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Recent experiments performed on the University of Maryland Electron Ring (UMER) have demonstrated the advantages of using a scaled electron machine to economically investigate the nonlinear physics of a space-charge-dominated beam. This physics is important to larger and much more expensive machines, including accelerator systems for the study High Energy Density Physics and Heavy Ion Fusion. UMER has been successfully used for studying source and injector physics, developing diagnostics, and benchmarking simulations, as well as for investigating the special sensitivity of a space-charge-dominated machine to small deviations from the nominal design parameters. A description will also be presented of studies that utilize the downstream consequences of a controlled initial perturbation of the beam distribution for the study of both longitudinal and transverse beam physics. Current work to optimize ring operation will also be discussed.

New coherent radiation sources in the hard X-ray and Terahertz regimes promise exciting new developments in science, as previously dark areas of the spectrum are brightly illuminated. Ultra-short, ultra-bright radiation packets can probe the structure of matter, and image chemical and biological processes well beyond the present state of the art. Production of this coherent radiation, however, places an unprecedented challenge on the production and acceleration of high-quality electron beams. To deliver a nano-Coulomb of charge with an emittance of less than one micron, while transporting the beam through long sections of acceleration and compression, is the prerequisite for unlocking the gates of this promising new science. Using a low-energy electron storage ring, we deliberately enhance the space charge force while slowing down the time-scale to easily measurable levels so as to maximize our understanding of the particle dynamics necessary for producing bright beams.

The University of Maryland Electron Ring (UMER) and the Long Solenoid Experiment (LSE) are two electron machines that were designed explicitly to study the physics of space-charge-dominated beams. The operating parameters of these machines can be varied by choice of apertures and gun operating conditions to access a wide range of parameters that reproduce, on a scaled basis, the full nonlinear time-dependent physics that is expected in much costlier ion systems. Early operation of these machines has demonstrated the importance of the details of beam initial conditions in determining the downstream evolution. These machines have also been a convenient tested for benchmarking simulation codes such as WARP, and for development of several novel diagnostic techniques. We present our recent experience with multi-turn operation as well as recent longitudinal and transverse physics experiments and comparisons to simulation results. Development of novel diagnostic techniques such as time-dependent imaging using optical transition radiation and tomographic beam reconstruction are also described.

Some of the most challenging and interesting problems in nature involve large numbers of objects or particles mutually interacting through long-range forces. Examples range from galaxies and plasmas to flocks of birds and traffic flow on a highway. Even in cases where the form of the interacting force is precisely known, such as the 1/r2-dependent Coulomb and gravitational forces, such problems present a formidable theoretical and modeling challenge for large numbers of interacting bodies. This paper reports on a newly constructed, scaled particle accelerator that will serve as an experimental testbed for the dynamics of swarms interacting through long-range forces. Primarily designed for intense beam dynamics studies for advanced accelerators, the University of Maryland Electron Ring (UMER) design is described in detail and an update on commissioning is provided. An example application to a system other than a charged particle beam is discussed.

The transport of intense beams for heavy-ion inertial fusion demands tight control of beam characteristics from the source to the target. The University of Maryland Electron Ring (UMER), which uses a low-energy (10 keV), high-current electron beam to model the transport physics of a future recirculator driver, employs real-time beam characterization and control in order to optimize beam quality throughout the strong focusing lattice. We describe the main components and operation of the diagnostics/control system in UMER. It employs phosphor screens, real-time image analysis, quadrupole scans and electronic skew correctors. The procedure is not only indispensable for optimum transport over a long distance, but also provides important insights into the beam physics involved. We discuss control/optimization issues related to beam steering, quadrupole rotation errors and rms envelope matching.

The injection Y has been designed and built for the University of Maryland Electron Ring (UMER). The design incorporates a combination of two unique printed circuit magnet designs. The dipole component of an offset quadrupole and a pulsed dipole are used to achieve the 10° bend required from the injection line. The current for each magnet is supplied by its own pulse-forming network (PFN). The dipole PFN is designed as a long pulse (300 V, 15 A, 20 μs duration) for multiple beam passes with a short pulse (2 kV, −30 A, 100 ns flat top duration) superimposed for beam extraction. To accommodate field penetration a glass gap covers the area near the pulsed dipole. The glass gap has a thin conductive coating on the inner surface to minimize perturbations on the beam due to changing boundary conditions. The completed Y assembly has been installed on the downstream end of the beam line to facilitate experimental tests before closure of the ring. Initial experimental results of the testing of this design will be presented.

