Time Resolved Emittance Measurements with a Freely Expanding Electron Beam

Time resolved rms emittance measurements have been made on the ETA by allowing the electron beam to freely expand into a magnetic field free vacuum region while measuring beam size versus time with x-ray probes at three axial positions. The beam is not required to be at a waist. Temporal resolution is limited only by the beam size measurement technique, which for the x-ray probe technique is subnanosecond. The analysis consists of matching parameters of the beam envelope equation with measured radii. Space charge effects were ignored since they were small for this experiment. They can be easily included but the resulting envelope equation must be solved numerically. Emittance measurements of the wire zone conditioned electron beam will be given.