Inova600 Cold Probe User Manual
Contents
1. per he minute until it freezes S a Cold He mE gas supply Warm He gas return ae Figure 2 Diagram of the Cold Probe Performing NMR Experiments with the Cold Probe Once the cold probe system has been properly installed and is fully stabilized at the operating temperature of 25 Kelvin doing NMR is not much different than a normal probe The CryoBay Monitor window will indicate READY when the system is ready to use The issues outlined in the Overview section above will be discussed in detail below I Monitoring the Status of the Cold Probe system CryoBay Monitor Status Window a When operating the CryoBay always displays the status of the system Figure 3 illustrates the CryoBay Monitor Status window showing all of the key elements of the window 2 CryoBay Front Panel 3 1 vi CryoBa Figure 3 CryoBay Monitor Current Temperature at the ColdHead this is the coil temperature and should not change more than 5 degrees If cooling will show time remaining until ready Cold Loop Impedance related to Helium mass flow Open Panel Tico a F3 Heater Power Watts being applied to maintain Temp READY Cryo System Status Must be READY to use I Instrument Probe Cabling a Cabling for C PN and H is the same as a conventional probe including the location of the bandpass filters b H cabling is different Refer to Figure 3 and the following instructions to ensure that t2. G IS DIFFERENT 3 p i a Caution Do not touch or Bump this Assembly Flexible cryogenic transfer line CCC uni t 1 Remove the thick cable connected to the top port of the cryopreamp driver J5303 ii Using a short BNC cable i e the P 4 wavelength cable connect J5303 to the PROBE port of the tune interface module iii Move the cable from J5302 OUTPUT to the OUTPUT port of the tune interface 1 DO NOT REMOVE the cables going to the H channel of the probe J5331 iv The system is now ready to tune the H channel of the probe CAUTION Extreme care must be exercised when working under the magnet such as when tuning the probe Be very careful not to touch the side arm or the vacuum connections on the probe Never use any part of the cold probe assembly to support or steady yourself while working under the probe ii Magnet Cold Probe Jamping pier 7 Vibration S gt d At the probe the mechanics of tuning are different Refer to Figure 5 which shows the tuning assembly at the bottom of the probe The larger Function selector knob is used to select which part of the probe circuit is being tuned IMPORANT The brass Tune Match knob muss be PULLED DOWN to its fully extended position before the Function selector knob is turned ii Once the Channel has been chosen for tuning and t
3. Using the Varian Cryogenic Probe System on the Inova 600 NMR Spectrometer Generally called the Cold Probe or Chili Probe in the Varian vernacular Thursday March 11 2004 by Rich Shoemaker corrected 9 27 07 This manual is intended for users who are experienced at operating the Varian NMR spectrometers at a relatively high level of proficiency The intent is to point out the issues pertaining to the cold probes how the use of the cold probe differs from a conventional probe and the issues that directly affect how one does spectroscopy with these probes Issues pertaining to the proper care and use of the cold probe system to ensure that the equipment is not damaged will also be discussed Note Many of the pictures amp figures have been taken from the Varian Cold Probe Manuals and have been used with permission Overview Doing NMR spectroscopy with a cold probe is essentially the same as with a conventional probe however certain properties of the cold probe must be understood to obtain optimal results Each of these will be address in further detail later in this document The primary issues that should be understood are e Rf Pulse Ringdown Times Due to the high Q Quality factor of these probes the ring down time of the tuned circuit is significantly longer This means that the delay between the end of the pulse and start of signal detection is longer Since pre acquisition delays can adversely effect the appear
4. ance of the spectrum mostly in frequency dependent phase errors and other baseline issues there are new parameters that deal with this problem The parameter qcomp for Q compensation is used and is dependent upon the settings of the dsp parameter e Rf Power Handling The cold head in the probe is maintained at a precise temperature through a process of super cooling helium gas in the cold loop and then an Intelligent Temperature Controller ITC re heats the probe head to maintain a stable temperature 25 0 Kelvin under normal operation When Rf power is inserted into the probe especially under broadband decoupling i e PN and C this causes heating The ITC detects these fluctuations and compensates by dropping the current through the heater The heater power in Watts is displayed in the CryoBay Monitor window As the net Rf power in an experiment increases the heater power will drop to maintain a steady probe head temperature of 25 0 Kelvin If too much power is used such that lowering the heater power cannot maintain the probe head temperature then the tuning will be lost and ultimately damage to the probe or the receiver pre amplifier in the probe could occur e Pulsed Field Gradient Performance The inductance of the gradient coil in these probes is much higher Adjustments have been made to the gradient amplifier to compensate for this in addition the software has built in rudimentary shaping of the rise fall tim