The understanding of collective interactions of particles in an intense beam by means of long-range forces is crucial for the successful development of heavy ion inertial fusion. Designs for heavy ion fusion drivers call for beam brightness and intensity surpassing traditional limits. Collective effects such as halo formation and emittance growth impose stringent limits on the driver and can raise the costs of the machine. The University of Maryland Electron Ring (UMER), currently near completion, is designed to be a scaled model (3.6-m diameter) for exploring the dynamics of such intense beams. The ring configuration permits the investigation of dispersion and other effects that would occur in bends and a recirculator machine, in addition to those occurring in a straight lattice. Using a 10 keV electron beam, other parameters are scaled to mimic those of much larger ion accelerators, except at much lower cost. An adjustable current in the 0.1–100 mA range provides a range of intensities unprecedented for a circular machine. By design, UMER provides a low-cost, well-diagnosed research platform for driver physics, and for beam physics in general. UMER is augmented with a separate setup, the Long Solenoid Experiment (LSE), for investigating the longitudinal beam dynamics and the evolution of energy spread due to Coulomb collisions in a straight geometry.

The University of Maryland Electron Ring (UMER), designed for transport studies of space-charge dominated beams in a strong focusing lattice, is nearing completion. UMER models, for example, the recirculator accelerator envisioned as a possible driver for heavy-ion inertial fusion. The UMER lattice will consist of 36 alternating-focusing (FODO) periods over an 11.5 m circumference. The main diagnostics are phosphor screens and capacitive beam position monitors placed at the center of each 20° bending section. In addition, pepper-pot and slit-wire emittance meters are in operation. We present experimental results for three cases of strong space-charge dominated transport (7.2, 24, and 85 mA, at 10 keV) and contrast them with one case in the emittance-dominated regime (0.6 mA at 10 keV). With focusing given by σ0=76°, the zero-current betatron phase advance per period, the range of currents corresponds to a space-charge tune depression of 0.2 to 0.8. This range is unprecedented for a circular machine. The b...

We report on the results of beam transport experiments at the University of Maryland Electron Ring (UMER) over a distance of approximately 4 m . The experiments involve a 10 keV , 25– 100 mA , 100 ns electron beam in a lattice consisting of one short solenoid, 24 printed-circuit magnetic quadrupole lenses, and a number of bending and steering dipole magnets. The diagnostics include capacitive beam-position monitors, phosphor screens, slit-wire emittance meters and others. We discuss the conditions required for matching the space-charge-dominated beam into the UMER lattice, as well as emittance measurements and initial studies of longitudinal dynamics in the ring.

The U.S. Heavy Ion Fusion program has recently commissioned several new experiments. In the High Current Experiment [P. A. Seidl et al., Laser Part. Beams 20, 435 (2003)], a single low-energy beam with driver-scale charge-per-unit-length and space-charge potential is being used to study the limits to transportable current posed by nonlinear fields and secondary atoms, ions, and electrons. The Neutralized Transport Experiment similarly employs a low-energy beam with driver-scale perveance to study final focus of high perveance beams and neutralization for transport in the target chamber. Other scaled experiments—the University of Maryland Electron Ring [P. G. O’Shea et al., accepted for publication in Laser Part. Beams] and the Paul Trap Simulator Experiment [R. C. Davidson, H. Qin, and G. Shvets, Phys. Plasmas 7, 1020 (2000)]—will provide fundamental physics results on processes with longer scale lengths. An experiment to test a new injector concept is also in the design stage. This paper will describe th...

A detailed understanding of the physics of space-charge-dominated beams is vital in the design of heavy ion inertial fusion (HIF) drivers. In that regard, low-energy, high-intensity electron beams provide an excellent model system. The University of Maryland Electron Ring (UMER), currently being installed, has been designed to study the physics of space-charge-dominated beams with extreme intensity in a strong focusing lattice with dispersion. At 10 keV and 100 mA, the beam from the UMER injector has a generalized perveance as much as 0.0015, corresponding to that of proposed HIF drivers. Though compact (11 m in circumference), UMER will be a very complex device by the time of its completion (expected 2003). We present an update on the construction as well as recent experimental results.

