greater than the plasma density, and the head of the bunch expels the plasma electrons leaving behind a uniform ion channel with transverse focusing fields of up to several thousand tesla per meter. The initial transverse beam size with σ=50–100 μm is larger than the matched size of 5 μm resulting in up to three beam envelope oscillations within the plasma. Time integrated optical transition radiation is used to study the transverse beam profile immediately before and after the plasma and to characterize the transverse beam dynamics as a function of plasma density. The head of the bunch deposits energy into plasma wakes, resulting in longitudinal accelerating fields which are witnessed by the tail of the same bunch. A time-resolved Cherenkov imag...

Observation of coherent Čerenkov radiation from a solid dielectric with short bunches of electrons

Abstract: Short bunches of 150-MeV electrons of a linear accelerator passed along the surface of a crystal quartz or a teflon and coherent Cerenkov radiation from the solid dielectrics has been observed in the wavelength range from 0.5 to 4 mm. Properties of the radiation have been experimentally investigated. The angular distribution of the observed radiation showed a maximum peak in the direction of the Cerenkov angle with several satellite peaks. The intensity increased linearly with increasing the length of the medium and was proportional to the square of the number of electrons in the bunch. The spectral intensity was enhanced by almost five orders of magnitude in comparison with the theoretical calculation of incoherent radiation.

Multiple-charge beam dynamics in an ion linac

Abstract: There is demand for the construction of a mediumenergy ion linear accelerator based on superconducting rf (SRF) technology. It must be capable of producing several hundred kilowatts of CW beams ranging from protons to uranium. A considerable amount of power is required in order to generate intense beams of rare isotopes for subsequent acceleration. At present, however, the beam power available for the heavier ions would be limited by ion source performance. To overcome this limit, we have studied the possibility of accelerating multiple-charge-state (multi-Q) beams through a linac. We show that such operation is made feasible by the large transverse and longitudinal acceptance which can be obtained in a linac using superconducting cavities. Multi-Q operation provides not only a substantial increase in beam current, but also enables the use of two strippers, thus reducing the size of linac required. Since the superconducting (SC) linac operates in CW mode, space charge effects are essentially eliminated except in the ECR/RFQ region. Therefore an effective emittance growth due to the multi-charge beam acceleration can be minimized.

Multiple-charge beam dynamics in an ion linac

Abstract: An advanced facility for the production of nuclei far from stability could be based on a high-power driver accelerator providing ion beams over the full mass range from protons to uranium. A beam power of several hundred kilowatts is highly desirable for this application. At present, however, the beam power available for the heavier ions would be limited by ion source capabilities. A simple and cost-effective method to enhance the available beam current would be to accelerate multiple charge states through a superconducting ion linac. This paper presents results of numerical simulation of multiple charge state beams through a 1.3 GeV ion linac, the design of which is based on current state-of-the-art superconducting elements. The dynamics of multiple charge state beams are detailed, including the effects of possible errors in rf field parameters and misalignments of transverse focusing elements. The results indicate that operation with multiple charge state beams is not only feasible but straightforward and can increase the beam current by a factor of 3 or more.

Transuranic waste detection by photon interrogation and on-line delayed neutron counting

Abstract: A comprehensive program is currently in progress at several laboratories for the development of sensitive, practical, non-destructive assay techniques for the quantification of low-level transuranics (TRUs) in bulk solid wastes. This paper describes the method being developed to assay high density TRU waste packages using photon interrogation. The system uses a pulsed electron beam from an electron linear accelerator to produce high-energy photon bursts from a metallic converter. The photons induce fissions in a TRU waste package which is inside an original neutron separating and counting cavity (NS2C). When fission is induced in trace amounts of TRU contaminants in waste material, it provides “signatures” from fission products that can be used to assay the material before disposal. We give here the results from counting photofission-induced delayed neutrons from 239Pu, 235U and 238U in sample matrices. We counted delayed neutrons emitted after each pulse of the LINAC by using the sequential photon interrogation and neutron counting signatures (SPHINCS) technique which had been developed in the present framework. The SPHINCS method enhances the available counts by a factor of about 20 compared with the counting of delayed neutrons only, after the irradiation period. Furthermore, the use of SPHINCS measurement technique coupled with the NS2C facility improves the signal-to-noise ratio by a factor of about 30. This decreases the detection limit. The electron linear accelerator operates at 15 MeV, 140 mA, and 2.5 μs wide pulse at a 50 and 6.25 Hz rate. The dynamics of photofission and delayed neutron production, NS2C advantages and performances, use of an electron linear accelerator as a particle source, experimental and electronics details, and future experimental works are discussed.

