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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 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 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 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.

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. 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 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.

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.

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.

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.

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) is a low-energy, high current recirculator for beam physics research [M. Reiser et al., in Proceedings of the 1999 Particle Accelerator Conference, New York, NY (IEEE, New York, 1999), p. 234]. Ring construction is completed for multiturn operation of beams over a broad range of intensities and initial conditions. UMER is an extremely versatile experimental platform with a beam current of up to 100mA and a pulse length as long as 100ns. 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 paper is to present experimental results in the areas of beam steering and multiturn operation of the ring. Unique beam steering algorithms now include measurement of the beam response matrix at each quadrupole and matrix inversion by singular value ...

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. At 10-keV, 100 mA, the UMER beam has a generalized perveance in the range of 0.0015. 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 simulation studies are reviewed.

A new optics design for beam injection into the University of Maryland Electron Ring (UMER) is proposed for multi-turn operations. We review the previous method where two pulsed and physically overlapped Panofsky quadrupoles (one is centered on the injector and the other is centered on the ring) are employed. The new design with only one DC quadrupole reduces both the mechanical and electrical complexities. The DC quadrupole is located symmetrically relative to the injector (+10/sup 0/) and the ring (-10/sup 0/). The beam's centroid motion as well as space-charge-dominated beam matching is studied to evaluate the new design. Some relevant beam issues such as stability and experimental considerations are also discussed for the multi-turn operations.