Cryoplot Descriptions

The NIRSPEC temperature plots graphically present the temperature measured in various parts of the NIRSPEC dewar. There are ten plots. Each thermistor has a different path to the dewar heat sources and cold sinks, and has a different thermal load associated with it. So interpretation of the plots can be challenging. Some notes may help:

• The most important plot may be the SPEC detector plot. This shows the detector temperature (or as close to it as we can get). In practice this line should be constant at a temperature of around 30-35 K. The detector is a small thermal mass and hence responds to warming or cooling relatively rapidly.
• The 350 cold head connects to the detector and also sees a small thermal mass. It is a good way to see spikes caused by, e.g., turning the helium compressors off.
• The 1050 cold head connects to a larger thermal mass, and at times shows significant noise in its readout. This appears to happen especially when it is cold, and can make it hard to determine what its real temperature is.
• The optical plate connects fairly directly to the 1050 cold head, and is a good plot to look at to see whether the 1050 cold head is actually properly cooling the dewar. Within ten minutes of the 1050 head either ceasing to cool, or starting to cool if the dewar has been warmed, the optical plate should noticeably drop in temperature.