Classifications

• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21B—FUSION REACTORS
  • G21B1/00—Thermonuclear fusion reactors
  • G21B1/11—Details
  • G21B1/23—Optical systems, e.g. for irradiating targets, for heating plasma or for plasma diagnostics
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E30/00—Energy generation of nuclear origin
  • Y02E30/10—Nuclear fusion reactors

Definitions

• IPCC Energy Information Agency and current Intergovernmental Panel on Climate Change
• ICF Inertial Confinement Fusion
• D deuterium
• T tritium
• MFE Magnetic fusion energy
• a final optics beam transport system is provided that meets the top level requirements appropriate for a Laser Inertial Fusion Engine (LIFE) system.
• the optics enable fast pointing and transport of 351 nm light through dual neutron pinholes and focusing of the beam on target (e.g., a target tracking system employed with embodiments described herein will be capable of making shot pointing corrections in the last 30 before ignition).
• the optical system described herein enables a target tracking system and coaligned diagnostic beam.
• the final optics have been engineered to be robust to neutron damage and target shock pressure waves while providing minimal loss to the 351 nm laser beam. A method of replacing the final optics is also described.
• Embodiments of the present invention are also applicable to other optical systems in a high radiation environment.
• a method of replacing an optical element positioned in a high radiation environment includes halting operations of a beamline, pulling a cable to transfer the optical element through a radiation wall, and exchanging the optical element with a replacement optical element.
• the method also includes pulling the cable to transfer the replacement optical element through the radiation wall, positioning the replacement optical element adjacent the first end face of the telescope, and seating the replacement optical element on the first end face of the telescope.
• the method further includes seating the replacement optical element on kinematic elements, verifying an optical alignment of the replacement optical element, and resuming operations of the beamline.
• an optical system includes a chamber having a first end and a second end and an optic mount mounted to the first end of the vacuum chamber.
• the optic mount has a mounting surface.
• the optical system also includes a Fresnel optic mounted to the mounting surface and a cable attached to the optic mount.
• the optical system further includes a second optical element mounted to the second end of the vacuum chamber.
• a system is provided.
• the system includes a laser system operable to provide a laser beam along an optical path and a fusion chamber coupled to the optical path.
• the system also includes a neutron pinhole disposed along the optical path between the laser system and the fusion chamber and a neutron attenuation region disposed along the optical path between the laser system and the fusion chamber.
• a thin Fresnel optic is used as the final optic.
• the final optic (which may be fabricated in fused silica) is mounted in a frame that is sealed to a transport telescope containing a neutron pinhole (e.g., a large cement structure connected to the building) via a gasket (e.g., an O-ring seal).
• the aperture of the final optic is approximately 0.6 x 43 x 43 cm with an external pressure of 21 torr (2800 Pa) and an internal pressure of -0.5 mtorr. In this embodiment, approximately 1 16 pounds of force is present on the surface of the optic.
• Embodiments of the present invention provide replaceable optics in an accessible mariner without use of electronics, motors, hydraulics, or the like, which are unable to withstand a high radiation environment with an acceptable lifetime.
• a final optics beam transport system is provided that meets the top level requirements associated with high radiation environments found, for example, in LIFE.
• the optics allow slow pointing and transport of the 351 ran light through optically transparent neutron shielding (also referred to as neutron pinholes, which can be implemented in a dual pinhole configuration) and focus the beam on target.
• the final optics have been engineered to be robust to neutron damage and target shock pressure wave while providing reduced or minimal loss to the 351 ran laser beam. A method of replacing these optics is provided by embodiments of the present invention.
• embodiments of the present invention provide methods and systems that enable the replacement of optics in a region that is shielded from a neutron source by a shield wall.
• the final optic used to focus laser light to a target provides for both focusing of light as well as a vacuum barrier and/or a tritium barrier.
