High-current Linear Accelerator Research Articles

Experimental Study of the Compressibility of a Helium Plasma at a Pressure up to 20 TPa

A nonideal helium plasma has been compressed to a density of ρ ≈ 14 g/cm3at a pressure ofP≈20TPa (200Mbar) in a spherical two-cascade device. The design of the device has been presented and the thermodynamic parameters of the helium plasma reached in it have been estimated. Data on the dynamics of the external and internal cascades in the device used to choose the calculation method have been obtained in a preliminary experiment with a hemispherical prototype. The experiment has been performed on the X-ray complex at the Russian Federal Nuclear Center All-Russian Research Institute of Experimental Physics, which includes BIM 234.3000 betatrons with a boundary energy of 60 MeV used in the multipulse bremsstrahlung generation regime with a multichannel optoelectronic system of recording X-ray images. A high-current linear accelerator LIU-R-T and an image detector assembly consisting of photochromic ADC screens have been used in addition to betatrons to detect the compressed shell cavity.

Experimental Study of the Compressibility of a Helium Plasma at a Pressure up to 20 TPa

A nonideal helium plasma has been compressed to a density of ρ ≈ 14 g/cm3 at a pressure of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P \\approx 20{\\kern 1pt} $$\\end{document} TPa (200 Mbar) in a spherical two-cascade device. The design of the device has been presented and the thermodynamic parameters of the helium plasma reached in it have been estimated. Data on the dynamics of the external and internal cascades in the device used to choose the calculation method have been obtained in a preliminary experiment with a hemispherical prototype. The experiment has been performed on the X-ray complex at the Russian Federal Nuclear Center All-Russian Research Institute of Experimental Physics, which includes BIM 234.3000 betatrons with a boundary energy of 60 MeV used in the multipulse bremsstrahlung generation regime with a multichannel optoelectronic system of recording X-ray images. A high-current linear accelerator LIU-R-T and an image detector assembly consisting of photochromic ADC screens have been used in addition to betatrons to detect the compressed shell cavity.

Evaluating the Reproducibility of Mouse Anatomy under Rotation in a Custom Immobilization Device for Conformal FLASH Radiotherapy.

The observation of an enhanced therapeutic index for FLASH radiotherapy in mice has created interest in practical laboratory-based FLASH irradiators. To date, systems capable of 3D conformal FLASH irradiation in mice have been lacking. We are developing such a system, incorporating a high-current linear accelerator to produce a collimated X-ray beam in a stationary beamline design, rotating the mouse about a longitudinal axis to achieve conformal irradiation from multiple beam directions. The purpose of this work was to evaluate the reproducibility of mouse anatomy under rotation at speeds compatible with conformal FLASH delivery. Three short-hair mice and two hairless mice were immobilized under anesthesia in body weight-specific contoured plastic molds, and subjected to three rotational (up to 3 revolutions/s) and two non-rotational movement interventions. MicroCT images were acquired before and after each intervention. The displacements of 11 anatomic landmarks were measured on the image pairs. The displacement of the anatomical landmarks with any of the interventions was 0.5 mm or less for 92.4% of measurements, with a single measurement out of 275 (11 landmarks × 5 interventions × 5 mice) reaching 1 mm. There was no significant difference in the displacements associated with rotation compared to those associated with moving the immobilized mouse in and out of a scanner or with leaving the mouse in place for 5 min with no motion. There were no significant differences in displacements between mice with or without hair, although the analysis is limited by small numbers, or between different anatomic landmarks. These results show that anatomic reproducibility under rotation speed corresponding to FLASH irradiation times appears to be compatible with conformal/stereotactic irradiation in mice.

X-Band Amplifier for the PAL-XFEL

Recent X-ray free electron lasers based on a high-energy high-current linear accelerator, such as the Pohang Accelerator Laboratory (PAL-XFEL) uses a third harmonic radio-frequency (RF) linearizer system to improve the laser's longitudinal beam quality. Because the X-ray free electron laser at the PAL-Xfel uses 2856 MHz RF accelerators, we realized a RF linearizer of 11.424 GHz which afforded a 50 MW RF power by using a SLAC X-band klystron. Operation of the X-band klystron required an X-band amplifier with a 1 kW level at the specified frequency of 11.424 GHz. We tested two types of X-band amplifier, a traveling wave tube amplifier and a solid state amplifier. In this work, we present the test results and discuss the features, especially focusing on the X-band solid state amplifier.

Beam Dynamics Design of a 50 mA D+ RFQ**Supported by the National Basic Research Program of China under Grant No 2014CB845503.

