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Our future engineers and scientists will likely be required to use advanced simulations to solve many of tomorrow's challenges in nanotechnology. To prepare students to meet this need, the Network for Computational Nanotechnology (NCN) provides simulation-focused research experiences for undergraduates at an early point in their educational path, to increase the likelihood that they will ultimately complete a doctoral program. The NCN summer research program currently serves over 20 undergraduate students per year who are recruited nationwide, and selected by NCN and the faculty for aptitude in their chosen field within STEM, as well as complementary skills such as coding and written communication. Under the guidance of graduate student and faculty mentors, undergraduates modify or build nanoHUB simulation tools for exploring interdisciplinary problems in materials science and engineering, and related fields. While the summer projects exist within an overarching research context, the specific tasks that NCN undergraduate students engage in range from modifying existing tools to building new tools for nanoHUB and using them to conduct original research. Simulation tool development takes place within nanoHUB, using nanoHUB’s workspace, computational clusters, and additional training and educational resources. One objective of the program is for the students to publish their simulation tools on nanoHUB. These tools can be accessed and executed freely from around the world using a standard web-browser, and students can remain engaged with their work beyond the summer and into their careers. In this work, we will describe the NCN model for undergraduate summer research. We believe that our model is one that can be adopted by other universities, and will discuss the potential for others to engage undergraduate students in simulation-based research using free nanoHUB resources.

The High-Current Experiment (HCX) at Lawrence Berkeley National Laboratory is part of the US program to explore heavy-ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. Four pulsed magnetic quadrupoles are being used to study gas and electron effects with a 0.2 A, 1-MeV K + beam. The magnets, originally designed and built for a prototype pulsed magnetic quadrupole array, have an elliptical beam tube (6×10 cm) and iron yoke. The magnet coil and field length are ≈31 cm, and operating gradients are 10–40 T/m. To establish that the field quality of the prototype quadrupoles is satisfactory for the experiments, a 1-cm pickup loop was used to measure the flux B r ( θ ) at the magnet mid-plane and also at the lead and return ends. A longer probe was used to measure the integrated flux of B θ ( θ ) along the magnet. The field quality appears satisfactory for the short transport experiments through these quadrupoles.

When a short-duration, small-amplitude energy perturbation is applied to a heavy-ion beam, positive- and negative-going longitudinal space–charge waves are generated on the beam. Longitudinal diagnostic kickers that provide ∼1% energy perturbation have been implemented for generating space–charge waves on HCX and NTX beams. The kickers consist of specially designed fast pulse generators combined with an existing aperture or ESQ structure to provide the longitudinal perturbation to the beam. The amplitudes of the resulting density waves are ∼10%, measured a few meters downstream of the kicker. The time-of-flight (TOF) of the wave provides an accurate measure of the beam energy. The TOF measurements will be described. Comparison of measured waves with a simple 1-D fluid model of the beam will be presented.

In this paper we report on two Heavy Ion Fusion (HIF) driver point design studies. The Robust Point Design (RPD) was completed over a year ago, and the Modular Point Design (MPD) is still in progress. The goal of any point design study is to construct a detailed design that is self-consistent and integrated from injector to target. This has been the primary theme of both studies.

In the planned heavy-ion Integrated Research Experiments (IRE), final beam kinetic energy will be low compared to a driver, giving perveance significantly larger than the driver, and making final focus to a small spot comparatively much more difficult. Splitting of beams ahead of the final focus system would allow economical transport of large beams through the IRE accelerator, while maintaining focusability. Since splitting decouples the number of beams transported in the accelerator from what is required at final focus, it could also lower the cost of a driver. In this paper we consider the effects on beam quality of transverse beam splitting. The system of most interest consists of one or more consecutive magnetic septa. PIC simulations of this case are discussed, along with engineering considerations.

We simulate fusion power plant driver efficiency by pulsing small induction cores at 5 Hz (a typical projected power plant repetition rate), with a resistive load in the secondary winding that is scaled to simulate the beam loading for induction acceleration. Starting from a power plant driver design that is based on other constraints, we obtain the core mass and acceleration efficiency for several energy ranges of the driver accelerator and for three magnetic alloys. The resistor in the secondary is chosen to give the same acceleration efficiency, the ratio of beam energy gain to energy input to the core module (core plus acceleration gap), as was computed for the driver. The pulser consists of a capacitor switched by FETs, Field Effect Transistors, which are gated on for the desired pulse duration. The energy to the resistor is evaluated during the portion of the pulse that is adequately flat. We present data over a range of 0.6–5 μs pulse lengths. With 1 μs pulses, the acceleration efficiency at 5 Hz is measured to be 75%, 52%, and 32% for thin-tape-wound cores of nanocrystalline, amorphous, and 3% silicon steel materials respectively, including only core losses. The efficiency increases for shorter pulse durations.