• FIG. 1 is a simplified schematic diagram illustrating elements of a final beam transport system according to an embodiment of the present invention
• FIG. 2 is a simplified schematic diagram illustrating a final beam transport system according to an embodiment of the present invention
• FIG. 3A is a schematic diagram illustrating a final beam transport system including two cascaded neutron pinholes according to an embodiment of the present invention
• FIG. 3B is a schematic diagram illustrating a final beam transport system including a single neutron pinhole according to an embodiment of the present invention
• FIG. 3C is a simplified schematic diagram illustrating elements of neutron pinhole telescopes according to an embodiment of the present invention
• FIG. 4A is a simplified plot of transmission in fused silica optics as a function of wavelength for a set of annealing conditions;
• FIG. 4B is a simplified plot of the absorption in fused silica optics as a function of temperature;
• FIG. 5 is a simplified graph illustrating a shock pressure waveform incident on the final optic according to an embodiment of the present invention
• FIG. 6A is a contour plot illustrating induced stress in the final optic from the target ignition shock
• FIG. 6B is a contour plot illustrating the maximum displacement of the final optic from target ignition shock
• FIG. 7 A is a simplified schematic diagram of a final optic changeout system according to an embodiment of the present invention
• FIG. 7B is a simplified schematic diagram of an optical pass-thru for final optic replacement including a labyrinth neutronics barrier in a shield wall according to an embodiment of the present invention
• FIG. 8B is a simplified schematic diagram illustrating a system including independent removability of window modules from any pair in the system according to an embodiment of the present invention
• FIG. 8C is a simplified flowchart illustrating a method of exchanging a final optic in a high radiation environment according to an embodiment of the present invention
• FIG. 9A is a simplified schematic diagram illustrating a laser bay labyrinth maintenance entrance to area between shield walls according to an embodiment of the present invention
• FIG. 9B is a simplified schematic diagram illustrating a laser bay labyrinth and neutron pinhole architecture according to an alternative embodiment of the present invention.
• FIG. 10 is a diagram illustrating the evolution of the environment near target chamber center as a function of time according to an embodiment of the present invention.
• FIG. 1 1 A is a simplified graph illustrating laser transmission as a function of distance from the laser entrance hole due to inverse Bremstrahlung absorption according to an embodiment of the present invention.
• FIG. 1 IB is a simplified graph illustrating saturation of the SRS signal in lead vapor according to an embodiment of the present invention.
• Embodiments of the present invention relate to fusion reaction chambers.
• Embodiments of the present invention are applicable to energy systems including , but are not limited to, a Laser Inertial-confmement Fusion Energy (LIFE) engine, hybrid fusion-fission systems such as a hybrid fusion-fission LIFE system, a generation IV reactor, an integral fast reactor, magnetic confinement fusion energy (MFE) systems, accelerator driven systems and others.
• LIFE Laser Inertial-confmement Fusion Energy
• MFE magnetic confinement fusion energy
• the energy system is a hybrid version of the LIFE engine, a hybrid fusion-fission LIFE system, such as described in International Patent Application No. PCT/US2008/01 1335, filed September 30, 2008, titled "Control of a Laser Inertial
• Embodiments of the present invention provide for protection of system elements from neutron fluence, which can potentially limit the lifetime of the optics.
• One of the optics at high risk is the final optic, which withstands all of the issues described in Table 1 in addition to the laser energy.
• the final optic is directly exposed to the gases from the target chamber (primarily xenon, but with target admixture of helium, hydrogen, deuterium, tritium, lead, carbon) and target shrapnel.
• the baseline output power is 1950 MW.
• the ions and x-rays are absorbed by the xenon gas in the target chamber, leaving 1560 MW of 14 MeV neutrons from the fusion reaction which yield an average exposure of 1.5x10 17 n/m 2 -sec at the final optic location.
• the optic is positioned in an environment coupled to the vibrations associated with the gas expansion from ignition and liquid lithium flow in the target chamber blanket. This is somewhat mitigated in some LIFE designs by mechanically decoupling the first wall and blanket from the vacuum chamber that is connected to the optical pipe assembly.
• the beamline apertures in the blanket also act to attenuate the gas shock incident on the final optic.
• the final optic is designed to survive the residual threat and efficiently transmit and focus the 351 nm laser light at -3 J/cm 2 (normal to the beam).
• the final beam transport system includes the optics utilized to transport the beam from the exit of the frequency converter to the target chamber center.
