Showing papers on "Linear particle accelerator published in 1989"

Radiosurgery with high energy photon beams: a comparison among techniques.

Abstract: The presently known radiosurgical techniques with high energy photon beams are based either on the commercially available Gamma unit utilizing 201 stationary cobalt beams or on isocentric linear accelerators. The techniques using linear accelerators are divided into the single plane rotation, the multiple non-coplanar arcs, and the dynamic rotation. A brief description of these techniques is given, and their physical characteristics, such as precision of dose delivery, dose fall-off outside the target volume, and isodose distributions are discussed. It is shown that the multiple non-coplanar arcs technique and the dynamic rotation give dose distributions similar to those of the Gamma unit, which makes these two linear accelerator based techniques attractive alternatives to radiosurgery with the Gamma unit.

High-gradient electron accelerator powered by a relativisitic klystron.

Abstract: We have used relativistic klystron technology to extract 290 MW of peak power at 11.4 GHz from an induction linac beam, and to power a short 11.4-GHz high-gradient accelerator. We have measured rf phase stability, field emission, and the momentum spectrum of an accelerated electron beam. An average accelerating gradient of 84 MV/m has been achieved with 80 MW of relativistic klystron power.

Stereotactically guided convergent beam irradiation with a linear accelerator: localization-technique.

Abstract: A stereotactic convergent beam irradiation technique using a linear accelerator has been developed in order to precisely apply single high doses of up to 50 gray and more to brain lesions (radiosurgery). Accurate positioning of the patient and the target point of irradiation is an absolute requirement for this method. The stereotactic localization system developed for this purpose is described.

NTT superconducting storage ring—Super‐ALIS

Abstract: A superconducting electron storage ring fully dedicated to x‐ray lithography has been developed. It has a racetrack shape, consisting of two superconducting bending magnets, other normal conducting multipole magnets, rf system, vacuum system, and beam monitoring systems. The storage ring circumference is 16.8 m. The critical wavelength (λc) is 17.3 A. The beam size (σ) at every synchrotron radiation source point is less than 1 mm. This machine employs the energy‐boost‐in‐the‐ring scheme; electrons are injected at around 15 MeV and then accelerated to 600 MeV in the ring. The injector is a newly developed linear accelerator with an energy compression system. Higher‐energy injection is also available.

Observation of beam-beam deflections at the interaction point of the SLAC Linear Collider.

Abstract: We report the first direct observation of the electromagnetic deflection of high-energy electron and positron beams as they pass each other with small impact parameters. Measurements of the deflection amplitude are found in agreement with theoretical expectations. This phenomenon, which is sensitive both to the relative position of the two beams and to their transverse sizes, has been used successfully to optimize and maintain collisions at the interaction point of the SLAC Linear Collider.

Colliding a Linear Electron Beam With a Storage Ring Beam

Abstract: We investigate the possibility of colliding a linear accelerator electron beam with a particle beam stored in a circular storage ring. Such a scheme allows e + e − colliders with a center-of-mass energy of a few hundred GeV and eP colliders with a center-of-mass energy of several TeV. High luminosities are possible for both colliders.

Dynamic multivane electron arc beam collimator

Abstract: This invention is a dynamic multivane electron arc beam collimator having collimation vanes, means for controlling the vanes, and local controllers at the collimation site which dynamically define an electron aperture which defines the electron field of an electron beam emitted by a linear accelerator during electron arc therapy. The collimator can be attached to or detached from the head of a linear accelerator. The collimator provides for improvement in electron arc therapy dose uniformity.

Beam-based alignment technique for the SLC linac

Abstract: It is pointed out that misalignments of quadrupole magnets and beam position monitors (BPMs) in the linac of the SLAC (Stanford Linear Accelerator Center) Linear Collider (SLC) cause the electron and positron beams to be steered off-center in the disk-loaded waveguide accelerator structures. Off-center beams produce wakefields which limit the SLC performance at high beam intensities by causing emittance growth. A general method is presented for simultaneously determining quadrupole magnet and BPM offsets using beam trajectory measurements. Results from the application of the method to the SLC linac are described. The alignment precision achieved is approximately 100 mu m, which is significantly better than that obtained using optical surveying techniques. >

Heavy ion induction linac drivers for inertial confinement fusion

Abstract: Intense beams of high energy heavy ions (e.g., 10 GeV Hg) are an attractive option for an ICF driver because of their favorable energy deposition characteristics. The accelerator systems to produce...

