Accelerator Module Research Articles

Parameter study on phase I of the VUV-FEL at the TESLA test facility

Currently, a SASE-FEL in the VUV, driven by the TESLA test facility accelerator, is under construction at DESY. As a first phase of the project, three of the eight TTF accelerator modules will be installed to deliver an electron beam with a nominal energy of approximately 380 MeV with a peak current of 500 A. With this energy, employing an undulator with the same parameters as for the final design, the resonant wavelength is around 44 nm. For this wavelength, the transverse beam emittance and energy spread conditions can be relaxed as compared to the design wavelength of 6 nm in the final stage. The proposed length of the planar undulator with the integrated FODO lattice is about 15 m. In this paper, we present a detailed study on how the performance around 300 MeV depends on the electron beam and undulator parameters. Also, the status of the project is briefly sketched.

Comparison of rectangular and damped sinusoidal dB/dt waveforms in magnetic stimulation

In magnetic (eddy-current) stimulation, sensory and motor nerve are stimulated by a time-varying magnetic field (dB/dt) produced in an appropriate coil. In this study, magnetic stimulation thresholds for a solenoidal coil encircling the forearm were determined in 14 healthy human volunteers, 11 males and 3 females. Damped sinusoidal dB/dt pulses with durations (onset to zero crossing) ranging from 120 /spl mu/s to 2500 /spl mu/s were produced by discharging a capacitor bank into the coil. Rectangular dB/dt pulses with durations ranging from 50 /spl mu/s to 2500 /spl mu/s were generated by a Gradient Ramp Accelerator Module (GRAM) in series with a linear amplifier. The threshold data were fitted to an equivalent circuit underlying the hyperbolic form of the strength-duration curve. Average electric field rheobases for the sinusoidal and rectangular pulses were 5.87 V/m and 5.36 V/m, respectively; chronaxies for these waveforms were 393 /spl mu/s and 395 /spl mu/s, respectively. This study shows that stimulation thresholds obtained with damped sinusoidal dB/dt pulses can be used to accurately predict the thresholds that would be obtained for rectangular waveforms.

Current status of the superconducting RF linac driver for the JAERI free electron laser

Abstract A prototype for a quasi-cw, and 1 kW high-average power free electron laser (FEL) driven by a 15 MeV superconducting rf linac has been developed, and constructed at Tokai, JAERI. Cryogenic stand-by loss ( 7 MV/m and Q ∼ 2 × 10+9) of four JAERI superconducting accelerator modules have been successfully demonstrated. Beam test and commissioning of the JAERI superconducting rf linac have been successfully performed to get electron beams ranging from 10 to 23 MeV and the fully transmitted of ∼ 16 A peak current around 17 MeV. The measured energy resolution of a pre-accelerated beam is about 3% of FWHM, and that of a fully-accelerated beam about 0.8% or less. The measured micropulse width is adjustable in the range from 10 to 60 ps. FEL opticals and beam transport elements around the undulator are now under commissioning. Spontaneous emissions in the wavelength of 20 to 80 μm or longer have been observed by using the Ge(Cu) and other detectors, a home-made fast current amplifier, and a 24 m long light transporting system.

High power electron accelerators for flue gas treatment

Over 1000 accelerators based on different principles have been constructed and used in the field of radiation chemistry and radiation processing. One of the radiation processes which was successfully demonstrated in many laboratories and pilot plant facilities is the reduction of SO2 and NOx pollutants from flue gases emitted during fuel combustion in boilers for electrical power and heat production. The full scale industrial implementation of an electron beam process for flue gases treatment would require accelerator modules with a beam power of over 500 kW and electron energy in the range 1–1.5 MeV. The 500 MW power plant may require 5–8 MW of electron beam power deposited in the flue gas.

Rf power tests for JAERI FEL superconducting accelerator modules

All four superconducting accelerator modules for the JAERI FEL linac are installed. Low power rf tests have been performed. The quality Q 0 is about 2 × 10 9 at an accelerating field of 5 MV/m for each cavity. A variable main coupler has been installed and can vary the coupling coefficient by about three decades. High power tests with the high power pulse amplifier show about 1% field fluctuation of the cavity field at the top.