5. d Cycle Chiller CCC which is the box in the corner of the 600 magnet room near the hole in the wall e Inside the CCC the cold head is cooled to well below 25 Kelvin Part of the compressed helium is split off and routed through the cold head in the CCC is cooled to below 25 Kelvin and flows through the flexible line to the side arm of the probe and up through the probe e Figure 2 illustrates the path of the cold helium in the cold loop as the internal components of the probe the tuning elements the coils and the receiver pre amplifier are cooled e All of this is maintained at 10 Torr vacuum to achieve thermal isolation from the outside world meaning the sample and the magnet components outside the probe are kept at or near room temperature Close Cycle Chiller He refrigerator qemu Vibration Cryogenic Vibration isolation plate damping pier probe Figure 1 Cold Probe System Diagram Sample tube e The Intelligent Temperature Controller ITC uses a variable heater in the probe assembly to Cryo cooled rf coil maintain the desired temperature at the Cryogenic heat exchanger coldhead caldhead e Note even though the sample is relatively well insulated from the cryogenic PIER PARR P temperatures inside the cold probe it is probe body imperative that dry air be flowing through the VT port in the probe Without VT air flow Universal coaxial adaptor the sample will cool at a rate of 1 C
6. es of the gradient pulses to further improve the gradient performance esp the amplitude stability A new parameter called gradientshaping a global flag parameter is used to activate the shaping of the gradient pulses e Instrument Cabling Since the first stage proton observe pre amplifier is inside the cryogenically cooled region of the probe a different receiver pre amplifier module called a Cryopreamp Driver is installed The way this system is setup for operation and probe tuning is different Furthermore no Rf filters can be inserted between the HBPROBE XMTR output J5331 and the proton input of the probe Cabling for tuning the H channel is also different e Probe Tuning In addition to cabling issues the cold probe has a different user interface for probe tuning A single brass knob is used to tune all channels A larger knob is used to position the tuning stick to engage the tuning element for each channel Tuning channels are available for H Tune H Match SC Tune 2N Tune and H Tune Description of the Cryogenic Probe System Everyone using the cold probe system should have a basic understanding of how the system functions and what the basic components are Figure below illustrates the entire cold probe system with the key parts labeled The basic theory of operation is as follows e Helium gas is compressed by the compressor in the CryoBay The compressed helium undergoes thermal expansion in the Close
7. he reflected power is displayed on the tune meter and all cabling is properly configured the reflected power is minimized using the Tune Match selector knob Figure 5 Function indication IV Figure 5 The tuning VI assembly IFC Tune Match Function VT gasbal and window ontheside plug selector knob selector knob socket connector Photo of probe in 1H Match mode with Brass Tune Match knob in the up einen iii Once the appropriate tuning function is selected Shown in the Function Indication Window the brass Tune Match knob is pushed up until it seats fully into the hexagonal receiver after which turning the brass knob will adjust the capacitor that controls the tuning function indicated in the window 1 Example Proton Channel Tuning a b T P Brass Tune Match knob pulled down to full extension Rotate the Function Selector to 1H T 1H Tune and push the brass Tune Match knob up until it is fully seated Adjust the 1H Tune for minimum reflected power LOWER the Brass Tune Match knob pull down and rotate the Function Selector so that 1H M is in the window then push up the brass knob and adjust the 1H Match for minimum reflected power Repeat until the probe is optimally tuned and matched Note that the tuning dip is extremely sharp with these probes therefore the sensitivity when tuning is very high It takes a careful touch and patience to properly tune these pr
8. he system is cabled properly a A i The cable from the High Band Transmitter plugs into the top port HB XMTR J5303 From en ii HBPROBE XMTR J5331 goes to the 1H XMTR HB amplifier port on the probe aa iii HB PROBE PREAMP J5335 connects to the 1H To EA RCVR port on the probe probe 1H iv OUTPUT J5302 is connected to the same cable as a normal pre amplifier Output cable connects to the mixer in the magnet leg interface v Signal path 1 The transmitter pulse is routed to the probe from port J5331 on the cryopreamp driver to CRYOPREAMP DRIVER From Probe the probe This cable a fat cable also HB PROBE PREAMP carries the DC voltage for gating the H RCVR Transmit Receive Switch on 2 After pulsing the NMR signal is amplifiedin To see the cooled pre amplifier in the probe and this HB preamp o amplified signal comes out to J5335 on the From cryopreamp driver The signal is further T isoa amplified and sent to the mixer via the Figure 4 CRYOPREAMP DRIVER OUTPUT J5302 port 3 JMI Probe Tuning For C N and H channels the cabling to tune the probe is the same as with a normal probe The Probe connector on the tune interface connects to the appropriate channel on the probe and the cable connected to the OUTPUT port of the BROADBAND Pre Amplifier is connected to the OUTPUT port of the tune interface For the H channel THE CABLING SETUP FOR TUNIN
