National Ignition Facility

Controlling the symmetry of indirect-drive inertial confinement fusion implosions remains a key challenge. Increasing the ratio of the hohlraum diameter to the capsule diameter (case-to-capsule ratio, or CCR) facilitates symmetry tuning. By varying the balance of energy between the inner and outer cones as well as the incident laser pulse length, we demonstrate the ability to tune from oblate, through round, to prolate at a CCR of 3.2 in near-vacuum hohlraums at the National Ignition Facility, developing empirical playbooks along the way for cone fraction sensitivity of various laser pulse epochs. Radiation-hydrodynamic simulations with enhanced inner beam propagation reproduce most experimental observables, including hot spot shape, for a majority of implosions. Specular reflections are used to diagnose the limits of inner beam propagation as a function of pulse length.

Lasers are of increasing interest to the accelerator community and include applications as diverse as stripping electrons from hydrogen atoms, sources for Compton scattering, efficient high repetition rate lasers for dielectric laser acceleration, peta-watt peak power lasers for laser wake field and high energy, short pulse lasers for proton and ion beam therapy. The laser requirements for these applications are briefly surveyed. State of the art of laser technologies with the potential to eventually meet those requirements are reviewed. These technologies include diode pumped solid state lasers (including cryogenic), fiber lasers, OPCPA based lasers and Ti:Sapphire lasers. Strengths and weakness of the various technologies are discussed along with the most important issues to address to get from the current state of the art to the performance needed for the accelerator applications. Efficiency issues are considered in detail as in most cases the system efficiency is a valuable indicator of the actual ability of a given technology to deliver the application requirements.

A novel high-dynamic-range cross-correlator is presented that enables single-shot characterization of pulse contrast for ultrahigh intensity lasers in the temporal region up to 200 ps.

This note was written based upon review of many papers, articles, and text books at time when we had little experience with an actual CORBA product. Some of the references conflicted with each other, and we now see that some of the comments made by other authors were misunderstandings or wrong. The product that we are currently using (and many others) do not implement all of CORBA - in fact, it is obvious that there is a great deal more to add to CORBA to meet all of the goals and expectations summarized herein. With all of its capability and promised advantage, CORBA is a complex package of technologies and products which requires quite a concentrated effort to master. We have developed a Test Package which to date has been used to send and receive data from up to 12 Servers on up to 5 computers in our office network, with up to 1000 objects per server. The data is expressed in all available IDL types including long arrays and unbounded strings. Performance measurements have established solid data upon which we can base estimates and models of the performance of the communication layer of the overall system after further design and prototyping on the frameworks and applications has been completed (see CORBA Test Package, ref. 14).

The National Ignition Facility, a stadium-size, 192-beam laser, is an essential tool for maintaining the safety and reliability of our nuclear weapons, harnessing fusion energy for future generations, and unlocking the origins of the universe. In the FY2001 Energy and Water Appropriations Act (FPN00-48), Congress appropriated $199.1 million for the continued construction of NIF. Immediately, $130 million became available. After March 31, 2001, $69.1 million was to be made available only after Department of Energy certification to Congress regarding six specific points: (1) recommend an appropriate path forward for the project; (2) certify that all established project and scientific milestones are on schedule and cost; (3) conduct 1st and 2nd quarter project reviews in FY01 and determine the project is on schedule and cost; (4) study alternatives to a 192-beam ignition facility for the stockpile stewardship program (SSP); (5) implement an integrated cost-schedule earned-value project control system; and (6) create a five-year budget plan for the SSP.

A testing facility for evaluating ITS hardware components has been established in Trailer 3907. In accordance with our acceptance testing of the Highland V880 digital delay generators (DDG), software has been written to allow long-term testing to be performed on the four V880 prototypes (NIF-5000375). Problems and discrepancies discovered through long-term testing have been documented, and a summary of the problems found and the corrective actions taken are presented in this report. For more background information about the National Ignition Facility and the Integrated Timing System, see UCRL-JC-135036.