A new 973 project was proposed by Peking University and Institute of Modern Physics of Chinese Academy of Sciences recently. The project requires a 50 mA, 162.5 MHz, cw mode radio frequency quadrupole (RFQ) to accelerate the D+ to 1 MeV. In a high-current linear accelerator, the strong space charge effect causes the growth of envelope and emittance along with heavy beam losses. In the beam dynamics design of this RFQ, beam envelope mismatching is discussed and a matching dynamics method is proposed to minimize the envelope and emittance growth. The influence of limiting current on the beam transmission is discussed and used in the optimization of transverse and longitudinal parameters. After the optimization, the beam transmission efficiency reaches higher than 98%.

High-Current Linear Transformer Driver Development at Sandia National Laboratories

Most of the modern high-current high-voltage pulsed power generators require several stages of pulse conditioning (pulse forming) to convert the multimicrosecond pulses of the Marx generator output to the 40-300-ns pulses required by a number of applications including X-ray radiography, pulsed high-current linear accelerators, Z-pinch, isentropic compression, and inertial fusion energy drivers. This makes the devices large, cumbersome to operate, and expensive. Sandia, in collaboration with a number of other institutions, is developing a new paradigm in pulsed power technology: the linear transformer driver (LTD) technology. This technological approach can provide very compact devices that can deliver very fast high-current and high-voltage pulses. The output pulse rise time and width can be easily tailored to the specific application needs. Trains of a large number of high-current pulses can be produced with variable interpulse separation from nanoseconds to milliseconds. Most importantly, these devices can be rep-rated to frequencies only limited by the capacitor specifications (usually 10 Hz). Their footprint, as compared with current day pulsed power accelerators, is considerably smaller since LTD do not require large oil and deionized water tanks. This makes them ideally suited for applications that require portability. In this paper, we present Sandia National Laboratories' broad spectrum of developmental effort to design construct and extensively validate the LTD pulsed power technology.

Coherent radiation from high-current electron beams of linear accelerators and its applications

The characteristics of the far-infrared light source using the coherent radiation emitted from a high-energy short electron bunch have been investigated. The coherent radiation has a continuous spectrum in a submillimeter to millimeter wavelength range and the brightness is relatively high. The spectrum of the radiation is determined by the longitudinal form factor of the electron bunch. The operational conditions of a high-current linear accelerator have been optimized using an electron bunch shape monitor. The coherent transition radiation light source has been applied to absorption spectroscopy for liquid water and to an imaging experiment for a leaf of rose.

Development of the versatile multi-particle code DYNAMION

The multiparticle code DYNAMION (DYNAMics of ION) was written in ITEP for precise beam dynamics simulation in high-current linear accelerators, and was used world-wide for linacs design and for study of linacs in operation. In collaboration between GSI and ITEP the DYNAMION code is in use since many years for the investigation of operation of the GSI high-current heavy-ion linac UNILAC. Results of the beam dynamics simulations are described and compared with other codes as well as with experimental data. The main feature of the code is the possibility to calculate the 3D particle motion in the whole linac potentially consisting of RFQs, different types of DTL structures, transport lines and other elements. During the last years, the development of the code was focused to the increasing of accuracy and reliability of calculations. These goals were reached by an improved description of the external fields inside the code. Additionally, data from measurements or from calculations done with external codes (e.g., focusing and accelerating fields, beam emittance, etc.) are usable. In the paper, the latest features of the DYNAMION code are presented.

Smart Diagnosis on the AIRIX Induction Accelerator

The AIRIX facility is a high-current linear accelerator (2-3.5 kA) used for flash-radiography at the CEA of Moronvilliers (France). The general background of this study is the predictive maintenance of the AIRIX components by smart diagnosis. We are interested in analyzing the performances of the high voltage (HV) generators, which furnish the energy for accelerating the beam, and the fault detection on the whole machine. We present a tool for fault diagnosis based on pattern recognition using a neural network. We use, among other things, statistical models to define an error vector, which must be classified. To reduce the redundancy of this information and the computation time, we study two algorithms, the principal components analysis and the curvilinear components analysis. A three-layer Radial Basis Function (RBF) neural network realizes the decision rule. We propose an original algorithm to construct the network with unsupervised data. In order to take into account new states or unknown failures, we propose a strategy to adapt the network in a continuous learning. Finally, we present the first results obtained with this tool on the installation.

Coulomb scattering within a spherical beam bunch in a high current linear accelerator

Beam halo formation issues are important for the design of high current linear ion accelerators. Various mechanisms can potentially cause beam halo. Some recent studies suggested that Coulomb collisions in the beam bunch can contribute significantly to beam bunch growth and halo development in linear accelerators. Despite the general belief that collisions are not important, it is clear that a rigorous treatment of this question is needed. In an effort to explore this issue in detail we have undertaken an analysis of the effects of Coulomb scattering between ions in a self-consistent spherical bunch.