The electron beam injector constructed by FM technologies for the University of Maryland Electron Ring (UMER) program is described. The program will use an electron beam to model space-charge-dominated ion beams in a recirculating linac for heavy ion inertial fusion, as well as for high-current muon colliders. The injector consists of a 10 keV, 100 mA electron gun with 50–100 nsec pulse width and a repetition rate of 120 Hz. The e-gun system includes a 6-mask, rotatable aperture plate, a Rogowski current monitor, an ion pump, and a gate valve. The injector beamline consists of a solenoid, a five-quadrupole matching section, two diagnostic chambers, and a fast current monitor. An independent diagnostic chamber also built for UMER will be used to measure horizontal and vertical emittance, current, energy, energy spread, and the evolution of the beam envelope and profile along the injector beamline.

A detailed understanding of the physics of space-charge dominated beams is vital in the design of heavy ion inertial fusion (HIF) drivers. In that regard, low-energy, high-intensity electron beams provide an excellent model system. The University of Maryland Electron Ring (UMER), currently under construction, has been designed to study the physics of space-charge dominated beams with extreme intensity in a strong focusing lattice with dispersion. At 10 keV, 100 mA, the UMER beam has a generalized perveance in the range of 0.0015, corresponding to that of proposed HIF drivers. Though compact (11 m in circumference), UMER is a very complex device. In this paper, the unique design features of this research facility, the beam physics to be investigated, and recent experimental results in the prototype injector as well as simulation studies will be reviewed.

At the University of Maryland our research on beam physics focuses on space-charge effects and collective phenomena in high-intensity, high-brightness beams for advanced accelerator applications such as drivers for heavy ion inertial fusion. In this paper, we present results of recent beam physics experiments including study of the resistive-wall instability and beam transport in a FODO lattice. We also report on the status of an electron ring project to study the recirculation of beam currents well beyond the normal tune-shift limit.

A 3-D particle-in-cell code, WARP, is being used to study the self-consistent nonlinear dynamics of the space-charge-dominated beam in the University of Maryland E-ring project. Early work was concentrated on general studies of beam propagation in the nominal ring lattice, as well as more detailed calculations in the injector transport line. Simulations of the ring lattice are being used to address fundamental questions such as emittance growth, which can be caused by nonlinearities in the focusing elements, as well as distortions in the beam equilibrium by the bends. A preliminary design of the injector matching section is presented. Simulations of the injector section emphasize the relationship between the predictions of numerical models and the experimental measurements, in order to understand the requirements for adequately modeling the specific focusing elements used.

A small electron ring is being designed at the University of Maryland for studies of space-charge-dominated beams in rapid-cycling rings and recirculating accelerator systems. The motivation and general features of the ring are given in an accompanying paper. In this paper we describe the electron gun, matching section and pulsed inflector. One solenoid and five quadrupoles will be used for the matching section. This section will also serve as an experimental test bed for the printed-circuit quadrupoles and, in part, the lattice design. Our preliminary design for the injector system is based on pulsed, single-turn injection of the full beam current located at one of 36 ring dipoles. A pulsed, Panofsky quadrupole replaces one of the ring quadrupoles to accomodate the injection line. The low energy and small fields enable reasonable voltage and current for these iron-free components, but require careful compensation for external fields, including the earth's field.

Rapid-cycling rings and other recirculator systems operating with intense beams beyond the conventional space charge limit are of great interest for applications in heavy ion inertial fusion, high energy physics, spallation neutron sources, and other fields. There is very little theoretical or experimental knowledge that would allow us to make any predictions on the beam behavior in such novel systems. We are proposing to build at the University of Maryland a small electron ring with a circumference of about 11 m for studying the evolution of a space-charge-dominated beam in a circular lattice. The general features of the lattice design with printed-circuit quadrupoles, dipoles, and other components and special problems are presented. Further details can be found in two related papers.

A two-year study of recirculating induction heavy-ion accelerators (recirculators) as low-cost drivers for inertial-fusion energy power plants has recently been completed. A summary of that study and other recent work on recirculators is presented.