CLIO: Collaboration for an infrared laser at Orsay

Abstract: The CLIO collaboration has started in 1986 in order to build an infrared laser at LURE at Orsay. It includes the design and construction of a new FEL dedicated rf linear accelerator. The goal is to make a broadly tunable laser (at least in the range 2–20 μm), of high peak power (MW range), and “medium” average power (a few tens of watts). It will be utilized as a “user facility” as well as for FEL fundamental studies. The linac uses a gridded disperser cathode gun, a 500 MHz prebuncher, a fundamental buncher and one accelerating section powered by a 3 GHz klystron (with 12 μs long pulses). The final energy will be adjustable between 30 and 75 MeV. The desired characteristics are: peak current >50 A, total energy spread ≈1%, normalized emittance <150πmm mrad. The numerical simulations made with PARMELA indicate that these performances will be reached with an emittance better by a factor of 2–4. The accelerator is followed by an achromatic and nearly isochronous 60° bend. It will allow to select the particles within a given energy spread, before the undulator, and to analyse, with respect to time, their energy distribution after the undulator. The optical cavity is 4.8 m long (32 ns roundtrip time), compatible with the laser risetime (typically 100 passes) and the klystron pulse length of 12 μs. The undulator is made of two independently adjustable identical parts, 0.96 m long (24 × 4 cm) each; the second one can be tapered. This will allow to optimize both the optical gain and energy extraction at different wavelengths. The laser is scheduled to operate by the end of 1990.

Timing and voltage control of magnetic modulators on eta II

Abstract: The Experimental Test Accelerator II is a high-average-power, high repetition-rate linear induction accelerator at Lawrence Livermore National Laboratory. Magnetic pulse compressors are used in the power conditioning chains that produce pulses used to accelerate the electron beam. Stable operation of each power-conditioning chain is essential to overall accelerator performance. Variations in voltage or timing ("jitter") of pulses driving the induction cells can cause unacceptable variations in electron-beam energy. This paper reviews techniques developed and implemented to regulate voltage and to control sources of timing jitter. These techniques have demonstrated subnanosecond jitter and /spl Ichemo/0.1% pulse-to-pulse voltage regulation of the accelerator drive pulses.

Calibration of the L3 BGO electromagnetic calorimeter with a radiofrequency quadrupole accelerator

Abstract: A new calibration technique based on radiative capture of protons from an RFQ accelerator in a lithium target, which makes use of the resultant high intensity flux of 17.6 MeV photons, has been developed and tested. The technique is capable of calibrating the thousands of BGO crystals in the L3 electromagnetic calorimeter at once, with an absolute accuracy of better than 1% in 1–2 h. Systematic errors in the calibration, which have been studied earlier through Monte Carlo simulations, have been experimentally proven to be small and calculable, and are expected to be much less than 1%. When installed in the L3 experiment at LEP, this system will help ensure that the high resolution of the L3 electromagnetic calorimeter is maintained during running.

RF pulse compression experiment at SLAC

Abstract: Using RF pulse compression it is possible to boost a 50-100 MW output, expected from high-power microwave tubes operating in the 10-20 GHz frequency range, to the 300-600 MW level required by the next generation of high gradient linear colliders. Experiments have been performed at Stanford Linear Accelerator Center to test, at low power, a two-stage binary energy compressor (BEC) operating at 11.424 GHz. Using over-moded delay lines and 3 dB hybrid couplers, a 312-ns pulse was compressed to 78 ns, giving a power multiplication ratio of approximately 3.2 and a power efficiency of 81%. Individual component insertion losses were measured to be in the range of 0.6% to 8.5%. Overall efficiency calculated using these values agreed with measured values to approximately 1.4%. >

