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A high-speed mass spectrometer for characterizing flash desorbed species in pulsed power applications




Ossareh, Susan J., author
Williams, John D., advisor
Yalin, Azer P., committee member
Roberts, Jacob L., committee member

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Sandia National Laboratories operates the largest pulsed power facility in the world that hosts the Z machine that is utilized for research in fusion, energy, and national security. It can simulate extreme environments in these research areas in a single "shot" or "pulse of power," where large capacitor banks are rapidly discharged simultaneously, sending power to the center of the machine where a load is compressed into a z-pinch. A shot on the Z machine occurs in 150ns with peak currents on the order of 26 mega-amperes. However, there is a power flow obstacle that limits its ability to reach these extreme conditions. Approximately 1-3 MA of current is lost per shot. This could be partially attributed to chemisorbed contaminants on the cathode and anode stack in the center section of the machine being liberated in a flash desorption process, forming a conductive plasma between the anode and cathode electrodes that causes current to bypass the load and limits the power flow into the load. This project is focused on the design and development of a high-speed mass spectrometer to make measurements of the gasses evolved from the electrodes that are heated to 1000°C in 100 nanoseconds. The measurements from this diagnostic would allow for more accurate predictive modeling of current loss for Next Generation Pulsed Power Drivers, such as the Z machine. Since a probe does not exist commercially, the project requires the development of new mass spectrometry technology, however a pre-existing probe was used to begin the design process. This probe is known as the Energy and Velocity Analyzer for Distributions of Electric Rockets (EVADER) probe, which combines an electrostatic analyzer and a Wien velocity filter. Within this study, two different plasma sources were used separately to simulate the plasma generated in the Z machine, and steady state measurements were made of the ions produced while working towards taking transient measurements. The design and development efforts described in this thesis were guided by: (1) using the EVADER to collect steady state data in its original configuration as a basis of comparison, (2) then replacing an ammeter in the experimental system with a transimpedance amplifier (TIA) circuit to speed up the data sampling rate over that of the ammeter, (3) incorporate a micro-channel plate within the probe to amplify the current feed to the TIA and enable even faster data sampling rates, and (4) design a high speed electric shutter to quickly turn "on" and "off" ion flow to the probe to enable measurement of the temporal response of the probe with the transimpedance amplifier and micro-channel plate elements. The end goal of the project is to improve transient performance of a probe from 10s of seconds to 10s of micro-seconds in a stepwise manner to support pulsed power research.


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