Date of Award:
Master of Science (MS)
Jan J. Sojka
This study presents the development, calibration, characterization, and use of new instrumentation for in situ measurements of electron-beam-induced surface voltage. The instrument capabilities allow for measurements of a full range of insulating materials that are of concern to NASA spacecraft charging experts. These measurements are made using moveable capacitive sensor electrodes that can be swept across the sample using an in vacu stepper motor. Testing has shown a voltage range of more than ±30 kV with a low-voltage resolution of 0.2 V. The movable sensors allow for a radial measurement of surface voltage with spatial resolution as low as 1.5 mm. The instrumentation has response time of ~7 s from the time the beam is shut off until the probe is in position to take data and uses computer automation to stabilize the system and acquire data over the period of several days or longer.
Three types of measurements have been made on two prototypical polymeric spacecraft materials, Low-density Polyethylene (LDPE) and polyimide (KaptonTM HN), to illustrate the research capabilities of the new system. Surface voltage measurements were made periodically during the charging process using a pulsed electron beam and subsequently as the surface voltage discharged to a grounded substrate; these were used to obtain information about the material’s electron yields and bulk resistivity. The spatial profile of the voltage across the sample surface was also measured by sweeping the electrode across the surface. Subsequent measurements monitored the time evolution of the magnitude and spatial charge distribution as charge dispersed radially across the sample surface. The results of these measurements are present and compared to literature values validating the instrument’s effectiveness.
Hodges, Joshua, "In Situ Measurements of Electron-Beam-Induced Surface Voltage of Highly Resistive Materials" (2012). All Graduate Theses and Dissertations. 1416.
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