A highly flexible bunch compressor for the APS LEUTL FEL.

Abstract: The Low-Energy Undulator Test Line (LEUTL) freeelectron laser (FEL) [1] at the Advanced Photon Source (APS) has achieved gain at 530 nm with an electron beam current of about 100 A [2, 3]. In order to push to 120 nm and beyond, we have designed and are commissioning a bunch compressor using a four-dipole chicane at 100-210 MeV to increase the current to 600 A or more. To provide options for control of emittance growth due to coherent synchrotron radiation (CSR), the chicane has variable R56. The symmetry of the chicane is also variable via longitudinal motion of the final dipole, which is predicted to have an effect on emittance growth [4]. Following the chicane, a three-screen emittance measurement system should permit resolution of the difference in emittance growth between various chicane configurations. A vertical bending magnet analysis line will permit imaging of correlations between transverse and energy coordinates [5]. A companion paper discusses the physics design in detail [4]. 1 APS LINAC OVERVIEW The APS injector consists of a linac, an accumulator ring, and a 7-GeV booster synchrotron. In addition to delivering beam to the accumulator, the linac can be configured [6] to deliver beam to the LEUTL experiment hall [1]. The linac consists of 13 Stanford Linear Accelerator Center (SLAC) type accelerating sections powered by four klystrons, two thermionic rf guns (TRFG) [7, 8, 9] powered (one at a time) by a single klystron, and one photocathode gun (PCG) [10] powered by a single klystron. Figure 1 shows a schematic of the system and the location of the newly-installed bunch compressor. The original purpose of the linac was to create positron beams and deliver them to the accumulator ring for injection into the APS. The positron target was subsequently removed when the APS switched to electron operation. In both situations, the requirements on the linac were modest in terms of emittance, energy spread, bunch length, and stability. However, the requirements for reliability were and are very high, which was one reason for elimination of positron operation. The FEL project requires much higher beam quality and beam stability. The required beam quality is typically only achieved using a photocathode gun; however, the reliability of such guns (particularly the drive laser) is insufficient to act as an injector for the APS. The dual thermionic guns have a distinct advantage here, having proven themselves as components of the injector at SSRL Work supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38. [11]. The use of alpha magnets [7] for magnetic bunch compression in these guns allows the guns to be placed off-axis, leaving the on-axis position for the PCG. This is an important consideration in preserving the PCG beam brightness. 2 MAGNETIC BUNCH COMPRESSION The principle of magnetic bunch compression is wellknown, so we only review the basic idea here. In a magnetic chicane (see Figure 1) the path length traveled by a particle is s = so+R56 , where so is the central path length and = (p po)=po is the fractional momentum deviation. For simple chicanes, R56 < 0 so that high-energy particles take a shorter path. Phasing the beam ahead of the crest in the precompressor linac introduces an “energy chirp” into the beam, so that the tail of the beam has higher energy than the head. As a result, the tail will catch up to the head in the chicane, giving a shorter bunch. If the beam is undercompressed, then the energy spread imparted in the precompressor linac can be removed by phasing behind the crest in the postcompressor linac. It is possible to derive formulae for the phasing required to obtain a desired bunch length and minimized energy spread. However, accurate calculation requires including wakefield effects and depends on the detailed initial bunch shape. Hence, we used simulation to find the optimal values [4]. 3 LEUTL BEAM REQUIREMENTS The primary goal of the bunch compressor is to provide higher current beam to the LEUTL FEL. A secondary goal is characterization of CSR effects. The bunch compressor was designed with two LEUTL operating points in mind. These operating points, distinguished primarily by the beam current of 300 or 600 A, are summarized in Table 1. The requirements for charge and emittance are not difficult compared to the state-of-the-art for photoinjector systems. We hope that these parameters can be achieved repeatably and easily to provide for routine and stable operation. Because of the very non-Gaussian longitudinal phasespace distributions one typically sees in the compressor, we use the following definition for the beam current: I80 = 0:8 Qtotal t80 where Qtotal is the total charge in the beam and t80 is the length in time of the central 80% of the beam. The value of 80% was used because this includes most of the particles but typically excludes high-current spikes that tend to occur at the head and tail. Also, when we refer to XX International Linac Conference, Monterey, California

