The National Ignition Facility (NIF) employs 192 laser beams to achieve inertial confinement fusion by irradiating a mm scale fusion target. Automatic alignment (AA) image processing algorithms are used to align 192 beams to the NIF target chamber center. Cameras placed along the beam path supply the images that are analyzed by AA algorithms to provide beam location and alignment information. NIF has the capability of using beam-specific database parameters. This allows beam line images to be processed using optimized algorithms tailored to individual beam alignment needs. For a given segment of alignment in the NIF beam path, 192 different versions of the algorithm can be run simply by changing data base parameters. This capability is vital to alignment precision in a system as complex and mature as NIF. Since optical components and devices age, laser parameters and beam alignment quality can and do change. Constant beam-by-beam monitoring of alignment performance is needed in order to mitigate any issues caused by such changes. The objective of this work is to evaluate how periodic AA algorithm beam parameter changes might better maintain alignment requirements over time in the NIF facility. We show examples from final optics assembly (FOA) and harmonic generator (THG, SHG) loops.
At the National Ignition Facility (NIF), the world’s largest most energetic laser facility with over 40,000 optics, image processing algorithms are essential to position 192 laser beams onto a mm scale fusion target. In its most general sense, an image processing algorithm consists of a series of steps which produce a desired outcome. When humans set out to solve specific tasks, they often exploit their own experience and intuition by decomposing the problem into subproblems. They then apply and develop techniques which are woven together in the end to maximize performance and minimize uncertainty. The fact that many options are available in each of these steps, can lead to a large variety of recipes from which one can choose. Consequently, the chosen solution is not unique, but multiple solutions evolve when combining the multiple choices from each step. The fact that some of the steps are nonlinear gives rise to interesting performance tradeoffs in arriving to the final solution. This paper will explore and illustrate various approaches to solving a specific image processing problem.
The Advance Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a laser system that employs up to
four petawatt (PW) lasers to produce a sequence of short-pulse kilo-Joule laser pulses with controllable delays that
generate X-rays to provide backlighting for high-density internal confinement fusion (ICF) capsule targets. Multi-frame,
hard-X-ray radiography of imploding NIF capsules is a capability which is critical to the success of NIF's missions. ARC
is designed to employ up to eight backlighters with tens-of-picosecond temporal resolution, to record the dynamics and
produce an X-ray "motion picture" of the compression and ignition of cryogenic deuterium-tritium targets. ARC will
generate tens-of-picosecond temporal resolution during the critical phases of ICF shots. Additionally, ARC supports a
variety of other high energy density experiments including fast ignition studies on NIF. The automated alignment image
analysis algorithms use digital camera sensor images to direct ARC beams onto the tens-of-microns scale metal wires.
This paper describes the ARC automatic alignment sequence throughout the laser chain from pulse initiation to target
with an emphasis on the image processing algorithms that generate the crucial alignment positions for ARC. The image
processing descriptions and flow diagrams detail the alignment control loops throughout the ARC laser chain beginning
in the ARC high-contrast front end (HCAFE), on into the ARC main laser area, and ending in the ARC target area.
The Advance Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a laser system that employs up to four petawatt (PW) lasers to produce a sequence of short pulses that generate X-rays which backlight high-density inertial confinement fusion (ICF) targets. ARC is designed to produce multiple, sequential X-ray images by using up to eight back lighters. The images will be used to examine the compression and ignition of a cryogenic deuterium-tritium target with tens-of-picosecond temporal resolution during the critical phases of an ICF shot. Multi-frame, hard-X-ray radiography of imploding NIF capsules is a capability which is critical to the success of NIF's missions. As in the NIF system, ARC requires an optical alignment mask that can be inserted and removed as needed for precise positioning of the beam. Due to ARC’s split beam design, inserting the nominal NIF main laser alignment mask in ARC produced a partial blockage of the mask pattern. Requirements for a new mask design were needed. In this paper we describe the ARC mask requirements, the resulting mask design pattern, and the image analysis algorithms used to detect and identify the beam and reference centers required for ARC alignment.
Four of the 192 beams of the National Ignition Facility (NIF) are currently being diverted into the Advanced Radiographic Capability (ARC) system to generate a sequence of short (1-50 picoseconds) 1053 nm laser pulses. When focused onto high Z wires in vacuum, these pulses create high energy x-ray pulses capable of penetrating the dense, imploding fusion fuel plasma during ignition scale experiments. The transmitted x-rays imaged with x-ray diagnostics can create movie radiographs that are expected to provide unprecedented insight into the implosion dynamics. The resulting images will serve as a diagnostic for tuning the experimental parameters towards successful fusion reactions. Beam delays introduced into the ARC pulses via independent, free-space optical trombones create the desired x-ray image sequence, or movie. However, these beam delays cause optical distortion of various alignment fiducials viewed by alignment sensors in the NIF and ARC beamlines. This work describes how the position of circular alignment fiducials is estimated in the presence of distortion.
