Showing papers on "Linear particle accelerator published in 1980"

Variable field coupled cavity resonator circuit

Abstract: In a resonant chain of coupled cavities such as used in a standing-wave linear particle accelerator it is often desirable to change the field strength in some cavities relative to some others. For example, if the output particle energy of an accelerator is changed by varying the fields of all cavities, the distribution of energies of output particles is disturbed. This distribution is largely controlled by the fields in the first group of cavities traversed by the particle beam. According to the invention, the fields can remain constant in the first group and be varied in following cavities. This is done by varying the distribution of electromagnetic field in one cavity asymmetrically with respect to the preceding and the following cavity. The asymmetric coupling produces different acceleration fields in one part of acceleration structure relative to another part. In an accelerator whose accelerating cavities are coupled via non-interacting side cavities, the different coupling may be produced by making the standing-wave field in one side-cavity asymmetric with respect to its coupling irises.

Off-axis beam quality change in linear accelerator x-ray beams

Abstract: The effective energy of the x-ray beam from linear accelerators changes as a function of the position in the beam due to nonuniform filtration by the flattening filter. In this work, the transmittance through a water column was measured in good geometry and the beam quality characterized in units of HVL in water. Measurements were made on a variety of linear accelerators from 4 to 10 MV. The beam energy decreased with increasing distance from the central ray for all accelerators measured.

Accelerator side cavity coupling adjustment

Abstract: In a standing-wave coupled-cavity linear particle accelerator the energy of the emergent particles can be adjusted by making the accelerating fields in one section of the accelerator different from those in another section into which the rf drive power is introduced. To do this the adjoining end cavities of the two sections are coupled through a "side" cavity which is not traversed by the particle beam. The coupling coefficients of the side cavity to the two accelerating cavities are made unequal to create the difference in accelerating cavity fields. Asymmetrical coupling is realized by varying the extension of center conductor posts into the side cavity by means of a vacuum sealed mechanism for moving the center posts while maintaining microwave current connection between the center posts and the side cavity.

Energy interlock system for a linear accelerator

Abstract: The energy interlock system contains a measuring device, a discriminator and a switch. The measuring device determines the level of the particle beam pulses which are emitted by the accelerator. For this purpose it contains a target which is exposed to the particle beam pulses. The discriminator determines whether the level of the particle pulses has crossed a predetermined value. The switch is operated by the discriminator. It is connected for supervision of the accelerator.

Helios: The new harwell electron linear accelerator, and its scientific programme

Abstract: HELIOS, the new 136 MeV electron linear accelerator (LINAC) opened in July 1979, will enable the area of nuclear physics that is of main relevance to the development of nuclear power to be studied at new levels of understanding. This article traces the history and describes the purpose of the accelerator.

Wobbling device for a charged particle accelerator

Abstract: A charged particle accelerator has an accelerator chamber in the interior of which a narrow beam of charged particles is accelerated. The particle beam is directed to a discharge window for discharging the particles therethrough. A device is provided for wobbling the beam of particles before the particles strike the discharge window, thereby enlarging the area where the particles strike the window. Preferably a magnetic wobbling device may be used. Such a device may have one or more magnetic coils which is/are arranged near the discharge window and which receive(s) a varying electric current. The accelerator may be a linear accelerator generating high energy electrons or X-rays for medical treatment.

X-ray beam characteristics of the Varian Clinac 6-100 linear accelerator

Abstract: Beam characteristics and dosimetry measurements of the 6 MV x-ray beam from a Varian Associates Clinac 6-100 linear accelerator are presented. Percentage depth dose tables are given as a function of field size for square fields. Tissue-maximum ratios and scatter-maximum ratios are tabulated as a function of depth and field size. Investigation of surface dose and depth of maximum dose reveal a dependence on field size. Other beam parameters measured are presented include field flatness, symmetry, SSD dependence, and penumbra. Treatment planning parameters including field size output factors and wedge factors are discussed.

