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.
The ETA-II linear induction accelerator utilizes four pulse power conditioning chains. Magnetic pulse compression modulators (MAG1-Ds) form the last stage of each chain. A single power conditioning chain is used to drive the injector; the remaining three are used to drive 60 accelerator cells. Nominal parameters of the MAG1-D are an output vohage of greater than 120 kV, pulse width of 70 ns, and an output impedance of 2 ohms. Our operations goal for ETA-II is stable high average power operation at 5 kHz PRF.We have begun upgrading and characterizing the power conditioning chain on our High Average Power Test Stand (HA.PTS). On HAPTS, the pulse to pulse amplitude stability has been improved to less than 0.7% (one sigma) and of order 3-5 ns random jitter about a systematic timing variation. In this paper we describe the status of our work to achieve the desired performance level of the MAG1-D to allow high average power operation of ETA-IL
An array of 24 field-effect transistors (FETs) is being used to switch a nominal 4-kV, I-its pulse onto a Metglas induction core at pulse rates exceeding 100 kHz. Each transistor receives isolated gate power from a de/de converter and analog pulse control via an optical fiber. The array is part of a specialized circuit architecture that generates bursts of pulses while providing for core reset between pulses. The circuit will accommodate variations in pulse width, repetition frequency (prf), pulse amplitude, burst length and reset interval. The various circuit elements are assembled directly onto the core structure to yield a compact, low-impedance package.Two prototype machines are presently under development. A 24-FET machine is :.n operation and capable of 4.2-kV, 1-its pulses (max.) at a 120-ktlz prf for short bursts. Pulse rise and fall times are 25 ns and 65 ns respectively. A 128-FET machine is under construction which should be capable of 6-kV, 1-its pulses (max.) at a 150-kHz prf for long bursts.
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