[Jason, Masayuki]

Summary

The PMC heater calibration was performed last week (Tuesday). The calibration involved adjusting the temperature loop set point and monitoring the corresponding changes in PMC temperature and length. The results were validated using previous measurements and compared to similar evaluations at LLO. Additionally, the necessity of the heater for JAC operations was assessed, highlighting it would be needed for long term operation.

Details

PMC Heater Calibration

• The calibration of the PMC heater was conducted. The PMC remained locked while the temperature loop set point was adjusted from the usual 3.7V to 1.7V. This adjustment corresponds to a PMC length change of 0.30 μm based on a prior measurement (alog entry 81385).
• A PMC temperature change of 0.023 K was recorded using the thermometer. From this result, the thermal expansion coefficient was calculated as:

  0.30 μm / 0.023 K = 13 μm/K

  This result is consistent with the thermal expansion coefficient of aluminum, 22e-6/K, and the approximate PMC length of 0.5 m.
• No significant changes in heater output were detected before and after the set point adjustment.
• First Plot Description:
  • Top panel: PZT input calibrated for PMC length.
  • Middle panel: PMC temperature measured with the thermometer.
  • Bottom panel: Heater output, with histograms shown for the middle and bottom panels.

Reference to LLO Calibration

• To further calibrate the PMC heater, the LLO heater calibration (alog entry 51467, attached plot) was used as a reference.
• At LLO, heater input changes from 2.5V to 4V resulted in PMC temperature changes from 292.2 K to 291.125 K, indicating a heater efficiency of \(0.67 \, \text{K}/\text{V}\). Using this efficiency, the PMC expansion rate per heater voltage was calculated as:

  13 μm/K × 0.67 K/V = 8.7 μm/V

Monthly Drift Analysis

• With this calibration, the monthly heater output was evaluated.
• Second Plot Description:
  • Top panel: Heater-induced temperature actuation (left axis) and the corresponding PMC expansion (right axis).
  • Bottom panel: Required PZT input for equivalent actuation without the heater.
• Periodic large spikes were observed daily. However, since each spike occurred within approximately 10 seconds, as shown in the attached screenshot, these spikes are not attributed to actual temperature changes. A moving median (red line) was applied to highlight the spikes. Note that this moving median is not an ideal representation, as the extracted data is already averaged over 1-minute intervals. However, it is still useful for illustrating the spikes.
• Despite the spikes, the heater compensated for a length change equivalent to approximately 500 V in PZT input is typical day-time drift, but sometime, it can drift more than 1000V in a day.
• A 10-day analysis of LLO PMC showed no spikes, and the results were consistent with LHO data. Result is shown in the third plot as same structure as the second plot.

Implications for JAC Operations

The PZT can be railed in a day from this measurement, so we would need the heater for JAC operation.

Additional Observations

Spikes observed at LHO caused glitches in transmitted power, as shown in the attached plot, and may require resolution. Redesigning the filters could potentially mitigate these anomalies.