We describe the development and demonstration of a high-repetition-rate-capable dual-channel (DC) x-ray spectrometer designed for high-intensity laser–plasma experiments (≥1×1021 W/cm2). The spectrometer, which operates at high repetition rates, is limited only by the refresh rate of targets and the camera’s frame rate. It features two channels, each equipped with a flat highly oriented pyrolytic graphite (HOPG) crystal and a unique detector plane, allowing it to resolve two distinct x-ray bands: approximately 7–10 and 10–13 keV. Each detector plate carrier holds two slots for active (scintillators) or passive (imaging plates) x-ray detectors. We present the design and testing of the HR-DC-HOPG using both the COMET laser (10 J, 0.5 ps shot/4 min) at LLNL’s Jupiter Laser Facility and the SCARLET laser (10 J, 30 fs shot/min) at Ohio State University. The results demonstrate the spectrometer’s performance across various laser energies, target materials, pulse shapes, and detector types.

We present the development of a flexible tape-drive target system to generate and control secondary high-intensity laser-plasma sources. Its adjustable design permits the generation of relativistic MeV particles and x rays at high-intensity (i.e., ≥1 × 1018 W cm-2) laser facilities, at high repetition rates (>1 Hz). The compact and robust structure shows good mechanical stability and a high target placement accuracy (<4 μm RMS). Its compact and flexible design allows for mounting in both the horizontal and vertical planes, which makes it practical for use in cluttered laser-plasma experimental setups. The design permits ∼170° of access on the laser-driver side and 120° of diagnostic access at the rear. A range of adapted apertures have been designed and tested to be easily implemented to the targetry system. The design and performance testing of the tape-drive system in the context of two experiments performed at the COMET laser facility at the Lawrence Livermore National Laboratory and at the Advanced Lasers and Extreme Photonics (ALEPH) facility at Colorado State University are discussed. Experimental data showing that the designed prototype is also able to both generate and focus high-intensity laser-driven protons at high repetition rates are also presented.

A scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (∼0.8 ps–20 ps). Maximum proton energies significantly greater than established scaling laws were observed, consistent with observations at other multi-ps laser facilities. In addition, maximum proton energies and electron temperatures in this regime were found to be strongly dependent on the laser pulse duration and preplasma conditions. A modified proton scaling model is presented that is able to better represent the accelerated proton characteristics in this multi-ps regime.

Laser absorption is one of the most important parameters governing laser–matter interactions. The laser energy absorption on nanowire array targets is measured for the first time in the relativistic regime at intensities of 1019 W/cm2 and compared to foil targets. The results show that the laser energy absorption of 0.7 ps frequency doubled (527 nm) pulses on Au nanowire targets varies widely with nanowire parameters, reaching laser energy absorption values up to ∼71% of the incident energy, significantly exceeding those of solid flat targets obtained in similar irradiation conditions. The analysis shows that the increase in absorption strongly correlates with larger effective target surface area over a broad range of nanowire parameters explored. These direct absorption measurements provide valuable data to benchmark simulations of the relativistic laser pulse interactions with nanostructures.

Received 28 February 2011DOI:https://doi.org/10.1103/PhysRevLett.106.109903© 2011 American Physical Society

We demonstrate the hohlraum radiation temperature and symmetry required for ignition-scale inertial confinement fusion capsule implosions. Cryogenic gas-filled hohlraums with 2.2 mm-diameter capsules are heated with unprecedented laser energies of 1.2 MJ delivered by 192 ultraviolet laser beams on the National Ignition Facility. Laser backscatter measurements show that these hohlraums absorb 87% to 91% of the incident laser power resulting in peak radiation temperatures of T(RAD)=300 eV and a symmetric implosion to a 100 μm diameter hot core.

We present a platform for producing long plasma channels suitable for guiding lasers over several centimeters by applying magnetic fields to limit the radial heat flux from a preforming laser beam. The resulting density gradient will be used as an optical plasma waveguide. The plasma conditions have been chosen to be consistent with the requirements for laser wakefield acceleration where multi-GeV electrons are predicted. A detailed description of the system used to produce the high (5 T) magnetic fields and initial results that show a 5 cm long plasma column are discussed.

A first set of shock propagation, laser-plasma interaction, hohlraum energetics and hydrodynamic experiments have been performed using the first 4 beams of the National Ignition Facility (NIF), in support of indirect drive Inertial Confinement Fusion (ICF) and High Energy Density Physics.

A near backscattering imaging diagnostic system has been implemented, qualified, and fielded on the first quad of beams on the National Ignition Facility [E. M. Campbell and W. J. Hogan, Plasma Phys. Controlled Fusion 41, B39 (1999)]. This diagnostic image diffusing scatter plates, placed around the final focus lenses on the NIF target chamber, to quantitatively measure the fraction of light backscattered outside of the incident cone of the focusing optics. The imaging system consists of a wide-angle lens coupled to a gated charged coupled device camera, providing 3mm resolution over a 2m field of view. To account for changes of the system throughput due to exposure to target debris the system was routinely calibrated in situ at 532 and 355nm using a dedicated pulsed laser source. The diagnostic and calibration methods will be described together with recent results from the NIF early light shots.

The soft x-ray imager (SXRI) built for the first experiments at the National Ignition Facility (NIF) has four soft x-ray channels and one hard x-ray channel. The SXRI is a snout that mounts to a four strip gated imager. This produces four soft x-ray images per strip, which can be separated in time by ∼60ps. Each soft x-ray channel consists of a mirror plus a filter. The diagnostic was used to study x-ray burnthrough of hot Hohlraum targets at the NIF and OMEGA lasers. The SXRI snout design and issues involved in selecting the desired soft x-ray channels are discussed.