Extensive studies have been performed to optimize the design of superconducting quadrupole arrays for beam transport in future heavy-ion fusion accelerators. In these arrays, 20 or more quadrupole coils are densely packed with their axes aligned in parallel. Field strengths between 3 and 5 tesla at the inner coil diameters have been investigated. The aperture of the individual quadrupoles has been varied between 60 mm and 240 mm. The coils have a typical length of 1 m, and special effort has been made to minimize the length of the interconnect region between the array and adjacent accelerator components. The relative orientation of quadrupoles in the array is chosen to optimize field sharing between neighboring cells. In the presented design, field uniformity in the boundary cells is maintained by placing concentric correction coils onto these cells. A novel approach for the mechanical stabilization and alignment of the individual quads in the array has been developed. Since Inertial Fusion Energy has to compete with other long-term energy sources, cost and reliability are major issues of the magnet array. The presented design uses a round NbTi mini-cable, which allows for a cost-effective, highly automated manufacturing of the required superconducting coils. A flexible, 37-strand mini-cable has been developed and prototype manufacturing has started.

This report was prepared by a Working Group at the request of the U.S. Department of Energy, Office of Fusion Energy Sciences in 1997. The report addresses technical opportunities for mutually beneficial collaboration between the United States and other international fusion research programs. A number of outstanding opportunities are discussed.

A multi-channel quadrupole array has been proposed to increase beam intensity and reduce space charge effects in a heavy ion fusion driver. A single array unit composed of several quadrupole magnets, each with its own beam line, will be placed within a ferromagnetic accelerating core whose cost is directly affected by the array size. A large number of focusing arrays will be needed along the accelerating path. The use of a superconducting quadrupole magnet array will increase the field and reduce overall cost. The authors report here on the design of a compact 3/spl times/3 superconducting quadrupole magnet array. The overall array diameter and length including the cryostat is 900/spl times/700 mm. Each of the 9 quadrupole magnets has a 79 mm warm bore and an operating gradient of 50 T/m over an effective magnetic length of 320 mm.

Transverse beam combining is a cost-saving option employed in many designs for induction linac heavy ion fusion drivers. The resultant transverse emittance increase, due predominantly to anharmonic space charge forces, must be kept minimal so that the beam remains focusable at the target. A prototype combining experiment has been built using the MBE-4 experimental apparatus. Four new sources produce up to 6.7 mA Cs+ beams at 200 keV. The ion sources are angled toward each other so that the beams converge. Focusing upstream of the merge consists of four quadrupoles and a final combined-function element (quadrupole and dipole). All lattice elements are electrostatic. Owing to the small distance between beams at the last element (about 3–4 mm), the electrodes here are a cage of small rods, each at different voltage. The beams emerge into the 30-period transport lattice of MBE-4 where emittance growth due to merging, as well as the subsequent evolution of the distribution function, can be diagnosed. The combiner design, simulation predictions and preliminary results from the experiment are presented.

We are currently constructing a prototype quadrupole electromagnet for the proposed Induction Linac Systems Experiments (ILSE) at LBNL. ILSE (PUB-5219, 1989 (Lawrence Berkeley Laboratory)) will address many physics and engineering issues relevant to the design of a heavy ion fusion driver accelerator. The pulsed electromagnet has two layers of current windings and will produce a field gradient of 28 T m −1 , with a usable aperture radius of 6 cm. It operates at a repetition rate of I Hz, steady state. In this paper, we discuss how the interaction of various concerns such as maximum dynamic aperture, short lattice period, field quality, iron yoke weight, heat transfer, and voltage stand-off have led to our particular design choices. We also present two- and three-dimensional numerical calculations concerning field topography and the results of transport simulations of space-charge-dominated ion beams with ILSE parameters.

This note was originally one of the parts of the work on a 50 MeV and 500 MeV Rb{sup +} driver and part of work on delay lines for a 60 GeV U{sup +12} driver. It is slightly expanded here to make it more generally applicable. The emphasis is on beam manipulations such as joining and separating beams at the two ends of a driver and providing various time delays between beams as required by the target.

