Linear Induction Accelerator Research Articles

Three-dimensional Poisson solver for a charged beam with large aspect ratio in a conducting pipe

In this paper, we present a three-dimensional Poisson equation solver for the electrostatic potential of a charged beam with large longitudinal to transverse aspect ratio in a straight and a bent conducting pipe with open-end boundary conditions. In this solver, we have used a Hermite–Gaussian series to represent the longitudinal spatial dependence of the charge density and the electric potential. Using the Hermite–Gaussian approximation, the original three-dimensional Poisson equation has been reduced into a group of coupled two-dimensional partial differential equations with the coupling strength proportional to the inverse square of the longitudinal-to-transverse aspect ratio. For a large aspect ratio, the coupling is weak. These two-dimensional partial differential equations can be solved independently using an iterative approach. The iterations converge quickly due to the large aspect ratio of the beam. For a transverse round conducting pipe, the two-dimensional Poisson equation is solved using a Bessel function approximation and a Fourier function approximation. The three-dimensional Poisson solver can have important applications in the study of the space-charge effects in the high intensity proton storage ring accelerator or induction linear accelerator for heavy ion fusion where the ratio of bunch length to the transverse size is large.

Erratum: Ion-hose instability in a long-pulse linear induction accelerator [Phys. Rev. ST Accel. Beams6, 030401 (2003)

Erratum: Ion-hose instability in a long-pulse linear induction accelerator [Phys. Rev. ST Accel. Beams<b>6</b>, 030401 (2003)

Investigation of a Relativistic Magnetron Supplied from a High-Current Linear Induction Accelerator

The physical processes in a system relativistic microwave generator - power supply unit with a strong feedback are investigated. A computer model is constructed to calculate the output parameters of these systems substituted by equivalent circuits. A model is constructed for a linear induction accelerator based on magnetic elements intended for operation with relativistic magnetrons the nonlinear units of the equivalent circuit of which are calculated in the context of the theory of average motion.

Ion-hose instability in a long-pulse linear induction accelerator

The ion-hose instability is a transverse electrostatic instability which occurs on electron beams in the presence of a low-density ion channel. It is a phenomenon quite similar to the interaction between electron clouds and proton or positron beams in high-energy accelerators and storage rings. In the DARHT-2 accelerator, the 2-kA, $2\mathrm{\text{\ensuremath{-}}}\ensuremath{\mu}\mathrm{s}$ beam pulse produces an ion channel through impact ionization of the residual background gas (${10}^{\ensuremath{-}7}--{10}^{\ensuremath{-}6}\text{ }\mathrm{torr}$). A calculation of the linear growth by Briggs indicates that the instability could be strong enough to affect the radiographic application of DARHT, which requires that transverse oscillations be small compared to the beam radius. We present semianalytical theory and 3D particle-in-cell simulations (using the Lsp code) of the linear and nonlinear growth of the instability, including the effects of the temporal change in the ion density and spatially decreasing beam radius. We find that the number of $e$-foldings experienced by a given beam slice is given approximately by an analytic expression using the local channel density at the beam slice. Hence, in the linear regime, the number of $e$-foldings increases linearly from head to tail of the beam pulse since it is proportional to the ion density. We also find that growth is strongly suppressed by nonlinear effects at relatively small oscillation amplitudes of the electron beam. This is because the ion oscillation amplitude is several times larger than that of the beam, allowing nonlinear effects to come into play. An analogous effect has recently been noted in electron-proton instabilities in high-energy accelerators and storage rings. For DARHT-2 parameters, we find that a pressure of $\ensuremath{\le}1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\text{ }\mathrm{torr}$ is needed to keep the transverse beam oscillation amplitude less than about 20% of the rms beam radius.

Wide-Range Inductive Sensors of Currents with Nanosecond Rise Times for Measuring Parameters of High-Current Pulses (Review)

The design and characteristics of inductive current sensors (modernized Rogovski coils) and inductive sensors on their basis (in the form of a part of a tore) with shielded coils for measuring the parameters of pulse currents in conductors with diameters of up to 1.7 m and electron beam currents of 10–2000 kA with durations of 10–100 ns in a self-integration mode. The Rogovski coils and sensors have current rise times of nanosecond duration and improved noise immunity and mechanical strength. Methods for the calibration of Rogovski coils for determining their transient response and amplitude sensitivity are presented. Specific features of the certification of large-diameter devices are pointed out, and a new method for certifying such sensors is expounded. The sensors are used in experimental investigations and the refinement of units of high-current linear induction accelerators as well is in the starting and adjustment work with a high-power LIA-30 electron accelerator with water-insulated radial lines in the inductors of accelerating modules and for monitoring its parameters (40 MeV, 100 kA, 20 ns). Such sensors are applicable for recording pulse current characteristics in other electrophysical facilities.