We have begun a two-year study on the problem of designing high-power pulse modulators for the induction cavities of a recirculating heavy-ion linac driver for inertial fusion. Recent studies have shown the potential of a recirculator for major cost reduction. However, important issues exist including beam stability and control, and severe tolerances. We are addressing the need for efficient, cost-effective modulators. Our example conceptual design uses a 3 ms, linearly rising dipole field and constant energy/turn for 96 turns. The modulator pulses must vary in duration and spacing by a factor of 4. For each 264 kV module we propose to use 50–100 Metglas cores, each driven by a number recently developed, solid-state, on-off switches. Several circuit methods are being studied, including delayed triggering of groups of switches and selective charging of pulse networks. Here we report on initial circuit studies and on preliminary experiments to characterize promising switches and related components. Plans are underway to assemble a scaled accelerating module and simulate an ion beam with a separte high-voltage modulator.

A two‐year study of recirculating induction heavy ion accelerators as low‐cost driver for inertial‐fusion energy applications was recently completed. The projected cost of a 4 MJ accelerator was estimated to be about $500 M (million) and the efficiency was estimated to be 35%. The principal technology issues include energy recovery of the ramped dipole magnets, which is achieved through use of ringing inductive/capacitive circuits, and high repetition rates of the induction cell pulsers, which is accomplished through arrays of field effect transistor (FET) switches. Principal physics issues identified include minimization of particle loss from interactions with the background gas, and more demanding emittance growth and centroid control requirements associated with the propagation of space‐charge‐dominated beams around bends and over large path lengths. In addition, instabilities such as the longitudinal resistive instability, beam‐breakup instability and betatron‐orbit instability were found to be controllable with careful design.

The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron beam current is adjustable from 0.7 mA, an emittance dominated beam, to 100 mA, a strongly space charge dominated beam. UMER is addressing issues in beam physics relevant to many applications that require intense beams of high quality such as advanced concept accelerators, free electron lasers, spallation neutron sources, and future heavy-ion drivers for inertial fusion. The primary focus of this presentation is experimental results and improvements in multi-turn operation of the electron ring. Results of high current, space charge dominated multi-turn transport will also be presented.

Beams with a high phase space density are useful for many modern applications such as free electron lasers, pulsed neutron sources, high-energy-density physics, and high-luminosity colliders. Production of such beams requires understanding the complex space charge dynamics at the low-energy end of the accelerator. The University of Maryland Electron Ring (UMER) has been designed and built with the purpose of investigating space charge effects using scaled low-energy electron experiments. We have recently circulated the highest- space-charge beam in a ring to date, achieving a breakthrough both in the number of turns and in the amount of current propagated. We have propagated a beam with an integer tune shift for over 100 turns, and other, even higher-current beams, for 5-50 turns albeit with some beam loss. One beam had a tune shift at injection of 5.0, which is several factors higher than anything propagated in the past. We report here as well on other interesting aspects of the UMER work.

The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. The electron storage ring has been closed and recent operations have been focused on achieving multi- turn transport. An entire suite of terminal diagnostics is available for time-resolved phase space measurements of the beam. These diagnostics have been mounted and tested at several points on the ring before it was closed and will complete the ring when mounted to the extraction section. UMER utilizes a unique injection scheme which uses the fringe fields of an offset quadrupole to assist a pulsed dipole in bending the beam into the ring. Similar concepts, along with a more traditional electrostatic method, are being considered for beam extraction. This presentation will focus on the recent efforts to design and deploy these major subsystems required for beam extraction.

The University of Maryland electron ring (UMER) is a low-energy, high current recirculator for beam physics research. The ring is completed for multi-turn operation of beams over a broad range of intensities and initial conditions. UMER is addressing issues in beam physics with relevance to any applications that rely on intense beams of high quality. Examples are advanced accelerators, FEL’s, spallation neutron sources and future heavy-ion drivers for inertial fusion. We review the ring layout and operating conditions, and present a summary of beam physics areas that UMER is currently investigating and others that are part of the commissioning plan. We also emphasize the computer simulation work that is an integral part of the UMER project.

