National Ignition Facility (NIF) is a high-energy laser facility comprised of 192 laser beams focused with enough power
and precision on a hydrogen-filled spherical, cryogenic target to initiate a fusion reaction. The target container, or
hohlraum, must be accurately aligned to an x-ray imaging system to allow careful monitoring of the frozen fuel layer in
the target. To achieve alignment, x-ray images are acquired through starburst-shaped windows cut into opposite sides of
the hohlraum. When the hohlraum is in alignment, the starburst pattern pairs match nearly exactly and allow a clear view
of the ice layer formation on the edge of the target capsule. During the alignment process, x-ray image analysis is
applied to determine the direction and magnitude of adjustment required. X-ray detector and source are moved in concert
during the alignment process. The automated pointing alignment system described here is both accurate and efficient. In
this paper, we describe the control and associated image processing that enables automation of the starburst pointing
alignment.
The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL)
routinely fires high energy shots (> 6 kJ per beamline) through the final optics, located on the
target chamber. After a high fluence shot, exceeding 4J/cm2 at 351 nm wavelength, the final
optics are inspected for laser-induced damage. The FODI (Final Optics Damage Inspection)
system has been developed for this purpose, with requirements to detect laser-induced damage
initiation and to track and size it's growth to the point at which the optic is removed and the site
mitigated. The FODI system is the "corner stone" of the NIF optic recycle strategy. We will
describe the FODI system and discuss the challenges to make optics inspection a routine part of
NIF operations.
The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory (LLNL) will routinely
fire high energy shots (approaching 10 kJ per beamline) through the final optics, located on the target
chamber. After a high fluence shot, exceeding 4J/cm2 at 351 nm wavelength, the final optics will be
inspected for laser-induced damage. The FODI (Final Optics Damage Inspection) system has been
developed for this purpose, with requirements to detect laser-induced damage initiation and to track and size
it's the growth to the point at which the optic is removed and the site mitigated. The FODI system is the
"corner stone" of the NIF optic recycle strategy. We will describe the FODI system and discuss the
challenges to make optics inspection a routine part of NIF operations.
We describe experimental techniques for characterizing the absolute response of charge-coupled devices (CCD) to incident hard x-rays using the high energy x-ray source at the Lawrence Livermore National Laboratory. We present responsivity and quantum detection efficiency measurements for a standard, front-illuminated, scientific CCD to monoenergetic 8-98 keV K-(alpha) x-rays. This systematic study out to high energies reveals the contribution of different absorption processes to the CCD detection efficiency. For lower energies below 20 keV the CCD behaves like an ideal photoelectric detector as expected. Increasingly above 40 keV the photoelectric effect in the CCD epitaxial region is augmented by incoherent or Compton scattering where a fraction of the energy from the photon scattering event is transferred to the electrons and subsequently detected. The Compton scattering mechanism dominates the photoelectric effect above 100 keV giving the CCD a predicted detection efficiency which remains constant from 150 keV to 1 MeV assuming that the scattered electrons finally come to rest within the active region. These physics issues will be briefly discussed and are particularly relevant to deep active region solid-state detectors with application for hard x-ray detection above 40 keV.
We describe a compact, vacuum compatible, large format, charge-coupled device (CCD) camera for scientific imaging and detection of 1 - 100 keV x-rays in experiments at the Lawrence Livermore National Laboratory JANUS-1 ps laser. A standard, front-illuminated, multi-pin phase device with 250 k electron full well capacity, low dark current (10 pA/cm2 at 20 degree(s)C) and low read noise (5 electrons rms) is cooled to -35 degree(s)C to give the camera excellent 15-bit dynamic range and signal-to-noise response. The intensity and x-ray energy linear response have been determined for optical and x-ray (< 65 keV) photons and are found to be in excellent agreement. Departure from linearity has been measured to be less than 0.7%. The inherent linearity and energy dispersive characteristics of CCD cameras are well suited for hard x-ray photon counting techniques in scientific applications. X-rays absorbed within the depletion and field-free regions can be distinguished by studying the pulse height spectrum. Results are presented for the detection of 1 - 100 keV Bremsstrahlung continuum, K-shell and L-shell fluorescence spectra emitted from high intensity (1018 W cm-2), 500 fs laser-produced plasmas.
This paper details the performance and shows images obtained from a 512 X 512 CCD camera capable of recording 400 digitized frames per second. A brief description of the data acquisition hardware and image analysis software is also included.
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