  Pyroelectric crystals are used to produce self-focused electron beams with
energies greater than 170 keV. No high voltage power supply or electron gun is
needed. The system works by simply changing the temperature of a crystal of
LiNbO3 or LiTaO3 by about 100oC in dilute gas. Electron beam energy spectra as
well as positive-ion-beam energy spectra and profiles are shown. A change in
the crystal temperature of 100oC will cause a spontaneous change in
polarization. The change in polarization will be manifested by a change in
charge on the surface of the crystal. It is this uncompensated charge that
produces the electric field, which accelerates the electrons, or the positive
ions and gives rise to the plasma, which in turn focuses them. The source of
the accelerated electrons or positive ions is gas molecules ionized near the
crystal surface. When the crystal surface is negative electrons are accelerated
away from it and positive ions are attracted to the surface. These positive
ions reduce the net negative charge on the surface thereby reducing the
electric field, which causes the electron energy to decrease over time even
though the focal properties remain unchanged. When the surface is positive the
reverse obtains and the positive ion beam energy decreases over time as well.
We will present video clips, photographic and electronic data that demonstrate
many of the characteristics and applications of these electron beams.
