The National Ignition Facility’s (NIF) harsh radiation environment can cause electronics to malfunction during high-yield DT shots. Until now there has been little experience fielding electronic-based cameras in the target chamber under these conditions; hence, the performance of electronic components in NIF’s radiation environment was unknown. It is possible to purchase radiation tolerant devices, however, they are usually qualified for radiation environments different to NIF, such as space flight or nuclear reactors. This paper presents the results from a series of online experiments that used two different prototype camera systems built from non-radiation hardened components and one commercially available camera that permanently failed at relatively low total integrated dose. The custom design built in Livermore endured a 5 × 1015 neutron shot without upset, while the other custom design upset at 2 × 1014 neutrons. These results agreed with offline testing done with a flash x-ray source and a 14 MeV neutron source, which suggested a methodology for developing and qualifying electronic systems for NIF. Further work will likely lead to the use of embedded electronic systems in the target chamber during high-yield shots.
The National Ignition Facility (NIF) is a 192 laser beam facility designed to support the Inertial Confinement Fusion program based on laser-target interactions. The Optical Thomson Scattering (OTS) diagnostic has the potential to transform the community’s understanding of NIF hohlraum physics by providing first principle, local, time-resolved measurements of under-dense plasma conditions. A deep-UV probe beam is needed to overcome the large background of self-Thomson scattering produced by the 351nm (3ω) NIF drive beams. A two-phase approach to OTS on NIF will mitigate the risk presented by background levels. In Phase I, the diagnostic will assess background levels around a potential deep-UV probe wavelength considered for 5ω Thomson scattering measurements to be conducted in Phase II. The Phase I design of the diagnostic includes an unobscured collection telescope, dual crossed Czerny-Turner spectrometers, and the shared use of one streak camera located inside of an airbox. The Phase II design will include a 5ω probe laser. We will describe the engineering design and concept of operations of the Phase I NIF OTS diagnostic, with a focus on optomechanical disciplines.
The Velocity Interferometer System for Any Reflector (VISAR) is a critical diagnostic in Inertial Confinement Fusion and High Energy Density research as it has the ability to track shock fronts or interfaces moving 0.1-100 km/s with great accuracy. At the National Ignition Facility (NIF), the VISAR has recently been used successfully for implosion tuning and equation of state measurements. However, the initial design of the companion Streaked Optical Pyrometer (SOP) to measure spectral radiance - hence shock temperature - suffers from large background levels and poor spatial resolution. We report on an upgrade to improve the spatial resolution in the 560-640nm band by using custom lenses and replacing the Dove prism with a K-mirror and implementing a gating-circuit for the streak camera to reduce background signal. We envision that upgraded SOP will provide high quality data collection matching NIF VISAR's standards.
The National Ignition Facility (NIF) utilizes several different pixelated sensor technologies for various measurement
systems that include alignment cameras, laser energy sensors, and high-speed framing cameras. These systems remain in
the facility where they are exposed to 14MeV neutrons during a NIF shot. The image quality of the sensors degrades as a
function of radiation-induced damage. This article reports on a figure-of-merit technique that aids in the tracking of the
performance of pixelated sensors when exposed to neutron radiation from NIF. The sensor dark current growth can be
displayed over time in a 2D visual representation for tracking radiation induced damage. Predictions of increased noise
as a function of neutron fluence for future NIF shots allow simulation of reduced performance for each of the individual
camera applications. This predicted longevity allows for proper management of the camera systems.
Images obtained through charged coupled device (CCD) cameras in the National Ignition Facility (NIF) are crucial to
precise alignment of the 192 laser beams to the NIF target-chamber center (TCC). Cameras in and around the target
chamber are increasingly exposed to the effects of neutron radiation as the laser power is increased for high energy
fusion experiments. NIF was carefully designed to operate under these conditions. The present work examines the
degradation of the measured TCC camera position accuracy resulting from the effects of neutron radiation on the sensor
and verifies operation within design specifications. Both synthetic and real beam images are used for measuring
position degradation. Monte Carlo simulations based on camera performance models are used to create images with
added neutron noise. These models predict neutron induced camera noise based on exposure estimates of the
cumulative single-shot fluence in the NIF environment. The neutron induced noise images are used to measure beam
positions on a target calculated from the alignment images with the added noise. The effects of this noise are also
determined using noise artifacts from real camera images viewing TCC to estimate beam position uncertainty.