Remote X ray measurements of the electron beam from the EXCEDE III Experiment

The EXCEDE III rocket experiment successfully produced an artificial aurora on April 27, 1990, with an injected ∼ 18‐A beam of ∼ 2.5‐keV electrons. The experiment consisted of an accelerator module and a sensor module in a mother‐daughter configuration. The beam was fired along the Earth's magnetic field lines between the altitudes of ∼62 and 115 km during the flight. A major concern prior to the flight was that the injection of such an overdense electron beam into the lower ionosphere would charge the accelerator module to a significant fraction of the beam potential. To monitor the primary electrons remote from the rocket, two X ray proportional counters were included as part of the sensor module. X ray spectra from bremsstrahlung emission yield a direct measure of the primary electron beam energy outside the plasma sheath surrounding the accelerator module. Analysis of these spectra yields a beam energy of 2.2 ± 0.5 keV which indicates no substantial charging of the accelerator module for the entire time that the beam was on. We also find that the X ray intensity was modulated at the few percent level by firings of the attitude control jets.

Recent progress of the superconducting accelerator modules for the JAERI FEL

The new cooling system of the JAERI superconducting accelerator module named “multi-refrigerators system” consists of a liquid He recondensor and a shield cooler utilizing a compact closed-loop He gas refrigerator, and their integration into each accelerator module cryostat. Because of restricted cooling power of the refrigerator, we designed 80K and 40 K heat shields to minimize the static heat load to a liquid He container of the cryostat. When thermal anchors are installed in optimized positions, the heat load to the liquid He container is calculated to be 1 W, and estimated to be less than 3 W by a simple 1-dimensional calculation. The cooling power of the 4 K refrigerator was about 11 W or more at 4.5 K, which is there times larger than required by the thermal design. The vibrational amplitude of the cryostat due to the refrigerators' motion was measured to be less than 0.2 μm (p-p) on a test cryostat surface, and it was well within our requirement. The multi-refrigerators system has been operated very reliably for several months.

JAERI quasi-cw, and high-average power free electron laser driven by a superconducting rf linac

We have developed and constructed a prototype for a quasi-cw, and high-average power free electron laser driven by a superconducting rf linac at the Japan Atomic Energy Research Institute (JAERI), Tokai. We have successfully demonstrated expected performances of the JAERI 250 keV electron gun and bunching system, and completed an extension to an old 5.5 MV electrostatic accelerator building as an FEL accelerator vault in the 1991 Japanese fiscal year. All solid state rf amplifiers, liquid He refrigerators, a hybrid undulator and vacuum pumping stations are ready for use now. The first superconducting accelerator module is now under preparation for a cold rf test, and the other three modules are now under assembly. A description and the latest results of the JAERI superconducting rf linac FEL will be discussed, and reported in detail.

Longitudinal expansion of space-charge dominated drifting beam bunches with a parabolic line charge density distribution

An experiment was performed for the first time to demonstrate linear longitudinal space-charge forces on drifting electron beam bunches with a parabolic line charge density distribution. The parabolic electron beam bunch was produced by a gridded electron gun and guided into a short transport channel consisting of an induction acceleration module and three matching lenses. The time-resolved beam energy was measured at the end of the channel by both a retarding field energy analyzer and a deflecting field energy analyzer. The experimental results were compared with theory and good agreement was found.

High-power, short-pulse generators based on induction voltage adders

High-power, short-pulse generators based on induction voltage adders were identified by the pulsed power community as the most important recent advance in this field. These systems use linear induction accelerator modules and self-magnetically insulated vacuum transmission lines to generate high-voltage (tens of megavolts), moderate-impedance (<or=200 Omega ), short-duration (tens of nanoseconds) output pulses. Hermes III is a 20-MV, 16-TW electron beam accelerator and represents the most powerful implementation to date of the induction voltage adder technology. The authors describe how these systems function, identify their advantages and limitations, and discuss present and proposed applications.<<ETX>>

