Plasma density from Cerenkov radiation, betatron oscillations, and beam steering in a plasma wakefield experiment at 30 GeV

Measurements of radiation near the 670.8 nm atomic spectral line of Lithium as a 30 GeV electron beam propagates through a long, high density heat pipe oven (∼ 1 meter, neutral density ∼ 1015cm−3) have been performed. Practical considerations in the use of Cerenkov radiation as an automatically synchronized diagnostic of the plasma source properties are investigated. Parametric scans of the Cerenkov spatial profile (temperature, pressure, wavelength and laser/ebeam delay) are presented and the source neutral and plasma density are estimated from the measurements. Large increases in the number of intercepted photons are noted in the presence of plasma near strong spectral lines which depend on laser/e beam timing and steering.