The National Ignition Facility (NIF) fields multiple varieties of x-ray imaging systems used to diagnose the implosion
physics of laser-driven fusion targets. The imagers consist of time-resolved x-ray detectors coupled with a snout
assembly for spatial and/or spectral imaging. The instrument is mounted onto a cart that extends into the NIF target
chamber, placing it in close proximity to the target and aligning with a tight tolerance using the Opposed Port Alignment
System (OPAS). The OPAS is a modified, commercial Schmidt-Cassegrain optical telescope mounted at the target
chamber port, opposite the Diagnostic Instrument Manipulator (DIM). In this paper, the approach used to characterize
and align the x-ray imaging instruments is described. The characterization includes offline measurements of the pinhole
assembly and the detector housing. Online, deviations of the DIM, as it is inserted along rails toward the target chamber
center, are characterized and related to the OPAS view. An overview of the offline measurement stations is provided
along with the process to develop the relationship between the offline alignment scopes and the OPAS as a function of
DIM insertion. The combination of these measurements is used to mathematically construct the predicted location of the
x-ray imager line of sight in the OPAS image space and determine the desired pinhole location to record data on a fusion
experiment. The alignment accuracy of this approach will be discussed, as demonstrated with various x-ray instruments
and pinhole configurations.
The requirements for beam and target alignment for successful ignition experiments on the National Ignition Facility
(NIF) are stringent: the average of beams to the target must be within 25 μm. Beam and target alignment are achieved
with the Target Alignment Sensor (TAS). The TAS is a precision optical device that is inserted into target chamber
center to facilitate both beam and target alignment. It incorporates two camera views (upper/lower and side) mounted on
each of two stage assemblies (jaws) to view and align the target. It also incorporates a large mirror on each of the two
assemblies to reflect the alignment beams onto the upper/lower cameras for beam alignment. The TAS is located in the
chamber using reference features by viewing it with two external telescope views. The two jaws are adjusted in elevation
to match the desired beam and target alignment locations. For some shot setups, a sequence of TAS positions is required
to achieve the full setup and alignment. In this paper we describe the TAS, the characterization of the TAS coordinates
for beam and target alignment, and summarize pointing shots that demonstrate the accuracy of beam-target alignment.
The National Ignition Facility (NIF) requires high resolution live images of regions inside the target chamber in order to align diagnostic instruments to fusion targets and to monitor target stability. To view the interior of the target chamber, we modified a commercial 11-inch Schmidt-Cassegrain telescope to develop the Opposed Port Alignment System (OPAS). There are two OPAS systems installed on the target chamber ports directly opposite the diagnostics. This paper describes the optical design, highlighting the two key modifications of the telescope. The first key modification was to reposition the Schmidt corrector plate and to uniquely mount the secondary mirror to a precision translation stage to adjust focus from 5.5 m to infinity. The stage is carefully aligned to ensure that the telescope’s optical axis lies on a straight line during focus adjustments. The second key modification was a custom three element lens that flattens the field, corrects residual aberrations of the Schmidt-Cassegrain and, with a commercial 1:1 relay lens, projects the final image plane onto a large format 50 mega-pixel camera. The OPAS modifications greatly extend the Schmidt-Cassegrain
telescope’s field of view, producing nearly diffraction-limited images over a flat field covering ±0.4 degrees. Also discussed in the paper are the alignment procedure and the hardware layout of the telescope.
D. Kalantar, P. Di Nicola, N. Shingleton, S. Burkhart, J. Dzenitis, J. Klingmann, J. Lawson, J. Lutz, D. Manha, A. Manuel, T. Mccarville, Elizabeth Palma, D. Pigg, K. Widmann, R. Wood
The National Ignition Facility (NIF) is a 192-beam high energy laser designed for Inertial Confinement Fusion (ICF),
and High Energy Density (HED) and basic science experiments. In order to achieve ignition with an ICF target, the
beam and target alignment must be performed within very tight specifications. At the same time, in order to be able to
conduct the wide range of HED and basic science experiments, the facility must be able to meet the tight tolerances for
both main and offset backlighter beams and targets. To diagnose the ignition event, many different target diagnostics are
employed, including optical, x-ray, and nuclear diagnostics. These target diagnostics must also be positioned accurately
and reliably within very tight specifications in order to ensure good data is acquired. In this paper, we describe the
strategy for beam, target, and diagnostic alignment at NIF.
The 192 laser beams in the National Ignition Facility (NIF) are automatically aligned to the target-chamber center using
images obtained through charged-coupled-device (CCD) cameras. Several of these cameras are in and around the target
chamber during an experiment. Current experiments for the National Ignition Campaign are attempting to achieve
nuclear fusion. Neutron yields from these high-energy fusion shots expose the alignment cameras to neutron radiation.
