High energy density plasma science with an ultra - relativistic electron beam

An intense, high-energy electron or positron beam can have focused intensities rivaling those of today's most powerful laser beams. For example, the 5 ps (FWHM), 50 GeV beam at the Stanford Linear Accelerator Center (SLAC) at 1 kA and focused to a 3 micron rms spot size gives intensities of > 10 W/cm at a repetition rate of > 10 Hz. Unlike a ps or fs laser pulse which interacts with the surface of a solid target, the particle beam can readily bore through several mm of steel. However, the same particle beam can be manipulated quite effectively by a plasma that is a million times less dense than air! This is because of the incredibly strong collective fields induced in the plasma by the Coulomb force of the beam. The collective fields in turn react back onto the beam leading to many clearly-observable phenomena. The beam particles can be: (1) deflected leading to focusing, defocusing, or even steering of the beam; (2) undulated causing the emission of spontaneous betatron x-ray radiation and; (3) accelerated or decelerated by the plasma fields. Using the 28.5 GeV electron beam from the SLAC linac we have carried out a series of experiments that demonstrate clearly many of the above mentioned effects. The results can be compared with theoretical predictions and 2D and 3D, one-to-one, PIC code simulations. These phenomena may have practical applications in future technologies including optical elements in particle beam lines, synchrotron light sources, and ultra-high gradient accelerators. REVIEW PAPER 11/6/01 Prepared for Physics of Plasmas