The pulsers used in most of the induction linacs evolved from the very large body of work that was done in the U.S. and Great Britain during the development of the pulsed magnetron for radar. The radar modulators started at {approx}100 kW and reached >10 MW by 1945. A typical pulse length was 1 {mu}s at a repetition rate of 1,000 pps. A very comprehensive account of the modulator development is Pulse Generators by Lebacqz and Glasoe, one of the Radiation Laboratory Series. There are many permutations of possible modulators, two of the choices being tube type and line type. In earlier notes I wrote that technically the vacuum tube pulser met all of our induction linac needs, in the sense that a number of tubes, in series and parallel if required, could produce our pulses, regulate their voltage, be useable in feed-forward correctors, and provide a low source impedance. At a lower speed, an FET array is similar, and we have obtained and tested a large array capable of >10 MW switching. A modulator with an electronically controlled output only needs a capacitor for energy storage and in a switched mode can transfer the energy from the capacitor tomore » the load at high efficiency. Driving a full size Astron induction core and a simulated resistive 'beam load' we achieved >50% efficiency. These electronically controlled output pulses can produce the pulses we desire but are not used because of their high cost. The second choice, the line type pulser, visually comprises a closing switch and a distributed or a lumped element transmission line. The typical switch cannot open or stop conducting after the desired pulse has been produced, and consequently all of the initially stored energy is dissipated. This approximately halves the efficiency, and the original cost estimating program LIACEP used this factor of two, even though our circuits are usually worse, and even though our inveterate optimists often omit it. The 'missing' energy is that which is reflected back into the line from mismatches, the energy left in the accelerator module's capacitance, the energy lost in the switch during switching and during the pulse, and the energy lost in the pulse line charging circuit. For example, a simple resistor-limited power supply dissipates as much energy as it delivers to the pulse forming line, giving a factor if two by itself, therefore efficiency requires a more complicated charging system.« less

A 2 MV, 800 mA, K+ injector for heavy-ion fusion studies is under construction. This new injector is a one-beam version of the proposed 4-beam ILSE injector. A new 36-module MARX is being built to achieve a 5 μs flat top. The high-voltage generator is stiff (

The conceptual design of a heavy ion fusion driver system is described, including all major components. Particular issues emerging from this exercise are identified and discussed. The most important conclusion of our study is that due to stringent requirements on ion pulse phase space, we are unable to find a credible accelerator design that meets the requirements of the example target. Either the target design must be modified to accept larger ion ranges and larger focal spot sizes, or we must consider other target options.

HIFAN 1757 HEAVY ION FUSION SCIENCE VIRTUAL NATIONAL LABORATORY, 3rd QUARTER 2009 MILESTONE REPORT, Upgrade plasma source configuration and carry out initial experiments. Characterize improvements in focal spot beam intensity by S. Lidia, A. Anders, F.M. Bieniosek, A. Faltens, W. Greenway, J.Y. Jung, T. Katayanagi, B.G. Logan, C.W. Lee, M. Leitner, P. Ni, A. Pekedis, M. J. Regis, P. K. Roy, P. A. Seidl, W. Waldron Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA J.J. Barnard, A. Friedman, D. Grote, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA M. Dorf, E. Gilson Princeton Plasma Physics Laboratory Accelerator Fusion Research Division Ernest Orlando Lawrence Berkeley National Laboratory University of California June 2009 This work was supported by the Director, Office of Science, Office of Fusion Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

The pulsed drift-tube accelerator (DTA) concept was revived by Joe Kwan and John Staples and is being considered for the HEDP/WDM application. It could be used to reach the full energy or as an intermediate accelerator between the diode and a high gradient accelerator such as multi-beam r.f. In the earliest LBNL HIF proposals and conceptual drivers it was used as an extended injector to reach energies where an induction linac with magnetic quadrupoles is the best choice. For HEDP, because of the very short pulse duration, the DTA could provide an acceleration rate of about 1MV/m. This note is divided into two parts: the first, a design based on existing experience; the second, an optimistic extrapolation. The first accelerates 16 parallel K{sup +} beams at a constant line charge density of 0.25{micro} C/m per beam to 10 MeV; the second uses a stripper and charge selector at around 4MeV followed by further acceleration to reach 40 MeV. Both benefit from more compact sources than the present 2MV injector source, although that beam is the basis of the first design and is a viable option. A pulsed drift-tube accelerator was the first major HIF experiment at LBNL. It was designedmore » to produce a 2{micro}s rectangular 1 Ampere C{sub s}{sup +} beam at 2MeV. It ran comfortably at 1.6MeV for several years, then at lower voltages and currents for other experiments, and remnants of that experiment are in use in present experiments, still running 25 years later. The 1A current, completely equivalent to 1.8A K{sup +}, was chosen to be intermediate between the beamlets appropriate for a multi-beam accelerator, and a single beam of, say, 10A, at injection energies. The original driver scenarios using one large beam on each side of the reactor rapidly fell out of favor because of the very high transverse and longitudinal fields from the beam space charge, circa 1MV/cm and 250 kV/cm respectively, near the chamber and because of aberrations in focusing a large diameter beam down to a 1mm radius spot at a distance of 10m. Almost all subsequent work and the present concept have invoked multiple beams. For HEDP the major differences are that the focal distance can be centimeters instead of meters, provided strong-enough lenses exist and they do, thereby allowing much higher transverse and longitudinal emittances than driver concepts, and focusing parallel small beams is easier than one big beam.« less