An Overview of the Spallation Neutron Source Project

Abstract: The Spallation Neutron Source (SNS) is being designed, constructed, installed and commissioned by the staff of six national laboratories, Argonne National Laboratory, Brookhaven National Laboratory, Jefferson National Accelerator Laboratory, Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, and Oak Ridge National Laboratory. The accelerator systems are designed to deliver a 695 ns proton-pulse onto a mercury target at a 60-Hz repetition rate and an average power of 2-MW. Neutron moderators that will convert the spallation neutrons into slow neutrons for material science research will surround the target. The Front-End systems are designed to generate an H- beam of minipulses, 68% beam on, 32% beam off every 965 ns, at 2.5 MeV for 1 ms, 60 times a second. The Front-End systems include a RF driven, volume-production ion source, beam chopping system, RFQ, and beam transport. The ion source will have to achieve about 65 mA to deliver 52 mA at the input to the linac. The linac consists of a drift tube linac up to 86.8 MeV, a coupled-cell linac to 185 MeV, and a superconducting RF linac to the nominal energy of 1 GeV. The design of the superconducting section includes 11 cryomodules with three, 0.61-beta cavities per cryomodule and 17 cryomodules with four, 0.81-beta cavities per cryomodule, with space to install four more 0.81-beta cryomodules. The accumulator ring is designed for charge exchange injection at full energy. The peak charge per bunch at the end of the accumulation cycle will reach 2.08x10**14 for 2-MW operation. The goal is to control beam losses to less than 1x10**-4.

Resolution and systematic limitations in beam-based alignment

Abstract: Beam based alignment of quadrupoles by variation of quadrupole strength is a widely-used technique in accelerators today. The authors describe the dominant systematic limitation of this technique, which arises from the change in the center position of the quadrupole as the strength is varied, and derive expressions for the resulting error. In addition, the authors derive an expression for the statistical resolution of such techniques in a periodic transport line, given knowledge of the line's transport matrices, the resolution of the beam position monitor system, and the details of the strength variation procedure. These results are applied to the Next Linear Collider main linear accelerator, an 11 kilometer accelerator containing 750 quadrupoles and 5,000 accelerator structures. The authors find that in principle a statistical resolution of 1 micron is easily achievable but the systematic error due to variation of the magnetic centers could be several times larger.

Monoenergetic Laser Wakefield Acceleration

Abstract: Three dimensional test particle simulations are applied to optimization of the plasma-channeled laser wakefield accelerator (LWFA) operating in a weakly nonlinear regime. Electron beam energy spread, emittance, and luminosity depend upon the proportion of the electron bunch size to the plasma wavelength. This proportion tends to improve with the laser wavelength increase. We simulate a prospective two-stage $\ensuremath{\sim}1\mathrm{GeV}$ LWFA with controlled energy spread and emittance. The input parameters correspond to realistic capabilities of the BNL Accelerator Test Facility that features a picosecond-terawatt ${\mathrm{CO}}_{2}$ laser and a high-brightness electron gun.

Beam test of gamma-ray large area space telescope components

Abstract: A beam test of Gamma-ray Large Area Space Telescope (GLAST) 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.

Estimates of emittance dilution and stability in high-energy linear accelerators

Abstract: In this paper, we present a series of analytic expressions to predict the beam dynamics in a long linear accelerator. These expressions can be used to model the linac optics, calculate the magnitude of the wakefields, estimate the emittance dilution due to misaligned accelerator components, and estimate the stability and jitter limitations. The analytic expressions are based on the results of simple physics models and are useful to understand the parameter sensitivities. They are also useful when using simple codes or spreadsheets to optimize a linac system.

