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High average power lasers.

John Sethian (Naval Research Laboratory) described the status of laser fusion energy and the High Average Power Laser Program (HAPL). He noted that the HAPL program had set "Phase I" goals at the fusion community meeting in Snow mass in 2002. "The HAPL program is developing the science and technology for inertial fusion energy with lasers, direct drive targets and solid wall chamber," he said. The goals set for the lasers is greater than 6 percent efficiency, repetition rate of 5-10 Hertz, greater than 100,000 shots continuous, proper wavelength, beam quality and pulse shape. The laser technologies must scale to reactor size modules and project to have attractive costs for commercial fusion energy, he said.

Two types of lasers are being developed in the HAPL program: Krypton Fluoride (an electron beam pumped gas laser) at the Naval Research Laboratory and a diode-pumped solid state laser at the Lawrence Livermore National Laboratory. He said the Mercury diode-pumped laser has so far produced 34 Joules per pulse at 3.5 Hertz in several hour-long runs. The goals for Mercury are 100 Joules at 10 Hertz with 10% efficiency in 3 ns pulses, he said. The Electra gas laser has produced over 400 Joules at 1 Hertz continuously for 5000 pulses (over an hour). The Electra goals are 400-700 Joules at 1 Hertz and 5 Hertz, with an efficiency of greater than 7 percent.

The HAPL is also developing final optics with goals of laser-induced damage threshold of more than 5 Joules per square centimeter, in large area optics and to develop a credible final optics design that is resistant to X-rays, energetic ions, debris, contamination and neutrons. Thus far they have demonstrated diamond-turned electroplated minors at 18 Joules per square centimeter for 100,000 shots on square millimeter scale. They need to verify this at larger spot sizes, improve high-cycle fatigue behavior and validate fabrication, Sethian said.

Programs are underway to develop a viable first wall concept and then to produce a viable point design for a fusion power plant. Research is also underway on target fabrication, with the goals of developing mass production methods to fabricate cryogenic DT targets that meet the requirements of the target design codes and chamber design and to combine these methods with established mass production costing models to project target costs of less than twenty five cents each. Thus far they are projecting target costs of 16 cents each. In the area of target injection and tracking, programs are underway to build an injector that can place targets at chamber center (6-9 m away) in 25 milliseconds (400 m/s) and to demonstrate target tracking with sufficient accuracy for a power plant (estimated to be within 100 microns). A target injector is in operation at General Atomics that has achieved the desired velocity and has a placement accuracy of 20 millimeters thus far. Target designs are being carried out in conjunction with inertial confinement fusion programs at the Naval Research Laboratory and the University of Rochester. Current designs have calculated gains of over 100.

In summary, Sethian said, "We are nearing the goals for the basic science and technology phase (Phase I) of the HAPL program."
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Title Annotation:laser fusion
Publication:Fusion Power Report
Geographic Code:1USA
Date:Jan 1, 2005
Words:531
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