Slow wave plasma structures for direct electron acceleration

Two highly versatile experimental techniques are demonstrated for making preformed plasma waveguides with a periodic structure capable of supporting the propagation of ultra-intense femtosecond laser pulses up to 2x10(17) W cm(-2), limited by the available laser energy. These waveguides are made in hydrogen, nitrogen and argon plasmas with a length of 15 mm and a modulation period as short as 35 mu m. Simulations show that these guides allow direct laser acceleration of electrons, achieving gradients of 80 MV cm(-1) and 10 MV cm(-1) for laser pulse powers of 1.9 TW and 30 GW, respectively. It is also shown that the periodic structure in these waveguides supresses the Raman forward instability, which could otherwise interfere with the direct acceleration scheme proposed.