Electron beam injector for longitudinal beam physics experiments

An electron beam injector has been constructed to study the longitudinal beam physics in the University of Maryland electron beam transport experiments, including studies of longitudinal beam pulse compression and resistive-wall instability. The injector consists of a variable-perveance gridded electron gun followed by three matching lenses and one induction acceleration module. In the beam pulse compression experiment, it produces a 50 ns, 40 mA and 2.5 to 7.5 keV electron beam pulse with an approximately linear time-dependent velocity tilt. This beam will be injected into an existing 5 m long periodic transport channel with 36 short solenoid lenses. With the given beam parameters and initial conditions, the beam pulse is expected to be compressed by a factor of 3 or greater when reaching the end of the solenoid channel. In the resistive-wall instability experiment, the injector produces an electron beam pulse of 5 to 50 ns in duration, about 100 mA in current and a few kilovolts in energy. This beam will be guided into a resistive-wall channel of a couple of meters in length for study of the longitudinal resistive-wall instability. This paper reports on the design features and the general performance characteritics of the injector system including its mechanical, electrical, and beam-optical properties.

A Light Ion Beam Driver for the Laboratory Microfusion Facility+

The Laboratory Microfusion Facility (LMF) is being planned to develop high-gain, high-yield (200 MJ-1000 MJ) ICF targets for applications to nuclear weapons effects simulation, thermonuclear weapons physics, and energy production. It is expected that a 1000-MJ yield will require ∼ 10–20 MJ input energy to the target. The light-ion beam driver concept for the LMF consists of 36 accelerator modules that drive independent Li+ ion diodes. Each ion beam is extracted from an annular ion diode and propagated to a solenoidal lens located near the wall of the target chamber. This magnetic lens focuses the beam on to the pellet located at the center of the target chamber. The temporal shape of the power pulse delivered to the target is controlled by the synchronized firing of the accelerator modules. This paper presents a status of the light-ion beam LMF driver concept.

Design and performance characteristics of a compact induction acceleration module for longitudinal pulse compression experiments

A compact induction acceleration module has been designed and constructed for electron beam experiments at the University of Maryland aimed at investigating the physics of longitudinal bunching and compression. The module imparts a front-to-tail energy shear to the pulsed electron beam (15–50 ns) causing longitudinal compression in a 5 m long periodic solenoid channel. The design parameters, operating principle and performance characteristics of this device are reported in this paper.

Proposal for a High-lntensity 14-MeV Cutoff Neutron Source Based on the1H(t,n)1He Source Reaction

AbstractA high-intensity, high-energy neutron source for fusion materials testing is proposed. Utilizing the 1H(t,n)3He neutron source reaction and bombarding a thick (totally absorbing) hydrogen-rich target with an intense beam of 21-MeV tritons provides a powerful continuous-energy-spectrum neutron source. The global spectrum of such a source is almost flat over the energy range from ∼1 to 14 MeV and exhibits a sharp energy cutoff level at 14.6 MeV. To meet near-term needs for fusion materials testing, a source concept is considered that involves multiple linear accelerator modules providing two 250-mA triton beams to bombard two water jet targets that face each other and irradiate the same test volume. Calculations of the source properties from well-established neutron production cross-section data for the 1H(t,n)3He reaction predict a test volume of 4.2 dm3 in which an average flux of ≥1 × 1014 n·cm-2·s-1 is achieved. The relevant properties of this source and the possibility of its realization, well ...

A high-flux accelerator-based neutron source for fusion technology and materials testing

Advances in high-current linear-accelerator technology since the design of the Fusion Materials Irradiation Test (FMIT) Facility have increased the attractiveness of a deuteriumlithium neutron source for fusion materials and technology testing. This paper discusses the conceptual design of such a source that is aimed at meeting the near-term requirements of a high-flux high-energy International Fusion Materials Irradiation Facility (IFMIF). The concept employs multiple accelerator modules providing deuteron beams to two liquid-lithium jet targets oriented at right angles. This beam/target geometry provides much larger test volumes than can be attained with a single beam and target and produces significant regions of low neutron-flux gradient. A preliminary beam-dynamics design has been obtained for a 250-mA reference accelerator module. Neutron-flux levels and irradiation volumes were calculated for a neutron source incorporating two such modules, and interaction of the beam with the lithium jet was studied using a thermal-hydraulic computer simulation. Approximate cost estimates are provided for a range of beam currents and a possible facility staging sequence is suggested.

