Deployment, commissioning, and operation of plasma electrode Pockels cells in the National Ignition Facility

Abstract

Large aperture Plasma Electrode Pockels Cells (PEPCs) are an enabling technology in the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory. The Pockels cells allow the NIF laser to take advantage of multipass main amplifier architecture, thus reducing costs and physical size of the facility. Each Pockels cell comprises four 40-cm x 40-cm apertures arranged in a 4x1 array. The combination of the Pockels cell and a thin-film polarizer, also configured in a 4x1 array, forms an optical switch that is key to achieving the required multi-pass operation.The operation of the PEPC is a follows: Before the arrival of the laser pulse, optically transparent, low-density helium plasmas are initiated to serve as electrodes for the KDP crystals mounted in the Pockels cell. During beam propagation through the main laser cavity a longitudinal electric field is impressed on the electro-optic crystals. The polarization of the propagating beams is rotated by 90° on each of two passes, thereby allowing the beam to be trapped in the main laser amplifier cavity for a total of four passes before being switched out into the cavity spatial filter.The physics aspects of the PEPC are well documented. Consequently, this paper will emphasize the PEPC subsystem in the context of its role and relevance within the broader NIF laser system, provide a view of the complexity of the subsystem and give an overview of PEPC's interactions with other elements of NIF, including interfaces to the Beamline Infrastructure, the NIF Timing Subsystem, and the Integrated Computer Control System (ICCS); along with dependence on the Optics Production, Transport and Handling (T&H), and Assembly, Integration and Refurbishment (AIR) and Operations organizations. Further, we will discuss implementation details related to the functional blocks and individual components that comprise PEPC, with particular emphasis on the unique constraints placed on the elements and the attendant engineering solutions. Finally, we describe performance, fabrication and assembly requirements unique to PEPC and the various considerations necessary for successfully commissioning and operation of each PEPC unit. These considerations include, but are not limited to, materials choices, materials preparation and processing (especially cleanliness), inspection, pre-and post-assembly testing.

Interferometric adaptive optics for high-power laser pointing, wavefront control, and phasing

“…The plasma electrode on the PEPC is activated every 5 seconds for approximately 3 minutes before the shot. 12 This involves formation of the plasma electrode ~15 μsec before the "nominal" laser shot and a 400 ns, 17kV pulse that activates the PEPC once the laser is within the main amplifier cavity. The existing PEPC electronics would have to undergo a significant redesign to accommodate a plasma formation and high voltage pulse a 100-200 microseconds before the laser pulse.…”

The National Ignition Facility: enabling fusion ignition for the 21st century

“…Detailed descriptions of NIF's laser architecture and the performance of the laser system have been presented recently [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The NIF laser system is shown in figure 1.…”

A High Current, High Voltage Solid-State Pulse Generator for the NIF Plasma Electrode Pockels Cell

“…Described in detail in previous publications, the NIF PEPC is an enabling technology, permitting the facility to take advantage of a four-pass architecture, reducing the overall size and cost of the laser. 1,2 Briefly, the Pockels cell, used in combination with an optical polarizer, forms an optical switch that can be employed to trap and then release a beam from an optical cavity, thereby taking full advantage of the available optical gain. PEPC interacts with the beam on its second and third passes through the main amplifier, introducing successive 90º polarization rotations that allow the beam to pass through and then reflect off a thin film polarizer.…”