The U.S. Heavy Ion Fusion program is developing superconducting focusing quadrupoles for near-term experiments and future driver accelerators. Following the fabrication and testing of several models, a baseline quadrupole design was selected and further optimized. The first prototype of the optimized design achieved a conductor- limited gradient of 132 T/m in a 70 mm bore, with measured field harmonics within 10 parts in 10 4 . In parallel, a compact focusing doublet was fabricated and tested using two of the first-generation quadrupoles. After assembly in the cryostat, both magnets reached

Modern diagnostic techniques provide detailed information on beam conditions in injector, transport, and final focus experiments in the HIF-VNL. Parameters of interest include beam current, beam energy, transverse and longitudinal distributions, emittance, and space charge neutralization. Imaging techniques, based on kapton films and optical scintillators, complement and, in some cases, may replace conventional techniques based on slit scans. Time-resolved optical diagnostics that provide 4-D transverse information on the experimental beams are in operation on the existing experiments. Current work includes a compact optical diagnostic suitable for insertion in transport lines, improved algorithms for optical data analysis and interpretation, a high-resolution electrostatic energy analyzer, and an electron beam probe. A longitudinal diagnostic kicker generates longitudinal space-charge waves that travel on the beam. Time of flight of the space-charge waves and an electrostatic energy analyzer provide an absolute measure of the beam energy. Special diagnostics to detect secondary electrons and gases desorbed from the wall have been developed.

Extensive studies have been performed to optimize the design of superconducting quadrupole arrays for beam transport in future heavy-ion fusion accelerators. In these arrays 20 or more quadrupole coils are densely packed with their axes aligned in parallel. Field strengths between 3 and 5 tesla at the inner coil diameters have been investigated. The aperture of the individual quadrupoles has been varied between 60 and 240 mm. The coils have a typical length of 1 m, and special effort has been made to minimize the length of the interconnect region between the array and adjacent accelerator components. The relative orientation of quadrupoles in the array is chosen to optimize field sharing between neighboring cells. Field uniformity in the boundary cells is maintained by placing concentric correction coils onto these cells. A conceptual cryostat design, which minimizes heat loads on the cryogenic system, has been analyzed. Since inertial fusion energy has to compete with other long-term energy sources, cost and reliability of these magnets are major issues. The presented design uses a round NbTi mini-cable, which allows for a cost-effective, highly automated manufacturing of the required superconducting coils.

Two recent developments enable induction accelerators to achieve better and more consistent performance with higher efficiency. First, better and more consistent performance is achieved with insulating coatings that allow magnetic cores to be annealed after winding. Second, losses are reduced by a factor of 2-3 with nanocrystalline alloys, while the flux swing is only slightly reduced to 2.0 T compared with 2.3 T with economical amorphous alloys. One metric for selecting between the alloys is the cost-of-electricity, COE. A systems code optimizes an accelerator and compares the COE for higher flux-swing amorphous and higher-efficiency nanocrystalline materials and for several variations in assumptions.

We present the design of a pulsed quadrupole magnet array for side by side transport of multiple high current particle beams in induction linear accelerators. The design is directly applicable to low field superconducting quadrupole arrays and can be modified for high fields. The magnetic design minimizes current requirements by placing a modified cosine 2/spl theta/ current distribution inside an elliptical iron boundary. The resulting magnet aperture more closely matches the beam's elliptical cross-section, and only the space the beam occupies is magnetized to the required field quality. By eliminating unneeded high field area in the magnet aperture, energy requirements are halved, as compared to an equivalent circular design. The magnet serves double duty as a UHV vacuum chamber/beam tube, and reduced radial thickness results from lower current requirements. Each interior magnet's neighbors serve as the return flux paths and the poles are placed as close as possible to each other to facilitate this. All the above features serve to reduce the beam-to-beam spacing, leading to significant reductions in the size and cost of the induction cores which surround the array, as well as the pulsed power supplies which drive them. The design shown here is for a 21 beam array, yet it is suitable for larger or smaller numbers of beams, as required.

