Content area
Full Text
Plasma/Laser Diagnostics
1.
Introduction
Hard x-ray emission with [formula omitted, refer to PDF] plays an important role in laser-driven inertial confinement fusion. When the laser or laser-produced soft x-rays compress the deuterium and tritium (DT) capsule, energetic electrons generated during the laser-plasma interaction preheat the DT fuel and thus disturb a low-entropy implosion. By measuring the emitted hard x-rays, the number of the energetic electrons can be quantified and the preheat levels inferred[1, 2]. Core hard x-ray emission of implosion targets can provide a signature of the mixing[3], symmetry[4, 5], temperature, and density conditions of the fuel capsule[6, 7]near its peak compression. X-rays of imploding targets can also be an efficient hard x-ray source for high-energy radiography of dense or high- [formula omitted, refer to PDF] targets[8, 9]. For Compton radiography of implosion targets[10], a hard x-ray backlighter source is generated by intense short pulses laser irradiation on a target, which is then transmitted through the implosion target to determine the area density and symmetry of the fuel capsule near peak compression. Precise diagnosis of the hard x-ray spectrum of the backlighter source, and the core radiation of the implosion target which induces the background, is crucial to obtain a sufficiently high signal over background for Compton radiography of implosion targets.
Solid-state detectors of single-photon counting CCDs (3-30ￂ keV)[11], dispersive x-ray detectors of transmission curved crystal spectrometers (10-120ￂ keV)[12], and non-dispersive x-ray detectors with filters, such as Ross pairs spectrometers (18-90ￂ keV)[13, 14], filter stack spectrometers (12-700ￂ keV)[15, 16]and filter-fluorescer spectrometers (20-220ￂ keV)[17, 18]are the conventional approaches for hard x-ray spectra diagnostics. The dispersive x-ray detectors of transmission curved crystal spectrometers are superior, especially in the 10-120ￂ keV range which is more applicable to laser fusion experiments, due to their high spectral resolution, broad energy coverage, and robustness in harsh environments. Transmission curved crystal spectrometers have been commissioned on almost all of the laser fusion facilities such as Omega[19-21]and NIF[22]. They were also utilized on many short pulse laser facilities[23, 24]and a fast Z-pinch facility[25]for experiments of x-ray source, atomic physics, medical radiography, etc.
Experiments...