Soft x-ray images of the laser entrance hole of ignition hohlraums

Laser produced soft x-ray source diagnostics with temporal, spectral, and spatial resolution

We demonstrate the use of three diagnostic tools which simultaneously view the target from nearly the same direction, and their results are combined to provide temporally, spectrally, and spatially resolved absolutely calibrated target emission information. To demonstrate this capability, Au targets were irradiated by 1.8 kJ, 3 ns laser pulses to produce broadband soft x-ray emission in the 0.1-3.5 keV spectral range. Target diagnostics included a time-resolved x-ray diode array, each measured a partial spectral band, time-integrated spectrally resolved absolutely calibrated transmission grating spectrometer, and static and time-resolved soft x-ray imagers coupled to a charge-coupled device camera and to a streak camera, respectively, measuring spatially and temporally resolved radiation at the main Au target emission bands. The combined temporally, spectrally, and spatially resolved absolutely calibrated target emission result can be compared to simulations and be used to design and analyze experiments in which the source emission is used as a drive for various physical processes.

A pinhole camera for ultrahigh-intensity laser plasma experiments

A pinhole camera is an important instrument for the detection of radiation in laser plasmas. It can monitor the laser focus directly and assist in the analysis of the experimental data. However, conventional pinhole cameras are difficult to use when the target is irradiated by an ultrahigh-power laser because of the high background of hard X-ray emission generated in the laser/target region. Therefore, an improved pinhole camera has been developed that uses a grazing-incidence mirror that enables soft X-ray imaging while avoiding the effect of hard X-ray from hot dense plasmas.

Interplay of Laser-Plasma Interactions and Inertial Fusion Hydrodynamics

The effects of laser-plasma interactions (LPI) on the dynamics of inertial confinement fusion hohlraums are investigated via a new approach that self-consistently couples reduced LPI models into radiation-hydrodynamics numerical codes. The interplay between hydrodynamics and LPI-specifically stimulated Raman scatter and crossed-beam energy transfer (CBET)-mostly occurs via momentum and energy deposition into Langmuir and ion acoustic waves. This spatially redistributes energy coupling to the target, which affects the background plasma conditions and thus, modifies laser propagation. This model shows reduced CBET and significant laser energy depletion by Langmuir waves, which reduce the discrepancy between modeling and data from hohlraum experiments on wall x-ray emission and capsule implosion shape.

A high-speed two-frame, 1-2 ns gated X-ray CMOS imager used as a hohlraum diagnostic on the National Ignition Facility (invited)

A novel x-ray imager, which takes time-resolved gated images along a single line-of-sight, has been successfully implemented at the National Ignition Facility (NIF). This Gated Laser Entrance Hole diagnostic, G-LEH, incorporates a high-speed multi-frame CMOS x-ray imager developed by Sandia National Laboratories to upgrade the existing Static X-ray Imager diagnostic at NIF. The new diagnostic is capable of capturing two laser-entrance-hole images per shot on its 1024 × 448 pixels photo-detector array, with integration times as short as 1.6 ns per frame. Since its implementation on NIF, the G-LEH diagnostic has successfully acquired images from various experimental campaigns, providing critical new information for understanding the hohlraum performance in inertial confinement fusion (ICF) experiments, such as the size of the laser entrance hole vs. time, the growth of the laser-heated gold plasma bubble, the change in brightness of inner beam spots due to time-varying cross beam energy transfer, and plasma instability growth near the hohlraum wall.