Experimental observations of longitudinal space-charge waves in intense electron beams

Abstract

Studies of the dynamics of longitudinal space-charge waves in space-charge dominated beams propagating through a transport channel with a long solenoid are performed at the University of Maryland. In this paper, we report some experimental results on the energy modulations converted from density modulations. By changing the working conditions of the electron gun, pure initial density modulations are generated. Energy perturbation waveforms are measured with a high-resolution energy analyzer. The experimental results are compared with both the linear theory and the simulation results. Good agreements are achieved for the relationship between the energy and current perturbation strengths.

Experimental study of large-amplitude perturbations in space-charge dominated beams

“…4. As expected from the 1D linear cold-fluid theory, for beams with a positive initial current perturbation, the fast wave exhibits a positive pulse while the slow wave shows a negative pulse, which has already been confirmed in an earlier experiment [20]. For beams with a negative initial current perturbation, the opposite scenario takes place.…”

“…Regarding comparison of the mean energy profiles, we have obtained good agreement in a previous study [20] between experimental and 1D theoretical results for beams with small perturbations. However, as shown in Fig.…”

“…The long solenoid experiment (LSE) at University of Maryland [20,[24][25][26] was designed to investigate the longitudinal dynamics of space-charge dominated beams. The apparatus consists of an electron gun [27], four short solenoids for matching, and a 1.5 m long solenoid.…”

“…Therefore, the measurements must resolve that time scale. Previously, we have reported the measurement of both the detailed mean energy profiles [20], and timeresolved transverse distributions [21] of space-charge waves. These results have informed on the expected correlations between the transverse and longitudinal beam distributions.…”

Gridded Electron Guns and Modulation of Intense Beams

“…This is a result of the expressions for current perturbation strength in space charge limited mode and triode amplification mode, which differ only by the presence of a factor of µ in eq. (13). Since most gridded guns have relatively large amplification factors, the extraction of large current perturbations will be easier when operating in triode amplification mode rather than space charge limited mode.…”