Showing papers on "Linear particle accelerator published in 1991"

Deep inelastic scattering: The early years

Abstract: The 1990 Nobel Prize for Physics lecture is reprinted. The author discusses the early research at the High Energy Physics Laboratory at Stanford in the 1950's and the building of the Stanford Linear Accelerator Center in the 1960's. (AIP)

Radiosurgery with unflattened 6-MV photon beams

Abstract: One of the major drawbacks to doing stereotactic radiosurgery with a linear accelerator is the long time required to deliver the target dose. Single fractions of 25 Gy delivered at the isocenter and at depth in the skull may require beam times in excess of 15 min for a typical linear accelerator with a maximum dose rate of 250 cGy/min in tissue. In an effort to decrease the treatment time for this technique, the flattening filter has been removed from an AECL Therac-6 linear accelerator and the characteristics of the resulting beam have been measured. Flatness is acceptable for the field sizes used with this technique and the dose rate is increased by a factor of 2.75.

A dispersion-free trajectory correction technique for linear colliders☆

Abstract: In this paper, we describe a new trajectory correction technique for high energy linear accelerators. Current correction techniques force the beam trajectory to follow misalignments of the beam position monitors (BPMs). Since the particle bunch has a finite energy spread and particles with different energies are deflected differently, this causes “chromatic” dilution of the transverse beam emittance. The algorithm which we describe in this paper reduces the chromatic dilution by minimizing the energy dependence of the trajectory. To test the method we compare the effectiveness of our algorithm with a standard correction technique in simulations of the Stanford Linear Collider (SLC) linear accelerator and a design linac for a Next Linear Collider (NLC). While the simulations do not indicate that chromatic dilutions are a serious problem in the SLC linac, they would be debilitating in a future linear collider because of the very small beam sizes required to achieve the necessary luminosity. For example, in simulations of the NLC we have found that with typical alignment tolerances the beam size increased substantially after correcting the trajectory with a standard correction algorithm. In contrast, after correcting with our technique, the dilution was negligible. We feel that this technique will prove essential for future linear colliders.

A prototype beam delivery system for the proton medical accelerator at Loma Linda

Abstract: A variable energy proton accelerator was commissioned at Fermi National Accelerator Laboratory for use in cancer treatment at the Loma Linda University Medical Center. The advantages of precise dose localization by proton therapy, while sparing nearby healthy tissue, are well documented [R. R. Wilson, Radiology 47, 487 (1946); M. Wagner, Med. Phys. 9, 749 (1982); M. Goitein and F. Chen, Med. Phys. 10, 831 (1983)]. One of the components of the proton therapy facility is a beam delivery system capable of delivering precise dose distributions to the target volume in the patient. To this end, a prototype beam delivery system was tested during the accelerator's commissioning period. The beam delivery system consisted of a beam spreading device to produce a large, uniform field, a range modulator to generate a spread out Bragg peak (SOBP), and various beam detectors to measure intensity, beam centering, and dose distributions. The beam delivery system provided a uniform proton dose distribution in a cylindrical volume of 20-cm-diam area and 9-cm depth. The dose variations throughout the target volume were found to be less than +/- 5%. Modifications in the range modulator should reduce this considerably. The central axis dose rate in the region of the SOBP was found to be 0.4 cGy/spill with an incident beam intensity of 6.7 x 10(9) protons/spill. With an accelerator repetition rate of 30 spills/min and expected intensity of 2.5 x 10(10) protons/spill for patient treatment, this system can provide 50 cGy/min for a 20-cm-diam field and 9-cm range modulation.(ABSTRACT TRUNCATED AT 250 WORDS)

High energy X-ray computed tomography for industrial applications

Abstract: A high-energy X-ray computed tomography system with an electron linear accelerator was developed to image cross-sections of large-scale and high-density materials. An electron linear accelerator is used for the X-ray source. The maximum X-ray energy is 12 MeV and the average energy is around 4 MeV. The intensity of an X-ray fan beam passing through the test object is measured by a 15-channel detector array. CWO (CdWO/sub 4/) scintillators and photodiodes are employed for the X-ray detectors. The crosstalk noise due to scattering at X-ray photons by adjacent detectors is reduced to less than 1.6% by installing a tungsten shield between the scintillators. Extra channels are used to compensate for the baseline shift of the circuits. These techniques allowed attainment of a dynamic range of more than 85 dB and a noise level comparable to the signal amplitude of X-ray transmitted in a 420 mm-thick iron block. A spatial resolution of 0.8 mm was confirmed with an iron test piece 200 mm in diameter. >