Commissioning of the University of Maryland Electron ring (UMER) is currently underway. We discuss the various electrical systems of UMER. The power system includes 114 supplies for 70+ air-core magnetic quadrupoles, 36 Bending dipoles and 30+ steering dipoles as well as earth’s field compensating coils. Systems for data collection comprise multiplexers and fast digitizers for diagnostics including 15 fast beam position monitors (BPMs) and video capture from fluorescent screen monitors. Several pulsers have been built in-house for injection and extraction magnets. The stringent timing scheme is also presented.

The combination of energy spread and space charge provides a rich domain for interesting beam dynamics that are currently not well understood. The University of Maryland Electron Ring (UMER) [1] is a small scaled ring designed to probe the little-known regions of higher beam intensities using low-energy electrons. As such, design, commissioning and operation of UMER present many challenges, some quite novel. For example the UMER beam energy of 10 keV makes the beam very sensitive to the Earth magnetic field, which we can fortunately use to assist in bending the beam. This paper presents a systematic simulation study of the interaction of space charge and energy spread, with and without the earth magnetic field.

Progress is described toward the development of pulse generators required for injection and extraction of the University of Maryland Electron Ring (UMER). The geometry, described elsewhere, employs a fast ironless dipole at the junction of a Y-shaped section of the ring. The dipole as developed has an inductance of 600nH. The required +21 A long pulse generator for multi-turn operation is installed. The first prototype pulse generator, providing –42 A for deflection of the beam in the opposite sense, has been installed on the beam line and tested. Successful multiple beam laps have been observed.

The University of Maryland Electron Ring (UMER) is built as a low-cost testbed for intense beam physics for benefit of larger ion accelerators [1]. The beam intensity is designed to be variable, spanning the entire range from low current operation to highly space-charge-dominated transport. The ring has recently been closed and multi-turn commissioning has begun. Although we have conducted many experiments at high space charge during UMER construction, lower-current beams have become quite useful in this commissioning stage for assisting us with beam steering, measurement of phase advance, etc. One of the biggest challenges of multi-turn operation of UMER is correctly operating the Y-shaped injection section, hence called the Y-section, which is specially designed for UMER multi-turn operation. It is a challenge because the system requires several quadrupoles and dipoles in a very stringent space, resulting in mechanical, electrical, and beam control complexities. This paper presents a simulation study of the beam centroid motion in the injection region.

The University of Maryland electron ring (UMER) is a low‐energy, high current recirculator for beam physics research with relevance to any applications that rely on intense beams of high quality. We review the space‐charge physics issues, both in transverse and longitudinal beam dynamics, which are currently being addressed with UMER: emittance growth and halo formation, strongly asymmetric beams, Montague resonances, equipartitioning, bunch capture and shaping, etc. Furthermore, we report on recent developments in experiments, simulations, and improved diagnostics for space‐charge dominated beams.

The University of Maryland Electron Ring (UMER) is a low energy, high current recirculator for beam physics research. Ring construction has been completed for multi‐turn operation of beams over a broad range of intensities and initial conditions. The electron beam current is adjustable up to 100 mA and pulse length as long as 100 ns. UMER is addressing issues in beam physics relevant to many applications that require intense beams of high quality, such as advanced concept accelerators, free electron lasers, spallalion neutron sources, and future heavy‐ion drivers for inertial fusion. The primary focus of this presentation is experimental results in the area of beam steering and control within the injection line and ring. Unique beam steering algorithms now include measurement of the beam response matrix at each quadrupole and matrix inversion by singular value decomposition (SVD). With these advanced steering methods, transport of an intense beam over 50 turns (3600 full lattice periods) of the ring has been achieved.

The University of Maryland Electron Ring (UMER) is built as a low‐cost testbed for intense beam physics for benefit of larger ion accelerators. The beam intensity is designed to be variable, spanning the entire range from low current operation to highly space‐charge‐dominated transport. The ring has been closed and multi‐turn commissioning has begun. One of the biggest challenges of multi‐turn operation of UMER is correctly operating the Y‐shaped injection/recirculation section, which is specially designed for UMER multi‐turn operation. It is a challenge because the system requires several quadrupoles and dipoles in a very stringent space, resulting in mechanical, electrical, and beam control complexities. Also, the Earth’s magnetic field and the image charge effects have to be investigated because they are strong enough to impact the beam centroid motion. This paper presents both simulation and experimental study of the beam centroid motion in the injection region to address above issues.