Linear induction accelerators for industrial applications

There are many industrial radiation processes that require electron beam sources capable of operating at 1–10 MeV and power levels of 50–500 kW. These processes include medical product sterilization, food sterilization and decontamination of waste products. Linear induction accelerators (LIAs) driven by magnetic pulse compression (MC) systems are particularly attractive for these applications. Pulse Sciences, Inc. has developed a prototype LIA/MC system to demonstrate the capabilities of this technology to meet industrial requirements where low cost, high efficiency and high reliability are essential. The prototype is designed to operate at a beam energy of 1.6 MeV and a beam current of 1–2 kA in 65 ns pulses at average powers exceeding 20 kW. Higher energies and average power levels can be achieved by adding more acceleration modules and by increasing the pulse repetition rate. This paper discusses the prototype system design and its performance characteristics.

A High-Performance D-Lithium Neutron Source for Fusion Technology Testing: Accelerator Driver Design

Recent advances in high-current linear accelerator technology have considerably increased the attractiveness of a deuterium-lithium high-energy neutron source for fusion materials and technology testing. This paper describes a new Los Alamos conceptual design for a deuteron accelerator aimed at meeting near-term flux requirements of an International Fusion Materials Irradiation Facility. The lithium target, neutronics, and irradiation facilities are discussed in a companion paper1 at this conference. The new neutron-source driver concept is based on the idea of multiple accelerator modules, with each module consisting of two 125-mA, 175-MHz radiofrequency quadrupoles funneling 3-MeV cw deuteron beams into a 35-MeV, 250-mA, 350-MHz drift-tube linac.

The high brightness test stand

The High Brightness Test Stand is a 2 MeV, ≤10 kA electron accelerator module. This accelerator module which was designed as an upgrade prototype for the Advanced Test Accelerator (ATA) combines solid state nonlinear magnetic drives with state-of-the-art induction linac technology. The facility serves a dual role as it not only provides a test bed for this new technology but is used to develop high brightness electron optics. In the following we will both further describe the accelerator as well as present some of the preliminary electron optics measurements.

Design and Performance of the 1.5 MV Injector for FXR

The new flash x-ray machine (FXR) at LLNL is scheduled for completion in late 1981. This is a 54 module, linear induction accelerator, designed to deliver 500 Roentgen at 1 m as bremsstrahlung from a 20 MeV, 4 kA, 60 ns pulsed electron beam. The 1.5 MV, cold cathode injector makes use of six accelerator modules as voltage sources. High voltage testing of the accelerator modules and their associated pulse forming lines and Marx banks has been completed, and beam tests of the complete injector assembly are in progress. Design information and preliminary test results are presented.

Status of the Stony Brook Superconducting Heavy-Ion Linac

We describe the present status of the State University of New York at Stony Brook Superconducting Heavy-Ion LINAC (SUNYLAC). The LINAC will extend at very modest cost the capabilities of the existing FN tandem Van de Graaff into the energy range 5-10 MeV/A for light heavy-ions from oxygen to bromine. The active elements are 43 lead-plated copper superconducting resonators of the split-loop type optimized for either velocity ß=v/c=0.055 or ß=0.10. Phase and amplitude of each resonator is independently set through RF-feedback controllers interfaced to an overall computer control system. Full scale construction work began in July, 1979 following the in-beam demonstration of a prototype LINAC module containing 4 low-ß resonators, and the majority of the installation work on the beam transport and refrigeration systems was completed in the summer of 1980. The project is now well into its final assembly and testing phase, with the completion of assembly scheduled in early 1982. We describe details of the design of key elements of the LINAC and the initial operating experience with the injection beam path, helium refrigerator and first production accelerator module. The progress of a continuing program aimed at optimizing crucial aspects of the LINAC is also reviewed.