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ISS Fiber Status

ISS Fiber Status. C.T. Mueller J. G. Coffer T. Giants IA 3/8/2000 (updated with results on 3/9/2000). Outline. Material Analysis of “spheres” and “rods” by EDAX (not presented)* Fiber absorption spectrum (not presented)* ESD theory experiments

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ISS Fiber Status

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  1. ISS Fiber Status C.T. Mueller J. G. Coffer T. Giants IA 3/8/2000 (updated with results on 3/9/2000)

  2. Outline • Material Analysis of “spheres” and “rods” by EDAX (not presented)* • Fiber absorption spectrum (not presented)* • ESD • theory • experiments • Measurement of bubble defects by Coherent Reflectometer (not presented)* • * A bomb scare took up some of the morning and we ran out of time at the meeting. This data will be sent out by email and discussed during the weekly teleconferences.

  3. Fiber Spectrum • Responded to request to assess whether hydrogen-induced absorption was an issue in the ISS Fiber • examined package of spectra taken by Dale Zevotek. at BiccGeneral • performed in-house measurement on 40 m of 1996 vintage cable • Observations (see next slide) • SiOH (1.39 µm) and GeOH (1.43 µm) evident in spectrum, as expected for optical fibers • insignificant amount of permanent hydrogen OH absorption • no evidence of molecular hydrogen peak at 1.24 µm • Long wavelength absorption edge related to Boron doping in the core

  4. Spectrum of ISS Fiber: 1996

  5. ESD Data we have • Electrical field data from BiccGeneral • Polyimide physical properties • dielectric constant and breakdown field strength • Dimensions • Carbon resistance Theory • model from electrostatics Experiment • resistance • tested 0-1000 V, 0-2000 V, 0-5000 V

  6. Electric Field inside Dielectric is Always Less than Electric Field outside it • charges redistribute to produce an internal electric field opposing the external field --> field strength reduced by dielectric constant Eo E

  7. Re-spooler Layout Pulley #2 E2(volts/in) Pulley #1 E1 (volts/in) carbon E2p polyimide polyimide E1p carbon

  8. ESD “Ground” Rules • Polyimide is a dielectric • it can charge and create an electric field around it • or it can effectively insulate two conductors at two different voltages and support an electric field within it i.e. be inserted into an electric field • To break down a dielectric, the electric field must exceed the a critical field or dielectric strength given in volts per unit length • If the only the pulleys charge, the polyimide will simply be immersed in the electric field • If the polyimide charges up it will create electric fields both inside and outside • If both charge up, combination of above Worst Case • Assume measurements of field strength were radial fields created by the pulleys • Ignore the reduction of the E-field inside the polyimide and base conclusions on dielectric strength of polyimide coating

  9. ESD Measurements at BiccGeneral • Two meters (furnished by NASA Goddard) were used to measure the electric field strengths near the fiber and the pulleys when the re-spooler was in operation. • No manuals were provided with these instruments • These meters may have difficulty measuring fields due to a line of charge, such as the fiber, but should respond well to sheets of charge like the pulleys • The highest field strength differences measured at BiccGeneral were: • 3.1 kV/in at a re-spooling speed of 20 m/min • 4.5 kV/in at a “ “ “ 50 m/min

  10. Assume a Radial Field E1 • Worst case polyimide E1p carbon Cross section of Polyimide/Carbon-Coated Fiber

  11. E1p = E1/k, where k = dielectric constant E2p = E2/k Open Closed E1 E1 polyimide E1p E1p Pulley #1 carbon carbon Pulley #2 E2p E2p polyimide E2 E2

  12. ESD Analysis • Polyimide (ref: Dupont Bulletin #PC-1 Table II) • dielectric constant = 3.5 • dielectric strength = 4000 v/mil (4000 kV/in) [air is 20-77 kV/in] • although the dielectric strength per unit thickness generally increases as the thickness of the coating decreases, this corresponds to 2400 V for 15 microns) • Measured electric fields at BiccGeneral were • -3.5 kV/in to + 0.05 kV/in at re-spool rate of 20 m/min • 0 kV/in to -4.0 kV/in at re-spool rate 50m/min • Choose max of 4.5 kV/in

  13. ESD Experiments • Stripped polyimide • completely for resistance tests • from ends to contact carbon coating for ESD tests • Measured resistance per unit length to be 15 kohm/cm • ESD (0-1000 V), (0-2000 V), and (0-5000 V) • Limited current by placing voltage across small capacitors • Electric field place across polyimide along entire length of fiber • 1st electrode: aluminum foil surrounding the polyimide coating • 2nd electrode: carbon coating • digital multimeter used to sample voltage across polyimide coating • No breakdown occurred below 2000 V as expected (later experimental results by Aerospace show breakdown occurred at 3900V) • pristine fiber • 3/31/99 fiber (in work) • 1996 vintage fiber (in work)

  14. Resistance of Carbon Layer 15 km/cm

  15. ESD Test Setup Polyimide Coating Fiber with carbon coating Al foil Al foil 0 - 1 kV DC Power Supply Capacitor and Switch in box (grounded) - + .001µF

  16. High Voltage ESD Setup • Insert circuit diagram for high voltage measurements showing resistance bridge in place of capacitors, switch, etc. • High voltage power supply, two 20 Mohm resistors in series, manual switch, DVM (100 Mohm) • Breakdown occurred at 3900 V 20 M 0-5 kV 20 M Fiber DVM

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