Progress in Chamber Simulation Experiments At UCSD Laser Facility Farrokh Najmabadi Kevin Sequoia, Sophia Chen HAPL Meeting September 24-25, 2003 University of Wisconsin, Madison Electronic copy: UCSD IFE Web Site:

Thermo-Mechanical Response of Chamber Wall Can Be Explored in Simulation Facilities Capability to simulate a variety of wall temperature profiles Requirements: Capability to isolate ejecta and simulate a variety of chamber environments & constituents Laser pulse simulates temperature evolution Vacuum Chamber provides a controlled environment A suite of diagnostics:  Real-time temperature (High-speed Optical Thermometer)  Per-shot ejecta mass and constituents (QMS & RGA)  Rep-rated experiments to simulate fatigue and material response Relevant equilibrium temperature (High-temperature sample holder) A suite of diagnostics:  Real-time temperature (High-speed Optical Thermometer)  Per-shot ejecta mass and constituents (QMS & RGA)  Rep-rated experiments to simulate fatigue and material response Relevant equilibrium temperature (High-temperature sample holder)

Status of Diagnostics Development and Fielding  High temperature sample holder has been operational for quite some time.  RGA system was installed on the chamber and is routinely used to monitor chamber environment. No trace of W was found in the chamber (from heating filament of the high-temperature sample holder).  QMS was tested but has been removed form the chamber until we are ready for test runs.  Fast Optical Thermometer: Proof-of-principle was demonstrated about 5 months ago. Focus of our effort has been on improving system reliability and user friendliness: Major progress, unexpected problem.  High temperature sample holder has been operational for quite some time.  RGA system was installed on the chamber and is routinely used to monitor chamber environment. No trace of W was found in the chamber (from heating filament of the high-temperature sample holder).  QMS was tested but has been removed form the chamber until we are ready for test runs.  Fast Optical Thermometer: Proof-of-principle was demonstrated about 5 months ago. Focus of our effort has been on improving system reliability and user friendliness: Major progress, unexpected problem.

Real-time Temperature Measurements Can Be Made With Fast Optical Thermometry Temperature deduction by measuring radiance at fixed  One-color: Use tables/estimates for  (   )  Two colors: Assume  ( 1,T) =  ( 2,T)  Three colors: Assume d 2  /d   [usually a linear interpolation of Ln(  ) is used] Temperature deduction by measuring radiance at fixed  One-color: Use tables/estimates for  (   )  Two colors: Assume  ( 1,T) =  ( 2,T)  Three colors: Assume d 2  /d   [usually a linear interpolation of Ln(  ) is used]  Spectral radiance is given by Planck’s Law (Wien’s approximation): L(,T) = C 1  (,T) -5 exp(-C 2 / T)  Since emittance is a strong function of, T, surface roughness, etc., deduction of temperature from total radiated power has large errors.  Spectral radiance is given by Planck’s Law (Wien’s approximation): L(,T) = C 1  (,T) -5 exp(-C 2 / T)  Since emittance is a strong function of, T, surface roughness, etc., deduction of temperature from total radiated power has large errors. Our observations  Two-color method achieves sufficient accuracy (~1%). Three-color method is too difficult. Our observations  Two-color method achieves sufficient accuracy (~1%). Three-color method is too difficult.

Schematic of Multi-Color Fiber Optical Thermometer System is configured as three independent two- color thermometer

 Temperature is calculated from measurement of radiated energy at two wavelengths:. Calibration of Thermometer  Calibration is difficult because the lamp filament is discontinuous – image point should be exactly on the lamp filament.  We developed the protocol to reliably calibrate the thermometer (in <5 minutes).  Calibration is so accurate that one point calibration is sufficient to ensure < 1% accuracy over T=1,500-3,500 K  Calibration is difficult because the lamp filament is discontinuous – image point should be exactly on the lamp filament.  We developed the protocol to reliably calibrate the thermometer (in <5 minutes).  Calibration is so accurate that one point calibration is sufficient to ensure < 1% accuracy over T=1,500-3,500 K Thermometer is calibrated with a tungsten lamp (calibrated for 7 temperatures in the range 1,500-3,500 K)

Thermometer Data Acquisition System  We have developed the software for downloading, post processing, and plotting of the thermometer data. Same interface is used for both calibration and data acquisition  We have developed the software for downloading, post processing, and plotting of the thermometer data. Same interface is used for both calibration and data acquisition Graphical User Interface Temperature PMT2 signal Significant reduction in the noise level

. Thermometer Reliability  Test 1: Successive calibration: the basis for developing calibration protocol.  Test 2: Chamber installation test: thermometer is removed from calibration stand, mounted in the chamber, returned to calibration stand. Calibration held in repeated tries  Test 2: Chamber installation test: thermometer is removed from calibration stand, mounted in the chamber, returned to calibration stand. Calibration held in repeated tries  Test 3: Long-term reliability, i.e., how long the calibration is holding. Calibration is lost in the hour time scale: limited set of data; maximum deviation is ~20%, data is stochastic. Likely problem are the PMTs.  Test 3: Long-term reliability, i.e., how long the calibration is holding. Calibration is lost in the hour time scale: limited set of data; maximum deviation is ~20%, data is stochastic. Likely problem are the PMTs.

Current Activities Improving Thermometer reliability:  We are in discussion with PMT manufacturer  We are developing 6-GHz amplifier system (30-40 dB gain) to replace PMTs with PD/amplifier system. The major issue here is achieving the desired signal to noise ratio. Improving Thermometer reliability:  We are in discussion with PMT manufacturer  We are developing 6-GHz amplifier system (30-40 dB gain) to replace PMTs with PD/amplifier system. The major issue here is achieving the desired signal to noise ratio. Slower/Cheaper Thermometer:  We have built a two-color thermometer with 50MHz bandwidth (20 ns resolution). This system is based on a single fiber connector and photodiodes with build-in amplifier.  The single fiber head has worked so well that we are modifying the high- speed thermometer head accordingly Slower/Cheaper Thermometer:  We have built a two-color thermometer with 50MHz bandwidth (20 ns resolution). This system is based on a single fiber connector and photodiodes with build-in amplifier.  The single fiber head has worked so well that we are modifying the high- speed thermometer head accordingly

Current Thermometer Fiber Has a High Insertion Loss and Is Quite Sensitive to Positioning  Insertion loss is very high  Uneven signal  Insertion loss is very high  Uneven signal  Fibers image four distinct points on the sample. Very sensitive to surface non-uniformity

We Have Demonstrated 4X Improvement In Insertion Loss With Single Fiber Coupler Single fiber from thermometer head Band-pass filter/focuser PMT or PD Expander/neutral filter assembly splitter  Can be configured with 2 or 4 channels (4 channel version is shown).  4 channel version would allow looking at IR band in order to extend temperature measurement to much lower temperature.  Can be configured with 2 or 4 channels (4 channel version is shown).  4 channel version would allow looking at IR band in order to extend temperature measurement to much lower temperature.