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Development of a Cryogenic Target Delivery System for HiPER
Abstract
For the future, we have to develop new sources of energy. These new sources may be based on nuclear fusion with magnetic confinement (as with the ITER experiment) or with a new concept based on inertial confinement. The European community plans to build a facility (HiPER project) which is dedicated to reaching high gain with cryogenic targets, and to test the concepts of target mass production and rep rate shots. The cryogenic system for the 1(st) phase experiments in HiPER is based on the cryogenic system developed for the French facility Laser MegaJoule (LMJ). The latter must be modified and upgraded for direct drive targets. In particular the target must be protected from the radiation flux from the vacuum vessel by a thermal shroud In addition, the LMJ system must be equipped with a thermal system to allow layering of the fusion fuel to take place.
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General Atomics is designing and building the OMEGA Cryogenic
Target System (Fig. 1) for the University of Rochester's Laboratory for
Laser Energetics. The purpose of this system is to deliver millimeter
sized polymer shell targets to the center of the target chamber for
inertial confinement fusion experiments. Prior to insertion, these
targets are filled to pressures as high as 1500 atm with hydrogen
isotopes (DT), the gas is cryogenically condensed, and the condensed
material is layered to form a uniform inner shell. GA has demonstrated
the successful filling with D<sub>2</sub> of plastic targets to 1100
atm, cooling, and cold transport utilizing prototype equipment. In
addition to proving the viability of the proposed fill process, the
prototypes have led to significant equipment simplifications and process
improvements for the University of Rochester system
The Laser Megajoule facility is the French equipment intended for studies of inertial fusion. Thermonuclear fusion is obtained by focusing 240 laser beams with an energy of 1.8 MJ on a cryotarget. The microballoon implosion, following laser beams impact, generates in its center the ignition conditions of temperature and pressure. The success of implosion strongly depends on the geometrical characteristics of the Deuterium Tritium ice layer: margin 1% for thickness, 1 μm for roughness. The Laser Megajoule requires a high resolution temperature regulation to obtain the cryotarget temperature conditions: a temperature slope of 1 mK/min with ±1 mK to reach the triple point 19.79 K and a regulation at constant temperature with ±1 mK. This regulation required a thermal model elaboration for the target and the process, a regulation module development with a ±50 μK resolution, and a specific algorithm of regulation. It runs on the prototype “Echelle 1,” the Cryotarget Positioner mock-up built at the Service des Basses Températures—CEA Grenoble. The temperature stability obtained on the cryostat “Echelle 1” is presented in the chapter.
The current status of the fabrication, injection, and tracking of fast ignition targets is summarized including on cryogenic technologies for direct-drive, laser fusion targets with and without a reentrant guide cone for additional heating lasers. The fabrication of low-density foam and the drilling of fragile foam shells are current issues in the fabrication of fast ignition targets with reentrant cones. Fuel loading to the targets is a challenging issue in the mass-production process of the targets for a fusion power plant. Two fuel-loading methods are proposed for the fast ignition target with the cone. Preliminary experiments of injection and tracking of real-size targets have started showing promising results.
To create a conceptual design of a tracking system of a target injected into a wet-walled, laser-fusion reactor, the influence of residual gas on the target trajectory is discussed based on a kinetic model, assuming all of the impinging molecules are adsorbed on the target surface. The model targets are a high-gain target for central ignition and a fast-ignition target with a cone as an optical guide for an additional heating laser. In the case of a fast-ignition target, tracking in the reactor might be skipped, depending on its condition, because of the heavy cone. Recent activities in fabrication of the fast-ignition target are briefly mentioned.
Laser Megajoule cryogenic target: a way from automatic transfer to laser conditions, 17th Target Fabrication Meeting
- G Paquignon
- J Manzagol
- V Lamaison
- D Brisset
- D Chatain
- P Bonnay
- E Bouleau
- D Communal
- J-P Périn
The Cryogenic Shroud Extractor Prototype for the Laser Megajoule Facility, 17th Target Fabrication Meeting
- D Chatain
- V Lamaison
- P Bonnay
- E Bouleau
- J-P Périn