C. Papadopoulos

Measurement and simulation of source-generated halos in the University Of Maryland Electron Ring (UMER)

One of the areas of fundamental beam physics that have served as the rationale for recent research on UMER is the study of the generation and evolution of beam halos. Recent experiments and simulations have identified imperfections in the source geometry, particularly in the region near the emitter edge, as a significant potential source of halo particles. The edge-generated halo particles, both in the experiments and the simulations are found to pass through the center of the beam a short distance downstream of the anode plane. Understanding the detailed evolution of these particle orbits is therefore important to designing any aperture to remove the beam halo.

Phase space tomography of beams with extreme space charge

A common challenge for accelerator systems is to maintain beam quality and brightness over the usually long distance from the source to the target. In order to do so, knowledge of the beam distribution in both configuration and velocity space along the beam line is needed. However, measurement of the velocity distribution can be difficult, especially for beams with strong space charge. Here we present a simple and portable tomographic method to map the beam phase space, which can be used in the majority of accelerators. The tomographic reconstruction process has first been compared with results from simulations using the particle- in-cell code WARP. Results show excellent agreement even for beams with extreme space charge and exotic distributions. Our diagnostic has also been successfully demonstrated experimentally on the University of Maryland Electron Ring, a compact ring designed to study the transverse dynamics of beams in both emittance and space charge dominated regimes. Special emphasis is given to intense beams where our phase space tomography diagnostic is used to shed light on the consequences of the space charge forces on the transport of these beams.

New Developments in Space‐Charge Beam Physics Research at the University of Maryland Electron Ring (UMER)

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.

Commissioning of the University of Maryland Electron Ring (UMER)

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.

Beam Control and Steering in the University of Maryland Electron Ring (UMER)

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.

Design of a scaled recirculator for Heavy Ion Inertial Fusion

An alternative concept for Heavy Ion Inertial Fusion (HIF) is the use of a recirculator to accelerate ion beams to energies in the range of 50–100 GeV [1]. The physics of an ion recirculator can be explored by means of scaled experiments in a compact machine like the existing University of Maryland Electron Ring (UMER). UMER has been successfully used for the study of the fundamental physics of space-charge-dominated transport using a 10 keV electron beam with up to 100 mA of current (or 10 nC per a 100 ns pulse) [2]. Due to the low energy and high perveance, the UMER beam accesses the same range of intensities as an HIF driver. In this paper we report on a computational study for the design of an acceleration stage for UMER using an induction cell. Using the two-dimensional transverse slice model in the particle-in-cell code WARP we show that it is possible to accelerate the UMER beam up to 20 keV without major modifications to the machine. Such acceleration enables future experiments on transverse resonance crossing and studies on longitudinal pulse behavior.

Modeling skew quadruple effects on the UMER beam

This is a numerical and experimental study of the effects of skew quadrupoles on the beam used in University of Maryland Electron Ring (UMER). As this beam is space- charge dominated, we expect new phenomena to be present compared to the emittance-dominated case. In our studies we find that skew quadrupoles can severely affect the halo of the beam and cause emittance growth, even in the first turn of the beam. For our simulations we use the WARP particle-in-cell code and we compare the results with the experimental study of skew quadrupole effects.

Beam extraction concepts and design for the university of maryland electron ring (UMER)

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.

Multi-turn operation of the university of maryland electron ring (UMER)

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.

Numerical investigations of mismatch induced halos in intense charged particle beams

In this paper, we discuss the parametric resonance model of halo creation, and compare it with self consistent simulation results. In particular, we employ two different initial distribution functions, and we find agreement with the particle‐core model, within the limitations of the latter. Furthermore, using a simple particle tracking algorithm, we are able to follow the trajectories of the halo particles, noting that a large number of them go through the core and re‐emerge later.