  A technique for production of an electron beam with a high transverse
emittance ratio. a "flat" beam, has been proposed by Brinkmann, Derbenev, and
Floettmann.[1] The cathode of an RF-laser gun is immersed in a solenoidal
magnetic field; as a result the beam emitted from a round laser spot has a net
angular momentum. Subsequent passage through a quadrupole channel that has a 90
degree difference in phase advance between the transverse degrees of freedom
results in a flat beam. Experimental study is underway at the Fermilab A0
Photoinjector. Thus far, transverse emittance ratios as high as 50 have been
observed, and the results are in substantial agreement with simulation.
  [1] R. Brinkmann, Ya. Derbenev, K. Floettmann, "A Flat Beam Electron Source
for Linear Colliders." TESLA Note 99-09, April 1999.
