Measurement of PWFA plasma source density using Stark broadening*

                Plasma Wakefield Acceleration (PWFA) is an advanced accelerator technique, which utilizes the oscillations of plasma electrons created by a relativistic electron beam to accelerate another relativistic electron beam up to tens of GeV within centimeters of distance. To accurately predict the accelerating gradient of a PWFA and the beam emittance preservation during the acceleration process, we must accurately measure the PWFA plasma source density profile. However, measuring the density of short-lived (tens of nanoseconds), low density (10^15-17 cm^-3), narrow (<1 mm) and long (>10 cm) PWFA plasma source is difficult. In this poster, I will demonstrate the technique to measure PWFA plasma source density using Stark broadening, which is a spectral-line broadening phenomenon caused by non-zero local electric field produced by plasma ions and electrons. Here I will present experimental results of measuring the density profile of a laser-ionized gas (Ar or He) PWFA plasma source using Stark broadening. The results are compared to theoretical models and the uncertainties due to time integration of the signal during the plasma decay process are estimated.