Improved Capillary Guided Laser Wakefield Accelerators based on Diamond Materials

The laser plasma accelerator (LPA) is a very promising technology for generating gamma rays for the detection of contraband bulk nuclear materials, but is currently limited by the rate at which the beam can be pulsed. Erosion of the capillary plasma channel is the main limiting factor and can be mitigated through the use of artificial diamond to construct the channel. Computational modeling and experimental testing of both diamond and sapphire capillaries are used to determine the relative erosion rates due to the discharge plasma and the laser pulse passing through the capillaries. In Phase I, numerical simulations showed that unlike sapphire, diamond could allow operation of the discharge at & gt;1 kHz repetition rates. Experiments demonstrated that diamond structures could be used as LPA capillaries. In addition, after exposure to 1.3 x 106 plasma pulses with a repetition rate ~5 Hz, diamond eroded by a factor of 20 less than sapphire under the same conditions. In Phase II we plan to: Perform refined thermal simulations including heat deposition from the laser pulse to define the LPA performance limitations of both diamond and sapphire capillaries; Manufacture improved design diamond and sapphire capillary waveguides; Minimize discharge heat deposition in the diamond and sapphire capillary waveguides; Build erosion diagnostics and perform erosion rate tests at 10 Hz and; Experimentally determine maximum achievable repetition rates (up to ~1 kHz). Commercial Applications and Other Benefits: Enabling compact LPAs with repetition rates up to several kHz could provide the rapid and accurate detection of nuclear or radiological weapons concealed in shipping containers by providing a high energy, monochromatic, rasterizable gamma source (by exploiting Thomson scattering of laser light from the electron beam). In addition the LPA electron beams and associated radiation that can range from THz to x-ray wavelengths have applications in basic physics, chemistry, biology, medicine, and material science.