|Ex-cBy| graph used to search for Numerical Cherenkov simulation instability Mr Alexander HarrisonGraduate Student Sub departmentAtomic and Laser Physics Research groupsLaser-plasma accelerator group alexander.harrison@physics.ox.ac.uk Denys Wilkinson Building, room 186.20.38 About Acceleration in a parabolic density curve with $a_0=4$ and $W_0=5um$ Research interests Laser Wakefield Accelerators