A virtual linear accelerator for verification of treatment planning systems

Abstract: A virtual linear accelerator is implemented into a commercial pencil-beam-based treatment planning system (TPS) with the purpose of investigating the possibility of verifying the system using a Monte Carlo method. The characterization set for the TPS includes depth doses, profiles and output factors, which is generated by Monte Carlo simulations. The advantage of this method over conventional measurements is that variations in accelerator output are eliminated and more complicated geometries can be used to study the performance of a TPS. The difference between Monte Carlo simulated and TPS calculated profiles and depth doses in the characterization geometry is less than ±2% except for the build-up region. This is of the same order as previously reported results based on measurements. In an inhomogeneous, mediastinum-like case, the deviations between TPS and simulations are small in the unit-density regions. In low-density regions, the TPS overestimates the dose, and the overestimation increases with increasing energy from 3.5% for 6 MV to 9.5% for 18 MV. This result points out the widely known fact that the pencil beam concept does not handle changes in lateral electron transport, nor changes in scatter due to lateral inhomogeneities. It is concluded that verification of a pencil-beam-based TPS with a Monte Carlo based virtual accelerator is possible, which facilitates the verification procedure.

Microwave production by a free-electron laser bunched beam driving a resonant cavity at 35 GHz

Abstract: In the two-beam accelerator scheme, a high-current electron beam, bunched at the resonant frequency, traverses extraction cavities, where it generates power intended to drive accelerating cavities on the main beam. Here, we report on work performed to test some aspects of this scheme. We used a free-electron-laser (FEL) amplifier at 35 GHz to bunch a beam of electrons, which is then transported and focused into a resonant cavity. The results of earlier bunching experiments had demonstrated the capacity of the FEL supplied by an induction linac to generate an appropriate drive beam. A summary of this earlier work is presented along with measurements of power from the cavity. This constitutes the first observation of high-frequency power extraction using a FEL in this scheme.

The rare isotope accelerator (RIA) facility project

Abstract: The envisioned Rare-Isotope Accelerator (RIA) facility would add substantially to research opportunities for nuclear physics and astrophysics by combining increased intensities with a greatly expanded variety of high-quality rare-isotope beams A flexible superconducting driver linac would provide 100 kW, 400 MeV/nucleon beams of any stable isotope from hydrogen to uranium onto production targets Combinations of projectile fragmentation, target fragmentation, fission, and spallation would produce the needed broad assortment of short-lived secondary beams This paper describes the project's background, purpose, and status, the envisioned facility, and the key subsystem, the driver linac RIA's scientific purposes are to advance current theoretical models, reveal new manifestations of nuclear behavior, and probe the limits of nuclear existence [3] Figures 1 and 2 show, respectively, examples of RIA research opportunities and the yields projected for pursuing them Figure 3 outlines a conceptual approach for delivering the needed beams

Mechanisms and Control of Beam Halo Formation in Intense Microwave Sources and Accelerators

Abstract: Halo formation and control in space-charge-dominated electron and ion beams are investigated in parameter regimes relevant to the development of high-power microwave (HPM) sources and high-intensity electron and ion linear accelerators. In particular, a mechanism for electron beam halo formation is identified in high-power periodic permanent magnet (PPM) focusing klystron amplifiers. It is found in self-consistent simulations that large-amplitude current oscillations induce mismatched beam envelope oscillations and electron beam halo formation. Qualitative agreement is found between simulations and the 50 MW 11.4 GHz PPM focusing klystron experiment at Stanford Linear Accelerator Center (SLAC) (D. Sprehn, G. Caryotakis, E. Jongewaard, and R. M. Phillips, “Periodic permanent magnetic development for linear collider X-band klystrons,” Proceedings of the XIXth International Linac Conference, Argonne National Laboratory Report ANL-98/28, 1998, p. 689). Moreover, a new class of cold-fluid corkscrewing elliptic...