This paper presents a cryogenic temperature control technique that demonstrated good disturbance rejection at the National Ignition Facility. Temperature excursions must be minimized to maintain DT fuel layer symmetry needed for ignition. The control scheme known as mid-ranging control effectively used two manipulated inputs and one output, which differs from traditional single-input-multiple-output control schemes like cascade control. Each input had different power constraints and substantially different dynamic effects on the output. One input acted as a bulk heat source whereas the other acted as a trimming heat source. During an upset, the controller manipulated both input variables simultaneously to maintain the desired temperature. The mid-ranging controller was tuned using an extension of the well-known Ziegler-Nichols (ZN) method. The derived SIMC tuning rules were not as attractive since, to be applied, they required prior knowledge of the target's thermal dynamics. The resulting control scheme rejected large and sudden increases in thermal loading quicker than a more conventional scheme. The technique and tuning equations may be applied to similar cryogenic control problems.

This SSDR establishes the performance, design, development and test requirements for the Final Optic Assembly (FOA). The FOA (WBS 1.8.7) as part of the Target Experimental System (1.8) includes vacuum windows, frequency conversion crystals, focus lens, debris shields and supporting mechanical equipment.

The NIF contains a large number of optics that also act as vacuum barriers. These are subject to brittle failures that may result in significant consequences. This Fracture Control Plan identifies the requirements, needed documentation, and required actions for minimizing the potential for brittle failures of these fracture critical components in the NIF laser system. The goal of this plan is to ensure that all fracture-critical systems present no more than a low level of risk. Risk considers both consequences (to workers, the environment, and public confidence) and probability of failure. This plan interprets and implements the guidance contained in the ME Design Safety Standard, Section 5.4, ''Design Safety Standards for Fracture Critical Components for High Power Laser Systems'' (LLNL, 2000).

The 192 laser beams that converge on the target at the output of the National Ignition Facility (NIF) originates from an all fiber laser system in the Master Oscillator Room (MOR). The architecture, design and performance of the NIF Master Oscillator Room will be presented.

This report will provide a summary report of work performed under Subcontract B324681 from November 1 through December 14, 1995 and covers work relevant to Subtasks 1-11. The work performed under this contract was presented and reviewed at the NIF Radiation Sciences Users Group meeting held on November 29-30. Present where senior representatives from the NIF Project, the DOE Office of the NIF, the DOE ICF program, and the Defense Nuclear Agency. This report is divided into seven sections, not including the Introduction to include; Potential Test Capability, Operational Scenarios, Facilitization Issues, Security Issues, Performance/Cost/Risk Considerations, a Summary of Requested Modifications to the NIF and finally, Conclusions. Within each section will be a short narrative and a copy of the view graph presentation.

A solid-state high voltage pulse generator developed as part of the Advanced Radiographic Capability (ARC) mission for the National Ignition Facility (NIF) has been deployed. This paper will provide details of the pulser design and the upgrades required to achieve reliable operation for multi-pulse bursts for an ever-increasing mission space. The pulser design has been demonstrated to be robust, reliable and to meet all performance specifications as they apply to the Plasma Electrode Pockels Cell (PEPC). This pulser is realized as a FET-driven twenty-seven stage magnetic adder operating with 700 volt primaries. It delivers a programmable multi-pulse burst of 18 kV, 3 kA pulses to a PEPC at repetition rates up to 1 Hertz. The typical pulse widths are 200ns with 20ns rise-and-fall-times at the pulser. A capacitive load, significant cable lengths between pulser and Pockels cell, fast transition times, and the microsecond type delays between pulses lead to non-ideal interactions that must be addressed to limit pulse distortion and reduce stress on the pulse electronics. In this paper we discuss the various options considered for resolving these issues, down-select decisions, and test results that demonstrate improvements.

John R. MurrayLawrence Livermore NationalLaboratoryNational Ignition Facility ProjectPO Box 808 L-462Livermore, California 94550E-mail: jrmurray65@alum.mit.eduJohn M. SouresUniversity of RochesterLaboratory for Laser EnergeticsNational Laser Users’ Facility250 East River RoadRochester, New York 14623E-mail: jsou@lle.rochester.edu

As of the end of August, the National Ignition Facility (NIF) is satisfactorily meeting its technical performance, cost and schedule milestones. Hensel Phelps Construction Company (HPCC) turned over the Laser Building to the Beampath Infrastructure System (BIS) Commissioning and Operations team for beneficial occupancy.

