Our research focused on obtaining a fundamental understanding of the source and properties of EMP at the Titan PW(petawatt)-class laser facility. The project was motivated by data loss and damage to components due to EMP, which can limit diagnostic techniques that can be used reliably at short-pulse PW-class laser facilities. Our measurements of the electromagnetic fields, using a variety of probes, provide information on the strength, time duration, and frequency dependence of the EMP. We measure electric field strengths in the 100's of kV/m range, durations up to 100 ns, and very broad frequency response extending out to 5 GHz and possibly beyond. This information is being used to design shielding to mitigate the effects of EMP on components at various laser facilities. We showed the need for well-shielded cables and oscilloscopes to obtain high quality data. Significant work was invested in data analysis techniques to process this data. This work is now being transferred to data analysis procedures for the EMP diagnostics being fielded on the National Ignition Facility (NIF). In addition to electromagnetic field measurements, we measured the spatial and energy distribution of electrons escaping from targets. This information is used as input into the 3D electromagnetic code, EMSolve, which calculates time dependent electromagnetic fields. The simulation results compare reasonably well with data for both the strength and broad frequency bandwidth of the EMP. This modeling work required significant improvements in EMSolve to model the fields in the Titan chamber generated by electrons escaping the target. During dedicated Titan shots, we studied the effects of varying laser energy, target size, and pulse duration on EMP properties. We also studied the effect of surrounding the target with a thick conducting sphere and cube as a potential mitigation approach. System generated EMP (SGEMP) in coaxial cables does not appear to be a significant at Titan. Our results are directly relevant to planned short-pulse ARC (advanced radiographic capability) operation on NIF.

We measured the absolute response of image plate (Fuji BAS SR2040) for electrons at energies between 100 keV and 4 MeV using an electron spectrometer. The electron source was produced from a short pulse laser irradiated on solid density targets. This paper presents the calibration results of image plate photon stimulated luminescence per electron at this energy range. The Monte Carlo radiation transport code MCNPX results are also presented for three representative incident angles onto the image plates and corresponding electron energy depositions at these angles. These provide a complete set of tools that allows extraction of our absolute calibration to other spectrometer setting at this electron energy range.

DECLNMER UPGRADES TO THE LLNL FLASH X-RAY INDUCTION LINEAR ACCELERATOR (FXR)The FXR is an induction linear acceleratorused for flash radiography at the Lawrence Livtmnore National Laboratory's Site 300 Test Facility. The FXR was originally completedin 1982and has been in continuoususe as a radiographictool. At that time the FXR produceda 17MeV, 2.2 kA burst of electronsfor a duration of 65 ns.An upgrade of the FXR was recentl completed. The purpose of this upgrade was to improve the performanceof the FXl by increasing the energy of the electron injector from 1.2 MeV to 2.5 MeV and the beam current from 2.2 kA to 3 kA, improving the magnetictransport system by redesigningthe solenoidaltransport fms coils, reducing the rf coupling of the electron beam to the accelerator cells, and by adding additional beam d@OStiC&We will desmibethe injectur upgradesand pdbrmanc~as well as our effbrts to tune the acceleratorby~g beam corkscrew motion and the impact of Beam Breakup Instabilityon beam centroidmotionthroughoutthe beam line as the currentis increasedto 3 kA.

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