Means and method for the focusing and acceleration of parallel beams of charged particles

Abstract: A novel apparatus and method for focussing beams of charged particles comprising planar arrays of electrostatic quadrupoles. The quadrupole arrays may comprise electrodes which are shared by two or more quadrupoles. Such quadrupole arrays are particularly adapted to providing strong focussing forces for high current, high brightness, beams of charged particles, said beams further comprising a plurality of parallel beams, or beamlets, each such beamlet being focussed by one quadrupole of the array. Such arrays may be incorporated in various devices wherein beams of charged particles are accelerated or transported, such as linear accelerators, klystron tubes, beam transport lines, etc.

Calculative technique to correct for the change in linear accelerator beam energy at off-axis points.

Abstract: The change in energy of linear accelerator x-ray beams from the central ray to off-axis points causes errors in the dose calculated by conventional techniques for large, irregularly shaped fields. A modification of conventional calculative methods to correct for the change in beam energy is presented. The results of measurements in irregular fields on a Clinac-4 are reported which verify the validity of the calculative method. A discussion of the clinical significance will point out errors of 3% to 4% in conventional dose calculations.

The Radio-Frequency Quadrupole: General Properties and Specific Applications

Abstract: The radio-frequency quadrupole (RFQ) linac structure is being developed for the acceleration of low-velocity ions. Recent experimental tests have confirmed its expected performance and have led to an increased interest in a wide range of possible applications. We review the general properties of RFQ accelerators and present beam dynamics simulation results for their use in a variety of accelerating systems. These include the low-beta sections of the Fusion Materials Irradiation Test Accelerator, a 200-MHz proton linear accelerator, and a xenon accelerator for heavy ion fusion.

Review of accelerator instrumentation

Abstract: Some of the problems associated with the monitoring of accelerator beams, particularly storage rings' beams, are reviewed along with their most common solutions. The various electrode structures used for the measurement of beam current, beam position, and the detection of the bunches' transverse oscillations, yield pulses with sub-nanosecond widths. The electronics for the processing of these short pulses involves wide band techniques and circuits usually not readily available from industry or the integrated circuit market: passive or active, successive integrations, linear gating, sample-and-hold circuits with nanosecond acquisition time, etc. This report also presents the work performed recently for monitoring the ultrashort beams of colliding linear accelerators or single-pass colliders. To minimize the beam emittance, the beam position must be measured with a high resolution, and digitized on a pulse-to-pulse basis. Experimental results obtained with the Stanford two-mile Linac single bunches are included.

A Review of Accelerator Instrumentation

Abstract: Some of the problems associated with the monitoring of accelerator beams, particularly storage rings’ beams, are reviewed along with their most common solutions. The various electrode structures used for the measurement of beam current, beam position, and the detection of the bunches’ transverse oscillations, yield pulses with sub-nanosecond widths. The electronics for the processing of these short pulses involves wide band techniques and circuits usually not readily available from industry or the integrated circuit market: Passive or active, successive integrations, linear gating, sample-and-hold circuits with nanosecond acquisition time, etc. This report also presents the work performed recently for monitoring the ultrashort beams of colliding linear accelerators or single-pass colliders. To minimize the beam emittance, the beam position must be measured with a high resolution, and digitized on a pulse-to-pulse basis. Experimental results obtained with the Stanford two-mile Linac single bunches are included.

rf quadrupole linac: a new low-energy accelerator

Abstract: A new concept in low-energy particle accelerators, the radio-frequency quadrupole (RFQ) linac, is currently being developed at the Los Alamos National Scientific Laboratory. In this new linear accelerating structure both the focusing and accelerating forces are produced by the rf fields. It can accept a high-current, low-velocity dc ion beam and bunch it with a high capture efficiency. The performance of this structure as a low-energy linear accelerator has been verified with the successful construction of a proton RFQ linac. This test structure has accelerated 38 mA of protons from 100 keV to 640 keV in 1.1 meters with a capture efficiency greater than 80%. In this paper a general description of the RFQ linac and an outline of the basic RFQ linac design procedure are presented in addition to the experimental results from the test accelerator. Finally, several applications of this new accelerator are discussed.

Transverse Wake Field Effects on Intense Bunches with Application to the SLAC Linear Collider

Abstract: The theory of transverse beam break-up is summarized and briefly discussed in this paper. It is then applied to the SLAC linear accelerator to give the various design tolerances for beam injection and alignment of accelerator components for the linear collider operation.

