Experimental studies of emittance growth in a nonuniform, mismatched, and misaligned space‐charge dominated beam in a solenoid channel

Experimental and numerical studies of emittance growth resulting from beam mismatch have been performed at the University of Maryland Electron Beam Transport Experiment. A 5‐beamlet distribution of energy 5 keV and total current 44 mA passes through two‐solenoid matching lenses and into a 36‐solenoid transport channel. Theory predicts substantial emittance growth due to density nonuniformity, beam mismatch, and beam misalignment. Experimentally, the 5‐beamlet configuration is mismatched and transported through the channel. Random misalignments in the channel produce a gradually growing offset in the beam. The final emittance is measured for the mismatched beam. Simulation results of the matched and mismatched beams reveal that a large halo accounts for the emittance growth in the mismatched case. This is supported by experiment. The difference between the experimental emittance data and the numerical simulation is analyzed and attributed to the fact that the density of the halo is below the detection threshold of the emittance meter. Simulation also predicts that misalignments contribute negligibly to the emittance growth. Excellent agreement is found between fluorescent screen images of beam structure and simulation results.