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. The tune shift in UMER will be more than an order of magnitude greater than exiting synchrotrons and rings. The 10-keV, 100 mA, UMER beam has a generalized perveance in the range of 0.0015, and a tune shift of 0.9. Though compact (11-m in circumference), UMER is a very complex device, with over 140 focusing and bending magnets. We report on the unique design features of this research facility, the beam physics to be investigated, and early experimental results.
The homogenization of a beam with a transversely nonuniform initial density distribution is examined by masking the ouput from a Pierce electron gun into five parallel beamlets, which are then propagated down a channel of periodically spaced solenoid focusing magnets. Experimental measurements, theoretical predictions, and PIC simulations are in excellent agreement for averaged beam quantities such as rms emittance and envelope radius. In addition, the fine-structure characteristic of the nonlinear evolution of the beam, including the formation of downstream images, is reproduced in detail by the simulations. PACS number(s): 52.40.Mj, 29.15.n, 52.25.Wz
The University of Maryland Electron Ring (UMER), currently under construction, has been designed to study the physics of space-charge dominated beams at extremely large values of the betatron tune shift which exceed those of existing strong-focusing synchrotrons and rings by more than an order of magnitude. In this paper, the unique design features of this research facility, the new beam physics to be investigated, and recent experimental results in the injector prototype as well as simulation studies will be reviewed.
An experiment was designed to check theoretical predictions of charge homogenization and emittance growth in nonuniform space-charge-dominated beams due to conversion of field energy into transverse kinetic energy. Five beamlets were masked out of a solid 5-keV electron beam and injected into a periodic solenoidal focusing channel. Phosphor screen images showed that the beamlets merged into an almost uniform density single beam. Images of the five-beamlet configuration were observed at a distance of 7-8 lens periods. Experimental results on merging distance and emittance growth were compared with theory and simulation and good agreement was found.PACS numbers: 52.40. Mj, 52.25.Wz
Stimulated rotational Raman scattering (SRRS) in the ultraviolet region (λ=248 nm) has been observed at the Nike laser over extended propagation paths in air during high power operation. Although this phenomenon is not significant for standard operating configurations at Nike, broadening of the laser spectrum and far-field focal profiles has been observed once the intensity-path length product exceeds a threshold of approximately 1 TW/cm. This paper presents experimental results and a new theoretical evaluation of these effects. The observations suggest that significantly broader spectra can be achieved with modest degradation of the final focal distribution. These results point to a possible path for enhanced laser-target coupling with the reduction of laser-plasma instabilities due to broad laser bandwidth produced by the SRRS.
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