A pyroelectric accelerator

A pyroelectric crystal has a permanent electric dipole moment, masked by adsorbed ions on the crystal’s faces until there is a change in temperature, which creates strong electric fields at those surfaces. Now, James Brownridge of SUNY Binghamton and Stephen Shafroth of the University of North Carolina, Chapel Hill, have used those electric fields to create stable, self-focused electron beams with energies as high as 170 keV. The beams were apparent in a dilute gas atmosphere, and emanated from the so-called −z face of crystalline LiNbO₃ after heating the +z face. The energy conversion was not especially efficient—watts of heating energy produced only microwatts of output electron beam energy—but that might not be important. Brownridge says that such a focused electron beam could be used in a portable, economical x-ray fluorescence device for the elemental analysis of complex materials like tree leaves, rocks, air filters, or blood samples. (J. D. Brownridge, S. M. Shafroth, Appl. Phys. Lett., 79, 3364, 2001 http://dx.doi.org/10.1063/1.1418458 .)