The Advanced Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a petawatt-class, short-pulse laser system designed to provide x-ray backlighting of NIF targets. ARC uses four NIF beamlines to produce eight beamlets to create a sequence of eight images of an imploding fuel capsule using backlighting targets and diagnostic instrumentation. ARC employs a front end that produces two pulses, chirps the pulses out to 2 ns, and then injects the pulses into the two halves of each of four NIF beamlines. These pulses are amplified by NIF pre- and main amplifiers and transported to compressor vessels located in the NIF target area. The pulses are then compressed and pointed into the NIF target chamber where they impinge upon an array of backlighters. The interaction of the ARC laser pulses and the backlighting material produces bursts of high-energy x-rays that illuminate an imploding fuel capsule. The transmitted x-rays are imaged by diagnostic instrumentation to produce a sequence of radiograph images. A key component of the success of ARC is the automatic alignment system that accomplishes the precise alignment of the beamlets to avoid damaging equipment and to ensure that the beamlets are directed onto the tens-of-microns scale backlighters. In this paper, we describe the ARC automatic alignment system, with emphasis on control loops used to align the beampaths. We also provide a detailed discussion of the alignment image processing, because it plays a critical role in providing beam centering and pointing information for the control loops.
KEYWORDS: National Ignition Facility, Cameras, Sensors, Databases, Optical alignment, Near field, Optical amplifiers, Near field optics, Diagnostics, Attenuators
The National Ignition Facility (NIF) utilizes 192 high-energy laser beams focused with enough power and precision on a hydrogen-filled spherical, cryogenic target to potentially initiate a fusion reaction. NIF has been operational for six years and during that time, thousands of successful laser firings or shots have been executed. Critical instrument measurements and camera images are carefully recorded for each shot. The result is a massive and complex database or ‘big data’ archive that can be used to investigate the state of the laser system at any point in its history or to locate and track trends in the laser operation over time. In this study, the optical light throughput for more than 1600 NIF shots for each of the 192 main laser beams and 48 quads was measured over a three year period from January 2009 to October 2012. The purpose was to verify that the variation in the transmission of light through the optics performed within design expectations during this time period. Differences between average or integrated intensity from images recorded by the input sensor package (ISP) and by the output sensor package (OSP) in the NIF beam-line were examined. A metric is described for quantifying changes in the integrated intensity measurements. Changes in light transmission from the NIF main laser over the three year time-frame are presented.
The current automation of image-based alignment of NIF high energy laser beams is providing the capability of executing multiple target shots per day. An important aspect of performing multiple shots in a day is to reduce additional time spent aligning specific beams due to perturbations in those beam images. One such alignment is beam centration through the second and third harmonic generating crystals in the final optics assembly (FOA), which employs two retro-reflecting corner cubes to represent the beam center. The FOA houses the frequency conversion crystals for third harmonic generation as the beams enters the target chamber. Beam-to-beam variations and systematic beam changes over time in the FOA corner-cube images can lead to a reduction in accuracy as well as increased convergence durations for the template based centroid detector. This work presents a systematic approach of maintaining FOA corner cube centroid templates so that stable position estimation is applied thereby leading to fast convergence of alignment control loops. In the matched filtering approach, a template is designed based on most recent images taken in the last 60 days. The results show that new filter reduces the divergence of the position estimation of FOA images.
The Advance Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a laser system that employs up to four petawatt (PW) lasers to produce a sequence of short pulses that generate X-rays which backlight highdensity internal confinement fusion (ICF) targets. Employing up to eight backlighters, ARC can produce an X-ray "motion picture" to diagnose the compression and ignition of a cryogenic deuterium-tritium target with tens-ofpicosecond temporal resolution during the critical phases of an ICF shot. Multi-frame, hard-X-ray radiography of imploding NIF capsules is a capability which is critical to the success of NIF's missions. The function of the Centering and Pointing System (CAPS) in ARC is to provide superimposed near-field and far-field images on a common optical path. The Images are then analyzed to extract beam centering and pointing data for the control system. The images contain the confluence of pointing, centering, and reference patterns. The patterns may have uneven illumination, particularly when the laser is misaligned. In addition, the simultaneous appearance of three reference patterns may be co-incidental, possibly masking one or more of the patterns. Image analysis algorithms have been developed to determine the centering and pointing position of ARC from these images. In the paper we describe the image analysis algorithms used to detect and identify the centers of these patterns. Results are provided, illustrating how well the process meets system requirements.