Beam funneling studies at Los Alamos

Abstract: Funneling two ions beams by interlacing their bunches can reduce the cost and complexity of systems producing intense beams. Applications of funneling could include accelerators for heavy-ion inertial fusion, electronuclear breeding and fusion materials irradiation. Funneling in an RFQ-like structure is an elegant solution at low energy where electric fields are needed to provide strong focusing. Discrete-element funnels, with separate focusing elements, bending magnets, rebunchers and rf deflectors, are more flexible. At sufficiently high energies magnetic-quadrupole lenses can provide strong focusing in a discrete-element funnel. Such a funnel has been designed as a preliminary example of a second funnel in the HIBALL-II accelerator system. In a simulation, two Bi1+ (mass = 209 amu) beams at 0.5 MeV/A, 20 MHz and 40 mA, separated by 55 cm and angled at ±6° were combined into a single 80 mA beam at 40 MHz. Emittance growth was calculated, by a modified version of the PIC (particle-in-cell) code PARMILA, to be about 1%. Funnel design experience at Los Alamos has evolved rules of thumb that reduce emittance growth. Some of these are to maintain focusing periodicity and strength in both transverse and longitudinal directions; use strong focusing so that the bunch will be small; minimize angles of bend and rf deflection; adjust longitudinal focusing to produce a short bunch at the rf deflector; and design rf deflectors for a uniform electrical field. fa]Work supported by Los Alamos National Laboratory Program Development under the auspices of the US Department of Energy.

Electron accelerators driven by modulated intense relativistic electron beams.

Abstract: This paper addresses the development of a new high-voltage-gradient linear accelerator. This accelerator was energized by a modulated intense relativistic electron beam with power in the multigigawatt range. A 0.2-cm-diam electron beam emerged from the accelerator with a peak current of \ensuremath{\sim}200 A and peak kinetic energy \ensuremath{\ge}60 MeV. The length of the accelerating structure was 1 m. Simple scaling laws suggest that similar accelerators with much higher average electric fields can be built.

Precision measurements of the SLC beam energy

Abstract: A method of precisely determining the beam energy in high-energy linear colliders has been developed using dipole spectrometers and synchrotron radiation detectors. The method of measurement indirectly observes the deflection of charged beams via the narrow beams of synchrotron radiation they emit. Beam lines implementing this method have been installed on the Stanford Linear Collider (SLC). An absolute energy measurement with an accuracy of better than delta E/E=5*10/sup -4/ can be achieved on a pulse-to-pulse basis. The operation of this system is described. >

Plane wave transformer linac structure

Abstract: A plane wave transformer linear accelerator structure for accelerating charged particles to velocities greater than one-half the speed of light. The accelerator includes a tank section having a generally cylindrical tank wall. End plates each containing a central aperture for accommodating the passage of a charged particle beam are positioned adjacent to the ends of the tank wall. Support rods extend between the end plates, partially defining at least one axially-extending outer cavity and at least one axially-extending inner cavity. A plurality of axially-spaced washers situated substantially on the central axis of the tank section are supported by the rods. The washers each have central apertures which together define a charged particle beam acceleration path through the tank section.

Measurements of backscattered radiation from Therac-20 collimator and trimmer jaws into beam monitor chamber

Abstract: The field size dependent photon output is known to be influenced by the existence of backscattered radiation (BSR) generated in the collimator or trimmer jaws of a linear accelerator. This paper describes the results of measurements made to study the existence of such backscatter by simulating the geometry of the treatment head of a Therac-20 linear accelerator. The machine's monitor chamber, flattening filter, and collimator jaws were simulated by another real monitor chamber, a 1-cm thick lead sheet and 2.5-cm thick low-melting-point alloy divergent blocks, respectively. BSR from the simulated collimator jaws (SCJ) was measured with the simulated monitor chamber (SMC) as a function of the openings of the SCJ and as a function of distance between SMC and SCJ. The present results demonstrate the presence of BSR in an 18-MV photon beam from a Therac-20 linear accelerator.

