Abstract: Using transversal pulse pre-ionization transversal pulse pre-ionization,a small diffusion-cooled longitudinal pulsed discharge CO2 laser is described.15mJ pulse energy with 375W pulse peak power has been achieved up with PRR to 56Hz from a discharge tube of 7.5mm inner diameter and 50cm long.The pre-ionization electrodes are designed as helical to improve the laser beam quality.