Wire scanners for beam size and emittance measurements at the SLC

Abstract: The authors describe the design, construction, commissioning and ultimate uses of wire scanners in the SLC (SLAC Linear Collider), focusing on the linear accelerator and upstream systems scanners. Of particular interest is the interaction between the wire and the scattered radiation from the wire with the extreme electric field of the beam. As this field reaches the level of several volts/angstrom, as it does easily at the SLC interaction point (and may in upstream parts of SLC), field emission from the wire may occur. A key feature of SLC operation is the degree of high level active control required to keep it optimized. Advanced high level control software allows the use of wire scanner data in feedback and beam optimization procedures. Non-invasive scans are performed almost continually and the results are logged so that long term trends in emittance can be examined. >

Sabre, A 10-mv Linear Induction Accelerator

Abstract: SABRE (Sandia Accelerator and Beam Research Experiment) is a 10-MV, 250-kA, 40-ns linear induction accelerator It was designed to be used in positive polarity output Positive polarity accelerators are important for application to Sandia's ICF (Inertial Confinement Fusion) and LMF (Laboratory Microfusion Facility) program efforts SABRE was built to allow a more detailed study of pulsed power issues associated, with positive polarity output machines, MITL (Magnetically Insulated Transmission Line) voltage adder efficiency, extraction ion diode development, and ion beam transport and focusing The SABRE design allows the system to operate in either positive polarity output for ion extraction applications or negative polarity output for more conventional electron beam loads Details of the design of SABRE and the results of initial machine performance in negative polarity operation are presented in this paper

Radiosurgery with a linear accelerator. Methodological aspects.

Abstract: Based on the concepts of Leksell and on recommendations of different Swedish physicists on the use of linear accelerator for radiosurgical use, we developed a new methodology coupling the Talairach stereotactic system with a commercial linac. Anatomical facts encouraged us to use coronal angles of irradiation employing the angular displacement of the linac above the horizontal plane. Different coronal planes are obtained by rotation of the stereotactic frame. The center of the irradiated target coincides with the irradiation and rotation center of the linear accelerator. Multiple targets can be irradiated in the same session. We use as recommended a secondary collimator in heavy alloy. Special software was prepared after different dosimetric controls. The use of a PC allows us to employ 1-6 targets and different collimators to displace the isocenters in order to obtain geometrical isodose modification, and to change the value of each irradiation arc or portions of each arc in some minutes. Simple or sophisticated neurosurgical strategies can be applied in the treatment of frequently irregular shape and volume AVMs.

Use of a FEL as a buncher for a TBA scheme

Abstract: The CERN linear collider (CLIC) [W. Schnell, Proc. Workshop on Physics of Linear Colliders, Capri, 1988, eds. l. Palumbo, S. Tazzari and V.G. Vaccaro (1989) p. 345] is a two-beam-accelerator (TBA) scheme in which the driving beam consists of an intense 3 to 5 GeV electron beam bunched at 30 GHz. One possible way to produce this drive beam is to start with a low-energy (or order 10 MeV), high-current (about 5 kA) beam from an induction linac. In passing through a wiggler, this beam is bunched at 30 GHz into micropulses, each with about 10 12 electrons. To construct the format required for the CLIC drive beam, the bunched beam is subsequently chopped at 350 MHz. It is then accelerated to 3 to 5 GeV in an rf linac driven by conventional, low-frequency klystrons. Rf power is extracted at the bunch frequency of 30 GHz and fed into high-gradient structures to accelerate electron or positron beams to TeV energies. The drive beam is repeatedly reaccelerated in 350 MHz superconducting cavities. This study examines the design trade-offs of the proposed “front end” of the CLIC TBA, the linear induction accelerator and FEL. We examine the relevant figure of merit, the efficiency of bunching, as a function of beam energy, current, and emittance, and we consider the effects of wiggler errors, energy spread and slew, and beam misalignment.