• the final optic system is robust, serviceable, delivers the laser through optically transparent neutron shielding (also referred to as neutron pinholes since laser light is able to propagate through the pinholes without substantial optical losses), and survives multiple threats from the target chamber.
• this final beam transport system includes optic M10 and all following optics.
• LI 1, LG1 and FL1 are exposed to neutron irradiation
• FL1 the final optic, is exposed to additional mechanical shock and target shrapnel from target ignition.
• FIG. 3A is a schematic diagram illustrating a final beam transport system including two cascaded neutron pinholes according to an embodiment of the present invention.
• the system can be referred to a "two neutron pinhole" system, it will be understood that the system utilizes two sets of neutron pinholes.
• Systems designed as illustrated in FIG. 3 A experience a radiation dose that is attenuated to 0.04 rem/year utilizing two cascaded neutron pinholes.
• the final optic 326/320 not only focuses, but deflects the beam from the axis of the second neutron pinhole relay telescope (including focus lens 314 and Fresnel lens (type 2a) 316 and matching focus lens 315 / Fresnel lens 318 to the target chamber center 386.
• the final optic i.e., Fresnel lens (type 2b) 326 and matching final optic (i.e., Fresnel lens (type lb) 320 deflects the laser beam, it only acts as a scattering source for neutrons, thereby preventing ballistic neutrons from passing through the neutron pinhole at location .
• the transmitted spectrum of neutrons from the pinhole 330 will be a roughly collimated beam of neutrons that have scattered from the surrounding shield materials and blanket after some collimation by the pinhole structure. As shown in FIG.
• the axis of the second neutron pinhole at location 332 is again deflected from axis of the first neutron pinhole at location 330, which prevents ballistic neutrons from the second pinhole from passing through the first one.
• the neutron dosage can be attenuated to levels such that human occupation of the laser bay is possible.
• the laser bays 31 OA and 310B include 2.2 m wide x 1.35 m high x 10.4 m long lco lasers/amplifiers. These laser bays are able to produce laser beams with 435 mm square beam dimensions suitable for fusion applications. Additionally, in some embodiments, the inner cone 324 is characterized by an angle of 26.9° and the outer cone 322 is characterized by an angle of 47.25°, but these particular angles are not required by the present invention. As an example, in other embodiments, the cone angles are 30° and 50°.
• the optical design of the final transport optical system meets many requirements simultaneously, including: the ability to point and center to incoming targets at the target chamber center, efficient transport of the 351 nm light to target chamber center, and focus of the energy into the Laser Entrance Hole (LEH) of the target hohlraum.
• the mirrors M10 and Ml 1 shown in FIG. 1 are used to maintain centering on the final transport optics and slow pointing to the target.
• the lenses L9, L10, and LI 1 in addition to transporting the beam through the first neutron pinhole, also serve to null out the chromatic dispersion induced by the Fresnel final optic, which has the opposite sign relative to traditional convex lenses.
• the grating LG1 compensates for the temporal skew induced by the deflection (diffraction) of the Fresnel final optic and also serves to provide the deflection required between neutron pinhole 1 and 2.
• the Fresnel optic can focus the 351 nm drive laser beam into the LEH of the target.
• Embodiments of the present invention utilize one of several optical elements as the final optic including: a grazing incidence metal mirror (GIMM), an elliptic mirror, a thin Fresnel optic, or the like.
• a grazing incidence metal mirror GIMM
• an elliptic mirror e.g., a thin Fresnel optic
• an additional vacuum window is included in the design upstream (e.g., immediately) of the final optic before the neutron spatial filter.
• This optic serves two purposes among others: to guarantee vacuum at the telescope focus so that the laser light can be transmitted, and to serve as a tritium barrier.
• the Fresnel optic illustrated in FIG. 1 acts as both the final focusing optic and as the vacuum barrier. By making this final optic thin, the neutron induced absorption can be reduced to level of a few percent.
• the angle between the optical axes of the two relay telescopes associated with the neutron pinholes is angled at an angle of about 60 °, this is not required by the present invention and other embodiments utilized different angles between telescopes.
