First set of gated x-ray imaging diagnostics for the Laser Megajoule facility

Abstract

The Laser Megajoule (LMJ) facility located at CEA/CESTA started to operate in the early 2014 with two quadruplets (20 kJ at 351 nm) focused on target for the first experimental campaign. We present here the first set of gated x-ray imaging (GXI) diagnostics implemented on LMJ since mid-2014. This set consists of two imaging diagnostics with spatial, temporal, and broadband spectral resolution. These diagnostics will give basic measurements, during the entire life of the facility, such as position, structure, and balance of beams, but they will also be used to characterize gas filled target implosion symmetry and timing, to study x-ray radiography and hydrodynamic instabilities. The design requires a vulnerability approach, because components will operate in a harsh environment induced by neutron fluxes, gamma rays, debris, and shrapnel. Grazing incidence x-ray microscopes are fielded as far as possible away from the target to minimize potential damage and signal noise due to these sources. These imaging diagnostics incorporate microscopes with large source-to-optic distance and large size gated microchannel plate detectors. Microscopes include optics with grazing incidence mirrors, pinholes, and refractive lenses. Spatial, temporal, and spectral performances have been measured on x-ray tubes and UV lasers at CEA-DIF and at Physikalisch-Technische Bundesanstalt BESSY II synchrotron prior to be set on LMJ. GXI-1 and GXI-2 designs, metrology, and first experiments on LMJ are presented here.

Turbulent hydrodynamics experiments in high energy density plasmas: scientific case and preliminary results of the TurboHEDP project

“…The first physics experiments on LMJ have been performed at the end of 2014 with 2 quadruplets (8 beams), and a total laser energy on target of 20 kJ [74]. The first diagnostic installed in 2014 on LMJ is a gated X-ray imager with grazing incidence mirrors, which provides a spatial resolution of in a 3 mm field of view [46] . The experimental capabilities of LMJ (number of beams and type of plasma diagnostics) will increase gradually during the following years.…”

“…The need of a large (0.5 mm) field of view 2D X-ray imager with the spatial resolution <10 µm has been identified on large scale laser facilities. These capabilities could be achieved with grazing angle-of-incidence mirrors imaging systems like Kirkpatrick-Baez microscopes [44][45][46] , which offer the best solution in terms of resolution versus signal to noise ratio. The X-ray imagers of the LIL facility were all based on the Kirkpatrick-Baez microscope [45] and the first LMJ imager operational in 2014 also works with grazing incidence mirrors [46] .…”

“…These capabilities could be achieved with grazing angle-of-incidence mirrors imaging systems like Kirkpatrick-Baez microscopes [44][45][46] , which offer the best solution in terms of resolution versus signal to noise ratio. The X-ray imagers of the LIL facility were all based on the Kirkpatrick-Baez microscope [45] and the first LMJ imager operational in 2014 also works with grazing incidence mirrors [46] . A high-resolution X-ray imaging diagnostic is operational on the NIF [44] , and under development on LMJ [47] .…”

“…The first diagnostic installed in 2014 on LMJ is a gated X-ray imager with grazing incidence mirrors, which provides a spatial resolution of 30 µm in a 3 mm field of view [46] . The experimental capabilities of LMJ (number of beams and type of plasma diagnostics) will increase gradually during the following years.…”

Preliminary results from the LMJ-PETAL experiment on hot electrons characterization in the context of shock ignition

“…Finally, an Au shield prevents diagnostics from strong emission of the coronal plasma. (iii) the shock propagation is observed with GXI-1 [20]. GXI-1 is a hard X-ray imager coupled to a framing camera with 2×4 time-resolved toroidal mirror channels and 4 pinhole channels.…”