High T served..

How high can I go with my VT setup ?  This is a nagging but relevant question that needs a definitive answer for many users.  I ran  the following test to figure this out.

Here is some useful info first, as to what we already know.

• The recommended temperature extremes that the room temperature bore can tolerate is between 0 C to 50 C.
• The shim stack itself can apparently handle +80C (this needs clear confirmation from Bruker and I am working on it).
• There is no active thermal shielding setup between the probe head sample space and what surrounds it.  In non-gradient model probes, there used to be a vacuum dewar that provided effective insulation. 
• The gradient coil takes up the space occupied by the vacuum jacket and this means that the heat will transfer from the coil space to the probe sleeve and then onto the RT shim stack and eventually to the RT bore itself (heat will flow in the opposite direction for low VT experiments)
• Bruker provides an active cooling mechanism by providing either a barbed connector or a compression coupling at the top of the BST (Bruker Sample Transport) assembly.  We are asked to provide an air flow of 200 to 300 L/hr through this to cool the shim stack. We don't need much pressure since this is supposed to be a free flow, where the cooling air exits out of the bottom of the shim stack.
• When we jacked up the flow beyond 600 L/hr., the sample is getting lifted from its seated position and so that should give us an upper cutoff.

We employed the temperature and humidity logger from a company called 'Onset'.  They have a windows based $$ware called HOBOware that controls the logger, transfers data to the PC and plots it.