• the first relay telescope is oriented in a horizontal plane and the second relay telescope is oriented in a vertical plane, with a right angle between the two optical axes.
• Other orientations are included within the scope of the present invention in addition to those illustrated.
• One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
• FIG. 3B is a schematic diagram illustrating a final beam transport system including a single neutron pinhole according to an embodiment of the present invention.
• laser sources 350A through 350N are provided in a first region 351.
• Light from the laser sources 350A through 350N is directed toward a shield wall 352, for example, a all 3 m in thickness.
• a set of neutron pinholes 353A through 353N are provided in the shield wall 352 to enable the laser radiation to pass through the shield wall after focusing using a set of optical system (e.g., a set of N relay telescopes).
• this system when this system is referred to as a "single neutron pinhole" system, this can be understood as utilizing a single set of neutron pinholes rather than two sets of neutron pinholes.
• Light passing through the set of neutron pinholes 353A through 353N reflects off parabolic mirrors 360 in the illustrated embodiment to impinge on Fresnel optics 362 and 364.
• the distance between Fresnel optics 326 and 364 is sufficient to enable parabolic mirrors 360 to be positioned under ledge 361. After focusing by Fresnel optic 364, light is focused onto target 386.
• Neutrons generated at the target 386 propagate out in all directions including cone 368, passing through the space between walls 366 and 365. Neutrons to the left of cone 368 are reflected or absorbed by wall 366.
• wall 363 and ledge 361 define the angular spread of cone 368. Although the neutrons impinge on Fresnel optic 364, wall 365 prevents neutrons from impinging on Fresnel optic 362. Because the neutrons are contained between wall 363 and ledge 361 , only a single set of neutron pinholes is needed to reduce the neutron density in region 351 to acceptable levels. [0046] FIG.
• 3C is a simplified schematic diagram illustrating elements of neutron pinhole telescopes according to an embodiment of the present invention.
• a first telescope 370 focuses light through the secondary shield wall 372 to pass through a second neutron pinhole 374.
• the light is refracted through Fresnel optic 376A, which forms an element of a second relay telescope 370.
• the second relay telescope 380 focuses light through the primary shield wall (not shown) to pass through a first neutron pinhole at location 382A.
• multiple, parallel light paths are provided by embodiments of the present invention, providing multiple neutron pinholes passing through the primary and secondary shield walls as illustrated by neutron pinhole 374B, light from which is collected by Fresnel optic 376B.
• Fresnel optic 384A Light passing through the first neutron pinhole at location 382 is incident on Fresnel optic 384A, which collects and focuses the light onto the target 386. Because both grating structures present in Fresnel optics 376A and 384A receive light from a point source and focus light to a corresponding point source, the manufacturing of these Fresnel optics is simplified, enabling a high quality manufacturing process to be utilized.
• a point source is utilized to define the grating structures since light passing through the gratings originates and terminates as a point source. As illustrated, the gratings are receiving divergent light and producing convergence of the received light. Thus, grating exposure can be accomplished using point sources.
• cone angles can be utilized according to embodiments of the present invention, for example, an angle of 26.9° for the inner cone between the target 386 and Fresnel optic 384A and an angle of 47.2 for the outer cone between the target 386 and Fresnel optic 384B.
• the manufacturing process is improved in comparison to other architectures since point sources can be utilized in the grating definition process.
• Fresnel optics manufactured for use in embodiments as illustrated in FIG. 3C have reduced aberrations in comparison with Fresnel optics in which a divergent beam is collimated.
• the inventors note that the neutron-induced absorption in fused silica saturates at fairly modest neutron irradiation levels, and this absorption can be partially annealed by raising the temperature of the substrate as illustrated in FIG. 4 A.
• a 5.3 mm thick fused silica substrate is utilized for the Fresnel optic, which is sufficient to serve as the vacuum barrier between the target chamber at 21 torr and the relay telescope at approximately 0.5 mtorr.
• the inventors have determined that if an optic of sufficient thickness (e.g., a 5.3 mm thick optic) is maintained at -580 °C, the absorption loss is reduced to ⁇ 0.5%. As illustrated in FIG.