Design and analysis of experimental performance of the Los Alamos HIBAF facility accelerator using the INEX computer model

Abstract: The authors review the accelerator design of the high brightness accelerator free electron laser (FEL) (HIBAF) at Los Alamos National laboratory and analyze its performance. HIBAF is the first high-brightness high-current (several hundred amperes) accelerator build using a photoelectric injector. The authors discuss the design philosophy and the integrated numerical experiment (INEX) design tool, and describe the accelerator components. Currently, the machine has only been operated at intermediate energies near 15 MeV. The INEX computer code package is used to examine the accelerator performance by comparing the measurements with simulations at that energy. The accelerator should be able to reach the design goal of 300 A current with the normalized 90% transverse emittance of less than 50 pi mm mrad for a 5-nC bunch after reaching the final energy of 40 MeV. >

SLC positron source pulsed flux concentrator

Abstract: SLC (SLAC Linear Collider) positron beams produced by a very high energy electron beam, impinging on a high Z target, have initially small transverse size but large divergence, a situation ill matched to the following S-band accelerator. The flux concentrator is an adiabatic matching device placed between the target and this accelerator, which trades divergence for size. It produces a magnetic field which rises sharply over less than 5 mm to its peak value, and then falls off adiabatically over 10 cm. It is a 12-turn, 10-cm-long copper coil with a cylindrical outside radius of 4 cm and a conical inside radius growing from 3.5 mm to 2.6 cm. The 0.2-mm gaps between the individual windings were manufactured by electric discharge machining out of one copper block. Excitation current and water cooling are provided by a hollow rectangular conductor brazed to the outside of the coil (also 12 turns). >

Measurements of reduced corkscrew motion on the ETA-II linear induction accelerator

Abstract: The ETA-II linear induction accelerator is used to drive a microwave free-electron laser (FEL). Corkscrew motion, which previously limited performance, has been reduced by: (1) an improved pulse distribution system which reduces energy sweep, (2) improved magnetic alignment achieved with a stretched wire alignment technique (SWAT), and (3) a unique magnetic tuning algorithm. Experiments have been carried out on a 20-cell version of ETA-II operating at 1500 A and 2.7 MeV. The measured transverse beam motion is less than 0.5 mm for 40 ns of the pulse, an improvement of a factor of 2 to 3 over previous results. Details of the computerized tuning procedure, estimates of the corkscrew phase, and relevance of these results to future FEL experiments are presented. >

Cell design for the DARHT linear induction accelerators

Abstract: The dual-axis radiographic hydrotest facility at Los Alamos National Laboratory will employ two linear induction accelerators to produce intense, bremsstrahlung X-ray pulses for flash radiography. The accelerator cell design for a 3-kA, 16-20-MeV, 60-ns flattop, high-brightness electron beam is presented. The cell is optimized for high-voltage stand-off while also minimizing the transverse impedance. Measurements of high-voltage RF characteristics are summarized. >

CLIA - A Compact Linear Induction Accelerator System

Abstract: CLIA (Compact Linear Induction Accelerator) is a 750-kV, 10-kA, 60-ns, 100-Hz driver in use at Physics International Company. The design and operational characteristics of the accelerator will be described in this paper. The CLIA system consists of a ten-cell accelerator with a cathode stalk to sum the voltage up to a single diode load, ten magnetically switched water insulated PFLs, a single two-stage magnetic compression unit (MCU) to charge the PFLs, and thyratron switched intermediate energy store (IES) and command resonant charge (CRC) units to drive the MCU. A linear induction accelerator system permits all pulse compression to be done at moderate voltage (40 to 150 kV) and then uses the accelerator structure to add parallel voltage pulses into a single high voltage output (750 W). This technique allows the switching to be done at moderate voltage and also makes the use of hydrogen thyratrons and magnetic switches possible.

Spectra from multiphoton electron detachment of H

Abstract: New data are reported on the multiphoton detachment process in a fast beam of H− ions. The angle-tuned relativistic Doppler shift is used to vary the photon energy of a focused (~10 GW/cm2) 10.6-μm CO2 laser beam from ~0.05 to ~0.4 eV in the rest frame (CM frame) of the fast ions. The ions are produced at 800 MeV (β = v/c = 0.84) by the Los Alamos Meson Physics Facility linear accelerator at Los Alamos and experience ~1-psec pulses in the CM frame as they cross the laser beam focus. Peaks in the detachment signal corresponding to each order for two- to six-photon processes are observed. At modest laser intensity in the gigawatt-per-square-centimeter range, observed shifts of the apparent two-photon threshold are found to be not more than 30–50% of the expected maximum shift, based on the value of the ponderomotive potential. Experimental uncertainties are due mainly to imprecise knowledge of the maximum laser intensity. The data analysis and modeling of the expected threshold shape experiments are continuing.

