  We present a detailed study of the six-dimensional phase space of the
electron beam produced by the Cornell Energy Recovery Linac Photoinjector, a
high-brightness, high repetition rate (1.3 GHz) DC photoemission source
designed to drive a hard x-ray energy recovery linac (ERL). A complete
simulation model of the injector has been constructed, verified by measurement,
and optimized. Both the horizontal and vertical 2D transverse phase spaces, as
well as the time-resolved (sliced) horizontal phase space, were simulated and
directly measured at the end of the injector for 19 pC and 77 pC bunches at
roughly 8 MeV. These bunch charges were chosen because they correspond to 25 mA
and 100 mA average current if operating at the full 1.3 GHz repetition rate.
The resulting 90% normalized transverse emittances for 19 (77) pC/bunch were
0.23 +/- 0.02 (0.51 +/- 0.04) microns in the horizontal plane, and 0.14 +/-
0.01 (0.29 +/- 0.02) microns in the vertical plane, respectively. These
emittances were measured with a corresponding bunch length of 2.1 +/- 0.1 (3.0
+/- 0.2) ps, respectively. In each case the rms momentum spread was determined
to be on the order of 1e-3. Excellent overall agreement between measurement and
simulation has been demonstrated. Using the emittances and bunch length
measured at 19 pC/bunch, we estimate the electron beam quality in a 1.3 GHz, 5
GeV hard x-ray ERL to be at least a factor of 20 times better than that of
existing storage rings when the rms energy spread of each device is considered.
These results represent a milestone for the field of high-brightness,
high-current photoinjectors.
