J.C.T. Thangaraj

Evolution of laser induced perturbation and experimental observation of space charge waves in the University Of Maryland Electron Ring (UMER)

The University of Maryland Electron Ring (UMER) is a scaled model to investigate the transverse and longitudinal physics of space charge dominated beams. It uses a 10-keV electron beam along with other scaled beam parameters that model the larger machines but at a lower cost. Understanding collective behavior of intense, charged particle beams due to their space charge effects is crucial for advanced accelerator research and applications. This paper presents an experimental study of longitudinal dynamics of an initial density modulation on a space-charge dominated beam. A novel experimental technique of producing a perturbation using a laser is discussed.Using a laser to produce a perturbation provides the ability to launch a pure density modulation and to have better control over the amount of perturbation introduced. Collective effects like space charge waves and their propagation over long distances in a quadrupole channel are studied.A one dimensional cold fluid model is used for theoretical analysis and simulations are carried out in WARP-RZ.

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.

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.

Longitudinal Acceleration of Intense Beams in the University of Maryland Electron Ring (UMER)

Summary form only given. With the ability to inject bright beams into the University of Maryland electron ring (UMER) comes the problem of longitudinal end erosion of both the head and tail from high space charge. It is important therefore to apply suitably-designed longitudinal focusing forces to confine the beam and prevent it from its normal expansion. This paper presents the design and prototyping of an induction cell and the technology used to pulse this cell. With successful operation of the induction cell, the confinement of the beam within UMER would increase the number of turns and also enable us to perform studies of the longitudinal physics of such highly space-charge beams. The pulsed voltage requirements for a confinement system on UMER would require ear-fields that switch 3 kV in about ~8 ns or so at a maximum rate of 5 MHz for the most intense flat-top rectangular beam injected into the ring. This places a considerable challenge on the noise-free delivery to a compact core.

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.

Fast Imaging of Time-dependent Distributions of Intense Beams

Longitudinal perturbations can be generated in the space-charge dominated regimes in which most beams of interest are born. To study the modification of transverse beam distributions by longitudinal beam dynamics, we have conducted experimental studies using low energy electron beams by taking time resolved images of a beam with longitudinal density perturbations. Two different diagnostics are used: optical transition radiation (OTR) produced from an intercepting silicon based aluminum screen and a fast (< 5 ns decay time) phosphor screen. It is found that the beam is significantly affected by the perturbation. However the OTR signal is very weak and requires over 45 minutes of frame integration. The fast phosphor screen has much better sensitivity (~1000 times enhancement). In this paper, we also report on the time resolved measurement of a parabolic beam, showing interesting correlations between transverse and longitudinal distributions of the beam.

Phase Space Tomography: A Simple, Portable and Accurate Technique to Map Phase Spaces of Beams with Space Charge

In order to understand the charged particle dynamics, e.g. the halo formation, emittance growth, x‐y energy transfer and coupling, knowledge of the actual phase space is needed. Other the past decade there is an increasing number of articles who use tomography to map the beam phase space and measure the beam emittance. These studies where performed at high energy facilities where the effect of space charge was neglible and therefore not considered in the analysis. This work extends the tomography technique to beams with space charge. In order to simplify the analysis linear forces where assumed. By carefully modeling the tomography process using the particle‐in‐cell code WARP we test the validity of our assumptions and the accuracy of the reconstructed phase space. Finally, we report experimental results of phase space mapping at the University of Maryland Electron Ring (UMER) using tomography.