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Vacuum surface flashover switch is a promising technique scheme of high repetitive frequency fast-closing switch applied to dielectric wall accelerator. In this paper, the switch is experimentally investigated, and a nanosecond pulse with 2.02-ns effective rise time is obtained. For a cylinder-fused quartz dielectric, the breakdown field of the switch is near 55 kV/cm, and the value for the frustoconical-shaped dielectric exceeds 120 kV/cm with a lifetime up to 69000 discharges. The repetitive frequency ability of the switch is better than 100 Hz, and the breakdown voltage increases slightly with higher frequency.

Benefiting from solid-state pulsed power system with GaAs-PCSS, dielectric wall accelerator (DWA) as a new kind of high acceleration gradient accelerator has a compact construction that makes it quite suitable for some certain applications, such as proton tumor treatment and industrial inspection. The solid-state pulsed power system is made up of several groups of pulsed power units. Each group contains 2 to 4 units, and each unit is set up as a 2-stage Blumlein line. It is constituted by GaAs-PCSS (Photoconductive Semiconductor Switch) and plate pulse forming lines, which are made of high-performance dielectric ceramic. The GaAs PCSS triggered by a high power laser diode driver works in nonlinear mode and its bias voltage and conduction current can be up to 20 kV and 800 A respectively. In the experiments, the 2-BL unit can provide a 34 kV, 10 ns pulse. Several groups have been used to load accelerating tubes at different intervals so as to accelerate the proton beams which are just passing through. Until now, the solid-state pulsed power system has performed well and a system with 6 groups (14 units in total) can accelerate proton from 40 keV (after the kicker) to 380 keV.

To demonstrate the acceleration capability of a Dielectric Wall Accelerator (DWA), a proton injector has been developed at Peking University (PKU). It is composed of a compact permanent magnet 2.45 GHz Electron Cyclotron Resonance Ion Source (PKU PMECRIS) associated with a LEBT of two electrostatic Einzel lenses [1]. This injector is named as Advanced Injector System of Light Ions (AISLI). The acceptance tests have been performed with a 40 keV–55 mA hydrogen beam successfully passing through a ϕ 10 mm aperture diaphragm. This diaphragm is located 200 mm downstream the plasma emission hole at the location of the future DWA entrance flange. The beam rms emittance reached about 0.10 π mm mrad in pulsed mode. This article describes the AISLI experimental setup, the measurement principle and the obtained beam characteristics.

A simulation study of a short-pulsed proton injector for, and beam transport in, a dielectric wall accelerator (DWA) has been carried out using the particle-in-cell (PIC) code Warp. It was shown that applying “tilt pulse” voltage waveforms on three electrodes enables the production of a shorter bunch by the injector. The fields in the DWA beam tube were simulated using Computer Simulation Technology’s Microwave Studio (CST MWS) package, with various choices for the boundary conditions. For acceleration in the DWA, the beam transport was simulated with Warp, using applied fields obtained by running CST MWS. Our simulations showed that the electric field at the entrance to the DWA represents a challenging issue for the beam transport. We thus simulated a configuration with a mesh at the entrance of the DWA, intended to improve the entrance field. In these latter simulations, a proton bunch was successfully accelerated from 130 keV to about 36 MeV in a DWA with a length of 36.75 cm. As the beam bunch progresses, its transverse dimensions diminish from (roughly) 0.5×0.5 cm to 0.2×0.4 cm. The beam pulse lengthens from 1 cm to 2 cm due to lack of longitudinal compression fields.

Two types of dielectric wall accelerator (DWA) structures, a bi-polar Blumlein line and zero integral pulse line (ZIP) structures were investigated. The high gradient insulator simulated by the particle in cell code confirms that it has little influence on the axial electric field. The results of simulations using CST microwave studio indicate how the axial electric field is formed, and the electric field waveforms agree with the theoretical one very well. The influence of layer-to-layer coupling in a ZIP structure is much smaller and the electric field waveform is much better. The axial of the Blumlein structure's electric field has better axial stability. From both of the above, it found that for a shorter pulse width, the axial electric field is much higher and the pulse stability and fidelity are much better. The CST simulation is very helpful for designing DWA structures.

