Diagnosing Incoming Heat Loads

If you are experiencing a high base temperature, it is important to understand where the heat load is coming from. Knowing the Stage 1, Stage 2, Platform, and Sample temperatures is critical for diagnosing the source of the heat load.

IDENTIFYING THE SOURCE

Under normal conditions and a standard system (Cryostation s50*), you should observe the following temperatures and temperature gradients between stages. Note: The temperatures between the platform and sample may change with various options installed.

  Stage 1 Stage 2 Platform Sample
Temperature 27 - 28K 2.4 - 2.7K 2.7 - 3.0K 2.8 – 3.2K
Temp Gradient     +0.2 – 0.4K +0.2 – 0.5K

By comparing your temperatures and temperature gradients to expected levels, you may be able to pinpoint the source of the heat load. Consider the following example:

Example 1 Stage 1 Stage 2 Platform Sample
Temperature 28K 5.0K 5.3K 5.7K
Temp Gradient     +0.3K +0.4K

In this scenario, Stage 2 has a higher than normal temperature, as does the Platform and Sample. However, Stage 1 is normal. The temperature gradient between Stage 2 and the Platform, and the Platform and the Sample, is also normal. This indicates that the heat load is coming in between Stage 1 and Stage 2.

Consider another example:

Example 2 Stage 1 Stage 2 Platform Sample
Temperature 26.5K 3.0K 3.3K 5.0K
Temp Gradient     +0.3K +1.7K

In this scenario, the Stage 2, Platform, and Sample temperatures are high. However, the most critical issue is the large temperature gradient between the Platform and Sample. The heat load is most likely coming in between the Platform and Sample, and since the Sample is high the temperatures of the Platform and Stage 2 are also being pulled up. This is also what is causing the slightly lower than normal temperature of Stage 1, as it is working harder to pull down the temperature of Stage 2.

POSSIBLE CAUSES

Once you’ve identified the source of the heat load, you can better diagnose the probable cause:

Between Stage 1 and Stage 2

  • Crosslink rod touching the side wall – contact your service representative for instructions to perform a touch test

Between Stage 2 and Platform

  • While it is rare to get a head load due to stage 2 and platform this could happen if the screws are not tightened adequately between stage 2 and the platform. This would only be an issue if the user takes off the platform, which is not recommended.

Between Platform and Sample

  • Wires are touching the radiation shield or wires are touching the sample mount directly after the thermal clamp (before the wire is thermalized). An especially large heat load can be added to the sample space if RF wires touch the sample mount right after the thermal clamp.
  • Use of copper wires (0.3K heat load per wire) instead of phosphor bronze
  • Screws not tightened down
  • No N-grease between metal components
  • Window missing on radiation shield

If all temperatures are high, start by inspecting the sample space for any touches or loose connections. If possible, remove as many options as possible, such as stages and sample mounts, to ensure the base temperature of the system is reaching the proper target temperature with no options.

It could take several iterations of cool downs to properly diagnose some instances of high base temperatures, but with a little investigation it should be solved. If the problem persists, contact your service representative for additional support. 

*If you have an s100 (Fusion) or s200 (Nanoscale): The s100 temperatures are similar to the Cryostation s50; typically just a few tenths of a Kelvin higher. Again, the differences will depend on the options installed. The s200 often has numerous options installed, so the gradients are typically quite different from system to system as it depends on the configuration.