This paper describes the hardware changes made to the triggering system of the HERMES III accelerator at Sandia National Laboratories, New Mexico. The HERMES III accelerator is a gamma ray simulator producing 100 kRad dose per shot with a full width half max pulse duration of approximately 25 nanoseconds and averaging six shots per day. For each accelerator test, approximately 400 probe signals are recorded over approximately 65 digitizers. The original digitizer trigger system employed numerous independent legacy signal generators resulting in non-referenceable digitizer time bases. We detail our efforts to reference the digitizer time bases together using a modular and scalable approach with commercial-off-the-shelf components. This upgraded trigger system presently measures a maximum digitizer trigger time spread of less than two nanoseconds across the 65+ digitizers. This document details the hardware changes, provides a summary of the accelerator charging process, presents 'one-line' trigger system diagrams and summarizes the times of interest for a typical HERMES accelerator shot.
This paper describes the software changes made to the data processing and display system for HERMES III accelerator at the Simulation Technology Laboratory (STL) at Sandia National Laboratories, New Mexico. The HERMES III accelerator is a gamma ray simulator producing 100kRad[Si] dose per shot with a full width half max pulse duration of 25 nanoseconds averaging six shots per day. For each accelerator test approximately 400 probe signals are recorded over approximately 65 digitizers. The original data processing system provided the operator a report summarizing the start of probe signal timings for groups of probes located within the power flow conductors. This timing information is indicative of power flow symmetry allowing the operator to make necessary adjustments prior to the next test. The report also provided data overlays concerning laser trigger light output, x-ray diode currents and x-ray source output. Power flow in the HERMES III accelerator is comprised of many circuit paths and detailed current and voltage information within these paths could provide a more thorough understanding of accelerator operation and performance, however this information was either not quickly available to the operators or the display of the data was not optimum. We expanded our data processing abilities to determine the current and voltage amplitudes throughout the power flow conductors and improved the data display abilities so data plots can be presented in a more organized fashion. We detail our efforts creating a software program capable of processing the 400 probe signals together with an organized method for displaying the dozens of current and voltage probes. This process is implemented immediately after all digitizer data has been collected so the operator is provided timing and power flow information shortly after each accelerator shot.
The HERMES III accelerator at Sandia National Laboratories is a 20-cavity multi-stage linear induction voltage accelerator typically producing a 20-MV, 40-ns, 600-kA output pulse. Energy is initially stored in Marx banks that are each discharged into two intermediate store capacitors. Each of these capacitors are then switched with an SF6-insulated high voltage Rimfire gas switch into four parallel pulse forming lines that further condition the discharge pulse and deliver it to the induction cavities arrayed along the axis of the machine. Presently, a single 0.9-J KrF laser operating at 248 nm, the output of which is divided into twenty beams, is used to trigger the 20 rim-fire switches. As part of an upgrade to the accelerator, however, a new solid state laser triggering system is being designed to replace this system and provide additional capabilities for the accelerator. The laser triggering system will be made up of 10 discrete compact flash-lamp pumped, Q-switched Nd:YAG lasers (Tempest 300), each having an output energy of 40 mJ at a wavelength of 266 nm. As each laser will be responsible for triggering only two of the rim-fire switches, it becomes possible to shape the output pulse by varying the times at which the individual lasers fire. Overall reliability for the accelerator's operation with these new lasers will be increased, as well. The general layout of this new laser triggering system design will be presented, along with details pertaining to the triggering of the lasers and the optical beam paths.
The HERMES III accelerator, which is located at Sandia National Laboratories' Tech Area IV, is the largest pulsed gamma X-ray source in the world. The accelerator is made up of 20 inductive cavities that are charged to 1 MV each by complex pulsed power circuitry. The firing time of the machine components ranges between the microsecond and nanosecond timescales. This results in a variety of electromagnetic frequencies when the accelerator fires. Testing was done to identify the HERMES electromagnetic noise signal and to map it to the various accelerator trigger events. This report will show the measurement methods used to capture the noise spectrum produced from the machine and correlate this noise signature with machine events.
The Sandia National Laboratories SPHINX accelerator is used to study the response of electronics to pulsed x-ray and electron environments. The system consists of a Marx generator and an oil-insulated pulse-forming line with self-closing oil switches. SPHINX has a peak load voltage of 2 MV and an adjustable pulse width ranging from 3 to 10 ns. The previous pulsed-power system had reliability and triggering issues with the Marx generator and subsequent undesired variations in voltage output. SPHINX was upgraded to a new Marx-generator system that has solved many of the voltage-output fluctuation and timing issues. The new Marx generator uses recently developed low-inductance 100-kV capacitors and 200-kV spark-gap switches. This paper provides an overview of SPHINX while capturing in detail the design, characterization, and comparative performance of the new Marx generator.
A new laser trigger system (LTS) has been installed on Z that benefits the experimenter with reduced temporal jitter on the x-ray output, the confidence to use command triggers for time sensitive diagnostics and the ability to shape the current pulse at the load. This paper presents work on the pulse shaping aspects of the new LTS. Pulse shaping is possible because the trigger system is based on 36 individual lasers, one per each pulsed power module, instead of a single laser for the entire machine. The firing time of each module can be individually controlled to create an overall waveform that is the linear superposition of all 36 modules. In addition, each module can be set to a long- or short-pulse mode for added flexibility. The current waveform has been stretched from ∼100 ns to ∼250 ns. A circuit model has been developed with BERTHA Code, which contains the independent timing feature of the new LTS to predict and design pulse shapes. The ability to pulse-shape directly benefits isentropic compression experiments (ICE) and equation of state measurements (EOS) for the shock physics programs at Sandia National Laboratories. With the new LTS, the maximum isentropic loading applied to Cu samples 750 um thick has been doubled to 3.2 Mb without generating a shockwave. Macroscopically thick sample of Al, 1.5 mm, have been isentropically compressed to 1.7 Mb. Also, shockless Ti flyer-plates have been launched to 21 km·s-1, remaining in the solid state until impact.