X-ray penumbral imaging has been successfully fielded on a variety of inertial confinement fusion (ICF) capsule
implosion experiments on the National Ignition Facility (NIF). We have demonstrated sub-5 μm resolution imaging of
stagnated plasma cores (hot spots) at x-ray energies from 6 to 30 keV. These measurements are crucial for improving
our understanding of the hot deuterium-tritium fuel assembly, which can be affected by various mechanisms, including
complex 3-D perturbations caused by the support tent, fill tube or capsule surface roughness. Here we present the
progress on several approaches to improve x-ray penumbral imaging experiments on the NIF. We will discuss
experimental setups that include penumbral imaging from multiple lines-of-sight, target mounted penumbral apertures
and variably filtered penumbral images. Such setups will improve the signal-to-noise ratio and the spatial imaging
resolution, with the goal of enabling spatially resolved measurements of the hot spot electron temperature and material
mix in ICF implosions.
Laser driven inertial confinement fusion (ICF) plasmas typically have burn durations on the order of 100 ps. Time resolved imaging of the x-ray self emission during the hot spot formation is an important diagnostic tool which gives information on implosion symmetry, transient features and stagnation time. Traditional x-ray gated imagers for ICF use microchannel plate detectors to obtain gate widths of 40-100 ps. The development of electron pulse-dilation imaging has enabled a 10X improvement in temporal resolution over legacy instruments. In this technique, the incoming x-ray image is converted to electrons at a photocathode. The electrons are accelerated with a time-varying potential that leads to temporal expansion as the electron signal transits the tube. This expanded signal is recorded with a gated detector and the effective temporal resolution of the composite system can be as low as several picoseconds. An instrument based on this principle, known as the Dilation X-ray Imager (DIXI) has been constructed and fielded at the National Ignition Facility. Design features and experimental results from DIXI will be presented.
This paper covers the preliminary design of a radiation tolerant nanosecond-gated multi-frame CMOS camera system for
use in the NIF. Electrical component performance data from 14 MeV neutron and cobalt 60 radiation testing will be
The recent development of nanosecond-gated multi-frame hybrid-CMOS (hCMOS) focal plane arrays by the Ultrafast
X-ray Imaging (UXI) group at Sandia National Lab has generated a need for custom camera electronics to operate in the
pulsed radiation environment of the NIF target chamber. Design requirements and performance data for the prototype
camera system will be discussed. The design and testing approach for the radiation tolerant camera system will be
covered along with the evaluation of commercial off the shelf (COTS) electronic component such as FPGAs, voltage
regulators, ADCs, DACs, optical transceivers, and other electronic components. Performance changes from radiation
exposure on select components will be discussed. Integration considerations for x-ray imaging diagnostics on the NIF
will also be covered.
Geometrically enhanced photocathodes are currently being developed for use in applications that seek to improve detector efficiency in the visible to X-ray ranges. Various photocathode surface geometries are typically chosen based on the detector operational wavelength region, along with requirements such as spatial resolution, temporal resolution and dynamic range. Recently, a structure has been identified for possible use in the X-ray region. This anisotropic high aspect ratio structure has been produced in silicon using inductively coupled plasma (ICP) etching technology. The process is specifically developed with respect to the pattern density and geometry of the photocathode chip to achieve the desired sidewall profile angle. The tapered sidewall profile angle precision has been demonstrated to be within ± 2.5° for a ~ 12° wall angle, with feature sizes that range between 4-9 μm in diameter and 10-25 μm depth. Here we discuss the device applications, design and present the method used to produce a set of geometrically enhanced high yield X-ray photocathodes in silicon.
Gated X-Ray imagers have been used on many ICF experiments around the world for time resolved imaging of the target implosions. DIXI (Dilation X-ray Imager) is a new fixed base diagnostic that has been developed for use in the National Ignition Facility. The DIXI diagnostic utilizes pulse-dilation technology [1,2,3,4] and uses a high magnification pinhole imaging system to project images onto the instrument. DIXI is located outside the NIF target chamber approximately 6.5m from target chamber center (TCC). The pinholes are located 10cm from TCC and are aligned to the DIXI optical axis using a diagnostic instrument manipulator (DIM) on an adjacent port. By use of an extensive lead and poly shielded drawer enclosure DIXI is capable of collecting data at DT neutron yields up to Yn~ 1016 on CCD readout and up to Yn~ 1017 on film. Compared to existing pinhole x-ray framing cameras DIXI also provides a significant improvement in temporal resolution, <10ps, and the ability to capture a higher density of images due to the fact the pinhole array does not require collimators. The successful deployment of DIXI on the NIF required careful attention to the following subsystems, pinhole imaging, debris shielding, filtering and image plate (FIP), EMI protection, large format CsI photocathode design, detector head, detector head electronics, control electronics, CCD, film recording and neutron shielding. Here we discuss the initial design, improvements implemented after rigorous testing, infrastructure and commissioning of DIXI on the NIF.
DIXI utilizes pulse-dilation technology to achieve x-ray imaging with temporal gate times below 10 ps. The longitudinal magnetic eld used to guide the electrons during the dilation process results in a warped image, similar to an optical distortion from a lens. Since the front end, where x-rays are converted into electrons at the beginning of the magnetic eld, determines the temporal resolution these distortions in uence the temporal width of the images at the back end, where it is captured. Here we discuss the measurements and methods used to reverse the magnetic warp e ect in the DIXI data. The x-ray measurements were conducted using the COMET laser facility at the Lawrence Livermore National Laboratory.
DIXI (dilation x-ray imager) will be used to characterize ICF (inertial confinement fusion) implosions on the NIF. DIXI utilizes pulse-dilation technology1 to achieve x-ray imaging with temporal gate times below 10 ps. Time resolved x-ray measurements were conducted using the COMET laser facility at the Lawrence Livermore National Laboratory. Here we focus on some of the challenges faced by the large aperture photo cathode of the instrument and report on how to maintain a at photo cathode as well as how the required spatial resolution of the instrument is achieved.