100 MW klystron development at SLAC

Abstract: A klystron designed to operate at 114 GHz and 440 kV is presently Stanford Linear Accelerator Center's (SLAC's) strongest RF power source candidate for the Next Linear Collider It is expected to provide 100 MW of RF power with a pulse width of 1 mu s The authors describe progress in the development of this device including results from single- and double-gap output cavities and various styles of RF output windows The design parameters for this klystron are shown Three X-band klystrons have been designed to test various alternatives to RF windows, output cavities, and beam optics At this time 72-MW RF power has been generated with a pulse width of 100 ns and 35 MW has been generated at 800 ns >

Parametric approach to linear induction accelerator design

Abstract: A parametric approach to defining effective accelerator designs is described. This method uses a computer optimization routine to iteratively seek out effective designs. The optimization routine is forced to search within a parameter space restricted to interesting and realistic parameters such as size, weight, voltage, and temperature rises. A filament model is used as the filter for the optimizer. Several linear induction accelerators have been designed using this method. The designed accelerators all used a switched capacitor power supply. While the run time of this code is moderately long, the resulting designs have good predicted performance. With realistic power supplies and materials, accelerator efficiencies in the 20 and 40% range were obtained. The effect of armature diameter, length-to-diameter ratio, and weight (as well as other parameters) on the optimum accelerator designed are described. >

Shielded coherent synchrotron radiation and its possible effect in the Next Linear collider

Abstract: Shielded coherent synchrotron radiation is discussed for two cases: (1) a beam following a curved path in a plane midway between two parallel, perfectly conducting plates, and (2) a beam circulating in a toroidal chamber with resistive walls. Wake fields and the radiated energy are computed with parameters for the high-energy bunch compressor of the Next Linear Collider (NLC). >

Thermalization of accelerator-produced neutrons in a concrete room.

Abstract: We investigated a thermalization of neutrons, which were produced by an accelerator in a concrete room, by experiments and calculations. It was clarified that the widely used simple empirical formula phi th = c x Q/S, where Q is the neutron source intensity and S is the total surface area of a room, gives about one-third the underestimated value to our experimental and calculated results and the coefficient, c, is not a constant, but dependent on the source neutron energy.

The Fermilab Linac Upgrade

Abstract: The Fermilab Linac Upgrade is planned to increase the energy of the H- linac from 200 to 400 MeV. This is intended to reduce the incoherent space-charge tuneshift at injection into the 8 GeV Booster which can limit either the brightness or the total intensity of the beam. The Linac Upgrade will be achieved by replacing the last four 201.25 MHz drift-tube tanks which accelerate the beam from 116 to 200 MeV, with seven 805 MHz side-coupled cavity modules operating at an average axial field of abut 7.5 MV/m. This will allow acceleration to 400 MeV in the existing Linac enclosure. Each accelerator module will be driven with a klystron-based rf power supply. A prototype rf modulator has been built and tested at Fermilab, and a prototype 12 MW klystron is being fabricated by Litton Electron Devices. Fabrication of production accelerator modules is in progress. 8 figs., 4 tabs.

Prompt bunch by bunch synchrotron oscillation detection via a fast phase measurement

Abstract: An electronic system which detects synchrotron oscillations of individual bunches with 4-ns separation is presented. The system design and performance are motivated by the requirements of the proposed B factory facility at SLAC (Stanford Linear Accelerator Center). Laboratory results show that the prototype is capable of measuring individual bunch phases with better than 0.5 degree resolution at the 476-MHz RF frequency. >

Electron linear accelerator based on Vp x B acceleration scheme

Abstract: A new type of electron linear accelerator realized in a vacuum system, based on the {bold V}{sub {ital p}}{times}{bold B} acceleration scheme observed originally in plasma, has been demonstrated. The present system has a static magnetic field applied vertically to the wave propagation direction, and the particles are accelerated along the wave front at constant phase with respect to the wave. In this scheme, a greater acceleration rate than that of conventional linear accelerators has been observed. The acceleration rate is also larger than that expected from the simple theoretical model presented so far.