Two types of pulse forming lines for dielectric wall accelerator (DWA) were investigated preliminarily. By simulation with CST Microwave Studio, the results indicate the pulse forming process, which can help to understand the voltage wave transmission process and optimize the line parameters. Furthermore, the principle of the pulse forming process was proved by experiments and some excellent pulse waveforms were obtained. During the experiments, the Blumlein line and zero integral pulse (ZIP) forming line, constructed with aluminum foil, poly plate and air gap self-closing switch, were tested. The full width at half maximum (FWHM) of the waveform is 16 nanoseconds (BL) and 17 nanoseconds (ZIP line), and the formed pulse voltage amplitude is 5 kV (BL) and +2.2 kV/–1.6 kV (ZIP line). The experiments result coincides well with the simulation.

An increasing number of proton therapy facilities are being planned and built at hospital based centers. Most facilities are employing traditional dose delivery methods. A second generation of dose application techniques, based on pencil beam scanning, is slowly being introduced into the commercially available proton therapy systems. New developments in accelerator physics are needed to accommodate and fully exploit these new techniques. At the same time new developments such as the development of small cyclotrons, Dielectric Wall Accelerator (DWA) and laser driven systems, aim for smaller, single room treatment units. In general the benefits of proton therapy could be exploited optimally when achieving a higher level in accuracy, beam energy, beam intensity, safety and system reliability. In this review an overview of the current developments will be given followed by a discussion of upcoming new technologies and needs, like increase of energy, on-line MRI and proton beam splitting for independent uses of treatment rooms.

The Beam Research Program at Lawrence Livermore National Laboratory is continuing development of the dielectric wall accelerator (DWA), a type of accelerator which uses stacked pulse-forming lines (PFLs) to apply an accelerating field directly to the beam through a nonconducting vacuum boundary. Here, we report operation of a DWA as an electron diode using a surface flashover plasma cathode. Peak perveances in excess of 6 times 10-6A/V3/2 were measured, with current extraction and pulse train format depending on flashover source timing and PFL switching speed.

Dielectric wall accelerators, a class of induction accelerators, employ a novel insulating beam tube to impress a longitudinal electric field on a bunch of charged particles. The surface flashover characteristics of this tube may permit the attainment of accelerating gradients on the order of 100 MV/m for accelerating pulses on the order of a nanosecond in duration. A virtual traveling wave of excitation along the tube is produced at any desired speed by controlling the timing of pulse-generating modules that supply a tangential electric field to the tube wall. Because of the ability to control the speed of this virtual wave, the accelerator is capable of handling any charge-to-mass-ratio particle; hence it can be used for electrons, protons and any ion. The accelerator architectures, key technologies and development challenges will be described.

A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is being developed as a compact flash X-ray radiography source. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be presented.

Semi-insulating Silicon Carbide (SiC) is an attractive material to use to construct high voltage, compact, photoconducting semiconductor switches (PCSS) due to its large bandgap, high critical electric field strength, high electron saturation velocity, and high thermal conductivity. The critical field strength of 3 MV/cm of 6H-SiC makes it particularly attractive for compact, high voltage, fast switching applications such as a Dielectric Wall Accelerator (DWA). To realize the benefits of the high bulk electric field strength of SiC and diffuse switch current, carriers must be excited throughout the bulk of the photo switch. Photoconducting switches with opposing electrodes were fabricated on "a" plane, Vanadium compensated, semi-insulating, 6H-SiC substrates. The PCSS devices were switched by optically exciting deep extrinsic levels lying within the 6H-SiC bandgap. The SiC photoswitches were tested up to a bias voltage of 11000 V with a corresponding peak current of 150 A. The 6H-SiC substrates withstood average electric fields up to 27 MV/m. Minimum PCCS dynamic resistances of 2 and 10 Ohms were obtained with 13 mJ optical pulses at 532 and 1064 nm wavelengths, respectively.

Compact solid-state system is the main development trend in pulsed power technologies. A compact solid-state high-voltage nanosecond pulse generator with output voltage of 300 kV amplitude, 10 ns duration (FWHM), and 3 ns rise-time was designed for a dielectric wall accelerator. The generator is stacked by 15 planar-plate Blumlein pulse forming lines (PFL). Each Blumlein PFL consists of two solid-state planar transmission lines, a GaAs photoconductive semiconductor switch, and a laser diode trigger. The key components of the generator and the experimental results are reported in this paper.