The authors report on initial experimental results of a high-efficiency L-band proof-of-principle microwave amplifier experiment. The prototype under experimental investigation employs a 120 kV, 20A, 5mm diameter, 4 {mu}sec pencil beam. The pencil beam is made to spiral through the interaction with a rotating mode microwave cavity. Efficient energy extraction from the spiral beam is obtained in an output cavity also supporting a rotating mode. The system is immersed in a uniform magnetic field with its amplitude properly adjusted to permit synchronization between the temporal oscillations of the spiral beam and the fields of the rotating modes. This device should be capable of providing coherent, efficient, multimegawatt microwave radiation for a variety of applications appropriate to its frequency range.

Several coherent emission processes operative within high-power, relativistic electron beams have been studied during the past few years. The spectral range of interest extends from centimeter to submillimeter wave-lengths. Effort within this field is presently concentrated in three areas: exploratory development of the electron cyclotron maser (gyrotron) for millimeter-wave sources; a basic study of scattering mechanisms whereby incident microwave radiation is Doppler-shifted to higher frequency; and the extension of conventional microwave sources to the gigawatt level using pulsed power techniques. The field is reviewed with emphasis on the several mechanisms employed and results of recent theoretical and experimental investigations.

Summary form only given. The University of Maryland Electron Ring (UMER), designed for transport studies of space-charge dominated beams in a strong focusing lattice, is nearing completion. UMER models, for example, the recirculator accelerator envisioned as a possible driver for heavy-ion inertial fusion. The UMER lattice consists of 36 alternating-focusing (FODO) periods over an 11.5-m circumference. The main diagnostics are phosphor screens and capacitive beam position monitors placed at the center of each 20/spl deg/ bending section. In addition, pepper-pot and slit-wire emittance meters are in operation. We present experimental results of beam transport over 2/3 of the ring, i.e. 24 FODO periods or 9.0 m, approximately, from the gun output. The range of beam currents, corresponding to space charge tune depressions from 0.2 to 0.8, is unprecedented for a circular machine. Issues associated with beam characterization, scaling of various parameters, alignment, rms envelope matching and halos are discussed.

Closure of the University of Maryland Electron Ring (UMER) is anticipated in May 2003. An initial prototype of the injection "Y" has been completed. Electro-mechanical aspects of the design and test results of this prototype are presented. The design incorporates an offset quadrupole and a pulsed dipole to achieve the 10-degree bend required from the injection line. To accommodate penetration of the pulsed dipole magnetic field a glass gap has been inserted at the point of injection. A fixture was used to align the sections of the assembly and serves as a permanent mount plate. A similar method will be used for extraction of the beam after the electron ring has been closed.

The University of Maryland Electron Ring (UMER), designed for studies of space-charge dominated beam transport in a strong focusing lattice, is nearing completion. UMER models, for example, the recirculator machine envisioned as a possible driver for heavy-ion inertial fusion. The UMER lattice consists of 36 FODO periods distributed among 18, 20/spl deg/-bending sections containing two dipole magnets each. The main diagnostics are phosphor screens and capacitive beam position monitors placed at the center of each bending section. In addition, pepper-pot and slit-wire emittance meters, as well as an energy analyzer are in operation. We present here results of beam matching and characterization for a range of currents extending from about 1 mA to 100 mA, all at 10 keV and 100 ns pulse duration. With typical focusing given by /spl sigma//sub 0/=76, the zero-current betatron phase advance per period, the range of currents corresponds to tune depressions of 0.8 to 0.2. This range covers both the emittance dominated and extreme space-charge dominated regimes, which is unprecedented for a circular machine.