Performance of the photoinjector accelerator for the Los Alamos free-electron laser

Abstract: The Los Alamos free-electron laser (FEL) facility has been modified by the replacement of the thermionic electron gun and bunchers with a 1300-MHz RF photoinjector. Two more accelerator tanks have been added to increase the beam energy to 40 MeV. Preliminary studies at 15 MeV have demonstrated excellent beam quality with a normalized emittance of 40 pi mm-mrad. The beam quality is sufficient to allow harmonic lasing in the visible. FEL experiments have been begun at a wavelength near 3 mu m. A report is presented of the performance of the photoinjector accelerator. >

The 3 GeV synchrotron injector for SPEAR

Abstract: A dedicated 3-GeV injector synchrotron for the storage ring SPEAR has been constructed at the Stanford Synchrotron Radiation Laboratory, SSRL. The injector consists of an RF-gun, a 120-MeV linear accelerator, a 3-GeV booster synchrotron, and associated beam transport lines. General design features and special new developments for this injector are presented, together with operational performance. >

Accelerator and feedback control simulation using neural networks

Abstract: Neural networks can adapt as the dynamics of a process changes with time. Using a process model, the accelerator network is first trained to simulate the dynamics of the beam for a given beam line. This accelerator network is then used to train a second controller network which performs the control function. In simulation, the networks are used to adjust corrector magnets to control the launch angle and position of the beam to keep it on the desired trajectory when the incoming beam is perturbed. >

Dispersion and betatron matching into the linac

Abstract: In high-energy linear colliders, the low-emittance beam from a damping ring has to be preserved all the way to the linear accelerator (LINAC), in the LINAC and to the interaction point. In particular, the ring-to-LINAC (RTL) section of the SLAC Linear Collider (SLC) should provide an exact betatron and dispersion match from the damping ring to the LINAC. A beam with a nonzero dispersion shows up immediately as an increased emittance, while with a betatron mismatch the beam forms filaments in the LINAC. Experimental tests and tuning procedures have shown that the linearized beta matching algorithms are insufficient if the actual transport line has some unknown errors not included in the model. Also, adjusting quadrupole strengths steers the beam if it is offset in the quadrupole magnets. These and other effects have led to a lengthy tuning process, which in the end improves the matching, but is not optimal. Different ideas are discussed to improve this matching procedure and make it a more reliable, faster, and simpler process. >

An electron-proton collider in the TeV range

Abstract: In ep colliding beam measurements, approximate equality of electron and quark energies is desirable for good detection efficiency. In the TeV CM energy regime, synchrotron radiation makes this requirement very expensive to meet using a storage ring for the electrons. A scheme is outlined that ameliorates this problem by using a superconducting linac for electron acceleration. Parameter lists show that such an approach may be practical for next-generation ep colliders beyond HERA (Hadron Electron Ring Accelerator). An example of a 300-GeV electron beam colliding with the HERA p ring is shown. Examples up to square root s=12 TeV are given. >

Hospital-based proton linear accelerator for particle therapy and radioisotope production

Abstract: Taking advantage of recent advances in linear accelerator technology, it is possible for a hospital to use a 70 MeV proton linac for fast neutron therapy, boron neutron capture therapy, proton therapy for ocular melanomas, and production of radiopharmaceuticals. The linac can also inject protons into a synchrotron for proton therapy of deep-seated tumors. With 180 μA average current, a single linac can support all these applications. This paper presents a conceptual design for a medical proton linac, switchyard, treatment rooms, and isotope production rooms. Special requirements for each application are outlined and a layout for sharing beam among the applications is suggested.

Progress on the development of APS beam position monitoring system

Abstract: The authors describe the development status of the beam position monitoring system for the Advanced Photon Source (APS). The accelerator complex will consist of an electron linac, a positron linac, a positron accumulator ring (PAR), an injector synchrotron, and a storage ring. For beam position measurement, striplines will be used on the injector synchrotron and the storage ring. A test stand with a prototype injector synchrotron beam position monitor (BPM) unit has been built, and the results of position calibration measurements using a wire are presented here. The results are compared with theoretical calculations. The current effort on similar storage ring BPM system measurements is also discussed. Calibration of the APS injector synchrotron BPM pickups is complete, and results agree well with theory. >