The Maryland transport experiment—General perspectives and recent results with off‐centered beams

The experiment at the University of Maryland was designed to study the physics of space‐charge‐dominated beam transport through a periodic focusing channel. Its major goal is to check theoretical predictions of current limits and instabilities and to investigate the effects of nonlinear lens forces, misalignments, and beam off‐centering. In the recently completed second phase, a 5 kV, 180–200 mA electron beam is transported through 36 equally spaced solenoid lenses. The focusing strength of the channel is measured in terms of the phase shift σ_o without space charge. Below σ_o=50⁰, the focusing is too weak to confine the beam within the pipe. Between 60⁰ and 80⁰ a ‘window’ of lossless transmission is observed. Above σ_o=80⁰, the transported current begins to drop. The structure of the transmission curve versus σ_o in this fall‐off region is not smooth, and is very sensitive to alignment errors of the gun and of individual magnets. Results are compared with computer simulations. The potential of the experiment and expected roles of instabilities, nonlinearities, and errors will be discussed.