The Compact Particle Accelerator Corporation is developing a Dielectric Wall Accelerator to produce pulsed proton beams for treatment of cancers. The accelerator subsystems include a RFQ proton injection system and a pulsed kicker for selecting the desired proton bunches. The linear accelerator is consists of a high gradient insulator beam pipe and stacked transmission lines, driven using optical switches, producing the required accelerating gradient. An engineering prototype has been constructed and initial experiments have been conducted. Results obtained from the engineering prototype support the development of a compact, single room, 150 MeV scanning beam medical system capable of modulating energy, beam current and spot size on a shot to shot basis within the next three years. The medical system will be intended for installation in existing facilities and will enable significant proliferation of proton therapy centers because of the significant reduction in both the cost of acquisition and cost of ownership. The paper will discuss the status of the accelerator development with focus on the design of the pulsed power system.

The Dielectric Wall Accelerator (DWA) offers the potential to produce a high gradient linear accelerator for proton therapy and other applications. The current status of the DWA for proton therapy will be reviewed. Recent progress in SiC photoconductive switch development will be presented. There are serious beam transport challenges in the DWA arising from short pulse excitation of the wall. Solutions to these transport difficulties will be discussed.

A compact accelerator system architecture based on the dielectric wall accelerator (DWA) for medical proton beam therapy has been developed by the Compact Particle Acceleration Corporation (CPAC). The major subsystems are a Radio Frequency Quadrupole (RFQ) injector linac, a pulsed kicker to select the desired proton bunches, and a DWA linear accelerator incorporating a high gradient insulator (HGI) with stacked Blumleins to produce the required acceleration energy. The Blumleins are switched with solid state laser‐driven optical switches integrated into the Blumlein assemblies. Other subsystems include a high power pulsed laser, fiber optic distribution system, electrical charging system, and beam diagnostics. An engineering prototype has been constructed and characterized, and these results will be used within the next three years to develop an extremely compact 150 MeV system capable of modulating energy, beam current, and spot size on a shot‐to‐shot basis. This paper presents the details the engineering prototype, experimental results, and commercialization plans.

To study the beam instability caused by wake field effect, a dielectric wall accelerator module model consisting of symmetric pulse forming line, micro-stacked insulator and conductor layer was established. The finite integral method was used to simulate the wake field in the accelerating structure of dielectric wall accelerator (DWA) for high-current electron beam, wake potential and wake field impedance were calculated for the single and two accelerating units. Structural parameters of distance between two modules, thickness of metal and dielectric constant of insulator in micro-stacked insulator were changed to study the influence of different parameters on wake field. The results shows the wake potential and wake field impedance was small in x, y direction and different structural parameters can influence the wake field effect. Also it proved the advantage of accelerating cavity length and continuity in the DWA structure.

High gradient insulating technology is one of the key technologies in new type dielectric wall accelerator. Micro-stacked insulators were prepared and preliminary experiment was done in this paper. Using high temperature laminated method, two types of micro-stacked insulators were designed and fabricated. The first was fabricated from interleaved layers of brass and polyimide (PI), and the other was fabricated from stainless steel and fluorinated ethylene propylene (FEP). Surface state of insulators was observed and out-gassing characteristics in vacuum were also detected. Based on the nanosecond (10ns/30ns) pulsed experimental platform, the vacuum surface flashover characteristics of micro-stacked samples were tested. Micro-stacked insulators exhibited favorable vacuum surface flashover performance and the maximum flashover field strength was close to 180kV/cm.

A novel compact CT-guided intensity modulated proton radiotherapy (IMPT) system is described. The system is being designed to deliver fast IMPT so that larger target volumes and motion management can be accomplished. The system will be ideal for large and complex target volumes in young patients. The basis of the design is the dielectric wall accelerator (DWA) system being developed at the Lawrence Livermore National Laboratory (LLNL). The DWA uses fast switched high voltage transmission lines to generate pulsed electric fields on the inside of a high gradient insulating (HGI) acceleration tube. High electric field gradients are achieved by the use of alternating insulators and conductors and short pulse times. The system will produce individual pulses that can be varied in intensity, energy and spot width. The IMPT planning system will optimize delivery characteristics. The system will be capable of being sited in a conventional linac vault and provide intensity modulated rotational therapy. Feasibility tests of an optimization system for selecting the position, energy, intensity and spot size for a collection of spots comprising the treatment are underway. A prototype is being designed and concept designs of the envelope and environmental needs of the unit are beginning. The status of the developmental new technologies that make the compact system possible will be reviewed. These include, high gradient vacuum insulators, solid dielectric materials, SiC photoconductive switches and compact proton sources.

