Linear Induction Accelerator Research Articles

Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns (FWHM) electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm (FWHM) in diameter and the corresponding beam divergence is about 10.5 mrad.

多脉冲直线感应加速器外接复位系统

多脉冲直线感应加速器外接复位系统

LIU-2 linear induction accelerator

The LIU-2 induction accelerator is described. It is used as an injector for the developed large linear induction accelerator with a maximum electron beam energy of 20 MeV, which is intended for smallangle pulse X-ray tomography. Owing to the good quality and high current of the electron beam (2 kA), the injector is capable of operating as an independent X-ray source with an electron energy of 2 MeV, the beam diameter at the target of 1 MeV is ∼20% of the total energy yield. The spread of the radiation intensity in the solid angle of 10° is ±5%, and the absorbed dose at a distance of 1 m from the target is 32 × 10−3 Gy, which allows this source to be used with attenuation of 103–104 for exposure of available X-ray films. This type of system is characterized by a high transmission capability with a 0.5-mm maximum spatial resolution of X-ray images and can be used in the X-ray imaging technique when carrying out gas-dynamic testing of products with an optical thickness as great as 90 mm of lead equivalent.

Tuning the DARHT Long-Pulse Linear Induction Accelerator

Flash radiography of large hydrodynamic experiments driven by high explosives is a well-known diagnostic technique in use at many laboratories. The Dual-Axis Radiography for Hydrodynamic Testing (DARHT) facility at Los Alamos produces flash radiographs of large hydrodynamic experiments. Two linear induction accelerators (LIAs) make the bremsstrahlung radiographic source spots for orthogonal views of each test. The 2-kA, 20-MeV Axis-I LIA creates a single 60-ns radiography pulse. The 1.7-kA, 16.5-MeV Axis-II LIA creates up to four radiography pulses by kicking them out of a longer pulse that has a 1.6- μs flat top. The DARHT LIAs use solenoidal focusing for transport of the beam through the accelerators. The long-pulse Axis-II LIA has 74 accelerating cells, and uses 91 solenoids and 80 pairs of dipoles for focusing, transporting, and steering the beam. The setting of the currents of these 251 magnets is called tuning the accelerator. Tuning is done in two stages. First, the solenoidal focusing magnets are set to values designed to provide a beam with minimal envelope oscillations, and little or no instability growth. Then, steering dipoles are adjusted to minimize the low-frequency motion of the beam centroid and center it at the LIA exit. The design of the focusing tune is computationally intensive. Focusing tune design methods, simulations, and validation are the main topics of this article.

Stabilization of the Frequency of Relativistic S-Band Magnetron With Radial Output

The results of experimental research on the stabilization and tuning of the frequency of a relativistic S-band six-resonator magnetron powered by a linear induction accelerator ( U ≈ 300 κB, I ≈ 2.5 kA, and τ ≈ 150 ns) are presented. The frequency of the microwaves was stabilized using a partial reflection of the generated microwave power P ≈ 300 MW from the output of the magnetron and a proper adjustment of the phase of the reflected microwaves.

Techniques for correcting velocity and density fluctuations of ion beams in ion inducti on accelerators

It is well known that the imperfection of pulse power sources that drive the linear induction accelerators can lead to time-varying fluctuation in the accelerating voltages, which in turn leads to longitudinal emittance growth. We show that this source of emittance growth is correctable, even in space-charge dominated beams with significant transients induced by space-charge waves. Two correction methods are proposed, and their efficacy in reducing longitudinal emittance is demonstrated with three-dimensional particle-in-cell simulations.

Multiple beam induction accelerators for heavy ion fusion

Induction accelerators are appealing for heavy-ion driven inertial fusion energy (HIF) because of their high efficiency and their demonstrated capability to accelerate high beam current (≥10kA in some applications). For the HIF application, accomplishments and challenges are summarized. HIF research and development has demonstrated the production of single ion beams with the required emittance, current, and energy suitable for injection into an induction linear accelerator. Driver scale beams have been transported in quadrupole channels of the order of 10% of the number of quadrupoles of a driver. We review the design and operation of induction accelerators and the relevant aspects of their use as drivers for HIF. We describe intermediate research steps that would provide the basis for a heavy-ion research facility capable of heating matter to fusion relevant temperatures and densities, and also to test and demonstrate an accelerator architecture that scales well to a fusion power plant.

