Based on NIF technology and developed with the assistance of LLNL scientists, a new plasma-electrode Pockels cell (PEPC) was developed at LLE for the OMEGA EP system. The LLE-engineered PEPC was assembled and active plasma testing was initiated. This single-unit electro-optic switch is an adaptation of the NIFPEPC design with circular windows and a single-beam plasma channel.
Photograph of OMEGA EP plasma electrode Pockels cell assembly
Work continues on the design of the OMEGA EP amplifiers. The LLE-designed amplifier configuration is similar to amplifiers currently used in the 60-beam OMEGA Laser System. However, each OMEGA amplifier uses four laser disks, while the OMEGA EP prototype amplifier will contain a single rectangular slab. Ultimately, 11 of these modules will be used in the main amplifier and five will be used in the booster amplifier. Other requirements include a modular design (three major assemblies: the amplifier frame assembly, the slab frame assembly, and the pump module); water-cooling for glass components; the ability to take at least one shot every two hours (i.e., the optics must cool down within this time frame to prevent damage); the ability to accommodate a 40-cm square laser beam, and maintenance similar to the existing OMEGA amplifiers.
Shown here is a Prototype laser amplifier with Jack Kelly, Milt Shoup, Drew Maywar, and Mike Miller
A major enhancement to the OMEGA Laser System, OMEGA EP (extended performance), included four new high-energy beamlines, a versatile high-intensity capability, and a new auxiliary target chamber. Construction began on 1 April 2003 with $13 million in FY03 funding. The National Nuclear Security Administration (NNSA) approval of “Mission Need” followed in May 2003. The University of Rochester authorized funding for an 82,000-square foot addition to LLE to house the new facility located adjacent to the existing OMEGA laser. Building construction began in August 2003 and was completed in January 2005.
OMEGA EP groundbreaking (Capt. Steven J. Loucks, Dr. Robert L. McCrory, Mr. Samuel F. B. Morse, and Mr. R. Wayne LeChase)
LLE is contracted to coat, assemble, and acceptance test deformable mirrors for use on the National Ignition Facility (NIF). LLE’s Optical Manufacturing Group optimizes a low-stress, high-reflectance coating process for the deformable mirror faceplate and has developed an aluminum coating that protects the epoxied post and transducer joint from flash-lamp radiation.
Each deformable mirror includes 39 actuators sandwiched between a coated glass faceplate and a metal reaction block. As the wavefront control system detects beam aberrations, information is sent to the metal reaction block. The actuators push against the reaction block to move the faceplate mirror surface and correct errors in the beam.
Shown here is a Deformable mirror being assembled by manufacturing engineer, Gary Mitchell
LLE scientists made significant progress in developing experimental designs for direct-drive ignition experiments on the NIF. Their 2002 work indicated that it may be possible to carry out high-performance direct-drive implosions on the NIF using the x-ray-drive beam configuration. In preparation for future direct-drive experiments on the NIF, a NIF-scale prototype target assembly was demonstrated at LLE. A 3.175-mm diameter spherical target was mounted onto a 125-µm thick, 7.34-mm-outside-diam Ti ring using four spider-silk strands. The target assembly had a resonant frequency of 125 Hz and was compatible with the NIF target chamber geometry.
Shown here is NIF-scale prototype target assembly
A key element of future ultrahigh-intensity lasers is a stable, high-efficiency laser source capable of generating broad-bandwidth pulses that can be amplified by a high-power amplifier system. Optical parametric chirped-pulse amplification (OPCPA) is a novel laser concept that is well suited for this application. LLE’s OPCPA system demonstrates one of the highest efficiencies for such systems currently available in 2002. The OPCPA concept is based in part on an LLE-invented concept: chirped-pulse amplification (CPA). The CPA idea created a revolution in laser technology by enabling the development of ultrahigh-intensity [i.e., >1015 W (petawatt)] lasers. LLE and LLNL are currently collaborating on the development of large diffraction gratings required for petawatt lasers.
Shown here is LLE’s OPCPA system in the Laser Development Laboratory (LDL)
A new target positioner (planar cryo) was deployed on OMEGA to measure the properties of condensed gasses at cryogenic temperatures. It used a closed-loop cooling system that is fully compatible with the infrastructure developed for spherical cryogenic targets. A single planar cryogenic system can field one target every two hours.
The plot shows the density of a shock propagating through a foam, simulated by the adaptive-mesh refinement code AMRCLAW, in collaboration with Adam Frank and Alexei Poludnenko of the University’s Department of Physics and Astronomy. The work is studying the effects of porosity on shock timing for wetted foam layers relevant to OMEGA and NIF target designs.
Shown here is a Simulation of Rayleigh-Taylor instability with the 2-D hydro code DRACO
With the completion of the improvements to the OMEGA Cryogenic Target Handling System in August 2001, cryogenic target implosions were restarted. Five target shots were successfully performed using layered and characterized thin-wall targets.
Simulations based on ray-tracing calculations show that the 60 OMEGA beams are both reflected from the front of the target and refracted from behind the target into the camera lens. In this way all 60 laser spots are visible in the photograph.
In October 2001, LLE proposed a major enhancement to the OMEGA Laser System to include four new high-energy beamlines, a versatile high-intensity capability, and a new auxiliary target chamber. The high-intensity beams would be generated using the CPA technique originally developed and demonstrated at LLE in 1985.
Shown here is a Preliminary OMEGA EP design