A multibeam injector being built to provide 16-500 mA beams of C/sup +/ at 2 MeV energy is presented. The sources are carbon cathode multiple arcs that provide plasma to a double-grid plasma switch. The plasma switch is a planar electrostatic device that prevents ions from entering the extraction gap before the extraction voltage pulse is fired. Data on the performance of this source in a test stand have been obtained. The 1- mu s current pulse will be injected into the acceleration column approximately 30 mu s after the voltage pulse is applied to the column. This allows voltages to equilibrate and the flat spot in the voltage pulse to be reached. The ions are accelerated in a column that consists of titanium electrodes mounted inside aluminum oxide insulator modules. Most of the 16 beam holes are in thick plates which are machined to provide a set of alternating aperture lenses. These lenses focus the beam and inhibit propagation of back streaming electrons. >

The design of a high-current heavy-ion induction linac driver for inertial confinement fusion is optimized by adjusting the acceleration units along the length of the accelerator to match the beam current, energy, and pulse duration at any location. At the low-energy end of the machine the optimum is a large number of electrostatically focused parallel beamlets, whereas at higher energies the optimum is a smaller number of magnetically focused beams. ILSE parallels this strategy by using 16 electrostatically focused beamlets at the low end followed by four magnetically focused beams after beam combining. Descriptions are given of the electric focusing section, the magnetic focus accelerator, the induction cores and pulsers, and the ILSE alignment systems. >

An update on the development of the 500-mA/beam sixteen-beam injector being built at Lawrence Berkeley Laboratory is presented. An inductively graded Marx bank provides the acceleration potential on the electrostatic column. A carbon arc source provides the pulsed current for the injector. Recent results on extracted beam parameters, column performance, generator performance and system design changes are reported. The carbon ion beam is diagnosed with Faraday cups and with a double-slit emittance measurement system. Controls for the final machine are also discussed. >

In ILSE (Induction Linac Systems Experiment), sixteen intense parallel ion beams are to be transversely combined into four by dispersionless double bends. Emittance growth due to electrostatic energy redistribution and to the geometry is evaluated. Most bending elements are electric, and alternate with AG electrostatic quadrupoles similar to those upstream. The final elements are magnetic, combining focusing and 'unbending'. Electrode shapes and pulsed-current arrays (with very small clearances), as well as mechanical and electric features of the combiner, are described. >

High-voltage electrostatic quadrupoles are used for focusing ion beams at low energies in the induction linac approach to heavy ion driven inertial confinement fusion for the production of electrical power. The transportable beam line charge density depends linearly on the operating voltage of the quadrupoles, so an experimental program was conducted to find the voltage breakdown dependence on the overall size of the quadrupoles which would then allow determination of the best geometry and operating voltage. The quadrupole electrodes are usually stainless steel cylinders with hemispherical end caps, mounted on stainless steel end plates. The end plates are precisely positioned with respect to each other and the vacuum chamber with alumina insulators with shielded triple points. It is advantageous for beam transport to employ an array of multiple beams for which a rather large number of interdigitated electrodes forms an array of quadrupoles. The trade-offs between very large numbers of small channels and a smaller number of large channels, and the dependence of the choice on the voltage breakdown dependence is discussed. With present understanding, the optimum is about 100 beamlets focused with quadrupoles which have a beam aperture radius of about 2.3 cm and art operated with about 150 kV between electrodes.

Transverse beam combining is a cost-saving option employed in many designs for induction linac heavy ion fusion drivers. The resultant transverse emittance increase, due predominantly to anharmonic space charge forces, must be kept minimal so that the beam remains focusable at the target. A prototype combining experiment has been built and preliminary results are presented. Four sources each produce up to 4.8 mA Cs/sup +/ beams at 160 keV. Focusing upstream of the merge consists of four quadrupoles and a final combined-function element (quadrupole and dipole). All lattice elements of the prototype are electrostatic. Due to the small distance between beams near the merge (/spl sim/3-4 mm), the electrodes here are a cage of small rods, each at different voltage.

Transverse beam combining is a cost-saving option employed in many designs for induction linac heavy ion fusion drivers. But resultant transverse emittance increase, due predominantly to anharmonic space charge forces, must be kept minimal so as not to sacrifice focusability at the target. A prototype combining experiment has been built, using the MBE-4 experiment. Four sources produce four 4 mA Cs/sup +/ beams at 200 keV. The ion sources are angled toward each other, so that the beams converge. Focusing upstream of the merge consists of 4 quadrupoles and a final combined-function element (quadrupole and dipole). All lattice elements are electrostatic. Due to the small distance between beams at the last element (/spl sim/2 mm), the electrodes here are a cage of small wires, each at different voltage. The beams emerge into the 30 period transport lattice of MBE-4 where emittance growth due to merging, as well as the subsequent evolution of the distribution function, can be diagnosed. The combiner design, simulation predictions, and preliminary results from the experiment are presented.