Very high pulse-energy accelerators

Abstract: The design and performance of the Hermes III are presented and the application of this technology to the light ion beam inertial confinement fusion program is discussed. Hermes III represents a new approach to efficiently generating higher voltages. It is designed to drive a 22-MV, 730-kA, 40-ns electron beam diode and combines conventional, modular pulsed power technology with linear induction acceleration concepts. High-power induction accelerator cavities are combined with voltage addition along a MITL (magnetically insulated transmission line) to generate the desired output. This design differs from a conventional linac in that the voltages are added by the MITL flow rather than by a drifting beam that gains kinetic energy at each stage. The design is a major extrapolation of previous state-of-the-art technology represented by the injector module of the Advanced Test Accelerator and has proven to be efficient and reliable. A key issue for ion beam applications relates to the efficiency of coupling power from the high-voltage MITL to an extraction ion diode. A conceptual design of a light ion beam driver for the LMF (Lase Microfusion Facility) has been developed. >

The small angle electromagnetic calorimeter at SLD: a 2m/sup 2/ application of silicon detector diodes

Abstract: The SLD (Stanford Linear Collider Large Detector) collaboration is preparing a solenoidal detector at SLAC (Stanford Linear Accelerator Center) to measure the properties of Z/sup 0/ decays at the SLC (Stanford Linear Collider). One feature of this detector is the nearly 4 pi coverage of the electromagnetic calorimetry extending down to 23 mrad from the beam axis. The smallest angle coverage (23-200 mrad) is provided by calorimeters using silicon detector readout. These calorimeters are twenty-three radiation lengths in depth, segmented longitudinally every radiation length, and the twenty-three layers of silicon detectors are ganged into towers of roughly 1-2-cm/sup 2/ cross section. These towers are read out as two signals, one from the first six radiation lengths and one from the last seventeen. The design and construction of these devices is presented. The potential of the approach for silicon hadron calorimeters at future colliders is also discussed. >

Measurement of neutron leakage spectra at a 500-MeV proton accelerator

Abstract: We have measured the neutron leakage spectra at a number of representative locations outside the shielding of a 500-MeV proton accelerator using a multisphere technique and the 12C(n,2n)11C reaction in a plastic scintillator. The inclusion of the 12C(n,2n)11C reaction in the set of responses has a pronounced effect on the shape of the unfolded neutron spectra and the ambient dose equivalent rate calculated from them.

High-Power Free-Electron Lasers Driven by RF Linear Accelerators

Abstract: : The free electron laser (FEL) has been developed to the point where projections of its high-power capability have made it an important component of the directed-energy research program within the Strategic Defense Initiative To achieve the desired near-visible wavelength and high intensity, stringent demands are placed on the electron beam that drives the FEL Typical requirements are high peak current (02 to 2 kA) at a kinetic energy of 100 to 150 MeV, small energy spread (<1%), small diameter (<3mm), and low divergence (<01 mrad) Either an induction linear accelerator (linac) or an rf linac may be a suitable candidate to provide the electron beam This review we describes the technical issues and technology needed to achieve a visible light FEL driven by an rf linac A recently installed fr linac at Boeing Aerospace is used as the principal illustrative example

Status of the Dutch Free-Electron Laser for Infrared Experiments

Abstract: We review the status of the Dutch Free Electron Laser for Infrared eXperiments (FELIX), with which radiation in the range between 3 μm and 3 mm will be generated. Among our research objectives are (i) rapid tunability and (ii) mode reduction by means of an intracavity etalon. The first stage of the project deals with generation of radiation with a wavelength between 8 and 80 μm. The undulator of the former UK-FEL project will be used in this stage. The design of the accelerator, with which 70-A, 3-ps bunches are accelerated to a maximum energy of 45 MeV, is presented. It consists of a triode, a 4-MeV buncher, and two travelling-wave linac structures. Gain calculations leading to the best choice for the number of undulator periods are discussed.