RF-chopper for the JHF proton linac

Abstract: An RF-chopper possesses merits in both its high deflecting field and compactness. For this reason, it is suitable for chopping a high-current beam in a medium-energy beam-transport line (MEBT) of an ion linear accelerator. The JHF linac, as a high-current H − accelerator with an average current of up to 0.2 mA or higher in the second phase, took these advantages of the RF-chopper in its design. Two RF-deflecting cavities as the chopper will be used in the MEBT just downward of the 3-MeV 324-MHz RFQ. A 324-MHz RF-chopper cavity has been designed with optimization for a fast rise/fall time, which is an essential requirement for the chopper in a high-current accelerator in order to avoid radioactivity induced by the lost particles due to insufficient chopping during the transient time. The rise time can be less than 8 ns by means of a pair of ports with large coupling loops. In this paper, the details concerning the R&D of the RF-chopper are presented. Some RF properties calculated with MAFIA and HFSS codes have been compared with the test results of a cold-model cavity, showing good agreement. To cut down on the required RF-power, two RF-deflecting cavities are connected with a coaxial line in the design. The simulation and measurement of the coupled system exhibit a quick rise time that is almost the same as that of an independent cavity. The designed RF-chopper will be used in the JHF linac, which is under construction.

TOUTATIS, the CEA Saclay RFQ code

Abstract: A CW high power linear accelerator can only work with very low particles losses and structure activation. At low energy, the RFQ is a very sensitive element to losses. To design the RFQ, a good understanding of the beam dynamics is requested. Generally, the reference code PARMTEQM is enough to design the accelerator. TOUTATIS has been written with goals of cross-checking results and obtaining a more reliable dynamics. This paper relates the different numerical methods used in the code. It is time-based, using multigrids methods and adaptive mesh for a fine description of the forces without being time consuming. The field is accurately calculated through a Poisson solver and the vanes are fully described, allowing to properly simulate the coupling gaps and RFQs extremities. Differences with PARMTEQM and LIDOS.RFQ are shown.

Toutatis, the Cea-Saclay RFQ code

Abstract: A CW high power linear accelerator can only work with very low particles losses and structure activation. At low energy, the RFQ is a very sensitive element to losses. To design the RFQ, a good understanding of the beam dynamics is requested. Generally, the reference code PARMTEQM is enough to design the accelerator. TOUTATIS has been written with goals of cross-checking results and obtaining a more reliable dynamics. This paper relates the different numerical methods used in the code. It is time-based, using multigrids methods and adaptive mesh for a fine description of the forces without being time consuming. The field is accurately calculated through a Poisson solver and the vanes are fully described, allowing to properly simulate the coupling gaps and RFQs extremities. Differences with PARMTEQM and LIDOS.RFQ are shown.

Single Pulse Damage in Copper

Abstract: The Next Linear Collider (NLC)[1] electron and positron beams are capable of damaging the linac accelerating structure and beamline vacuum chambers during a single accelerator pulse. Machine protection system (MPS) considerations have an impact on the engineering and design of most machine components downstream of the damping ring injector complex. Beam tests have been done at the SLAC Final Focus Test Beam (FFTB)[2] to examine the behavior of copper at and above the damage stress threshold. In this paper the authors present results of damage studies in copper as the beam pulse heating is varied from below melting to near vaporization. The goal of the tests was to determine allowable limits on beam size and intensity of a benign single bunch pilot beam to be used in testing linac systems. Typical expected pilot beam parameters (compared with nominal) are: 10 times reduced intensity, 10 times increased horizontal emittance and 1,000 times increased vertical emittance, resulting in a reduction in charge density of 10{sup 5}. The tests they report here used short (1 mm) beam pulses of between I = 3 x 10{sup 9} and 20 x 10{sup 9} electrons with transverse sizes sigma{sub xy} between 45 mu-m{sup 2} and 200more » mu-m{sup 2}.« less

The new high current ion accelerator at gsi and perspectives for linac design based on h-mode cavities

Abstract: In 1999 a new High Current Injector HSI was installed to replace the Wideroe section of the Unilac. Designed for a high mass-to-charge ratio A/q ≤ 65 it additonally provides high ion beam currents, e.g. U 4+ -ions up to 15 mA. The new linac has an RFQ section, which is 9.4 m long and uses mini-vanes inside an IH-cavity. It is followed by a 20 m IH drift-tube linac with the KONUS beam dynamics layout as used for instance for the CERN lead injector. This concept provides rf-acceleration within lens-free drift tube sections and at a strongly reduced defocusing action of the rf-fields. For the first time this concept was tested with high beam currents at a large tune depression of σ /σ 0 ~ 0.70. The application of H-mode cavities in the design of high-current proton and heavy ion linacs will be discussed on a more general base. For the energy range from 5 to 150 MeV, that is the first part of a high intensity proton machine behind the RFQ section, a new DTL concept based on Cross-Bar CH-cavities (H210-mode) is proposed. This CH structure can be designed for operation at about 350 MHz in the first section and at twice the frequency in the main section. CH-designs for room temperature and for superconducting operation will be discussed, as well as a 45 MeV, 100 mA proton linac design with a total length of 8.5 m.

