Difference between revisions of "Running with No Helium for Optics"

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(New page: ;This procedure has not yet been edited by target coordinator. ===Assumptions:=== *NMR System is tuned *Magnet is at full field, persistent mode, leads are ramped down *Nose is over 50%, ...)
 
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;This procedure has not yet been edited by target coordinator.
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===Conditions:===
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*The run plan requires very low helium to allow the beam to solely interact with the carbon disk
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===Assumptions:===
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*NMR System is tuned
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*Magnet is at full field, persistent mode, leads are ramped down
 
*Magnet is at full field, persistent mode, leads are ramped down
 
*Nose is over 50%, run valve in PID mode
 
*Nose is over 50%, run valve in PID mode
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*Baseline taken and set
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*The carbon Target is in place
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*TE has been taken and new calibration constant feed into PDP
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*Target in correct position along with NHR Channel setting
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*Roughing and Bypass valve open with mechanical pumps on
 
*Roughing and Bypass valve open with mechanical pumps on
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*Beam Permit but no beam on target
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===Preparation:===
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===Prepare Fridge:===
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*With beam on (~80nA) check and remember the T1 and T3 event rate at the third person station (usually ~2.7kHz)
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*Close Roughing valve
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*Close the run valve to start emptying out the nose (the microwave can assist in this)
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*Turn on Blower 1 and wait 2 minutes
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*Once the nose level drops below 8% you can not expect an accurate reading but having the level far below this is not beneficial
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*Turn on Blower 2 and wait 2 minutes
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*Once you see the rates in T1 and T3 drop to ~0.9kHz then the nose has emptied enough, this is about a factor of 3 from your initial check with Helium in
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*Close Bypass valve
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*Note: You may need to get the cup temps up above 10K before you see the rate in T1 and T3 drop (a good run valve position is 0.43 at ~10K using 50nA beam current)
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*Turn on Blower 3
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*Wait a little while
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===Maintain:===
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===Begin Polarization:===
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*Once you have emptied the nose enough open the run valve to 0.3
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*Press "TRANSMIT" on the microwave control panel under Control Unit Status (WARNING: Do not touch the button to the right)
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*Keep a very close eye on the cup temperatures (lower left side of PDP screen under Cx Top and Bott)
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*Press "Take Data" on PDP
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*The cup temperatures should be between 12-19K averaging around 16K, if they get above 20K open the run valve in increments of 0.05 until they cool
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*Try to maximize polarization by moving the bellows position
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*If the cup temperatures get above 30K stop the beam, if you can't cool them down call target expert
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*Watch the frequency in the top left monitor
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*Monitor the main flow and check that it stays above 1.0 if it drops below 1.0 this can indicate that the helium in the nose is completely gone, it is necessary to keep a flow of vapor on the target at all times, open the run valve in increments of 0.05 until you see the flow increase keeping the run valve between 0.3-0.5
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*You can try to start out in the frequency range in the plot of frequency vs Dose since last annel
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*Generally you have to search for the "best" frequency When searching, make changes by 5MHz, 10MHz at the most
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*After making a change, wait about 3 NMR updates to see if it helped/hurt
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*Beam trips will change pol quickly and obscure the effect of your changes especially over 50nA
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*If the frequencies display does not work look also at the poltarcama/Jpeg/CamImgs.jpg using Camera Set 0, use F5 to update (This shows in Hall bellows position)
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*As radiation damage accumulates, frequency will move if polarizing positively, frequency will move down and if polarizing negatively, frequency will move up
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*Use the logbook − see what frequencies worked for other people
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*Log all of your best frequencies when you find them in the Target Operator Microwave Frequency Notebook
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*Tell shift leader you are ready for beam
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Latest revision as of 00:32, 12 April 2012

Conditions:

  • The run plan requires very low helium to allow the beam to solely interact with the carbon disk
  • Magnet is at full field, persistent mode, leads are ramped down
  • Nose is over 50%, run valve in PID mode
  • The carbon Target is in place
  • Roughing and Bypass valve open with mechanical pumps on

Preparation:

  • With beam on (~80nA) check and remember the T1 and T3 event rate at the third person station (usually ~2.7kHz)
  • Close the run valve to start emptying out the nose (the microwave can assist in this)
  • Once the nose level drops below 8% you can not expect an accurate reading but having the level far below this is not beneficial
  • Once you see the rates in T1 and T3 drop to ~0.9kHz then the nose has emptied enough, this is about a factor of 3 from your initial check with Helium in
  • Note: You may need to get the cup temps up above 10K before you see the rate in T1 and T3 drop (a good run valve position is 0.43 at ~10K using 50nA beam current)

Maintain:

  • Once you have emptied the nose enough open the run valve to 0.3
  • Keep a very close eye on the cup temperatures (lower left side of PDP screen under Cx Top and Bott)
  • The cup temperatures should be between 12-19K averaging around 16K, if they get above 20K open the run valve in increments of 0.05 until they cool
  • If the cup temperatures get above 30K stop the beam, if you can't cool them down call target expert
  • Monitor the main flow and check that it stays above 1.0 if it drops below 1.0 this can indicate that the helium in the nose is completely gone, it is necessary to keep a flow of vapor on the target at all times, open the run valve in increments of 0.05 until you see the flow increase keeping the run valve between 0.3-0.5
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