The design of plasma diagnostics for the future MJ class lasers (LMJ–Laser MégaJoule—in France or NIF—National Ignition Faciliy— in the USA) must take into account the large increased radiation field generated at the target and the effect on the diagnostics components. These facilities will focus up to 1.8 MJ ultraviolet laser light energy into a volume of less than 1 cm3 in a few nanoseconds. This very high power focused onto a small target will generate a large amount of x rays, debris, shrapnel, and nuclear particles (neutrons and gamma rays) if the DT fuel capsules ignite. Ignition targets will produce a million more of 14 MeV neutrons (1019 neutrons) by comparison with the present worldwide most powerful laser neutron source facility at OMEGA. Under these harsh environmental conditions the survivability goal of present diagnostic is not clear and many new studies must be carried out to verify which diagnostic measurement techniques, can be maintained, adapted or must be completely changed. Synergies with similar environment studies conducted for magnetic fusion diagnostic design for ITER facility are considered and must be enhanced.

The diagnostic designs for the Laser Megajoule (LMJ) will require components to operate in environments far more severe than those encountered in present facilities. This harsh environment will be induced by fluxes of neutrons, gamma rays, energetic ions, electromagnetic radiations, and, in some cases, debris and shrapnel, at levels several orders of magnitude higher than those experienced today on existing facilities. The lessons learned about the vulnerabilities of present diagnostic parts fielded mainly on OMEGA for many years, have been very useful guide for the design of future LMJ diagnostics. The present and future LMJ diagnostic designs including this vulnerability approach and their main mitigation techniques will be presented together with the main characteristics of the LMJ facility that provide for diagnostic protection.

In high flux (1013–15 W/cm2) laser-plasma interaction, a large part of the incoming laser energy is radiated into soft x-rays. To determine both the shape of this spectrum and the conversion efficiency, we have designed and tested an absolutely calibrated broadband soft x-ray spectrometer with a high temporal resolution (100 ps). The detector in this spectrometer is a new coaxial x-ray diode coupled with a fast single shot oscilloscope (French IN7100 with 7 GHz frequency response cutoff). Both absolute calibrations (x-ray response of diodes) and relative calibrations (filters and mirrors) have used the French synchrotron beam lines at Laboratoire pour l’utilisation du Rayonnement Electromagnétique (LURE) in Orsay. The initial version of this instrument was first successfully implemented on laser plasmas experiments at the Phébus facility in France and an improved version is now operating at the Omega laser facility in Rochester, New York. The emitted x-ray spectrum is absolutely measured in 18 broad bands from 50 eV up to 20 keV. The softer bands (<1.5 keV) combine mirror and filter responses coupled with the coaxial diode response to improve hard x-ray rejection. Intermediate energy channels (1.5 keV<hν<5 keV) used only a filter and coaxial diode. For the hardest channels (>5 keV) we replace the x-ray diode (not sufficiently sensitive) with a photoconductive detector (neutron-damaged GaAs). An equivalent instrument will be designed for the future National Ignition Facility (NIF) in the United States and the Laser Mégajoule (LMJ) in France.