室动力学和结算先进能源.pptxVIP

室动力学和结算先进能源第1页/共20页 Plans from the last Meeting1) Error in Temperature Measurement:Thermometer is calibrated based on melting point of W (3,700K). This leads to relatively larger errors (~10-15%) in lower temperatures (~2,000-2,500oC).At present, thermometer cannot measure temperature below ~2,000oCAbove issues will be addressed before next set of runs:Upgrade of the thermometer (Absolute calibration, lower temperature)In-vacuum re-positioning of laser imprint/thermometer2) Profilometry of treated sample3) Test samples at lower temperature (i.e., lower laser energy)4) Test sample with He from UW第2页/共20页 Thermometer Calibration第3页/共20页 History of Thermometer Calibration IssuesDevelopment of single-fiber based thermometer coincided with rebuilt of our laser and reduction of laser output to achieve a smoother spatial profiles.Afterwards only one flat region was observed in T vs E measurements.The thermometer was giving the maximum temperature of about 5,000K for the flat region (W melting= 3,700K, evaporation = 6,000K).It was assumed that thermometer calibration at low frequencies (mechanical chopper) should be different than high-frequency response needed for laser irradiation.Could not find a way to calibrate at higher frequencies.Early measurements of temperature rise versus laser energy (multiple-fiber based thermometer).The two flat regions were identified as melting and evaporation regions.第4页/共20页 Detailed modeling indicates that: Thermometer will not see the meltingPlateau (duration is too short).Large sublimation above the melting point . Calculation from R. Raffray with a 8ns square pulseAbsolute Calibration Is Now AchievedManaged to reduce the light pulses from chopper wheel to ~100 ms intervals. Thermometer calibration was checked against an electronic camera flash (10-20 ms, ~5,500K).Temperature measurement as low as 1,500K was achieved with thermometer in mid-gain (1,000K reading with high gain is expected).第5页/共20页 Measured Temperature Rise in WRamp d