Lawrence Livermore National Laboratory's (LLNL) National Ignition Facility (NIF) uses a variety of diagnostics and image capturing optics for collecting data in High Energy Density Physics (HEDP) experiments. However, every image capturing system causes blurring and degradation of the images captured. This degradation can be mathematically described through a camera system's Point Spread Function (PSF), and can be reversed if the system's PSF is known. This is deconvolution, also called image restoration. Many PSFs can be determined experimentally by imaging a point source, which is a light emitting object that appears infinitesimally small to the camera. However, NIF's Kirkpatrick-Baez Optic (KBO) is more difficult to characterize because it has a spatially-varying PSF. Spatially varying PSFs make deconvolution much more difficult because instead of being 2-dimensional, a spatially varying PSF is 4-dimensional. This work discusses a method used for modeling the KBO's PSF by modeling it as the sum of products of two basis functions. This model assumes separability of the four dimensions of the PSF into two, 2-dimensional basis functions. While previous work would assume parametric forms for some of the basis functions, this work attempts to only use numeric representations of the basis functions. Previous work also ignores the possibility of non-linear magnification along each image axis, whereas this work successfully characterizes the KBO's non-linear magnification. Implementation of this model gives exceptional results, with the correlation coefficient between a model generated image and an experimental image as high as 0.9994. Modeling the PSF with high accuracy lays the groundwork to allow for deconvolution of images generated by the KBO.

Lawrence Livermore National Laboratory’s (LLNL) National Ignition Facility (NIF) is a key component of the National Nuclear Security Administration’s (NNSA) Stockpile Stewardship Program, whose purpose is to maintain the safety, reliability, and effectiveness of our nation’s nuclear stockpile without underground nuclear testing. The NIF is crucial to the Stockpile Stewardship Program because it is the only facility that can create the conditions of extreme temperature and pressure—conditions that exist only in stars or in exploding nuclear weapons—that are relevant to understanding how our modern nuclear weapons operate. As such, the NIF’s primary mission is to attain fusion ignition in the laboratory. Fusion ignition not only supports Stockpile Stewardship needs, but also provides the basis for future decisions about fusion’s potential as a long-term energy source. Additionally, NIF provides scientists with access to high-energy-density regimes that can yield new insight and understanding in the areas of astrophysics, hydrodynamics, material properties, plasma physics, and radiative properties. The use of the NIF to support the Stockpile Stewardship Program and the advancement of basic high-energy-density science understanding is planned and managed through program-level execution plans and NIF directorate-level management teams. An example of a plan is the National Ignition Campaign Execution Plan. The NIF Operations Management Plan provides an overview of the NIF Operations organization and describes how the NIF is supported by the LLNL infrastructure and how it is safely and responsibly managed and operated. Detailed information on NIF management of the organization is found in a series of supporting plans, policies, and procedures. A list of related acronyms can be found in Appendix A of this document. The purpose of this document is to provide a roadmap of how the NIF Operations organization functions. It provides a guide to understanding the requirements, document flow down, organizational vision and mission, performance metrics, and interrelationship of the NIF Operations organization with other directorate and laboratory organizations. This document also provides a listing of roles and responsibilities, core processes, procedures, authority matrices, change control boards, and other information necessary for successfully functioning in the NIF Operations organization. This document, the NIF Shot Operations Plan, and the NIF Maintenance Plan together represent the primary documents satisfying our Conduct of Operations compliance requirement.

Chirped pulse amplification (CPA), originally proposed by Strickland and Mourou, is a critical enabling technology for creating very short laser pulses with very high peak power. It consists of three optical components: a stretcher, an amplifier, and a compressor. An initial laser pulse of short duration and low energy content is first stretched out in time by the stretcher, resulting in a pulse with longer duration, low energy content, and very low peak power. The pulse is then amplified to increase its energy content without changing its duration in time. The amplified pulse is finally compressed in time in the compressor, resulting in a laser pulse with very short duration and very high peak power. The objective of this work is to develop numerical techniques that enable small-scale grating aberrations in the compressor to be analyzed through high performance computer simulations.

Pulsed fiber laser systems are under development at Lawrence Livermore National Laboratory as photo-cathode drive lasers for linear accelerators and injection seed lasers. The presents status and future potential will be reviewed.