A high-power vircator based on an ironless linear induction accelerator of electrons

A high-power vircator that is based on the Korvet ironless linear induction electron accelerator built around radial pulse-forming lines is implemented for the first time. Results on the computer simulation and experimental optimization of the vircator are discussed. The experimentally found parameters of the vircator are the following: cathode current 35 kA (at a limit current of 19 kA), microwave pulse base widths 40 and 18 ns, and peak microwave power more than 500 MW.

Linear Induction Accelerators with Magnetic Elements

A new class of linear induction accelerators with magnetic elements used as the sources of electron beams for relativistic high-power microwave generators is presented [1, 2]. Such accelerators have been under development at the Nuclear Physics Institute of Tomsk Polytechnical University (NPI TPU) since the 1990s on the basis of an original configuration with the use of low-impedance strip forming limes laid over the induction system as an Archimed helix [4]. By now, the designed accelerators have electron energies of 0.4–2.4 MeV at currents of 2–6 kA and pulse repetition rates of up to 400 Hz in the continuous operation mode and up to 3.3 kHz in the pulse-burst mode.

Application of fast CVD diamond photoconductor detectors to MeV X-ray metrology for the AIRIX flash radiographic facility

Diamond has many attractive properties which make it an ideal material for X-ray dosimetry both in physics experiments and medical fields. However, diamond detector abilities have not been well explored under pulsed X-ray irradiations in the range of the MeV energy. To improve the measurement accuracy for use with quantitative radiography of very dense object undergoing an implosion, the detector Mucaddix, composed with five X-ray CVD diamond-sensitive elements, has been developed. It will be integrated into the nearby structures of AIRIX, an induction linear accelerator which is now built in CEA Moronvilliers for detonic experiments with MeV- Bremsstrahlung radiation fields of more than 500 rad per pulse at 1 m from the source. This paper describes, the specifications required for the AIRIX hardness environment, the detector design, and presents experimental results from BALZAC III, a MeV X-ray flash generator.

TLD Audit in Radiotherapy in the Czech Republic

The National Radiation Protection Institute in Prague organises the TLD audit. The aim of the audit is to provide a basic control of clinical dosimetry in the Czech Republic for purposes of state supervision in radiotherapy. The TLD audit covers absorbed dose measurements under reference conditions for 60 Co and 137 Cs beams, high energy X ray and electron beams of linear accelerators and betatrons. Absorbed dose measured by TLD is compared with absorbed dose stated by the radiotherapy centre. Encapsulated LiF:Mg,Ti powder is used for the measurement. A deviation of ±3% between the stated and TLD measured dose is considered acceptable. The first TLD audit was in 1997. A total of 110 beams were checked. Seven major deviations (more than ±6%) were found, which were investigated in depth. Medical physicists from these departments reported a set-up error. However, at most of those hospitals with major deviations, an in situ audit in detail was carried out soon after the TLD audit. Discrepancies were found in clinical dosimetry but some of the irradiation units were poor, technically. Regular TLD audit seems to be a good way of eliminating errors in basic clinical dosimetry.

Derivation of scaling laws for intense light ion beam divergence with the KALIF–HELIA accelerator

A short description of a new accelerator called KALIF–HELIA is given, that is presently under construction at the Forschungszentrum Karlsruhe. This High Energy Linear Induction Accelerator couples a self-magnetically insulated transmission line with the induction linac technology: the 1 MV pulses from 6 induction cells are added in a “magnetically insulated voltage adder” (MIVA) delivering for 50 ns a pulse of 6 MV and 400 kA to a matched load. This technology is considered in all light ion beam driven reactor concepts as a low cost alternative for the production of energy by inertial fusion (IFE). The pulses delivered by these generators are coupled to diodes that generate the intense light ion beams. Focusing of these beams is presently insufficient and requires scaling to IFE conditions. However, the available scaling laws for beam divergence are not in agreement with the few results from experiments performed at high power levels. Therefore, a verification and improvement of these scaling laws is necessary in order to extrapolate more reliably to beams needed for IFE conditions. For the start-up phase – foreseen for end 1997 – KALIF–HELIA will be operated first in negative polarity generating an electron beam. The subsequent operation of the accelerator in positive polarity will allow the verification of the voltage dependence in the divergence scaling laws for proton beams and acceleration voltages up to 6 MV. In a second step, the predicted influence of the ion mass on the beam divergence will be investigated by accelerating Li + ions instead of protons.

