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Entry  Sat Sep 9 23:21:04 2017, awade, Notes, Vacuum, New shield installation planning 2017-09-09_22.15.05.jpg
    Reply  Fri Sep 15 19:32:10 2017, awade, Notes, Vacuum, Solder in vacuum for Kapton heaters 
       Reply  Mon Sep 18 15:08:35 2017, rana, Notes, Vacuum, Solder in vacuum for Kapton heaters 
       Reply  Thu Jan 11 00:28:07 2018, awade, Notes, TempCtrl, Soldering Kapton heaters 
          Reply  Wed Jan 17 13:55:29 2018, awade, DailyProgress, TempCtrl, Soldering Kapton heaters 
    Reply  Wed Sep 20 22:22:37 2017, awade, Notes, Vacuum, Preparing for shield bake 2017-09-20_20.51.34.jpg
Message ID: 1908     Entry time: Sat Sep 9 23:21:04 2017     Reply to this: 1922   1932
Author: awade 
Type: Notes 
Category: Vacuum 
Subject: New shield installation planning 

We need to get going on planning for the Au shield switch.

This will involve removing the old shields (with teflon caps) from around the reference cavities and replacing them with the new gold coated shields with Platinum (PT100, 100 Ω @ 25 C) sensors properly affixed, kapton heaters stuck to the inside and shiny (also gold coated) end caps.  We also need to line the inside of the can with reflective aluminium foil to lower the emissivity pointing in towards the cavities. CRaIg and I were also musing on the idea of putting an additional layer of thickish copper foil between vacuum can and aluminum foil to increase transfer around the edges of the tank and lower the differential drifts across otherwise poorly conducting steel.

So the process will involve

  1. (4 days + lead time) Gathering tools and supplies
  2. (2 days) Cleaning and baking the shields and any additional screws and parts to go in vacuum;
  3. (3 days) Gluing and clamping sensors to new shields, crimping them to  26-30 AWG vacuum compatible wire, put some teflon or peak jacked around the exposed parts, putting sensible strain relieve as most of the previous sensors seemed to have failed after pump down;
  4. (2 days) Find a way to solder or crimp contacts of the kapton heaters to 26-30 AWG vacuum compatible wires.  There is more than one kapton heater so we will need to come up with a scheme for stringing them together in a very tight space. Soldering seems bad, but options for crimping are limited. If we can find a better quality solder with no flux in it then maybe that is the way to go; 
  5. (1 day) Venting the tank and temporarily removing the the PLL board, we will need to find a roughing + turbo pump to get back down, something with a pressure gauge so we know what is going on;
  6. (1 day) Removing the stack from the chamber to to the flow bench where shilds will be removed from cavities and new ones put in place
  7. (2 days) Do a thorougher inspection of the state of cavity coatings.  We may need some bright touches and an SLR camera to document. We also want to know why the heaters and sensors failed last time. Documentation;
  8. (2 days) Reinstall cavity shields with wiring ready to attach to feed through wires
  9. (4 days) Reinstall and pump down, followed by realignment

I checked through the lab to get an idea of what we have. We have a full set of pliers, screwdrivers, wrenches etc. all ready and clean to go.  We also have all the gloves masks etc. We do NOT have a crimping tool, I will check with cryo people if they have one, also maybe the 40m. We also don't have high quality solder for the Kapton heater wire attachment.

We have some barrels and pins (pictures attached at bottom) that go into sub d connectors for the feed throughs. We also have one spare in vacuum sub d 9 that could be pre-wired for speeding up things once the tank is open. We should be connecting lengths of wire to the shields once the stack ensemble is half inserted back into the can. We have about 20 barrels and 20 pins as well as some accuglass Female Contacts, Type-T1 that could be used as wire connectors.  We might want to reorder but there are probably enough around campus that we will be ok. We will need to order insulating jackets for the exposed conducting surfaces in tight spaces.  I saw some clearish heat shrinky looking stuff that the MIT people were using for in vacuum squeezer, that might be what we need.

We need to clear some space on the flow bench to work.  There is some stuff left over from one of the SURFs (Adele) doing some first contact and attempted optical contacting with silicon.  I have move this to above the bench.  Someone from cryo will need to come and collect this. We also  need to find a clean space to move the PLL raised optical breadboard.  This would probably be the south side of the optical table.  We should move the population of mounted optics to elsewhere on the table to give us space to work.

We need to have a neat solution for strain relieve of sensor wires. These have historically broken a LOT. Maneuvering the full stack ensemble into the tank is heavy (>9 kg?) and awkward and so we need to make sure the wires are not easily bent causing strain related failure later. Kapton tape or some kind of clippy things onto the shields? 

Buy list:

  • 26-30 AWG wire good for vacuum (we have none)
  • insulating jackets (Teflon), to prevent shorts in vacuum
  • Any copper gadgets we don't have two sets of
  • Thermally conductive epoxy (masterbond $$$ maybe)
  • Fitting for temp sensor clip
  • Any remaining Kapton heaters (check if Aidan has them)

 

Things we need to find out:

  • Full list of all the screws needed to fix the shields in place (so we know we have them in handy)
  • A good source of vacuum compatible thermally conductive epoxy
  • How to solder to Kapton heaters.  All our attempts so far have been mediocre.

Other thoughts:

  • Kevin and Kira should think about circuitry that can potentially sense failure of load and shut down. Could be something as simple as a current limit on supply or fancy like sensing voltage drop and having a comparator to input and shut down if there is a mismatch. We just don't want shorts in vacuum doing crazy things. The new beefier drivers can potentially source a lot of current and we need a way to crimp this.
  • Are 100 Ω @ 25 C platinum RTDs the correct choice? 1000Ω is also an option and there are also 10 kΩ thermistors. We need some liso models and back of the envelope calculations to work out pros and cons.
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