Beam Transport Experiments over Half-turn at the University of Maryland Electron Ring (umer)∗

The University of Maryland Electron Ring (UMER), designed for studies of space-charge dominated beam transport in a strong focusing lattice, is nearing completion. UMER models, for example, the recirculator machine envisioned as a possible driver for heavy-ion inertial fusion. The UMER lattice consists of 36 FODO periods distributed among 18, 20-bending sections containing two dipole magnets each. The main diagnostics are phosphor screens and capacitive beam position monitors placed at the center of each bending section. In addition, pepper-pot and slit-wire emittance meters, as well as an energy analyzer are in operation. We present here results of beam matching and characterization for a range of currents extending from about 1 mA to 100 mA, all at 10 keV and 100 ns pulse duration. With typical focusing given by σ0=76, the zero-current betatron phase advance per period, the range of currents corresponds to tune depressions of 0.8 to 0.2. This range covers both the emittance dominated and extreme space-charge dominated regimes, which is unprecedented for a circular machine.