A novel plasma source for plasma wakefield accelerators

Abstract

World's first proton driven plasma wakefield accelerator experiment will be conducted at CERN by the AWAKE1 collaboration starting in 2016. In this experiment a 12 cm long 400 GeV proton bunch is sent through a 10 m long 2 mm diameter 1-10e14/cc field-ionized plasma. As a result of the self-modulation instability the proton bunch becomes transversely modulated, and near the axis effectively turns into a train of micro-bunches separated by approximately the plasma wavelength (∼ 1 mm). This bunch train can resonantly drive a large scale wakefield (GV/m). For an externally injected electron bunch to stay in the accelerating and focusing phase of this plasma wake the density of the plasma must be uniform to better than ∼0.2%. This uniformity is achieved by field ionizing a rubidium vapor confined in a custom made oil heat exchanger. The imposed temperature uniformity insures the Rb vapor density uniformity. The plasma is formed by a TW peak power Ti:sapphire laser system. The access to the plasma is provided through custom made ultrafast valves. Rubidium sources are also custom made reservoirs attached to the ends. We describe the plasma source2,3 and diagnostic measurements for characterizing it.