EPHIN Rates v Sensor Temperature (5EPHINT)

As we continue to relax the Mission Planning Guideline that covers the EPHIN Thermal Limit, we need to trend the EPHIN performance to monitor for unexpected changes in performance. The plots here show the trends observed during the period from 2011-03-06 to 2011-07-16. During this interval the TEPHIN planning limits was 132 degF (last raised in 2010 December). The interval contains the 2011 July safemode event for which the EPHIN temperature reached a new mission maximum.

EPHIN data were selected for times outside the rad-zone; that is selecting samples after the latest XEF1000 orbital event after perigee and before the earliest EEF100 orbital event before the next perigee. Data from solar events have not been excluded.

There is new behavior observed in detectors B0 and C for temperatures above ~55.5 degC. The behavior in the B0 detector has an effect on the E150 rate.

EPHIN E150 Coincidence Rate

The E150 rate shows some increases over a baseline value at all temperatures. Most of these are an increase on approaching the Earth's radiation zone, likely due to electrons. There is also a slight increase associated with increased solar proton flux on August 3. Additionally there is a gradual upward trend in the baseline rate as the sensor temperature increases. The rate increase with temperature is due to a decrease in detector C sensitivity, resulting in a mis-assignment of higher energy particles into this coincidence channel. There is a secondary increase in the rate for temperatures above ~55.5 degC associated with an increase in the detector B0 rate.

EPHIN E150 rate vs 5EPHINT
Figure 1: EPHIN E150 coincidence channel rate vs EPHIN sensor temperature The sensor temperature values have a small, uniformly-distributed random valued added for display purposes. The red curve is the median rate as a function of temperature.

E1300 Rate

The E1300 rates show drops associated with higher EPHIN sensor temperatures. The decrease in rate with higher temperature is due to a decrease in detector C sensitivity as the temperature increases. There is no rate increase in conjunction with the detector C rate increase for temperatures above ~55.5 degC since the signals are not in coincidence with those from other detectors.

E1300 rate vs 5EPHINT
Figure 2: EPHIN E1300 coincidence channel rate vs EPHIN sensor temperature, similar to figure 1.

Detector B0 (Center Segment)

The detector B0 rate increases as the Earth's radiation zone is approached, similar to the increases in the E150 rate as expected given that the B0 signal is the dominant component of the E150 coincidence channel. There is an increase in the rate for temperatures above ~55.5 degC; this increase is likely due to the detector leakage current.

Detector B0 rate vs 5EPHINT
Figure 3: EPHIN detector B0 rate vs EPHIN sensor temperature, similar to figure 1.

Detector C

The detector C rate decreases with increasing sensor temperature above roughly 43 degrees C. This behavior is the same as observed prior to setting detector A failure-mode on. The decrease in rate implies a decreased sensitivity to particles and is due to a lower voltage across the detector. The upturn in the rate above 55.5 degC (similar to detector B0) is likely due to leakage current.
Detector C rate vs 5EPHINT
Figure 4: EPHIN detector C rate vs EPHIN sensor temperature, similar to figure 1.

Detector D

The detector D rate decreases with increasing sensor temperature above roughly 50 degrees C, somewhat higher than detector C. As with detector C, the decrease in rates implies a decreased sensitivity to particles. The higher temperature of the on-set of the decrease is consistent with the different detector thickness
Detector D rate vs 5EPHINT
Figure 4: EPHIN detector D rate vs EPHIN sensor temperature, similar to figure 1.

Detector E

The detector E rate decreases with increasing sensor temperature above roughly 50 degrees C, similar to detector D. As with detectors C and D, the decrease in rates implies a decreased sensitivity to particles.
Detector E rate vs 5EPHINT
Figure 4: EPHIN detector E rate vs EPHIN sensor temperature, similar to figure 1.

Detector F

The detector F rate shows an increase as the rate exceeds roughly 53 degrees C. This may be due to increasing noise that would be reflected in a higher leakage current. Unfortunately, the ceiling on the telemetry reading for the leakage current has been reached at 48 degrees C.
Detector F rate vs 5EPHINT
Figure 4: EPHIN detector F rate vs EPHIN sensor temperature, similar to figure 1.
Mike Juda
Last modified: Mon Jul 18 10:30:50 EDT 2011