The generation
of high-brightness, high-average-current electron beams opens up new
possibilities in a variety of fields, from 100?s of kilowatt average
power FELs, ultra-high brightness and flux Energy Recovery Linac based
synchrotron light sources, electron ion colliders of extreme luminosity
and much more. It is a great challenge to get both the small emittance
beams (on the order of one micron) and the high average current (on
the order of a good fraction of an ampere) from the photocathode and
electron gun.We report a new approach to the generation of high-current,
high-brightness electron beams. Primary electrons are produced by a
photocathode and are accelerated to a few thousand electron-volts, then
strike a specially prepared diamond window. The large Secondary Electron
Yield (SEY) provides a multiplication of the number of electrons by
about two orders of magnitude. The secondary electrons drift through
the diamond under an electric field and emerge into the accelerating
proper of the electron gun through a Negative Electron Affinity surface
of the diamond. The advantages of the new approach include the reduction
of the number of primary electrons by the large SEY, i.e. a very low
laser power, low thermal emittance due to the NEA surface and the rapid
thermalization of the electrons, protection of the cathode from possible
contamination from the gun, and of the gun from possible contamination
by the cathode. This paper presents the criteria that need to be taken
into account in designing the amplifier and experimental data, among
other things showing measurements of SEY of a few hundred and transport
across hundreds of microns of diamond window.