Deposition of maximum laser energy into a small, high-Z enclosure in a short laser pulse creates a hot environment. Such targets were recently included in an experimental campaign using the first four of the 192 beams of the National Ignition Facility [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technology 26, 755 (1994)], under construction at the University of California Lawrence Livermore National Laboratory. These targets demonstrate good laser coupling, reaching a radiation temperature of 340 eV. In addition, the Raman backscatter spectrum contains features consistent with Brillouin backscatter of Raman forward scatter [A. B. Langdon and D. E. Hinkel, Physical Review Letters 89, 015003 (2002)]. Also, NIF Early Light diagnostics indicate that 20% of the direct backscatter from these reduced-scale targets is in the polarization orthogonal to that of the incident light.

A near backscattering imaging diagnostic system is being implemented on the first quad of beams on the National Ignition Facility. This diagnostic images diffusing scatter plates, placed around the final focus lenses on the National Ignition Facility target chamber, to quantitatively measure the fraction of light backscattered outside of the focusing cone angle of incident laser beam. A wide-angle imaging system relays an image of light scattered outside the lens onto a gated charge coupled device camera, providing 3 mm resolution over a 2 m field of view. To account for changes of the system throughput due to exposure to target debris the system will be routinely calibrated in situ at 532 and 355 nm using a dedicated pulsed laser source.

The production of supersonic jets of material via the interaction of a strong shock wave with a spatially localized density perturbation is a common feature of inertial confinement fusion and astrophysics. The behavior of two-dimensional (2D) supersonic jets has previously been investigated in detail [J. M. Foster, B. H. Wilde, P. A. Rosen, T. S. Perry, M. Fell, M. J. Edwards, B. F. Lasinski, R. E. Turner, and M. L. Gittings, Phys. Plasmas 9, 2251 (2002)]. In three dimensions (3D), however, there are new aspects to the behavior of supersonic jets in compressible media. In this paper, the commissioning activities on the National Ignition Facility (NIF) [J. A. Paisner, J. D. Boyes, S. A. Kumpan, W. H. Lowdermilk, and M. Sorem, Laser Focus World 30, 75 (1994)] to enable hydrodynamic experiments will be presented as well as the results from the first series of hydrodynamic experiments. In these experiments, two of the first four beams of NIF are used to drive a 40Mbar shock wave into millimeter scale aluminum targets backed by 100mg∕cc carbon aerogel foam. The remaining beams are delayed in time and are used to provide a point-projection x-ray backlighter source for diagnosing the three-dimensional structure of the jet evolution resulting from a variety of 2D and 3D features. Comparisons between data and simulations using several codes will be presented.

Gated, microchannel-plate-based (MCP) framing cameras have been deployed worldwide for 0.2–9 keV x-ray imaging and spectroscopy of transient plasma phenomena. For a variety of spectroscopic and imaging applications, the angular sensitivity of MCPs must be known for correctly interpreting the data. We present systematic measurements of angular sensitivity at discrete relevant photon energies and arbitrary MCP gain. The results can been accurately predicted by using a simple two-dimensional approximation to the three-dimensional MCP geometry and by averaging over all possible photon ray paths.

We have used a large format (4000×4000) high resolution (9 μm pixels) charge coupled device (CCD) to record images from the rear of a gated micro-channel plate (MCP) intensifier, and compared the results with conventional film recording. Measurements of linearity, dynamic range, dark noise, and distortion all show that the CCD is a superior replacement for film. Furthermore, its excellent registration allows for easy flat fielding, using data from a uniformly exposed MCP. As we increase the signal level to where the signal to noise is not dominated by photon counting statistics, we find that this flat fielding procedure produces a significant improvement in signal to noise. The small spatial scale of this noise has led to its identification as high spatial frequency variations in the MCP phosphor.

A 1-mm-square diamond photoconductive detector (PCD) has been installed on the LLNL Nova laser system, for use as a broadband soft x-ray power diagnostic. The PCD is installed behind an array of pinholes, which cast multiple, overlapping images of the source onto the diamond. This allows reduction of the x-ray intensity, to avoid saturation problems, while avoiding the spectral dependency of thin film filters. The diode current is read out on a 5 GHz bandwidth scope. The system is calibrated by comparison to an absolutely calibrated array of filtered vacuum x-ray photodiodes (“dante”). The time response of the PCD and its bias electronics have been characterized using the 5th harmonic (210 nm) of a short pulse (<1 ps) Ti: sapphire laser. The data show a fast rise, limited by the 5 GHz scope bandwidth, and a slower fall off, characterized by an RC time of order 200 ps.

Microchannel plates (MCPs) are used in many diagnostic systems to study laser-plasma interactions. Typically the front surface of a MCP is coated with some photocathode (PC) material to convert x ray to electron. This is followed by electron multiplication along the microchannels. Materials such as CsI, Al, and Au have been identified as good PC materials, but the overall quantum efficiencies of these materials are low, so that electron multiplication along the channel has been the only path to signal amplification. This approach is known to have some problems (J. D. Wiedwald, University of California UCRL-JC-110906, August 1992). We investigated the effect of pairing transmission PC to standard MC’s and found that CsI and Au foils used in multilayered configuration, significantly enhance the overall quantum efficiency of the combination. The findings could lead to better MCP design and fabrication.

There are many different types of measurements that require a continuous time history of x-ray emission that can be provided with an x-ray streak camera. In order to properly analyze the images that are recorded with the x-ray streak cameras operated on Nova, it is important to account for the streak characterization of each camera. We have performed a number of calibrations of the streak cameras both on the bench as well as with Nova disk target shots where we use a time modulated laser intensity profile (self-beating of the laser) on the target to generate an x-ray comb. We have measured the streak camera sweep direction and spatial offset, curvature of the electron optics, sweep rate, and magnification and resolution of the electron optics.