This paper reports progress in the HCX experimental program since the last HIF-VNL Program Advisory Committee Review (February 14-15 2002). On July 25 2002 the experiment was shut down for about four weeks to move the control room. A principal area of effort has been to obtain and evaluate the first experimental results carried out with a matched and well-aligned K + ion beam transported through 10 electrostatic transport quadrupoles. These are the main results and highlights to date: A1. There is no emittance growth within the sensitivity of the diagnostics, and little beam loss. The beam centroid is aligned to within 0.5 mm and 2 mrad of the central axis of the channel, and the envelope mismatch amplitude is

Vacuum ballistic focusing is the straightforward method to obtain a heavy ion beam spot size necessary to drive an inertial confinement fusion target. The beam is first expanded then focused to obtain the desired convergence angles at the exit of the last element. This is done in an attempt to achieve a focal spot size in which emittance is the limiting factor; however, aberrations and space charge will influence the spot radius. Proper scaling of particle energy, mass, beam current, beam emittance, and magnetic field replicates the dynamics of a full driver beam at the focus in a small laboratory experiment. By scaling the beam current to ~;100 mu A, 160 keV Cs+ has been used to study experimentally a proposed driver design at one-tenth scale. Once a nominal focal spot is achieved, the magnet strengths are deliberately de-tuned to simulate the effect of an off-momentum slice of the beam. Additionally, several methods will be used to inject electrons into beam following the last focusing element in order to study the neutralization of space charge and its effect on the focus. Transverse phase space and beam current density measurements at various stages of the focus will be presented as well spot size measurements from the various trials. This data will be compared to the results of a PIC model of the experiment.

Vacuum ballistic focusing may be a straightforward method to obtain the heavy ion beam spot size necessary to drive an inertial confinement fusion target. Proper scaling of particle energy, mass, beam current, beam emittance, and magnetic field replicates the dynamics of a full driver beam in a small laboratory experiment. By expanding the beam and then focusing to a very small spot, the effects of aberrations and space charge on this method of final focus can be studied. To date, 200 /spl mu/A of 120 keV K/sup +/ has been focused to test the matching and focusing elements. A recently designed high brightness contact ionization source is being tested for upcoming focusing measurements with an 87 /spl mu/A Cs beam that will duplicate the dynamics of a proposed driver design at one-tenth scale. Transverse phase space and beam current density at various stages of the focus will be presented. Follow-on measurements studying electron neutralization of space charge and its effect on the focus will be explored.

Previous heavy-ion fusion driver system studies suggest that transverse beam combining significantly reduces driver cost. In a combiner, several beams are brought together to a common transport channel which accommodates the increased line charge density. Combining intense beams increases the transverse emittance mainly due to the heating of the beam by space charge forces as the non-uniform original beam configuration becomes more uniform. The combiner itself introduces additional aberrations, which are small for the present design. Those aberrations are due to the reduced available space for the focusing electrodes and reduced clearance from the beamlets to the surrounding electrodes, thereby generating field aberrations and larger image forces. These aberrations can also lead to particle loss. We have studied a particular design of the proposed induction linac system experiment (ILSE) combiner which is a first-order achromat that tolerates a rather large fractional head-to-tail momentum tilt of ± 10%. Using a 2D particle-in-cell code we have found that ≈7% of particles are lost in the combiner. The emittance growth after the combiner is large enough so that the emittance growth due to combiner aberrations is unimportant. The scaled projection to a driver shows the growth is small enough to be tolerated. At present, methods of improving combiner design to reduce particle loss and to minimize emittance growth are being studied.

Intense beams of heavy ions are well suited for heating matter to regimes of emerging interest. A new facility, NDCX-II, will enable studies of warm dense matter at ∼1 eV and near-solid density, and of heavy-ion inertial fusion target physics relevant to electric power production. For these applications the beam must deposit its energy rapidly, before the target can expand significantly. To form such pulses, ion beams are temporally compressed in neutralizing plasma; current amplification factors of ∼50–100 are routinely obtained on the Neutralized Drift Compression Experiment (NDCX) at the Lawrence Berkeley National Laboratory. In the NDCX-II physics design, an initial non-neutralized compression renders the pulse short enough that existing high-voltage pulsed power can be employed. This compression is first halted and then reversed by the beam’s longitudinal space-charge field. Downstream induction cells provide acceleration and impose the head-to-tail velocity gradient that leads to the final neutraliz...