The University of Maryland Electron Ring (UMER), designed for transport studies of space‐charge dominated beams in a strong focusing lattice, is nearing completion. Low energy, high intensity electron beams provide an excellent model system for experimental studies with relevance to all areas that require high quality, intense charged‐particle beams. In addition, UMER constitutes an important tool for benchmarking of computer codes. When completed, the UMER lattice will consist of 36 alternating‐focusing (FODO) periods over an 11.5‐m circumference. Current studies in UMER over about 2/3 of the ring include beam‐envelope matching, halo formation, asymmetrical focusing, and longitudinal dynamics (beam bunch erosion and wave propagation.) Near future, multi‐turn operation of the ring will allow us to address important additional issues such as resonance‐traversal, energy spread and others. The main diagnostics are phosphor screens and capacitive beam position monitors placed at the center of each 200 bending section. In addition, pepper‐pot and slit‐wire emittance meters are in operation. The range of beam currents used corresponds to space charge tune depressions from 0.2 to 0.8, which is unprecedented for a circular machine.

Numerical simulation using particle-in-cell codes is a powerful tool in understanding the nonlinear dynamics of space-charge-dominated beams. The University of Maryland Electron Ring (UMER) will explore the transport of beams with intensity previously inaccessible to circular machines. The ring will also function as a testbed for accelerator codes. Applications such as heavy ion fusion and colliders require the preservation of beam quality during transport over large distances. This need for low beam emittance and small particle losses constrains the design and fabrication of the lattice and the injector. Furthermore, the non-zero energy spread leads to dispersion in the circular lattice. Simulations using the WARP code address these issues: the magnets, including the fringe field nonlinearities, are modeled realistically; dispersion matching is attempted; and effects of lattice and beam errors are examined. The simulations aid in understanding experimental results, such as the transverse density waves observed in the injector.

Two Panofsky quadrupoles with rectangular aperture and fast rise time are proposed for the injection area in the University of Maryland electron ring project (UMER). The theoretical current distribution needed on the surface of a rectangular aperture to produce a quadrupole field is derived. The conductor location is determined mostly by the theoretical current distribution, with some free factors to optimise the field. The design is based on the linearity of longitudinal integrated field. Each quadrant of the Panofsky quadrupole consists of 10 loops of conductors to minimize inductance while retaining the field quality. A 2:1 scaled model has been made and the magnetic field was measured. Two 1:1 models have been made to measure inductance, mutual inductance and the rise time. Simulations of beam propagation with Panofsky quadrupoles demonstrated the linearity of the design.

It is noted that optimization is important to the development of high-current, heavy-ion accelerators for power production based on inertial confinement fusion. Two heavy-ion recirculating linac configurations are examined that eliminate the necessity to provide reset pulses for the cores used in the linac induction accelerator modules. The configurations considered use the reset pulse to accelerate beam bunches traveling in the reverse direction and thus potentially improve system efficiency and/or reduce cost. A three-linac recirculator and a bidirectional recirculator are considered. >

A proof-of-principle experiment has been assembled and is being tested to validate a novel microwave amplifier concept. The method uses transverse deflection modulation of a collimated electron beam which is converted to axial bunching by a magnet designed to bend the beam 105 degrees . Since the mechanism avoids the well-known problem of longitudinal bunching at relativistic velocities, it is suitable for high-voltage beams. Design considerations and preliminary initial results are presented. The results give confidence that the basic mechanism is valid. It is believed that the present results are limited by a combination of finite beam size effects and space charge, both of which tend to dilute effective bunching. >

A printed-circuit quadrupole has been designed for low-energy electron beam research in the Institute for Plasma Research at the University of Maryland. Previously, solenoid focusing has been employed. Quadrupoles will allow more realistic beam studies to be performed in straight beams, and are necessary for a ring geometry currently under consideration.

We report here on a study of circuits for the accelerating modules in a recirculator. Future requirements are challenging: flat-top (or slightly rising) pulses with varying duration; beam currents as high as a kiloampere; a train of 50-100 pulses with instantaneous repetition rate as high as 50 kHz; and high efficiency. An accelerating module providing 200-400 kV to the beam might house 30-100 cores. Our study uses cores of moderate size - we chose 20.3 cm diameter. The pulsers use tapered pulse-forming networks and provide core reset, 20-/spl mu/s recovery and variable duration. A novel addition is a separate, 150-kV, 200-A modulator used to simulate a constant-current ion beam, allowing a direct measurement of the cell dynamic impedance and the modulator-to-beam conversion efficiency. The basic goal of the project is to explore the use of solid-state switches and low-voltage circuits with efficiency and low cost in mind. In this report we describe our circuits and salient results, then offer comments and conclusions.