Status of experiments leading to a small recirculator

A heavy ion linear induction accelerator is considered to be the leading driver candidate for an Inertial Fusion Energy reactor. To deliver a space-charge-dominated beam at the appropriate energy (several GeV), such an accelerator would be several kilometers in length. Since total length has a strong influence on accelerator cost, we are considering the potential advantages and practical implementation of a recirculating induction accelerator. To address the critical scientific and technical challenges of a recirculating space-charge-dominated heavy ion beam, we have begun to develop the elements of a scaled “small recirculator”. An operating recirculator must demonstrate full beam control including multi-lap operation, beam insertion/extraction, acceleration and pulse compression. At present, experiments have been conducted using a 2 mA, 80 keV K + beam transported through a 45° bend; experiments on a 90° bend with five induction modulators will begin soon. This paper briefly summarizes the recirculator specifications and operational features and reports the latest experimental data as well as the developmental status of beam diagnostics.

Single-mode and multimode operation conditions in JINR-IAP millimeter-wave FEL-oscillator

The influence of the Q-factor of a two-mirror Bragg resonator on the efficiency and spectrum of radiation was studied both theoretically and experimentally for the JINR-IAP millimeter-wave free-electron laser (FEL)-oscillator driven by a linear induction accelerator (1 MeV/200 A/200 ns). In accordance with theoretical predictions, single-frequency operation in a low (optimal) Q-factor resonator and multifrequency operation in a high Q-factor resonator were observed. For an optimal resonator configuration at the frequency 31 GHz, single-mode generation with power of approximately 35 MW and efficiency of 26% was obtained. A significant drop in FEL efficiency was observed for multifrequency generation.

Experimental observation of mode competition and single-mode operation in JINR-IAP millimeter-wave FEM oscillator

The paper is devoted to a progress in experimental study of Bragg FEM-oscillator with reversed guide magnetic field based on a linear induction accelerator (0.8 MeV/200 A/200 ns). In accordance with theoretical predictions single-frequency operation in a low- Q-factor resonator and multi-frequency operation in a high- Q-factor resonator were observed. Under optimal resonator configuration at the frequency 31 GHz single-mode generation with power 35 MW and efficiency 26% was obtained.

CONFINEMENT OF ELECTRON BEAMS BY MESH ARRAYS IN A RELATIVISTIC KLYSTRON AMPLIFIER

Theoretical and experimental results of intense beam confinement by conducting meshes in a relativistic klystron amplifier (RKA) are presented.Electron motions in a steady intense electron beam confined by conducting meshes are analyzed with an approximate space charge field distribution. And the conditions for steady beam transportation are discussed.Experimental results of a long distance (60cm) transportation of an intense beam (400kV,2.5kA) generated by a linear induction accelerator are presented.Experimental results of modulated beam transportation confined by the mesh array are presented also.The results show that the focusing ability of the conducting meshes is not very sensitive to the beam energy.And the meshes can be used effectively in a RKA to replace the magnetic field system.

Beam dynamics studies with the heavy-ion linear induction accelerator MBE-4

Current amplification of heavy-ion beams is an integral feature of the induction linac approach to heavy-ion fusion (HIF). In this paper we report on amplification experiments conducted on a single beam of the Multiple Beam Experiment (MBE-4), a heavy-ion (Cs+) induction linac. Earlier MBE-4 experiments [H. Meuth et al., Nucl. Instrum. Methods Phys. Res. A 278, 153 (1989)] had demonstrated up-to-9× current amplification but had been accompanied by an up-to-2× increase of normalized transverse emittance. Experiments to pinpoint the causes of this emittance growth indicated various factors were responsible, including focusing aberrations and mismatch difficulties between the injector diode and the accelerator transport lattice, a localized quadrupole misalignment problem, and the interaction of transversely large beams with the nonlinear elements of the focusing lattice. Following ameliorative measures, new current amplification experiments, both with and without acceleration, showed that current amplifications of up to 3× and line charge density increases of up to ≈2× could be achieved without increasing the beam’s normalized transverse emittance. Finally, both the transverse beam dynamics, and beam current and energy measurements were accurately modeled by numerical particle-in-cell simulations and longitudinal dynamics codes, respectively.