The SLAC Linear Collider

Abstract: The SLAC LINEAR COLLIDER is designed to achieve an energy of 100 GeV in the electron-positron center-of-mass system by accelerating intense bunches of particles in the SLAC linac and transporting the electron and positron bunches in a special magnet system to a point where they are focused to a radius of about 2 microns and made to collide head on. We discuss the rationale for this new type of colliding beam system, describe the project, discuss some of the novel accelerator physics issues involved, and briefly describe some of the critical technical components.

NBS-LASL cw microtron

Abstract: The NBS-LASL racetrack microtron (RIM) is a joint research project of the National Bureau of Standards and the Los Alamos Scientific Laboratory. The project goals are to determine the feasibility of, and develop the necessary technology for building high-energy, high-current, continuous-beam (cw) electron accelerators using beam recirculation and room-temperature rf accelerating structures. To achieve these goals, a demonstration accelerator will be designed, constructed, and tested. Parameters of the demonstration RIM are: injection energy - 5 MEV; energy gain per pass -12 MeV; number of passes - 15; final beam energy - 185 MeV; maximum current 550 ..mu..A. One 450 kW cw klystron operating at 2380 MHz will supply rf power to both the injector linac and the main accelerating section of the RTM. The disk and washer standing wave rf structure being developed at LASL will be used. SUPERFISH calculations indicate that an effective shunt impedance (ZT) of about 100 M..cap omega../m can be obtained. Thus, rf power dissipation of 25 kW/m results in an energy gain of more than 1.5 MeV/m. Accelerators of this type should be attractive for many applications. At beam energies above about 50 MeV, an RTM should be considerably cheaper to build and operate thanmore » a conventional pulsed rf linac of the same maximum energy and time-average beam power. In addition, the RTM provides superior beam quality and a continuous beam which is essential for nuclear physics experiments requiring time-coincidence measurements between emitted particles.« less

Build-up curves of scanned high energy electron beams from the Sagittaire linear accelerator

Abstract: A study of the build-up curves using an extrapolation chamber for 7, 10, 13, 16, and 19 MeV electron beams, from a Sagittaire linear accelerator, is presented. The effect of the ionization chamber bias polarity, field size, collimation and surface obliquity on the shape of the relative ionization curve was investigated. No clinically significant change is observed except the displacement of the maximum ionization point was observed for the oblique incidence of the beam.

Measurements on the radiation protection of patients irradiated with an 18-MeV electron linear accelerator.

Abstract: In order to quantify the influence of some physical and geometrical treatment parameters on the stray radiation dose absorbed by patients undergoing radiotherapy on an 18-MeV linear accelerator, dose distributions were measured in a polystyrene phantom by means of LiF-dosimeters. For 10-MV X-rays, 6-MeV and 18-MeV electron radiation dose profiles, depth dose and isodose curves were obtained at various field sizes and treatment couch positions. By covering the phantom with 1 or 2 mm thick lead sheets a remarkable dose reduction was found. A two-exponential expression was derived to estimate stray radiation dosage in routine radiotherapy. The validity of the calculation method was demonstrated by comparing the gonadal load measured in an Alderson phantom with the calculated data.

Intense linear ion accelerators

Abstract: Intense linear ion accelerators are playing an ever more important role in the program of seeking new energy sources. The fundamental physical effects that limit the beam current and technical problems associated with these effects are discussed. The prospects for building intense linear accelerators for energetics and possible parameters of these machines are discussed.

Optimized design for PIGMI

Abstract: PIGMI (Pion Generator for Medical Irradiations) is a compact linear proton accelerator design, optimized for pion production and cancer treatment use in a hospital environment. Technology developed during a four-year PIGMI Prototype experimental program allows the design of smaller, less expensive, and more reliable proton linacs. A new type of low-energy accelerating structure, the radio-frequency quadrupole (RFQ) has been tested; it produces an exceptionally good-quality beam and allows the use of a simple 30-kV injector. Average axial electric-field gradients of over 9 MV/m have been demonstrated in a drift-tube linac (DTL) structure. Experimental work is underway to test the disk-and-washer (DAW) structure, another new type of accelerating structure for use in the high-energy coupled-cavity linac (CCL). Sufficient experimental and developmental progress has been made to closely define an actual PIGMI. It will consist of a 30-kV injector, and RFQ linac to a proton energy of 2.5 MeV, a DTL linac to 125 MeV, and a CCL linac to the final energy of 650 MeV. The total length of the accelerator is 133 meters. The RFQ and DTL will be driven by a single 440-MHz klystron; the CCL will be driven by six 1320-MHz klystrons. The peak beam current is 28more » mA. The beam pulse length is 60 ..mu..s at a 60-Hz repetition rate, resulting in a 100-..mu..A average beam current. The total cost of the accelerator is estimated to be approx. $10 million.« less