The present work explores modeling and predicting laser alignment performance degradation due to neutron radiation
effects, and introduces techniques to mitigate performance degradation. Camera performance models have been created
based on the predicted camera noise from the cumulative neutron fluence at the camera location. We have found that the
effect of the neutron-generated noise for all shots to date have been well within the alignment tolerance of half a pixel,
and image processing techniques can be utilized to reduce the effect even further on the beam alignment to target.
The Discovery Channel Telescope (DCT) is a 4.3-meter telescope designed for dual optical configurations, featuring an
f/6.1, 0.5° FoV, Ritchey-Chretien prescription, and a corrected f/2.3, 2° FoV, prime focus. The DCT is expected to
typically deliver sub-arcsecond images, with a telescope and local seeing contribution of <0.28" FWHM at the R-C
focus and <0.38" FWHM at the prime focus. The Delivered Image Quality (DIQ) budget considers errors from design
residuals, manufacturing, environmental effects, and control system limitations. We present an overview of the
analytical methods used, including sensitivity analysis for determining collimation effects, and a summary of
contributors to the overall system performance.
The New Solar Telescope (NST) is an off-axis Gregorian telescope at Big Bear Solar Observatory (BBSO). This
paper presents the expected aberrations due to misalignments of the secondary mirror for a general Gregorian
telescope using an optical model of the on-axis "parent" telescope version of NST. The sensitivities of linear
astigmatism and constant coma found by perturbing the axisymmetric model are presented and shown to match
those predicted by the theory. Then we discuss how the actual aberrations are different due to the off-axis nature
of the NST. Finally, we discuss the effect of the misalignments on the pointing of the telescope.
Telescopes use primary mirrors with spherical shape to reduce the cost of the mirror fabrication and to allow the mirror
to operate at fixed elevation. These advantages become significant as the size of the telescope grows. However, the
disadvantage of the spherical primary is a large amount of spherical aberration which needs to be corrected. We present
an analysis of alignment issues for four-mirror spherical aberration correctors for spherical primary mirror telescopes.
The sensitivities of image quality across the field (in terms of spot size) to mirror misalignments are found. These
sensitivities are useful in choosing the tolerances for the mechanical assembly holding the corrector. A singular value
decomposition of the sensitivity matrix shows the combination of element motions that result in orthogonal aberration
modes. Studying these combinations of modes and misalignments can lead to a conceptual understanding of the system,
which aids in the initial and operational alignment of the spherical aberration corrector.
Telescopes are ultimately limited by atmospheric turbulence, which is commonly characterized by a structure function.
The telescope optics will not further degrade the performance if their errors are small compared to the atmospheric
effects. Any further improvement to the mirrors is not economical since there is no increased benefit to performance.
Typically the telescope specification is written in terms of an image size or encircled energy and is derived from the best
seeing that is expected at the site. Ideally, the fabrication and support errors should never exceed atmospheric turbulence
at any spatial scale, so it is instructive to look at how these errors affect the structure function of the telescope. The
fabrication and support errors are most naturally described by Zernike polynomials or by bending modes for the active
mirrors. This paper illustrates an efficient technique for relating this modal analysis to wavefront structure functions.
Data is provided for efficient calculation of structure function given coefficients for Zernike annular polynomials. An
example of this procedure for the Giant Magellan Telescope primary mirror is described.
The Large Synoptic Survey Telescope (LSST) is a three mirror modified Paul-Baker design with an 8.4m primary, a
3.4m secondary, and a 5.0m tertiary followed by a 3-element refractive corrector producing a 3.5 degree field of view.
This design produces image diameters of <0.3 arcsecond 80% encircled energy over its full field of view. The image
quality of this design is sufficient to ensure that the final images produced by the telescope will be limited by the
atmospheric seeing at an excellent astronomical site. In order to maintain this image quality, the deformations and rigid
body motions of the three large mirrors must be actively controlled to minimize optical aberrations. By measuring the
optical wavefront produced by the telescope at multiple points in the field, mirror deformations and rigid body motions
that produce a good optical wavefront across the entire field may be determined. We will describe the details of the
techniques for obtaining these solutions. We will show that, for the expected mirror deformations and rigid body
misalignments, the solutions that are found using these techniques produce an image quality over the field that is close to
optimal. We will discuss how many wavefront sensors are needed and the tradeoffs between the number of wavefront
sensors, their layout and noise sensitivity.
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