The Advance Radiographic Capability (ARC) at the National Ignition Facility (NIF) is a laser system designed to produce a sequence of short pulses used to backlight imploding fuel capsules. Laser pulses from a short-pulse oscillator are dispersed in wavelength into long, low-power pulses, injected in the NIF main laser for amplification, and then compressed into high-power pulses before being directed into the NIF target chamber. In the target chamber, the laser pulses hit targets which produce x-rays used to backlight imploding fuel capsules. Compression of the ARC laser pulses is accomplished with a set of precision-surveyed optical gratings mounted inside of vacuum vessels. The tilt of each grating is monitored by a measurement system consisting of a laser diode, camera and crosshair, all mounted in a pedestal outside of the vacuum vessel, and a mirror mounted on the back of a grating inside the vacuum vessel. The crosshair is mounted in front of the camera, and a diffraction pattern is formed when illuminated with the laser diode beam reflected from the mirror. This diffraction pattern contains information related to relative movements between the grating and the pedestal. Image analysis algorithms have been developed to determine the relative movements between the gratings and pedestal. In the paper we elaborate on features in the diffraction pattern, and describe the image analysis algorithms used to monitor grating tilt changes. Experimental results are provided which indicate the high degree of sensitivity provided by the tilt sensor and image analysis algorithms.
The National Ignition Facility (NIF) utilizes 192 beams, four of which are diverted to create the Advanced Radiographic Capability (ARC) by generating a sequence of short laser pulses. This ARC beam after being converted to X-rays will act as a back lighter to create a radiographic movie and provide an unprecedented insight into the imploding dynamics and serve as a diagnostic for tuning the experimental parameters to achieve fusion. One such beam is the centering beam of the pre-amplifier module which due to a split path obstructs the central square alignment fiducials. This fiducial is used for alignment and also as reference for the programmable spatial shaper (PSS) system. Image processing algorithms are used to process the images and calculate the position of various fiducials in the beam path. We discuss the algorithm to process ARC split beam injector (SBI) centering images with partial fiducial information.
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.
A challenging aspect of preparing cryogenic targets for National Ignition Facility (NIF) ignition experiments is growing a single crystal layer (~ 70 m thick) of solid frozen deuterium-tritium (DT) fuel on the inner surface of a spherical hollow plastic capsule 2 mm in diameter. For the most critical fusion experiments, the layer must be smooth, having uniform thickness, and largely free of isolated defects (e.g. grooves). A single target layer typically takes up to 18 hours to form. X-ray images on 3 orthogonal axes are used to monitor the growth of the crystal and evaluate the quality of the layer. While these methods provide a good indicator of target layer condition, new metrics are currently being developed to take advantage of other properties in the x-ray image, which may give earlier indications of target quality. These properties include symmetry of texture, seed formation, and eigenimage analysis. We describe the approach and associated image processing to evaluate and classify these metrics, whose goal is to improve overall layer production and better quantify the quality of the layer during its growth.
S. Burkhart, A. Awwal, M. Borden, T. Budge, J. Campbell, S. Dixit, M. Henesian , K. Jancaitis, D. Jedlovec, R. Leach, R. Lowe-Webb, B. MacGowan, S. Pratuch, J. Palma, T. Salmon, D. Smauley, L. Smith, S. Sommer, P. Wegner, K. Wilhelmsen, M. Witte, N. Wong
The National Ignition Facility (NIF) is the world’s most energetic laser, having demonstrated in excess of 1.9MJ @351nm with Inertial Confinement Fusion pulse-shapes in July, 2012. First commissioned with 192 operational beamlines in March, 2009, NIF has since transitioned to routine operation for stockpile stewardship, inertial confinement fusion research, and basic high energy density science.
KEYWORDS: Calibration, Image processing, Liquid crystal on silicon, Control systems, National Ignition Facility, Spatial light modulators, Detection and tracking algorithms, Apodization, Process control, Optical components
The heart of the National Ignition Facility is a megajoule-class laser system consisting of 192 beams used to drive
inertial confinement fusion reactions. A recently installed system of programmable, liquid-crystal-based spatial light
modulators adds the capability of arbitrarily shaping the spatial beam profiles in order to enhance operational flexibility.
Its primary intended use is for introducing "blocker" obscurations shadowing isolated flaws on downstream optical
elements that would otherwise be damaged by high fluence laser illumination. Because an improperly shaped blocker
pattern can lead to equipment damage, both the position and shape of the obscurations must be carefully verified prior
to high-fluence operations. An automatic alignment algorithm is used to perform detection and estimation of the
imposed blocker centroid positions compared to their intended locations. Furthermore, in order to minimize the
spatially-varying nonlinear response of the device, a calibration of the local magnification is performed at multiple sub-image
locations. In this paper, we describe the control and associated image processing of this device that helps to
enhance the safety and longevity of the overall system.