Summary form given only. The dielectric wall accelerator (DWA) is a compact pulsed power device where the pulse forming lines, switching, and vacuum wall is integrated into a single compact geometry. We are presently in the process of fabricating an accelerator cell for test on ETA-II (a 5.5 MeV, 2 kA, 70 ns pulsewidth electron beam accelerator). For this effort, we embarked on an extensive compact pulsed power development program and have pursued the study of switching (gas, oil, laser induced surface flashover and photoconductive), dielectrics (ceramics and nanoparticle composites), pulseforming line topologies (asymetric and symetric Blumleins and zero integral pulse forming lines) and multilayered vacuum insulator (HGI) technology. We review our past results and report on the progress of accelerator cell testing.

The Dielectric Wall Accelerator (DWA) is an approach for manufacturing particle accelerators that can be an order of magnitude more compact than conventional accelerators. To realize the associated high level of electric field gradient it is necessary to develop and characterize materials that can maintain electric fields in excess of 100 MV/m (=1MV/cm). This high value for the breakdown strength must be maintained for many thousands of pulses under conditions of voltage reversal. The present work reports the performance of a candidate composite material composed of high dielectric constant nanoparticles dispersed in an epoxy matrix loaded to achieve a dielectric constant = 10. The effect of peak voltage on number of pulses that can be sustained is given. In addition the effects of electrode gap spacing and charging rate are explored.

High energy density materials are being developed for use in pulsed power area, such as Transmission Line in pulse generator, symmetric Blumlein or asymmetric Blumlein in Dielectric wall Accelerator. The High energy density materials could reduce the device physical size and improve the device's efficiency. The ceramics and polymer/ceramics composition have been studied in our lab. To increase the breakdown strength, the dielectric compositions are being developed based on glass, and Epoxy. The nano-technology has been used in glass composite for getting better electrical performance. The diameter of BaTiO3 powder adding in epoxy is about 2 to 4 micron. The test samples have been fabricated. The permittivitv of glass/BaTiO3 is over 400 and its field strengths over 100 kV/cm and 300 kV/cm under DC voltage and nanosecond pulses, respectively.

Proton accelerator structures for medical applications using Dielectric Wall Accelerator (DWA) technology allow for the utilization of high electric field gradients on the order of 100 MV/m to accelerate the proton bunch. Medical applications involving cancer therapy treatment usually desire short bunch lengths on the order of hundreds of picoseconds in order to limit the extent of the energy deposited in the tumor site (in 3D space, time, and deposited proton charge). Electromagnetic simulations of the DWA structure, in combination with injections of proton bunches have been performed using 3D finite difference codes in combination with particle pushing codes. Electromagnetic simulations of DWA structures includes these effects and also include the details of the switch configuration and how that switch time affects the electric field pulse which accelerates the particle beam.

A compact proton accelerator for medical applications is being developed at Lawrence Livermore National Laboratory. The accelerator architecture is based on the dielectric wall accelerator (DWA) concept. One critical area to consider is the switch region. Electric field simulations and thermal calculations of the switch area were performed to help determine the operating limits of silicon carbide (SiC) switches. Different geometries were considered for the field simulation including the shape of the thin indium solder meniscus between the electrodes and SiC. Electric field simulations were also utilized to demonstrate how the field stress could be reduced. Thermal simulations results were analyzed to find the average power capability of the switches.

As part of our ongoing development of the dielectric wall accelerator, we are studying the performance of multilayer high-gradient insulators. These vacuum insulating structures are composed of thin, alternating layers of metal and dielectric, and have been shown to withstand higher gradients than conventional vacuum insulator materials. This paper describes these structures and presents some of our recent results.

The dielectric wall accelerator (DWA) is a compact induction accelerator structure that incorporates the accelerating mechanism, pulse forming structure, and switch structure into an integrated module. The DWA consists of stacked stripline Blumlein assemblies, which can provide accelerating gradients in excess of 100 MeV/meter. Blumleins are switched sequentially according to a prescribed acceleration schedule to maintain synchronism with the proton bunch as it accelerates. A finite difference time domain code (FDTD) is used to determine the applied acceleration field to the proton bunch. Particle simulations are used to model the injector as well as the accelerator stack to determine the proton bunch energy distribution, both longitudinal and transverse dynamic focusing, and emittance growth associated with various DWA configurations.

