Absolute x-ray calibration of a gated x-ray framing camera for the Laser MegaJoule facility in the 0.1 keV-1 keV spectral range

X-ray framing cameras (XRFCs) are routinely used at the Laser MegaJoule facility in x-ray imaging plasma diagnostics around the target chamber. Most of these diagnostics are based on multilayer x-ray toroidal mirrors under grazing incidence. The absolute calibration of the XRFCs is expressly expected both to optimize the signal-to-noise ratio for the dynamic range for specific experiments and to quantitatively process the data. The purpose of this paper is to describe our technique to routinely calibrate these instruments in the sub-keV spectral range. The calibration presented in this work was carried out using the XRFC enclosed in a sealed "airbox" structure. This calibration relies on a Manson source recently upgraded to operate at high emission current (5 mA) with 10 kV accelerating voltage to work with a 1-m grazing-incidence Rowland circle monochromator. The framing camera sensitivity was absolutely determined over the 0.1-1.2 spectral range with an average uncertainty of 2.4% rms while operating in DC mode. Finally, we compare the results with a synchrotron source calibration previously obtained and a theoretical model.