Short high charge bunches in the SLAC linac for plasma experiments

The linac at the Stanford Linear Accelerator Center (SLAC) can provide beams to different experiments during PEP-II operations. It is planned to have a 30 GeV beam to the end of the linac into the FFTB (Final Focus Test Beam) area, where there will be two plasma experiments installed, which will demonstrate plasma focussing and plasma acceleration up to 1 GeV/m. The acceleration goes linear with the current and is inversely proportional to the square of the bunch length. These high charge, short bunches will create strong longitudinal wakefields in the linac. They create a strong double-horned energy profile and have different beam dynamics in the linac. Therefore we made a test run in Fall of 1998 to measure and quantify the beam properties, like stability, distributions, tails, and backgrounds, which will be discussed in this paper. The actual plasma experiments are planned for the spring of 1999