Physics design and scaling of recirculating induction accelerators: from benchtop prototypes to drivers

Recirculating induction accelerators (recirculators) have been investigated as possible drivers for inertial fusion energy production because of their potential cost advantage over linear induction accelerators. Point designs were obtained by Barnard et al. (UCRL-LR-108095, 1991; Phys. Fluids B Plasma Phys. 5 (1993), 2698) and many of the critical physics and technology issues that would need to be addressed were detailed. A collaboration (Friedman et al., 32–33 (1996) 235) involving Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory researchers is now developing a small prototype recirculator in order to demonstrate an understanding of nearly all the critical beam dynamics issues that have been raised by Barnard et al. and subsequently. We review the design equations for recirculators (which have been incorporated into a MATHEMATICA-based design code) and demonstrate how, by keeping crucial dimensionless quantities constant, a small prototype recirculator was designed which will simulate the essential beam physics of a driver. We further show how important physical quantities such as the sensitivity to errors of optical elements (in both field strength and placement), insertion-extraction, vacuum requirements and emittance growth scale from small prototype to driver-size accelerator.

Elise plans and progress

Elise is a heavy-ion induction linear accelerator that will demonstrate beam manipulations required in a driver for inertial fusion energy. With a line charge density similar to that of heavy-ions drivers, Elise will accelerate a beam pulse (duration of 1 μs or more) of K + ions from an initial energy of 2 MeV to a final energy 5 MeV or more. In the present design, the Elise electrostatic quadrupoles (ESQs) will have an aperture of radius 2.33 cm operating at ± 59 kV. The half-lattice periods range from 21 to 31 cm. The entire machine will be approximately 30 m long, half of which is the induction accelerator with the remaining half being the injector (including the Marx generator) and the matching section. Elise will be built in a way that allows future expansion into the full Induction Linear Accelerator Systems Experiments (ILSE) configuration, so it will have an array of four ESQ focusing channels capable of transporting up to a total of 3.2 A of beam current. Elise will also have an active alignment system with an alignment tolerance of less than 0.1 mm. Initially, only one beam channel will be used during nominal Elise operation. At the currently expected funding rate, the construction time will be 4.75 years, with FY95 being an extra year for research and development before construction. Total project cost is estimated to be US$25.9m, including contingency costs.

Physics design and scaling of Elise

Elise is an electrostatically focused heavy-ion accelerator being designed and constructed at Lawrence Berkeley Laboratory. The machine is intended to be the first half of the four-beam Induction Linear Accelerator (LINAC) Systems Experiment (ILSE), which will ultimately test the principal beam dynamics issues and manipulations of induction heavy-ion drivers for inertial fusion. Elise will use an existing 2 MeV injector and will accelerate space-charge-dominated pulses to greater than 5 MeV. The design objective of Elise is to maximize the output beam ‘rules of thumb’ used for choosing the beam and lattice parameters for heavy-ion induction accelerators, and we discuss incorporating these relations in a spreadsheet program that generates internally consistent lattice layouts and acceleration schedules. These designs have been tested using a one-dimensional particle simulation code (SLIDE), a three-dimensional fluid/envelope code (CIRCE) and a three-dimensional particle-in-cell code (WARP3d). Sample results from these calculations are presented. Results from these dynamics codes are also shown, illustrating sensitivities to beam and lattice errors, and testing various strategies for longitudinal confinement of the beam ends.

Quadrupole field geometries for intense electron beam acceleration

High-intensity electron beams could be focused in low-frequency RF accelerators and induction linear accelerators by adding transverse components to the accelerating electric field. Calculations with a 3D code show that quasielectrostatic focusing is sufficient to transport kiloampere electron beams in RF accelerators and the high-energy sections of induction accelerators. The elimination of conventional magnetic focusing systems could lead to reductions in the volume and weight of high-current electron accelerators. Two novel quadrupole geometries are investigated: a periodic array of spherical electrodes with alternating displacements and a set of plate electrodes with elliptical apertures.

FEL system with the linear induction accelerator as the laser fusion reactor driver

An FEL based energy driver for inertial confinement fusion (ICF) is proposed. Construction of such a driver becomes possible due to application of a novel FEL amplifier scheme — a multi-channel, multi-stage FEL amplifier with a diaphragm focusing line. The driving beam for the FEL amplifier is generated by the linear induction accelerator. The laser system operates at the radiation wavelength of 0.5 μm with the total energy of laser flash of 1.5 MJ, pulse duration of 4 ns and repetition rate of 40 pulses/s. Total efficiency (i.e. conversion efficiency of net electrical power to the radiation power) of the proposed system is equal to 12%. The brightness of the output radiation is 10 22 W/cm 2 sr. The scale and the cost of the FEL based energy driver are close to those of the heavy ion fusion driver.