A compact dielectric wall accelerator (DWA)[1,2,3], with field gradient up to 100 MW/m is being developed to accelerate proton bunches for use in cancer therapy treatment. The injector must create a proton pulse up to several hundred picoseconds, which is then shaped and accelerated with energies up to 250 MeV. The particle-in- cell (PIC) code LSP is used to model several aspects of this design. First, we use LSP to obtain the voltage waveform in the A-K gap that will produce a proton bunch with the requisite charge. We then model pulse compression and shaping in the section between the A-K gap and the DWA. We finally use LSP to model the beam transport through the DWA.

A new type of compact induction accelerator is under development at the Lawrence Livermore National Laboratory that promises to increase the average accelerating gradient by at least an order of magnitude over that of existing induction machines. The machine is based on the use of high gradient vacuum insulators, advanced dielectric materials and switches and is stimulated by the desire for compact flash X-ray radiography sources. Research describing an extreme variant of this technology aimed at proton therapy for cancer will be described. Progress in applying this technology to several applications will be reviewed.

We are developing compact pulsed power systems for various defense missions. Although the system is primarily intended for pulsed radiography, its modularity makes it well suited for compact neutron sources for explosives detection and as an HPM driver for various DOD missions. To date, we have performed extensive research at the component level and are now pursuing the integration of the technology into a single accelerator cell. Cost is 10J/cm3), specialized transmission line designs, HGI insulator technology, multi-gap low jitter (

Using dielectric wall accelerator technology, we are developing a compact induction accelerator system primarily intended for pulsed radiography. The accelerator would provide a 2-kA beam with an energy of 8 MeV, for a 20-30 ns flat-top. The design goal is to generate a 2-mm diameter, 10-rad x-ray source. We have a physics design of the system from injector to the x-ray converter. We present the results of injector modeling and PIC simulations of beam transport. We also discuss the predicted spot size and the on-axis x-ray dose.

Dielectric Wall Accelerator (DWA) technology incorporates the energy storage mechanism, the switching mechanism, and the acceleration mechanism for electron beams. Electromagnetic simulations of DWA structures includes these effects and also details of the switch configuration and how that switch time affects the electric field pulse which accelerates the particle beam. DWA structures include both bi-linear and bi-spiral configurations with field gradients on the order of 20MV/m and the simulations include the effects of the beampipe, the beampipe walls, and the DWA High Gradient Insulator (HGI) insulating stack. Design trade-offs include the transmission line impedance (typically a few ohms), equilibration ring optimization, driving switch inductances, and layer-to-layer coupling effects and the associated affect on the acceleration pulse’s peak value.

Using the dielectric wall accelerator technology, we are developing a compact induction accelerator system primarily intended for pulsed radiography. Unlike the typical induction accelerator cell that is long compared with its accelerating gap width, the proposed dielectric wall induction accelerator cell is short and its accelerating gap width is comparable with the cell length. In this geometry, the RF modes may be coupled from one cell to the next. We will present recent results of RF modeling of the cells and a prediction of the transverse beam instability on a 2-kA, 8-MeV beam.

Using the high-gradient vacuum dielectric wall accelerator technology, the authors are developing a compact induction accelerator system primarily intended for pulsed X-ray radiography. The accelerator would provide a 2-kA beam for a 20-30 ns flat-top. The design goal is to generate a 2-mm diameter X-ray source. There are two physics designs of the system from the injector to the X-ray converter for two different final energies (8 MeV and 20 MeV). The design goal for the 8-MeV system is to generate 10-rad of X-ray, and the design goal for the 20-MeV system is to generate 300-rad of X-ray. Modeling results were presented and the beam physics in the system were discussed. The predicted spot sizes and the on-axis X-ray doses for both energies were also presented

We are developing a compact accelerator system primarily intended for pulsed radiography. Design characteristics are an 8 MeV endpoint energy, 2 kA beam current, and a cell gradient of approximately 3 MV/m: overall accelerator length is 2-3 m. Such designs have been made possible with the development of high specific energy dielectrics (> 10J/cm3), specialized transmission line designs and multi-gap laser triggered low jitter (< 1 ns) gas switches. In this geometry, the pulse forming lines, switches, and insulator/beam pipe are fully integrated within each cell to form a compact, stand-alone, stackable unit. We detail our research and modeling to date, recent high voltage test results, and the integration concept of the cells into a radiographic system.