Experimental results and technical research and development at ctf ii

Abstract: The second phase of the Compact Linear Collider Test Facility (CTF II) has demonstrated the feasibility of two key ingredients of the Compact Linear Collider scheme (CLIC) [1], namely the acceleration with a 30 GHz normal conducting linac and the 30 GHz RF power production by a tightly-bunched, high-charge drive beam running parallel to the main beam. This beam is produced and accelerated with a 3 GHz linac using an RF-photoinjector and two travelling-wave sections, all specially developed for handling very high charges. A magnetic chicane compresses the micro-bunches to their nominal length. A mm-wave spectrometer, coupled to the beam pipe, allows non-destructive measurements of bunch length. So far a total acceleration of 60 MeV has been obtained using a string of five accelerating structures with a total active length of 1.4 m. The corresponding drivebeam deceleration is 6 MeV. The flexibility and extensive beam instrumentation allows a variety of other experiments, such as measurements of emittance growth and energy loss in bunch compressors due to coherent synchrotron radiation, high-gradient tests in single-cell 30 GHz cavities, high-power tests of a planar 30 GHz RF structure and tests of beam position monitor prototypes.

LEDA beam diagnostics instrumentation: Measurement comparisons and operational experience

Abstract: The Low Energy Demonstration Accelerator (LEDA) facility has been used to characterize the pulsed- and cw-beam performance of a 6.7 MeV, 100 mA radio frequency quadrupole (RFQ). Diagnostic instrumentation, primarily located in a short beam transport downstream of the RFQ, allow facility commissioners and operators to measure and monitor the RFQ’s accelerated and total beam transmission, beam loss, bunched beam current, beam energy and output phase, and beam position. Transverse beam profile measurements are acquired under both low and high duty-factor pulsed beam conditions using a slow wire scanner and a camera that images beam-induced fluorescence. The wire scanner is also used to acquire transverse beam emittance information using a technique known as a “quad scan”. This paper reviews the measurement performance and discusses the resulting data.

High Energy X-Ray Computed Tomography for Industrial Applications

Abstract: A high energy industrial X-ray computed tomography system using silicon semiconductor detectors (Si-SSD) and electron linear accelerator (LINAC) was developed to obtain high resolution 3D images of high density and large scale object. To increase photon sensitivity, detector elements were placed parallel to the X-ray beams. The obtained sensitivity of 20% for X-ray of 3MeV was 3×104 times higher than that of X-ray films. It was clarified that the photon sensitivity of X-ray detectors restricts the performance of high energy X-ray CT, and it is shown that a CT image of 200mm thick iron object can be obtained with 0.2mm space resolution.

Beam emittance measurements for the low-energy demonstration accelerator (LEDA) radio-frequency quadrupole (RFQ)

Abstract: The Low-Energy Demonstration Accelerator (LEDA) radio-frequency quadrupole (RFQ) is a 100% duty factor (CW) linac that delivers >100 mA of H beam at 6.7 MeV. The 8-m-long, 350-MHz RFQ structure accelerates a dc, 75-keV, 110-mA H beam from the LEDA injector with >90% transmission. LEDA [1,2] consists of a 75-keV proton injector, 6.7-MeV, 350-MHz CW RFQ with associated high-power and low-level rf systems, a short high-energy beam transport (HEBT) and high-power (670-kW CW) beam stop. The beam emittance is inferred from wire scanner measurements of the beam profile at a single location in the HEBT. The beam profile is measured as a function of the magnetic field gradient in one of the HEBT quadrupoles. As the gradient is changed the spot size passes through a transverse waist. Measurements are presented for peak currents between 25 and 100 mA.