Stability of anisotropic beams with space charge

Based on self-consistent Vlasov-Poisson equations, we derive coherent frequencies and stability properties of anisotropic or ``nonequipartitioned'' beams with different focusing constants and emittances in the two transverse directions. The thus obtained dispersion relations of transverse multipole oscillations with quadrupolar, sextupolar, and octupolar symmetries are solved numerically. We find that for sufficiently large energy anisotropy some of the eigenmodes become unstable in the space-charge-dominated regime. Applying our results to high-current linear accelerators, we find that ``nonequipartitioned'' beams may exist in relatively large regions of parameter space under stable conditions. It is only in beams with strongly space-charge-depressed betatron tunes that harmful instabilities leading to emittance exchange should be expected.

Stability and halo formation of a breathing axisymmetric uniform-density beam.

An analysis of the stability and halo formation is presented for a breathing axisymmetric beam of uniform density [Kapchinsky-Vladimirsky (KV) beam] in a uniform focusing channel. Theoretical results are obtained for the form of modes involving nonuniform charge density. In particular, the mismatch-tune depression space is explored, both analytically and by numerical particle-in-cell simulations, to determine the stability limits and growth rates of the most unstable modes. The implications for halo formation are then explored. Halo parameters obtained by simulations are compared with predictions of an analytical model for halo formation from the breathing KV beam developed earlier. The practical applications of the results for high-current linear accelerators are discussed. {copyright} {ital 1996 The American Physical Society.}

Performance of a bunch width control system for coherent radiation with a high-current linear accelerator

A bunch width control system installed in a beam transport line of the high current L-band linear accelerator at Osaka University has been tested to study the coherent radiation of millimeter and submillimeter wavelengths. A 270° bending magnet having a debunching factor of 9mm/% for a nominal energy of 30 MeV was applied. Longitudinal distributions of electrons in the high-current single bunch have been analyzed by the observation of Cherenkov radiation using a streak camera. For a single bunch of a high-quality 30 nC beam having a natural bunch width of (35±3) ps in FWHM, possibility of a changing range 20–90 ps is proved with the 270° bending magnet and a quadrupoles lens system.

Numerical calculation of the effect of Coulomb forces on physical characteristics of the charged particle beam in a linear accelerator

An algorithm Is proposed for numerical calculation of the effect of Coulomb repulsion forces on the physical characteristics of a high-current linear accelerator with asymmetric phase-variable focusing. The problem of maximizing the initial particle trapping region is considered.

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.

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.

Optimising a High-Current Injector to Incorporate a Fast Beam Kicker

In addition to the requirement that the beam current limit imposed by space charge forces be as high as possible, provision should also be made in the injector for fast switching of the high-power beam. The intolerableness of beam losses in a high-current linear accelerator, such as proposed for the German spallation neutron source (SNQ) project, requires that the beam switching occurs cleanly between the beam bunches. The method of accomplishing this technically demanding beam switching is limited by the constraints on the injector chain such as the final energy and operating frequency. These boundary conditions, plus the choice of ion source voltage also come to bear on the current limit in the injector. In the SNQ the injector is asked to supply 200 mA of protons at 200 MHz at an energy of 2 MeV, while the ion source voltage has been chosen to be 50 keV. In order to satisfy all the constraints on the injector and at the same time deliver the maximum current, a frequency jump becomes necessary. The requirements for rf power efficiency in the high-energy linac also demand that all rf buckets be filled. A funneling scheme has been proposed for the SNQ wheremore » this can be achieved by doubling the current and bunch frequency from a pair of injectors operating at half the frequency. A new technique is also put forward in this paper for debunching a beam at an intermediate energy between two RFQ accelerators allowing an arbitrarily large frequency transition to be made between the two RFQ's and raising the current limit even further.« less

Multistage Pulsed-Power Electron Accelerators

Pulse power developments in high-current linear accelerators (RADLAC I) and low impedance water transmission lines (PBFA I) are reviewed. The design of Hermes III, a 1.1 MA, 15 MV linear accelerator based on these technologies is discussed and initial data on the development of this accelerator is presented.

Emittance Growth of High Current Beams in Transport Lines

The rms emittance increase of high current beams in transport lines, caused by nonlinear space charge forces, can be understood as the development of the initial particle distribution to an equilibrium one. For a small beam radius, we get less rms emittance increase and the equilibrium distribution is reached earlier than for a large beam radius. The beam can now be transported over a long distance without further rms emittance growth in all 3 directions. These results are incorporated in the design of a funneling section for the high current linear accelerator of the HIBALL concept.

Beam Transport Issues in High Current Linear Accelerators

Stable beam transport may be the limiting factor in the development of a new generation of high current linear induction accelerators. In this paper we analyze several important beam stability topics, including radial oscillations induced by an accelerating gap, the diocotron, resistive wall, and cyclotron maser instabilities, and the transverse beam breakup and image displacement instabilities. At present image displacement appears to represent the most serious limitation to high current beam transport in linear accelerator structures.