Insulators composed of finely spaced alternating layers of dielectric and metal are thought to minimize secondary emission avalanche (SEA) growth. Most data to date was taken with small samples (order 10 cm/sup 2/ area) in the absence of an ion or electron beam. We have begun long pulse (>1 /spl mu/s) high voltage testing of small hard seal samples. Further, we have performed short pulse (20 ns) high voltage testing of moderate scale bonded samples (order 100 cm/sup 2/ area) in the presence of a 1 kA electron beam. Results thus far indicate a 1.0 to 4.0 increase in the breakdown electric field stress is possible with this technology.

Fast, low jitter command triggered switching is key to the successful implementation of the dielectric wall accelerator (DWA). We are studying a UV induced vacuum surface flashover switch for this purpose. We present our initial data using a Nd:YAG (/spl lambda/=0.06 nm) laser incident onto a high gradient insulator surface at 1/spl omega/, 2/spl omega/, 3/spl omega/, and 4/spl omega/. Best 1/spl sigma/ jitter was

Purpose: To characterize and parametrically study the key components of a dielectric wall accelerator through electromagnetic modeling and particle tracking. Methods: Electromagnetic and particle tracking simulations were performed using a commercial code (CST Microwave Studio, CST Inc.) utilizing the finite integration technique. A dielectric wall accelerator consists of a series of stacked transmission lines sequentially fired in synchrony with an ion pulse. Numerous properties of the stacked transmission lines, including geometric, material, and electronic properties, were analyzed and varied in order to assess their impact on the transverse and axial electric fields. Additionally, stacks of transmission lines were simulated in order to quantify the parasitic effect observed in closely packed lines. Particle tracking simulations using the particle-in-cell method were performed on the various stacks to determine the impact of the above properties on the resultant phase space of the ions. Results: Examination of the simulation results show that novel geometries can shape the accelerating pulse in order to reduce the energy spread and increase the average energy of accelerated ions. Parasitic effects were quantified for various geometries and found to vary with distance from the end of the transmission line and along the beam axis. An optimal arrival time of an ion pulse relative to the triggering of the transmission lines for a given geometry was determined through parametric study. Benchmark simulations of single transmission lines agree well with published experimental results. Conclusion: This work characterized the behavior of the transmission lines used in a dielectric wall accelerator and used this information to improve them in novel ways. Utilizing novel geometries, we were able to improve the accelerating gradient and phase space of the accelerated particle bunch. Through simulation, we were able to discover and optimize design issues with the device at low cost. Funding: Morgridge Institute for Research, Madison WI; Conflict of Interest: Dr. Mackie is an investor and board member at CPAC, a company developing compact accelerator designs similar to those discussed in this work, but designs discussed are not directed by CPAC. Funding: Morgridge Institute for Research, Madison WI; Conflict of Interest: Dr. Mackie is an investor and board member at CPAC, a company developing compact accelerator designs similar to those discussed in this work, but designs discussed are not directed by CPAC.

The beam transport design of a novel proton dielectric wall accelerator is introduced in this paper. The protons will be accelerated from 40 keV to nearly 1 MeV under an accelerating gradient that is as high as 20 MV/m. A consideration of the beam line as well as the transport simulation is presented. The influences of the injection timing jitter and the accelerating pulse timing jitter are also discussed.

The solid-state pulse forming lines (PFL) of CaO-TiO2-Al2O3 composite ceramic are designed and manufactured for the dielectric wall accelerator. The PFLs geometric parameters are 300 mm long, 15 mm wide, 1mm thick of ceramic dielectric and 280 mm long, 2 mm wide of silver electrode. The electrical parameters are 23.5 relative dielectric constant, about 26 characteristic impedance, 4.5 ns characteristic time, 20 kV/mm and 25 kV/mm breakdown field strength for DC and pulsed high voltage. The solid-state PFLs design gives consideration to operating requirement of photoconductive semiconductor switches (PCSS), design parameters of high gradient insulator, charged particle beams transport and accelerators structural design. Combined with the PCSS, the experimental research of solid-state Blumlein PFL is performed. The solid-state Blumlein PFL could output about 23 kV pulsed voltage on the load under about 25 kV pulsed voltage.

