Conditioning procedure for cryogenic probes

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The information below is taken from Decoupling Noise in HCN Cold Probe manual

Cryogenic Probe Conditioning

NMR experiments that require X-nucleus decoupling perform best when the rf coils are conditioned. Conditioning imparts just enough energy into the rf coils to disperse any extraneous condensed material into the vacuum space so that the material is carried away by the pump.

Use the following procedures to condition the rf coils if the Cold Probe has been left idle for a number of days or thermal cycled. Both procedures (run in the order presented) are required during the initial installation of the probe.

  1. Install the probe in the magnet.
  2. Start cryogenic operations, refer to the Cryogenic Systems Operation and Installation manual.
  3. Determine the approximate 90ยบ pulse width and powers for all channels. Refer to the contract for pulse widths and use the procedures in Testing Probe NMR Performance, page 19.
  4. Take the sample out of the probe.
  5. Proton Channel
    1. Enter s2pul temp=25 tn='H1' pw=200 d1=0.1 at=0.1 nt=3000 dp='y'
    2. Set tpwr to the normal high-power level
    3. Run experiment with go
  6. X Nucleus Channels - Do this procedure for both X Nucleus Channels.
    1. Enter pwxcal, at the prompts select decoupler channel and nucleus.
    2. For channel 2 (13C) enter pw=0 pwx1=200 pwx2=0 temp=25 at=0.1 d1=0.1 nt=3000 dp='y' dm='nnn' dm2='nnn'
      For channel 3 (15N) enter pw=0 pwx1=0 pwx2=200 temp=25 at=0.1 d1=0.1 nt=3000 dp='y' dm='nnn' dm2='nnn'
    3. Set pwxlvl1 or pwxlvl2 (dpwr or dpwr2, in older VNMRJ versions) to the corresponding high-power level.
    4. Run experiment with go
  7. When completed, replace the sample in the magnet. Either monitor the real data as it comes in or set up the experiment but run the first increment a number of times using array('nt',200,1,0) to see if the conditioning has been successful.

cryo_noisetest Macro Procedure (Lower Power, Longer Time)

This is an rf decoupling coil conditioning procedure that also quantifies the noise profile of a Cold Probe. The macro runs forever by cycling between periods of prolonged pulsing and testing.

  1. Remove the sample from the magnet.
  2. Ensure that the probe parameter is set to a valid probefile name.
  3. Enter cryo_noisetest. Enter the number of minutes that the decoupler coil conditioning will run before another quantitative test is done. Add five minutes (for the quantitative testing) to the number you entered to get a total recycle time. For example, 40 will run the conditioning for forty minutes followed by five minutes of tests and then start over. Results are printed out at the end of the tests. Reduce the number for more testing (per unit time), increase it for more.
  4. Enter desired number (use 40 during the initial installation of the probe). The procedure starts and a quantitative test is done straight away as a baseline measurement. Four mini-tests are done consecutively; two carbon and two nitrogen, if more than 2 channels are present. For each nucleus CW and WALTZ decoupling modes are selected. An array of dpwr and dpwr2 is done for each nucleus and for each decoupling mode. The noise is estimated from each spectrum and saved in two date-stamped text files in the local users vnmrsys/data/testlib directory and also plotted out in graphical form.
  5. Enter aa or halt to stop the acquisition(s) and procedure.

-- Main.AlexEletski - 07 Mar 2008

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