A conceptual design for an LMF accelerator module

Abstract: The US Department of Energy has initiated a design study of a Laboratory Microfusion Facility (LMF) that will be used to develop high-gain ICF (inertial confinement fusion) targets. A conceptual design for a light ion beam accelerator, has been developed for a multimodule LMF system based on technology demonstrated on Sandia's Hermes-III accelerator. The LMF accelerator module incorporates 32 linear induction cavities, each operating at 1 MV, to produce an output voltage pulse that ramps from 27 to 32 MV with a peak current of 1.2 MA. The power for the accelerator module is derived from 16 Marx generators that drive 128 4- Omega , 54-ns pulse forming lines (PFLs). Four PFL pulses are combined in each inductive cavity. Nanosecond synchronization of the PFL output pulses is accomplished using KrF-laser-triggered output gas switches and low jitter, self-breakdown water switches. The outputs of the cavities are added in a magnetically insulated transmission line and then delivered to an extraction ion diode. Singly ionized lithium ions are accelerated in the diode. Voltage ramping is used to achieve power compression of the ion beam when ballistically drifted to the ICF target. An equivalent circuit has been developed to model the module from the Marx generator to the ion diode. The timing performance of the gas and water switches has been included in the model to calculate the resulting output waveform and system jitter. >

HERA status

Abstract: The electron-proton collider HERA (Hadron-Electron Ring Accelerator) consists of two independent accelerators designed to store, respectively, 820-GeV protons and 30-GeV electrons and to collide the counterrotating beams head on in four interaction regions spaced uniformly around its 6.3 km circumference. In addition to HERA, several booster accelerators must either be constructed or modified. The civil engineering work has been completed; electrons were stored for the first time in the HERA electron ring in August 1988. Commissioning of the first two accelerators in the proton injection chain, the 50-MeV H/sup -/ linear accelerator and the 7.5-GeV DESY III synchrotron, has started. The central helium refrigerators have been running routinely for nearly two years. Production of superconducting magnets is well underway in industry, and the first magnets have already been installed in the tunnel. >

Design of a 100 MW X-band klystron

Abstract: Future linear colliders require klystrons with higher peak power at higher frequency than are currently in use. SLAC (Stanford Linear Accelerator Center) is designing a 100-MW klystron at 11.4 GHz as a prototype for such a tube. The gun has been designed for 440 kV and 510 A. Transporting this beam through a 5-mm radius X-band drift tube presents the major design problem. The area convergence ratio pf 190:1 is over ten times higher than that found in conventional klystrons. Even with high magnetic fields of 6 to 7 kG, careful matching is required to prevent excessive scalloping. Extensive EGUN and CONDOR simulations have been made to optimize the transmission and RF efficiency. The EGUN simulations indicate that better matching is possible by using resonant magnetic focusing. CONDOR calculations indicate efficiencies of 45% are possible with a double output cavity. The results of the simulations and the status of the experimental program are discussed. >

RF phase distribution systems at the SLC

Abstract: Through the use of existing RF coaxial waveguides, and additional installation of phase reference cables and monitoring equipment, a stable RF distribution for the SLC (Stanford Linear Collider) has been achieved. With the use of interferometry as part of an active feedback, and using phase and amplitude detectors to keep all RF devices correctly phased, the long-term stability of the Stanford Linear Accelerator seems to just meet the needs and requirements of the SLC. Higher frequencies, longer distances, and lower emittance specifications require that the next generation of engineers produce an accelerator with an intrinsically more stable RF distribution system. >

Physics of particle accelerators: Volume 2

Abstract: This volume is based on lectures presented at the 1987 US Particle Accelerator School, held at Fermi National Accelerator Laboratory in July and August 1987, in addition to selected material from the school at Cornell University in August 1988. As is our custom, review articles are also included for completeness and to enhance the book's quality. In addition to topics on the Fermilab tevatron the following are discussed: a compendium of computer codes used in particle accelerator design and analysis; superconducting magnet system; superconductor developments; radio-frequency acceleration; principles and technology of RFQs; photocathode RF guns; low emittance thermionic electron guns; intense, low emittance injectors for RF electron linacs; final focus systems for linear colliders; positrons for linear colliders; free-electron lasers; free-electron lasers; fundamentals on intense relativistic electron beams; application of pulse power technology to ultra high energy electron accelerators; coherence and statistical properties of photon beams with application to the free-electron laser; and plasma acceleration of particle beams.