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 automatic alignment system for the National Ignition Facility (NIF) is a large-scale parallel system that directs all
192 laser beams along the 300-m optical path to a 50-micron focus at target chamber in less than 50 minutes. The
system automatically commands 9,000 stepping motors to adjust mirrors and other optics based upon images acquired
from high-resolution digital cameras viewing beams at various locations. Forty-five control loops per beamline request
image processing services running on a LINUX cluster to analyze these images of the beams and references, and
automatically steer the beams toward the target. This paper discusses the upgrades to the NIF automatic alignment
system to handle new alignment needs and evolving requirements as related to various types of experiments performed.
As NIF becomes a continuously-operated system and more experiments are performed, performance monitoring is
increasingly important for maintenance and commissioning work. Data, collected during operations, is analyzed for
tuning of the laser and targeting maintenance work. Handling evolving alignment and maintenance needs is expected for
the planned 30-year operational life of NIF.
Video images of laser beams are analyzed to determine the position of the laser beams for alignment purpose in the
National Ignition Facility (NIF). Algorithms process beam images to facilitate automated laser alignment. One such
beam image, known as the corner cube reflected pinhole image, exhibits wide beam quality variations that are processed
by a matched-filter-based algorithm. The challenge is to design a representative template that captures these variations
while at the same time assuring accurate position determination. This paper describes the development of a new
analytical template to accurately estimate the center of a beam with good image quality. The templates are constructed
to exploit several key recurring features observed in the beam images. When the beam image quality is low, the
algorithm chooses a template that contains fewer features. The algorithm was implemented using a Xilinx Virtex II Pro
FPGA implementation that provides a speedup of about 6.4 times over a baseline 3GHz Pentium 4 processor.
Extremely high quality data was acquired using an experimental ultrasound scanner developed at Lawrence Livermore National Laboratory using a 2D ring geometry with up to 720 transmitter/receiver transducer positions. This unique geometry allows reflection and transmission modes and transmission imaging and quantification of a 3D volume using 2D slice data. Standard image reconstruction methods were applied to the data including straight-ray filtered back projection, reflection tomography, and diffraction tomography. Newer approaches were also tested such as full wave, full wave adjoint method, bent-ray filtered backprojection, and full-aperture tomography. A variety of data sets were collected including a formalin-fixed human breast tissue sample, a commercial ultrasound complex breast phantom, and cylindrical objects with and without inclusions. The resulting reconstruction quality of the images ranges from poor to excellent. The method and results of this study are described including like-data reconstructions produced by different algorithms with side-by-side image comparisons. Comparisons to medical B-scan and x-ray CT scan images are also shown. Reconstruction methods with respect to image quality using resolution, noise, and quantitative accuracy, and computational efficiency metrics will also be discussed.
In contrast to standard reflection ultrasound (US), transmission US holds the promise of more thorough tissue characterization by generating quantitative acoustic parameters. We compare results from a conventional US scanner with data acquired using an experimental circular scanner operating at frequencies of 0.3 - 1.5 MHz. Data were obtained on phantoms and a normal, formalin-fixed, excised breast. Both reflection and transmission-based algorithms were used to generate images of reflectivity, sound speed and attenuation.. Images of the phantoms demonstrate the ability to detect sub-mm features and quantify acoustic properties such as sound speed and attenuation. The human breast specimen showed full field evaluation, improved penetration and tissue definition. Comparison with conventional US indicates the potential for better margin definition and acoustic characterization of masses, particularly in the complex scattering environments of human breast tissue. The use of morphology, in the context of reflectivity, sound speed and attenuation, for characterizing tissue, is discussed.
New ultrasound data, obtained with a circular experimental scanner, are compared with data obtained with standard X-ray CT. Ultrasound data obtained by scanning fixed breast tissue were used to generate images of sound speed and reflectivity. The ultrasound images exhibit approximately 1 mm resolution and about 20 dB of dynamic range. All data were obtained in a circular geometry. X-ray CT scans were used to generate X-ray images corresponding to the same 'slices' obtained with the ultrasound scanner. The good match of sensitivity, resolution and angular coverage between the ultrasound and X-ray data makes possible a direct comparison of the three types of images. We present the results of such a comparison for an excised breast fixed in formalin. The results are presented visually using various types of data fusion. A general correspondence between the sound speed, reflectivity and X-ray morphologies is found. The degree to which data fusion can help characterize tissue is assessed by examining the quantitative correlations between the ultrasound and X-ray images.
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