Electron linear accelerator technology for high-power, short-wavelength free-electron lasers is reviewed.

A sixteen beam injector to supply 500mA per beam of C/sup +/ ions, which was initially designed and partially constructed at Los Alamos National Laboratory, is under further development at LBL. We report on development work involving single and multiple carbon arc sources. These sources are useful because they can easily supply the 25 mA/cm/sup 2/ needed for the device. They are pulsed sources which do not cause unacceptable background gas loads in the column. We present emittance and reproducibility data. Acceleration is by a high gradient column using a succession of aperture lenses to focus the beam. The electrodes are arranged with holes for parallel beams inside 28 inch alumina insulators. Data on beam propagation and electron trapping in the column is presented. The acceleration potential is provided by a Marx bank with inductive grading along the structure. The resulting 34 ..mu..sec rise time pulse allows the accelerating potential to equilibrate along the column before the current is injected. Acceleration occurs during a 1 ..mu..sec window at the peak of the pulse, kn which the voltage is flat within 0.1%. 8 refs., 7 figs.

A pulsed electron accelerator has been constructed and is now in operation at the Lawrence Radiation Laboratory, Berkeley. It was designed specifically for and is used as an injector for ERA (electron ring accelerator) studies. Electron bursts of 1200 amperes and 40 nanoseconds duration can be produced at energies of 1.0 MeV to 4.25 MeV. The present repetition rate is approximately one per second. Acceleration is accomplished by means of ferrite loaded accelerating sections, each of which is capable of maintaining a 250 kV voltage pulse across the accelerating gap for a period of 40 ns. The voltage pulse has a rise time of 12 ns and the total timing jitter is of the order of one nanosecond. Five sections stacked together and operated as a unit function as the electron gun. The gun employs a field emission cathode and is operated at approximately 1 MV. Additional acceleration is achieved by means of an iterated system of accelerator sections and solenoidal magnetic lenses.

Several fast-transfer systems using kicker magnets are needed for the proposed 200-GeV Accelerator. A possible system for transfer from the injector synchrotron to the main ring using stationary, full-aperture kicker magnets presents the most stringent requirements. The extraction kicker for the injector synchrotron will be about 4 m in length, have a 4-by-14-cm aperture, and require a field or 300 G. For 100% efficient transfer the rise time of the magnetic field must be shorter than 17 ns, which is the time between beam bunches, and which is nearly an order of magnitude less than the rise times achieved in existing kicker magnets. Because of the required rise time and the limited length, each magnet is divided into 48 modules operated as 24 push-pull pairs. Each module is analyzed as a short-circuited ferrite-and dielectric-loaded transmission line. The short-circuited mode of operation ensures that voltage on the magnet is applied for only about 12 ns, thus reducing HV problems, and at the same time produces a kick twice as great as can be obtained from terminated magnets. Each module is energized by a tapered coaxial pulse line and switched on with a triggered spark gap.

This report describes a 20 channel ``stepper'' magnet assembly designed to cause the incoming Bevatron particle beam to scan across the 1.83 m hydrogen bubble chamber in discrete steps. The purpose of this device is to avoid superimposing tracks. Stepping was triggered by an ``events'' counter placed in the beam. The system was built with low voltage, silicon controlled rectifiers. Magnet pulsing was accomplished in two parts, rapid rise of field was produced by a fast circuit and pulse length was maintained by a slow circuit. Cost was approximately $15 000, exclusive of the surplus components.

The construction and assembly of a Cs ion injector consisting of a pulsed source and 3 pulsed drift tubes has been complete since April, 1980. The measurement program, underway since then to characterize the beam, has been interspersed with the development of diagnostic equipment. The Cs contact ionization source and each of the 3 drift tubes are driven by 500 kV Marx generators. The injector has been operated reliably at 300 kV/stage at a repetition rate of 1 pulse/4 sec. About 105 pulses have been accumulated. The space charge limited diode and drift tube acceleration system were designed with the aid of the EGUN code of Herrmannsfeldt. Measurements of the beam envelope have been made by means of a movable biased charge collector. Good agreement with the EGUN calculation is found. Measurements of the beam emittance have been made at the exit of the third drift tube. The normalized emittance ? ?N = 2 x 10-6 ? m-rad is of better optical quality than that required for further acceleration and transport in a Heavy Ion Fusion (HIF) Induction Linac Driver.