• FIG. 4A is a graph illustrating corrected transmission percentage as a function of wavelength for a final optic according to an embodiment of the present invention.
• FIG. 4B is a graph illustrating laser absorption versus temperature for a 5.3 mm thick fused silica optic.
• FIG. 4A the annealing processing of neutron damaged silica demonstrates a large change in 351 nm transmission as a result of the annealing process.
• a shock wave generated by the target ignition will be incident on the final optic.
• FIG. 5 is a simplified graph illustrating a shock pressure waveform incident on the final optic according to an embodiment of the present invention.
• FIG. 6A is a contour plot illustrating induced stress in the final optic from the target ignition shock.
• FIG. 6B is a contour plot illustrating the maximum displacement of the final optic from target ignition shock. As illustrated in FIGS.
• This optic can be mounted in a frame that can be sealed using a gasket seal to a transport telescope containing a neutron pinhole, which is a large cement structure connected to the building.
• the aperture of the fused silica optic is approximately 0.53 x 43 x 49.65 cm 3 (43cm aperture at angle of 30°) with an external pressure of 21 torr (2800 Pa) and an internal pressure of 0.5 mtorr, which results in 134 pounds of force on the surface of the optic.
• mounting of the final optic can be designed to avoid resonance at the modal frequency or induced vibration from the building due to the previous shot and/or support equipment fluid flow (e.g., blankets, cooling, or the like).
• Engineering of passive damping mechanisms for the vibration can be performed based on the spectrum for this final optic including effects based on the chamber environment and the mechanical mounting hardware design.
• the global maximum effective surface stress is 4.06 x 10 4 with a global minimum of zero.
• the global maximum displacement of the final optic is 2.62 x 10 "6 m and the global minimum displacement is -2.47 x 10-6.
• Embodiments of the present invention provide methods and systems for
• FIG. 7A a system for replacement of the thin Fresnel optic 705 is provided that does not utilize any hydraulic or motorized devices in the high radiation area.
• this system and method uses cables with pulleys or rollers to guide damaged Fresnel lenses out of the high radiation environment through curved slits in the shield wall that serve as neutron labyrinths but allow exchange of the final optic.
• FIG. 7B A close- up of one of these labyrinths is shown in FIG. 7B with dimensions that are used in an exemplary embodiment suitable for neutronics modeling.
• the kinematic mounts are reversed, with the magnets and kinematic registration points provided on the opposing elements (i.e., magnets mounted on the LRU and registration points on the telescope end face).
• the Nd-based high power magnets which may be replaced with other suitable high strength to mass ratio magnets
• the Fresnel optic and vacuum gasket 830
• the precision frame can be fabricated from a rigid material such as stainless steel with cable attachments 840.
• two pairs of cable drives are provided as shown in the front view illustrated in FIG. 8B.
• Embodiments of the present invention operate such that the pressure of this environment is low ( ⁇ 21 torr), which will prevent all but the lightest of particulates from remaining suspended in the chamber gas and thereby promote cleanliness.
• Gas purge nozzles can be located in the region of the final optic with their ultimate purpose being both to provide counter flow pressure to offset the "puffs" of chamber gas from target ignition and also to provide a low pressure "air knife” to clean the final optic as it is being replaced and maintain that cleanliness during operations. Control of this purge flow rate can be done using pneumatic valves located in low radiation areas outside of the primary shield wall. During maintenance operations this purge pressure can be briefly increased to enable gas cleaning of the final optic to meet requirements.

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• General Engineering & Computer Science (AREA)
• High Energy & Nuclear Physics (AREA)
• Particle Accelerators (AREA)
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• 2012
  • 2012-01-24 EP EP12739844.4A patent/EP2668652A2/fr not_active Withdrawn
  • 2012-01-24 WO PCT/US2012/022443 patent/WO2012103150A2/fr not_active Ceased
  • 2012-01-24 CA CA2824080A patent/CA2824080A1/fr not_active Abandoned
  • 2012-01-24 RU RU2013139868/07A patent/RU2013139868A/ru not_active Application Discontinuation
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