Experimental Observations of Beam Fluctuations in Space-Charge Dominated Beams

With more research and applications demanding high current, high quality electron beams, understanding of longitudinal dynamics of space-charge dominated beams becomes very important. For example, heavy ion beams for High-Energy Density Physics studies need be longitudinally compressed by orders of magnitude to deliver the needed energy on the target, requiring careful control of energy spread. In high-brightness electron injectors for free electron laser applications, fluctuations in the beam waveform must be minimized so as to minimize the effects of coherent synchrotron radiation. At the University of Maryland, we perform experiments on a scaled set-up with low-energy electrons to assess the impact of fluctuations that we deliberately introduce. In this paper, we report experimental observation of the conversion of density modulations into energy modulations. The initial density modulations are generated in the electron gun by varying the operation conditions. Energy perturbation waveforms are measured with a high-resolution energy analyzer. The experimental results are compared with both the linear theory and particle-in-cell code simulations. We discuss the experimental results and the experimental challenges