Measurements are reported on the dc and pulsed magnetic properties of three MetglasRa) alloys in the as‐cast, box annealed, and rewound conditions. Alloys 2605SC, 2605S‐2 and 2605CO were evaluated for possible use in an induction linear accelerator. It is found that the 2605SC and 2605S‐2 give similar good performance and the 2605CO slightly less good performance in this application in the microsecond pulse‐width region.

Results are presented on the design and testing of a pressurized gas blown spark-gap switch capable of high repetition rates in a burst mode of operation. The switch parameters which have been achieved are as follows: 220 kV, 42 kA, a five-pulse burst at 1 kHz, 12-ns rise time, 2-ns jitter at a pulsewidth of 50 ns.

A compact monitor has been developed which measures beam current and beam position without intercepting or appreciably affecting the particle beam being measured. It is a broad band device which prevents the development of beam disturbing resonant modes. Although developed specifically for use on a short-pulse electron induction accelerator, it might be applied to other accelerator beams of pulsed or rf-bunched nature. The monitor consists of a resistive band inserted in the beam pipe wall with connections for reading the voltage across the band at each vertical and horizontal axis intercept. For pulsed or rf beams, return current equal in magnitude to the beam current flows on the beam pipe inside wall and through the resistive band. If the beam is centered, equal voltage appears on all four monitor connections. If the beam is off-center, the return currents are unsymmetrical and unequal voltages appear at the monitor connections. Beam current is proportional to the sum of all monitor voltages, while beam position is approximately proportional to the difference in voltage at opposing monitors. Tests and operating experience confirm its operation.

A linear induction accelerator that produces a beam of energetic (5 to 20 GeV) heavy (130 to 210 amu) ions is a prime candidate as a driver for inertial fusion. Continuing developments in sources for ions with charge state greater than unity allow a potentially large reduction in the driver cost and an increase in the driver efficiency. The use of high undepressed tunes (sigma/sub 0/ approx. = 85/sup 0/) and low depressed tunes (sigma approx. = 8.5/sup 0/) also contributes to a potentially large reduction in the driver cost. The efficiency and cost of the induction linac system are discussed as a function of output energy and pulse repetition frequency for several ion masses and charge states. The cost optimization code LIACEP, including accelerating module alternatives, transport modules, and scaling laws, is presented. Items with large cost-leverage are identified as a guide to future research activities and development of technology that can yield substantial reductions in the accelerator system cost and improvement in the accelerator system efficiency. Finally, a cost-effective strategy using heavy ion induction linacs in a development scenario for inertial fusion is presented. 34 refs., 6 figs., 7 tabs.

The Lawrence Livermore Laboratory is constructing an induction linac with the following parameters 10kA, 50ns FWHM pulse width, 5MeV, and 5PPS. This paper describes the design features of the 2.5 MeV injector and it's associated pulsed power system.

A computer model of an accelerator system is a necessary ingredient in estimating the cost of construction and operation of an ion-driven ICF power plant. The LBL computer program LIACEP (Linear Induction Accelerator Cost Evaluation Program) is used to estimate the cost and efficiency of a heavy ion induction linear accelerator as a function of the ion mass, charge and energy for a specified beam output energy, power and pulse repetition frequency. In addition to estimating the accelerator system cost and efficiency, LIACEP can be used to identify the components and materials that have a high leverage on the cost and efficiency of the accelerator system. These high leverage items are logical areas for research and technology development to reduce the cost and increase the efficiency of the accelerator system.

The Heavy Ion Fusion (HIF) Program is developing superconducting focusing magnets for both near-term experiments and future driver accelerators. In particular, single bore quadrupoles have been fabricated and tested for use in the High Current Experiment (HCX) at Lawrence Berkeley National Laboratory (LBNL). The next steps involve the development of magnets for the planned Integrated Beam Experiment (IBX) and the fabrication of the first prototype multi-beam focusing arrays for fusion driver accelerators. The status of the magnet R&D program is reported, including experimental requirements, design issues and test results.

Two beam choppers were constructed which produce an approximately square, 20-ns pulse of 3+-MeV electrons out of the best portion of the 300-ns Astron beam or an 8-?s microwave electron linac beam for injection into the electronring accelerator (ERA) compressor. The choppers are impedance-matched traveling-wave devices which deflect the beam with equal strength electric and magnetic forces, and are powered with either three-electrode spark gaps or thyratrons and a 20-ns pulse line. The electron beam is biased out of the beam-transport system with a dc magnetic field, and switched into it with the chopper.