Ion fast ignition, like laser fast ignition, can potentially reduce driver energy for high target gain by an order of magnitude, while reducing fuel capsule implosion velocity, convergence ratio, and required precisions in target fabrication and illumination symmetry, all of which should further improve and simplify IFE power plants. From fast-ignition target requirements, we determine requirements for ion beam acceleration, pulse-compression, and final focus for advanced accelerators that must be developed for much shorter pulses and higher voltage gradients than today's accelerators, to deliver the petawatt peak powers and small focal spots ({approx}100 {micro}m) required. Although such peak powers and small focal spots are available today with lasers, development of such advanced accelerators is motivated by the greater likely efficiency of deep ion penetration and deposition into pre-compressed 1000x liquid density DT cores. Ion ignitor beam parameters for acceleration, pulse compression, and final focus are estimated for two examples based on a Dielectric Wall Accelerator; (1) a small target with {rho}r {approx} 2 g/cm{sup 2} for a small demo/pilot plant producing {approx}40 MJ of fusion yield per target, and (2) a large target with {rho}r {approx} 10 g/cm{sup 2} producing {approx}1 GJ yield for multi-unit electricity/hydrogen plants, allowing internal T-breeding with low T/D ratios, >75 % of the total fusion yield captured for plasma direct conversion, and simple liquid-protected chambers with gravity clearing. Key enabling development needs for ion fast ignition are found to be (1) ''Close-coupled'' target designs for single-ended illumination of both compressor and ignitor beams; (2) Development of high gradient (>25 MV/m) linacs with high charge-state (q {approx} 26) ion sources for short ({approx}5 ns) accelerator output pulses; (3) Small mm-scale laser-driven plasma lens of {approx}10 MG fields to provide steep focusing angles close-in to the target (built-in as part of each target); (4) beam space charge-neutralization during both drift compression and final focus to target. Except for (1) and (2), these critical issues may be explored on existing heavy-ion storage ring accelerator facilities.

A new accelerator technology, the dielectric wall accelerator (DWA), is potentially an ultra compact accelerator/pulsed power driver. This new accelerator relies on three new components: the ultra-high gradient insulator, the asymmetric Blumlein and low jitter switches. In this report, we focused our attention on the first two components of the DWA system the insulators and the asymmetric Blumlein. First, we sought to develop the necessary design tools to model and scale the behavior of the high gradient insulator. To perform this task we concentrated on modeling the discharge processes (i.e., initiation and creation of the surface discharge). In addition, because these high gradient structures exhibit favorable microwave properties in certain accelerator configurations, we performed experiments and calculations to determine the relevant electromagnetic properties. Second, we performed circuit modeling to understand energy coupling to dynamic loads by the asymmetric Blumlein. Further, we have experimentally observed a non-linear coupling effect in certain asymmetric Blumlein configurations. That is, as these structures are stacked into a complete module, the output voltage does not sum linearly and a lower than expected output voltage results. Although we solved this effect experimentally, we performed calculations to understand this effect more fully to allow better optimization of this DWA pulse-forming line system.

Purpose:IMRT is common for x‐ray treatment, but protontreatment is still only performed at a few angles. Expanding protonradiation therapy to many angles may reduce dose to surrounding tissue. Beam technologies are moving forward (e.g., dielectric wall accelerator) making this practicable. This study seeks to quantify the reduction in dose to surrounding healthy tissue using proton arc therapy. Materials and Methods:Monte Carlo simulations were performed using Geant4. Proton beams impinged on a 100mm radius cylindrical water phantom with a 10mm radius treatment region. Protons were delivered equally over all angles with − r initial direction, producing kernals of rings of dose for each of several energies. Results: Reduction in dose outside of the treatment region is dramatic for the high dose regions. Single beam therapy PDD is presented, the entrance dose is a large portion of the total dose, with a >50% of peak dose from 60mm from peak. The entrance dose may be spread through the typical clinical use of 2 or 3 angles, but this still leaves significant entrance dose. The lateral drop off can be sharp though. The PDD is presented for proton arc therapy. The difference from the large entrance dose is significant. The distance to 50% dose is similar to the lateral drop‐off with traditional beams, and drops to 10% within 25mm of peak, leading to a much lower average dose to irradiated tissue outside the prescription area. Proton arc therapy has the conformity of the lateral dose — without similar entrance dose — of traditional proton therapy. Calculations are ongoing for avoidance regions and comparison with few angle treatments.Conclusions:Proton arc therapy shows great potential for reduction of high dose to tissues outside the treatment region compared with traditional protontreatment.