1185010330 U-103S0 LA—10380 UC-21 DE85 010330 Issued: March 1985 Summary of Research for the Inertial Confinement Fusion Program at Los Alamos National Laboratory Compiled by David C. Cartwright Principal ICF Program Manager DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Los Alamos National Laboratory Los Alamos.New Mexico 87545 wmmm OF m imm is mwna. CONTENTS ABSTRACT / Inertial Confinement Fusion Overview 3 High-Energy-Density Plasma Physics with Lasers 8 The KrF Laser: The Advance Toward Shorter Wavelengths 23 Diagnosis of Laser-Driven Implosions 34 High-Power CO2 Systems 48 Target Fabrication for Inertial Confinement Fusion Research 72 Heavy-Ion Fusion 80 ABSTRACTS OF ICFSUPPPORTED RESEARCH PUBLICATIONS SINCE 1982 91 Summary of Research for the Inertia! Corfinement Fusion Program at Los Alamos National Laboratory compiled by David C. Cartwright Principal ICF Program Manager ABSTRACT The information presented in this report is a summary of the status of the Inertial Confinement Fusion (ICF) program at the Los Alamos National Laboratory as of February 1985. This report contains material on the existing high-power CO2 laser driver (Antares), the program to determine the potential of KrF as an ICF driver, heavy-ion accelerators as drivers for ICF, target fabrication for ICF, and a summary cf our understanding of laser-plasma interactions. A classified companion report contains material on our current understanding of capsule physics and lists the contributions to the Laboratory's weapons programs made by the ICF program. The information collected in these two volumes is meant to serve as a report on the status of some of the technology components of the Los Alamos ICF program rather than a detailed review of specific technical issues. Inertial Confinement Fusion Overview by David C. Cartwright he accomplishment of energy gain through nuclear small masses of deuterium-tritium fuel to thermonuclear fusion in laboratory experiments will require the burn conditions. The goals of the national program are: T solution of a number of interesting, although very • to support nuclear weapons physics research, and complex, scientific and technological problems. Both the • to do research on the potential of inertial fusion for Inertial Confinement Fusion (ICF) and Magnetic Fusion energy production. Energy (MFE) programs have been somewhat overly Key technical elements within the ICF program are: optimistic in their initial evaluations of the difficulties • the design and confirmation of performance of fuel- involved in controlling nuclear fusion. In both programs, filled targets requiring minimum input energy, and most of the major problems were identified only after the » the development of a laboratory driver suitable for construction and operation of a new and usually more driving such targets (at an acceptable cost). powerful experimental facility. Researchers in both the Whether addressing weapons applications or possibie ICF and MFE programs are now trying to build solid long-term potential as an energy source, there is no technical foundations for their programs in order to be significant difference in the short-term program. In the able to predict results under different experimental condi- longer term, important scientific and engineering prob- tions. Los Alamos completed construction of the Antares lems would have to be addressed before ICF could be CO2 laser facility in December 1983 and placed it on considered for commercial electrical power generation. operational status for experiments in ICF. Antares, the Since the primary source of the funding is the DOE world's largest operational laser, is the first in a series of defense programs, the weapon physics goals will continue new. higher intensity ICF drivers and is the successor to to receive emphasis throughout this decade. the smaller (< 10-kJ) Helios eight-beam CO laser facility : Since Antares has been in operation for more than a at Los Alamos. The two others in the US are Nova, at year, and Helios was operational for 5 years before Lawrence Livermore National Laboratory (LLNL). to be Antares, it is appropriate to review our present under- operational in the spring of 1985. and PBFA-II at Sandia standing of ICF physics based on CO laser drivers. The National Laboratories (SNL), to begin operation in the 2 purpose of this technical review is to present our level of fall of 1987. These three new facilities will permit ex- knowledge of the coupling of CO laser energy to the perimentation with ICF targets under conditions of tem- 2 target, acquired by experiments with both the Helios arid perature and pressure that more closely simulate those Antares laser facilities. In the subsequent chapters, :'u required for an energy gain target. scientific and technological progress that has been made The ICF mission statement for the Los Alamos Na- in the fields of plasma physics, capsule physics, materials tional Laboratory is as follows: fabrication, CO2 and KrF laser systems, and heavy-ion The Los Alamos ICF program is one of the main efforts fusicn (in support of the ICF program at Los Alamos) by the Department of Energy (DOE) to evaluate the will be reviewed. A review of the Los Alamos program to scientific feasibility of inertially confined fusion, using study the physics of laser fusion at short wavelength (that intense lasers or particle beams to compress and heat is 1/4 urn) will be presented in a future publication. GENERAL REQUIREMENTS FOR ICF compression in Fig. 1. What is treated as an assertion at this level is explained, and qualified, in the articles that Inertia! confinement fusion attempts to mimic on a follow. miniature scale the physics of a thermonuclear weapons device. A fuel of deuterium and tritium (i>T) is heated rapidly to temperatures highenbugh to promote fusion CHARACTERISTICS OF CO2-IRRADIATED reactions in the fuel, and at the same time, the fuel is TARGETS compressed to densities large enough to facilitate reaction of a large * fraction of the fuel before cooling by When high-intensity laser radiation (<10li W/cm2) hydrodynamic expansion. However, the efficient use of strikes a solid surface, a plasma is formed. The infrared the DT fuel in ICF is much more difficult than in a radiation (10.6 urn) produced by the CO2 laser is ab- nuclear weapon. sorbed by the plasma through a collective process known The difficulty arises from the requirement to contain as resonant absorption. This process, which we have (in the laboratory) the energy released by the fusion come to understand primarily through theoretical work, reaction. This can be accomplished only if the yield is converts almost all of the absorbed laser energy into sufficiently low, which implies a small mass of fuel. For energetic electrons. The measured absorption for flat small fuel masses to support thermonuclear burn, in surfaces is about 40%, and refraction of the incident light which the energy produced by fusion reaction is used to in the plasma reduces the absorption to about 30% for sustain the burn, the fuel must be condensed to high curved surfaces. The energetic electrons produced during density. Specifically, to trap the energy of the a-particles the resonant absorption process approach temperatures produced in the DT fusion reaction, the areal density of 80 keV. This distribution of so-called "hot electrons" (pR) must be equal to or greater than a certain constant can exist superimposed on a second "cold" distribution C. That is. a fundamental scaling parameter for all ICF is because there are very few collisions in the low-density the product of fuel density p and the radius R of the corona formsd around the target. Experiments show that volume containing the fuel. It can be shown that if the hot-electron temperature increases with laser intensity as product pR is equal to a constant, then the density to I04. which the fuel must be compressed increases as the Because all of the energy absorbed from the laser beam reciprocal of the square root of the fuel mass, that is. p ss initially resides in the hot electrons, it is mandatory to l/\/M. Achieving the required compression without understand the subsequent transport of the electrons in expending excessive energy from the driver is the basic order to predict how energy can be delivered to other requirement of ICF. portions of the target. Very large electric and magnetic Figure 1 shows schematically the various steps re- fields develop, for conditions characteristic of CO2-laser- quired to convert the incident laser energy into driven targets, as a result of the large spatial gradients in hydrodynamic compression of the fuel. Information on temperature and density present in the plasma. The steps (a) and (b) is being obtained using laboratory magnetic Fields are confined to within a few hundred drivers such as Helios and Antares, but data concerning micrometers of the surface and may exceed a megagauss. steps (c) and (d) will require new and more powerful Consequently, the magnetic forces dominate the motion drivers. Keep in mind that the objective is to achieve net of most electrons, and their transport is not described by energy gain from the fusion reaction.