The University of Maryland Electron Ring (UMER) is a compact experiment that will be used to study the fundamental properties of space-charge dominated beams. Because of the small physical dimensions and weak fields involved, maintaining the beam's orbit is a difficult challenge. Accurate characterization of the magnets, careful alignment, and an effective control system are all critical to the project's success. In this report, the key challenges are outlined and the procedures that will be implemented to address them are explained. Existing portions of the system are described, and future plans are evaluated with computer simulation.

A detailed understanding of the physics of space-charge dominated beams is vital for many advanced accelerators that desire to achieve high beam intensity. In that regard, low-energy, high-intensity electron beams provide an excellent model system. The University of Maryland Electron ring (UMER), currently under construction, has been designed to study the physics of space-charge dominated beams with extreme intensity in a strong focusing lattice with dispersion. The tune shift in UMER will be more than an order of magnitude greater than exiting synchrotrons and rings. The 10-keV, 100 mA, UMER beam has a generalized perveance in the range of 0.0015, and a tune shift of 0.9. Though compact (11-m in circumference), UMER is a very complex device, with over 140 focusing and bending magnets. We report on the unique design features of this research facility, the beam physics to be investigated, and early experimental results.

The short printed-circuit quadrupoles for UMER produce fields with small gradients that meet our needs for the focusing and bending of a 10 keV, 100 mA electron beam over a circumference of 11.5 m. The field quality of the magnets has been established [see W.W. Zhang et al., Phys. Rev. ST Accel. Beams 3, 122401 (2000)], but correcting elements are needed to compensate for quadrupole rotation errors that lead to undesirable beam rotations in the injector line as well as in the main lattice. The correcting elements consist of printed-circuit quadrupoles; that are mounted over the main quadrupoles, with a relative angle of 45 degrees. In this way, a skew quadrupole component can be easily, independently and electronically adjusted to rotate the quadrupole field. Results are presented of field measurements of the modified quadrupoles, as well as preliminary observations in the UMER injector, and corresponding computer simulations.

Results are presented of the first experiments with a 10 keV, 100 mA beam in the matching section for UMER. The section, about 1.5 m long, consists of one short solenoid, six printed-circuit (PC) quadrupoles, a bend PC dipole, a number of steering dipoles, and two sets of Helmholtz coils for balancing the Earth's field. The 2 RMS beam radius as a function of axial distance in the straight part of the beam line is obtained from fluorescent screen pictures. The results are compared with calculations using the K-V envelope equations. The importance of an accurate determination of the initial conditions, i.e. beam envelope size and slope at the entrance plane, as well as the emittance, is emphasized. Furthermore, the role of different types of errors, specially misalignment and quadrupole rotations is discussed.

We describe design and testing of an induction cell with modulator for the Relativistic Klystron Two-Beam Accelerator (RK-TBA) concept, an option for the power source for the Next Linear Collider (NLC). FM Technologies has designed and built a prototype induction accelerator, which we call a re-accelerator, for a joint LLNL/LBNL TBA technology test-bed experiment.

The 10 keV, 100 mA, Pierce-type electron gun and injector for the University of Maryland Electron Ring (UMER) Project are described. Using a pulsed control grid located 0.15 mm from the 4-mm radius cathode, 100-ns bunches are generated. The A/K gap is variable, producing beam currents ranging from 50 to 160 mA. A rotatable aperture plate is included to allow six different masks, including a pepperpot. Beam current after the aperture plate is measured with a built-in Rogowski coil. The injector line consists of a solenoid lens, five printed-circuit quadrupoles, and two in-line diagnostic chambers. A separate, multi-purpose chamber is placed at the end of the injector line during gun characterization studies for emittance, profile, and energy analysis.

The University of Maryland Electron Ring (UMER), currently under construction, has been designed to study the physics of space-charge dominated beams at extremely large values of the betatron tune shift which exceed those of existing strong-focusing synchrotrons and rings by more than an order of magnitude. In this paper, the unique design features of this research facility, the new beam physics to be investigated, and recent experimental results in the injector prototype as well as simulation studies are reviewed.