An induction cell has successfully been demonstrated to longitudinally confine a space-charge dominated bunch for over a thousand turns ͑Ͼ11.52 km͒ in the University of Maryland Electron Ring ͓Haber et al., Nucl. Instrum. Methods Phys. Res. A 606, 64 ͑2009͒ and R. A. Kishek et al., Int. J. Mod. Phys. A 22, 3838 ͑2007͔͒.With the use of synchronized periodic focusing fields, the beam is confined for multiple turns overcoming the longitudinal space-charge forces. Experimental results show that an optimum longitudinal match is obtained when the focusing frequency for containment of the 0.52 mA beam is applied at every fifth turn. Containment of the beam bunch is achievable at lower focusing frequencies, at the cost of a reduction in the transported charge from the lack of sufficient focusing. Containment is also obtainable, if the confinement fields overfocus the bunch, exciting multiple waves at the bunch ends, which propagate into the central region of the beam, distorting the overall constant current beam shape.
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.
This paper describes the design and simulation of a proof-of-concept quasi-integrable octupole lattice at the University of Maryland Electron Ring (UMER). This experiment tests the feasibility of nonlinear integrable optics, a novel technique that is expected to mitigate resonant beam loss and enable low-loss high-intensity beam transport in rings. Integrable lattices with large amplitudedependent tune spreads, created by nonlinear focusing elements, are proposed to damp beam response to resonant driving perturbations while maintaining large dynamic aperture [Danilov and Nagaitsev, PRSTAB, 2010]. At UMER, a lattice with a single octupole insert is designed to test the predictions of this theory. The planned experiment employs a low-current high-emittance beam with low space charge tune shift (∼ 0.005) to probe the dynamics of a lattice with large externally-induced tune spread. Design studies show that a lattice composed of a 25-cm octupole insert and existing UMER optics can induce a tune spread of ∼ 0.13. Stable transport is observed in PIC simulation for many turns at space charge tune spread 0.008. A maximum spread of ∆ν = 0.11 (RMS 0.015) is observed for modest octupole strength (peak 50 T /m 3 ). A simplified model of the system explores beam sensitivity to steering and focusing errors. Results suggest that control of orbit distortion to < 0.2 mm within the insert region is essential. However, we see only weak dependence on deviations of lattice phase advance (≤ 0.1 rad.) from the invariant-conserving condition.
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.
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