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Entry  Tue Jun 24 14:07:13 2014, Evan, Notes, PMC, Todo list for PMC heater 
    Reply  Wed Jul 2 09:56:18 2014, Evan, Notes, PMC, Todo list for PMC heater pmc_heater_schematic.jpg
       Reply  Wed Jul 2 17:37:43 2014, Evan, Notes, PMC, PMC heater circuit pmc_heater.jpg
          Reply  Mon Jul 7 23:19:57 2014, Evan, Notes, PMC, PMC heater circuit 
             Reply  Wed Jul 9 22:04:17 2014, Evan, Notes, PMC, PMC heater pmc_copper_20140709.jpgpmc_foam_20140709.jpg
                Reply  Sun Jul 13 11:25:46 2014, Evan, Notes, PMC, PMC heater 
                   Reply  Tue Jul 15 23:40:16 2014, tara, Notes, PMC, PMC heater 
                   Reply  Sun Aug 10 18:42:48 2014, Evan, Notes, PMC, PMC heater, v2 pmc_heater_2.jpg
Message ID: 1450     Entry time: Tue Jul 15 23:40:16 2014     In reply to: 1448
Author: tara 
Type: Notes 
Category: PMC 
Subject: PMC heater 

How hot do you need to heat it? if the thermal expansion of aluminum/steel is much higher than that of fused silica, then just heating the end cap might be a better idea. Thermal conductivity is also better.

Quote:

Quote:

I took some hard yellow foam, made it into a U-shape, and wrapped it with a combination of aluminum and duct tape.

This insulation fits snugly over the PMC and its copper shield. In retrospect, the foam is probably a little too thick. I had to temporarily move the beam dump at the input of the Faraday isolator.

Putting 20 V across the 105 Ω heater produces a change of 5 V on the PMC PZT (when locked). So we need better insulation or more heating.

The CTE of fused quartz is something like 0.5×10−6 K−1, and the CTE of steel is more like 15×10−6 K−1. So I suspect there's not much point in heating the glass spacer if I'm going to leave the steel end cap open to air.

A possible solution is to put a heater on the end cap, but I worry that the differential expansion of steel vs. glass will cause the end cap to pop off the spacer (it looks like it's only held on by epoxy).

A better solution is to improve the insulation on the back end of the PMC. I'll do that next.

 

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