Particle Beam Radiography

Particle beam radiography, which uses a variety of particle probes (neutrons, protons, electrons, gammas and potentially other particles) to study the structure of materials and objects noninvasively, is reviewed, largely from an accelerator perspective, although the use of cosmic rays (mainly muons but potentially also high-energy neutrinos) is briefly reviewed. Tomography is a form of radiography which uses multiple views to reconstruct a three-dimensional density map of an object. There is a very wide range of applications of radiography and tomography, from medicine to engineering and security, and advances in instrumentation, specifically the development of electronic detectors, allow rapid analysis of the resultant radiographs. Flash radiography is a diagnostic technique for large high-explosive-driven hydrodynamic experiments that is used at many laboratories. The bremsstrahlung radiation pulse from an intense relativistic electron beam incident onto a high-Z target is the source of these radiographs. The challenge is to provide radiation sources intense enough to penetrate hundreds of g/cm2 of material, in pulses short enough to stop the motion of high-speed hydrodynamic shocks, and with source spots small enough to resolve fine details. The challenge has been met with a wide variety of accelerator technologies, including pulsed-power-driven diodes, air-core pulsed betatrons and high-current linear induction accelerators. Accelerator technology has also evolved to accommodate the experimenters' continuing quest for multiple images in time and space. Linear induction accelerators have had a major role in these advances, especially in providing multiple-time radiographs of the largest hydrodynamic experiments.

直线感应加速器输运磁场遗传算法优化

直线感应加速器输运磁场遗传算法优化

多脉冲强流直线感应加速器测控系统中仪器通信与控制

多脉冲强流直线感应加速器测控系统中仪器通信与控制

Monte Carlo simulations for 20 MV X-ray spectrum reconstruction of a linear induction accelerator

To study the spectrum reconstruction of the 20 MV X-ray generated by the Dragon-I linear induction accelerator, the Monte Carlo method is applied to simulate the attenuations of the X-ray in the attenuators of different thicknesses and thus provide the transmission data. As is known, the spectrum estimation from transmission data is an ill-conditioned problem. The method based on iterative perturbations is employed to derive the X-ray spectra, where initial guesses are used to start the process. This algorithm takes into account not only the minimization of the differences between the measured and the calculated transmissions but also the smoothness feature of the spectrum function. In this work, various filter materials are put to use as the attenuator, and the condition for an accurate and robust solution of the X-ray spectrum calculation is demonstrated. The influences of the scattering photons within different intervals of emergence angle on the X-ray spectrum reconstruction are also analyzed.

High-power free-electron maser with frequency multiplication operating in a shortwave part of the millimeter wave range

The possibility of using frequency multiplication in order to obtain high-power short-wavelength radiation from a free-electron maser (FEM) with a Bragg resonator has been studied. Preliminary experiments with an LIU-3000 (JINR) linear induction accelerator demonstrate the operation of a frequency-multiplying FEM at megawatt power in the 6- and 4-mm wave bands on the second and third harmonic, respectively.

Beam-energy-spread minimization using cell-timing optimization

Beam energy spread, and related beam motion, increase the difficulty in tuning for multipulse radiographic experiments at the dual-axis radiographic hydrodynamic test facility's axis-II linear induction accelerator (LIA). In this article, we describe an optimization method to reduce the energy spread by adjusting the timing of the cell voltages (both unloaded and loaded), either advancing or retarding, such that the injector voltage and summed cell voltages in the LIA result in a flatter energy profile. We developed a nonlinear optimization routine which accepts as inputs the 74 cell-voltage, injector voltage, and beam current waveforms. It optimizes cell timing per user-selected groups of cells and outputs timing adjustments, one for each of the selected groups. To verify the theory, we acquired and present data for both unloaded and loaded cell-timing optimizations. For the unloaded cells, the preoptimization baseline energy spread was reduced by 34% and 31% for two shots as compared to baseline. For the loaded-cell case, the measured energy spread was reduced by 49% compared to baseline.

Conceptual design of an intense positron source based on an LIA

Accelerator based positron sources are widely used due to their high intensity. Most of these accelerators are RF accelerators. An LIA (linear induction accelerator) is a kind of high current pulsed accelerator used for radiography. A conceptual design of an intense pulsed positron source based on an LIA is presented in the paper. One advantage of an LIA is its pulsed power being higher than conventional accelerators, which means a higher amount of primary electrons for positron generations per pulse. Another advantage of an LIA is that it is very suitable to decelerate the positron bunch generated by bremsstrahlung pair process due to its ability to adjustably shape the voltage pulse. By implementing LIA cavities to decelerate the positron bunch before it is moderated, the positron yield could be greatly increased. These features may make the LIA based positron source become a high intensity pulsed positron source.

