Diagnostics hardening for harsh environment in Laser Mégajoule (invited)

Abstract

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.

Advanced gated x-ray imagers for experiments at the National Ignition Facility

“…ICF experiments at the NOVA and OMEGA laser demonstrated that careful consideration must be given to neutroninduced backgrounds associated with ICF experiments at NIF-class facilities [11][12][13][14]. Initial pre-ignition experiments with THD-filled targets will have Y n 10 15 , and a successful DT ignition experiment with produce more than 10 18 neutrons.…”

“…The effects of these localized background events can be mitigated through image-processing techniques [17]. A more diffuse background is created by energetic electrons that deposit energy in the sensitive region through ionization energy loss [14,15]. This background effectively raises the noise floor and is mainly responsible for limiting the useful range of CCD-based systems to experiments that result in neutron fluences less than 510 7 cm -2 , corresponding to a Y n = 10 13 for a GXD fielded at the typical distance of 1.3m from the target.…”

Mitigation technique for use of CMOS image sensors in megajoule class laser radiative environment

“…Today, the different technologies useful for the LMJ and NIF plasma diagnostics for high neutron yield experiments are identified and work is in progress to improve the tolerance of the different subsystems to the harsh environment associated with such experiments [1,2]. However, some of the existing diagnostics for capturing and analysing the fusion plasma cannot stand the high neutron yields associated with the future experiments planned at these facilities.…”

Measurement of cathode luminescence efficiency of phosphors for micro-channel plate based x-ray framing cameras

“…It is known that radiation background on the MCP can be reduced by turning off the bias voltage before neutrons hit the MCP [6,12]. Radiation effects on the recording device can also be reduced by transferring the phosphor signal using image-relay optics and protecting the recording device with a massive radiation shielding enclosure [7][8][9]. However the phosphor and the FOFP are still exposed to the ionizing radiation with no significant shielding.…”

“…On planned high neutron yield experiments, the expected neutron yield (14 MeV) can be 10 17 or higher. In order to record x-ray emission images of the imploded core, x-ray framing cameras will have to be operated in that harsh neutron environment [2][3][4][5][6][7][8][9]. One of the simplest ways to increase signal level against the radiation background is use of higher phosphor potential.…”