1 / 10

Progress Report on Charging Measurements at Trinity University

This report discusses the development and implementation of a vacuum-compatible capacitive probe to measure charge magnitude and relaxation time constant on LIGO optics at Trinity University. The report also outlines the setup, measurement results, and potential next steps.

lchampagne
Download Presentation

Progress Report on Charging Measurements at Trinity University

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Progress Report on Charging Measurements at Trinity University Dennis Ugolini, Robert McKinney, Mark Girard Trinity University March LSC Meeting March 21, 2007 Goal: To develop a vacuum-compatible capacitive probe to measure the charge magnitude and relaxation time constant on LIGO optics D. Ugolini, LSC March 2007

  2. The Capacitive Probe • Use chopper to alternately expose/occlude sample • Aluminum probe body with Kapton-shielded wire • Sensitivity calibrated with surface DC voltmeter to be (3.5 +/- 0.5) × 105e-/cm2(to be published in Rev. Sci. Instr.) D. Ugolini, LSC March 2007

  3. Optical Measurement Setup • Chopper shielded by aluminum box • Optic held by viton O-rings epoxied to aluminum clamps D. Ugolini, LSC March 2007

  4. Measurement Setup (cont.) Viton O-rings D. Ugolini, LSC March 2007

  5. Vacuum System Pressure gauge goes here (returned for servicing) Feedthrough (on either side) Glass viewport Pfeiffer-Balzers Turbomechanical drag pump (~10-5 torr) D. Ugolini, LSC March 2007

  6. Obstacles in Moving to Vacuum • Pickup by probe signal lead from chopper driver wires • Used two feedthroughs, one for chopper, one for probe • Chopper wires tied to optical table, kept far from probe lead • Intermittent probe noise peak • Caused by contact between probe lead and nearly anything (chopper shielding box, optical table, walls of the vacuum chamber) • Vibrational or electrical? • Kapton wire is rigid, hold position well • Applied charge decays too rapidly to pump down system • Strong function of humidity, dehumidifier purchased • Spark? • Options for applying charge inside chamber (brush?) D. Ugolini, LSC March 2007

  7. Readout Problem • Finally trapped large charge on optic on February 20th • Probe readout oscillated, didn’t damp out over many hours • Drift in chopper frequency shifted peak on spectrum analyzer • Switched to lock-in amp, used chopper driver as reference D. Ugolini, LSC March 2007

  8. 16-Day Results Corresponds to time constant of ~170 days Appears to level off around day 13 Large phase change on “dropouts” – problem with reference? D. Ugolini, LSC March 2007

  9. UV Discharging Exposed to Hg discharge tube (no UV) for several hours – no effect Exposed to Pen-Ray UV Lamp (253.7nm, 4.4mW/cm2 at 19mm), exhibits discharging shown Glass viewport has ~15% transmission at this wavelength D. Ugolini, LSC March 2007

  10. Summary • Probe has been successfully moved to vacuum • Decay of charge deposited on optical sample has been observed with a time constant of ~170 days • What are the differences between this setup and Moscow State? Optical substrate? Surface contact? Pressure? • Demonstrated UV discharging with glass viewport • Next steps Longer time Triplicate setup Charge vs. position Different substrates, coatings, etc. Besocke Kelvin probe Quartz viewport? Discharging vs. λ? D. Ugolini, LSC March 2007

More Related