Intense beam transport experiments in a multi-bend system at the University of Maryland Electron Ring☆
Introduction
The University of Maryland Electron Ring (UMER) is designed for scaled experiments employing low energy (up to ), high current (up to ) electron beams [1], [2]. With a strong-focusing (FODO) lattice consisting of 36 periods over a circumference (see Table 1), UMER can operate in a regime of unprecedented high beam intensity. Beam transport in this regime is dominated by space charge and is characterized by very low tune depression, i.e., the ratio of phase advances per lattice period of the betatron oscillations with and without space charge [3]. As an example, the nominal at in UMER models the beam physics of a kA beam of heavy ions at GeV energies in a future heavy-ion fusion driver. Construction of a machine with a layout similar to UMERs was undertaken a few years ago at Lawrence Livermore National Laboratory. In the Livermore ring, a (initial energy) potassium-ion beam was successfully transported and accelerated over one-quarter turn [4]. While an electron ring can address beam physics issues in a low-cost way, the LLNL ring did also address issues peculiar to ions. At the time of writing, UMER is also approaching completion of a one-quarter turn. Figs. 1a and b show the current experiment layout.
In the next section, we briefly describe the UMER electron gun. The main results from matching experiments in a straight section about long are summarized in Section 3. In Section 4, the first results of bend experiments over eight FODO periods, or , approximately, are presented. The last section is devoted to conclusions.
Section snippets
Electron source and beam parameters
The electron source is a Pierce-type gridded gun with variable perveance, similar to the gun described in Ref. [5]. The gun is cathode-driven, i.e., the cathode is pulsed to overcome the DC voltage applied to a control grid placed in front of it. The gun operates in the 3–, 1– ranges with current pulses around . The output current at a given energy can be varied by one of three methods or combinations thereof: by changing the anode–cathode gap (over a range), by
Matching experiments and scaling
Preliminary design calculations for any periodic focusing lattice can be based on the smooth approximation of the lattice [3]. In this approximation, the differential equations for the effective envelope radii X(z) and Y(z) in the two transverse planes reduce to the algebraic equation for the “average” beam radius R of the matched beamHere, k0=2π/λ0 is the wave number, λ0 is the wavelength of the transverse betatron oscillations without space charge. It can be written in
Bend experiments
Following the straight section, a pipe with a 10° bend part was added. The new section (see Fig. 1b) accommodates three additional magnetic quadru-poles before the (DC) injection bend dipole, and one quadrupole after the bend which constitutes the first ring quadrupole (QR1). The four 20° bend sections contain four quadrupoles and two bend dipoles each. All magnets, except for the short solenoid before Q1, are made of flexible printed-circuits (PC) and have been extensively characterized [11].
Conclusions
Current experiments at the University of Maryland Electron Ring (UMER) use a matching/injection section and eight FODO full periods for a total length of nearly four meters from the output of the electron gun. Experiments with different currents in the straight section following the electron gun show that the average beam size is approximately proportional to the inverse of the tune depression, in agreement with predictions from the smooth approximation of the lattice. Further, transport
Acknowledgements
We thank D. Feldman for the picture of the UMER experiment, and D. Brosius for invaluable help with LateX.
References (14)
Nucl. Instr. and Meth. A
(2001)- O'Shea, et al., Nucl. Instr. and Meth. A 464 (2001)...
- O'Shea, et al., Laser Part. Beams 20 (2002)...
Theory and Design of Charged-Particle Beams
(1994)- et al.
IEEE Trans. Electron Device
(1990) - Y. Zou, H. Li, M. Reiser, P.G. O'shea, Study of Emittance Growth in Gridded Electron Gun, Nucl. Instr. and Meth. A,...
- I. Haber, et al., Collective Space-Charge Phenomena in the Source Region, Nucl. Instr. and Meth. A, 2004, these...
Cited by (14)
Simulation studies on matching of space-charge-dominated beams for the University of Maryland Electron Ring
2004, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentPropagation and detection of RF-modulated electron and X-ray beams in air
2018, Journal of Applied PhysicsSolenoid transport of beams with current-dependent initial conditions
2017, Journal of Applied PhysicsPractical considerations in the modeling of field emitter arrays with line charge distributions
2017, Journal of Applied PhysicsDesign and simulation of an extraction section for the university of maryland electron ring
2013, IPAC 2013: Proceedings of the 4th International Particle Accelerator ConferenceTransverse-longitudinal correlations in electron guns
2012, Journal of Applied Physics
- ☆
Supported by the US Department of Energy.