Magnetic cores made of an amorphous tape for the induction accelerator

It is proposed to use induction cells with cores wound by a thin tape made of an iron-based amorphous alloy in the linear induction accelerator for flash radiography. The comparison of pulse magnetization characteristics of the toroidal cores made with layer insulation and without it is given. The results of switching on of the injector based on the manufactured cores are presented.

A pulse power supply of the linear induction accelerator

A pulse power system of the induction electron accelerator intended for parameters of 2 MeV, 2 kA, and operating in the double-pulse mode is presented. The schematic diagram and main elements of the pulse system are described, and the main technical solutions intended to produce a set of pulses with 21-kV peak voltages, peak currents of up to 8 kA, and 200-ns durations across a resistive-inductive load are indicated. The experimental data, which were obtained when separate units and the whole power system operated on the rated duty, are given.

Outgassing property of carbon nanotube cathode with intense pulsed emission

In order to study the properties of the carbon nanotube(CNT) cathode with intense pulsed emission, the outgassing property of cathode is investigated on the 2MeV linear induction accelerator(LIA) injector. Results show that the cathode has a capability of desorbing gases from the CNT cathode under pulsed high voltage. The outgassing plays an important role in the formation of the cathode plasma. The amounts of outgassing for the several experiments are estimated to be 0.081.12PaL, the corresponding ratios between outgassing amount and electron number are roughly calculated to be in a range of 254203atoms/e- by numerical integral of pressure, showing that the cathode plasma is weakly ionized. The relationship between diode voltage, emission current density, outgassing amount, and the outgassing molecule number per electron are analyzed.

3D PIC Method for Modeling and Simulating the Beam Transport System of a Linear Induction Accelerator

Firstly, we introduced the architecture of the Linear Induction Accelerator Particle in Cell (LIAPIC) code, and the structure of the induction cell in a linear induction accelerator. Then, we used code to model an induction cell, and on this basis, we completed a numerical simulation of the solenoid coils and steering coils in the acceleration section by developing an independent calculation module for the magnetic components. Next, on the platform of the MPICH2 message passing system, we provided a proper method for computing in parallel more acceleration section in parallel and solved the great scale problems of the linear induction accelerator. Finally, the 18 acceleration section was simulated by using the software, and the results were compared with the envelope diagram of reference, which proved the correctness of the method used.

Beam Dynamics in a Long-pulse Linear Induction Accelerator

The second axis of the Dual Axis Radiography of Hydrodynamic Testing (DARHT) facility produces up to four radiographs within an interval of 1.6 microseconds. It accomplishes this by slicing four micro-pulses out of a long 1.8-kA, 16.5-MeV electron beam pulse and focusing them onto a bremsstrahlung converter target. The long beam pulse is created by a dispenser cathode diode and accelerated by the unique DARHT Axis-II linear induction accelerator (LIA). Beam motion in the accelerator would be a problem for radiography. High frequency motion, such as from beam breakup instability, would blur the individual spots. Low frequency motion, such as produced by pulsed power variation, would produce spot to spot differences. In this article, we describe these sources of beam motion, and the measures we have taken to minimize it.

Suppressing beam-centroid motion in a long-pulse linear induction accelerator

The second axis of the dual-axis radiography of hydrodynamic testing (DARHT) facility produces up to four radiographs within an interval of $1.6\text{ }\text{ }\ensuremath{\mu}\mathrm{s}$. It does this by slicing four micropulses out of a $2\mathrm{\text{\ensuremath{-}}}\ensuremath{\mu}\mathrm{s}$ long electron beam pulse and focusing them onto a bremsstrahlung converter target. The 1.8-kA beam pulse is created by a dispenser cathode diode and accelerated to more than 16 MeV by the unique DARHT Axis-II linear induction accelerator (LIA). Beam motion in the accelerator would be a problem for multipulse flash radiography. High-frequency motion, such as from beam-breakup (BBU) instability, would blur the individual spots. Low-frequency motion, such as produced by pulsed-power variation, would produce spot-to-spot differences. In this article, we describe these sources of beam motion, and the measures we have taken to minimize it. Using the methods discussed, we have reduced beam motion at the accelerator exit to less than 2% of the beam envelope radius for the high-frequency BBU, and less than $1/3$ of the envelope radius for the low-frequency sweep.