Picosecond resolution of a Cerenkov cell-streak camera arrangement for monitoring charged particle bunches

Abstract: An experiment is described in which the picosecond temporal structure of a Cerenkov radiation source has been measured using an optical streak camera. Electrons in the Stanford Linear Accelerator Center (SLAC) three kilometer linear accelerator, bunched by the 2856 MHz acceleration fields, are used to generate Cerenkov radiation in a helium-filled gas cell. We show that it is possible to construct a Cerenkov cell which introduces subpicosecond time spread and allows for nondestructive monitoring of the electron beam.

A semi-empirical model for the generation of dose distributions produced by a scanning electron beam.

Abstract: There are linear accelerators (Sagittaire and Saturne accelerators produced by Compagnie Generale de Radioiogie (CGR/MeV) Corporation) which produce broad, flat electron fields by magnetically scanning the relatively narrow electron beam as it emerges from the accelerator vaccum system. A semi-empirical model, which mimics the scanning action of this type of accelerator, was developed for the generation of dose distributions in homogeneous media. The model employs the dose distributions of the scanning electron beams. These were measured with photographic film in a polystyrene phantom by turning of the magnetic scanning system. The mean deviation of calculated from measured dose distributions is about 0.2 % , a few points have deviations as large as 2–4 % inside of the 50 % isodose curve, but less than 8 % outside of the 50 % isodose curve. The model has been used to generate the electron beam library required by a modified version of a commercially-available computerized treatment-planning system. (The RAD-8 treatment planning system was purchased from the Digital Equipment Corporation. It is currently available from Electronic Music Industries (EMI), Ltd.)

SIS - An Accelerator Facility for Relativistic Heavy Ions

Abstract: At GSI a new facility for the acceleration of heavy ions to relativistic energies was designed. A large synchrotron dubbed SIS will provide high current heavy ion beams in the extremely broad energy range from 20 MeV/u up to 14 GeV/u. The UNILAC - a 10 MeV/u linear accelerator now in use for atomic and nuclear physics - will serve with a few pulses per second as injector machine for the synchrotron. In order to boost beam intensities up to 2 mA by acceleration of singly or doubly charged ions a small new injector linear accelerator will be installed in front of the UNILAC. In a review of relativistic heavy ion accelerators the SIS will be compared to other concepts. Relevant design features such as charge exchange processes and vacuum requirements are discussed.

An intercomparison of neutron measurements for a 25 MV x-ray radiotherapy accelerator

Abstract: High‐energy x‐ray radiotherapy machines produce neutrons by photonuclear reactions which present a potential radiation hazard to the personnel and patient. A series of measurements of the neutron flux from a 25 MV x‐ray linear accelerator, inside and outside the treatment room, have been performed using a multisphere spectrometer, Nemo dosimeter, and activation detectors. These results are compared with other mixed photon–neutron field measurements for the same machine performed using an argon/propane ionization chamber, silicondiode, track‐etching detectors, and Monte Carlo calculations. It is found that these measurements agree with each other within a factor of two except for silicondiode measurements in the photon beam. Measured neutron spectra at various locations in the treatment room are also compared with the results of Monte Carlo transport calculations.

Linearbeschleuniger und Tandem-van-de-Graaffs: Werkzeuge der Schwerionenforschung

Abstract: The basic principles of dc-tandem and high-frequency linear accelerator are discussed by referring to the pioneering work of H. Kallmann and R. Wideroe. The 30 MV Supertandem in Daresbury, the Heidelberg combination of tandem and linac, and the universal linear accelerator Unilac of the GSI at Darmstadt serve as examples of modern heavy-ion accelerators.