9. iled on the 600 will use the gradient shaping 3 Itis recommended that lower gradient amplitudes be used i e gzlvl lt 18000 Larger gradient amplitudes can lead to a loss in gradient amplitude reproducibility 4 You can check the gradientshaping parameter by typing gradientshaping Data Acquisition Issues Your data acquisition with the cold probe is affected by the long ring down times of the Rf pulses To deal with this a new global flag parameter called gcomp is used in conjunction with oversampling dsp 1 1 Make sure that dsp 1 dsp ti The parameter gcomp should be set to y by typing qcomp y ii The parameter rof2 should remain the same as in a normal acquisition rof2 3 or 4 usec iv More notes about dsp oversamp and qcomp 1 The FID going to the Sun must be oversampled for gcomp to function properly a dsp 1 should always work b If you know how to use fsq and if you set fsq y you can also use dsp r MAKE SURE you fully understand how fsq works if you want to do this if you aren t sure then don t use dsp r or fsq y 2 If digital signal processing is turned off at any time dsp n then qcomp will also be set to n It must be reset to y manually after dsp 1 is executed 6 3 The software will reset the oversampling any time the spectral window sw 1s adjusted The parameter oversamp indicates the amount of oversam
10. multi day experiments it s common to periodically check the progress of the experiment Make sure to check the information in the CryoBay Monitor Window each time you check on your acquisition
11. obes 2 After the probe is tuned be sure to re cable the system for normal operation see section I above for cabling information 3 For tuning the C and N channels tune only no match adjustment the cabling for probe tuning is the same as for a conventional probe Setting Up Experiments Once the sample is inserted and the probe is properly tuned performing NMR using the cold probe is not much different than with a conventional probe As with any probe using too much Rf power for too long a time can damage the probe The cold probe is more efficient in terms of B1 field vs Rf power therefore the user must be cognizant of the correct calibrations for this probe a Variable Temperature Sample Temperature The cold probe has a VT range of 0 to 50 degrees Celsius DO NOT EXCEED THESE LIMITS i Do not set the FTS below 15 degrees C i ALWAYS ensure that there is VT gas flow to the probe This is very important to prevent the sample from freezing b Radiofrequency Power Handling Issues The values below represent safe operating limits for C and N Broadband Decoupling and H Spin Locks AS ALWAYS if multiple spin locks and multi nucleus decoupling is used care must be taken to ensure that you don t put too much power into the probe 1 On the CryoBay Monitor there is a value for HEATER This represents the number of watts being used in the heater to maintain the probe temperature of 25 Kelvin As more Rf p
12. ower is delivered to the probe the HEATER wattage will drop PAY ATTENTION to this heater power when an experiment is started If the heater power drops by more than 1 5 Watts you may be using too much Rf Power STOP your ACQUISITION aa if this happens ii Safe Levels for C Decoupling 1 dpwr 43 3 3 KHz field for a maximum of 120msec 2 dpwr 41 2 6 KHz field for a maximum of 250msec 3 C Spinlock pwr 51dB 8 2 KHz for a maximum of 30msec iii Safe Levels for N Decoupling 1 dpwr 2 48 1 6 KHz field fora maximum of 120msec 2 dpwr 2 45 1 1 KHz field fora maximum of 250msec iv Safe Levels for H Spin Locks 1 TOCSY spin lock pwr 40 8 0 KHz field for a maximum of 100msec 2 ROESY spin lock pwr 30 2 5 KHz field for a maximum of 500msec v Safe Levels for H Decoupling 1 1 0 KHz decoupling field for a maximum of 60 msec 2 Note at the time of this writing the power levels for 2H decoupling have not been determined Make sure you have the 2H decoupling fields calibrated and do not exceed the above power duty cycle Using Pulsed Field Gadients 1 To improve the stability of gradient pulses with the cold probe a rather crude shaping is applied to the rise amp fall period of the gradient pulses This is activated via a global flag parameter called gradientshaping 1 Type gradientshaping y to turn on gradient shaping 2 All gradient pulses that use the zgradpulse statement that are comp
13. pling being used If oversamp is too large and the pulse repetition rate is short i e dl 1 sec or less then acquisition errors can occur a BEFORE STARTING YOUR ACQUISITION type oversamp to check the amount of oversampling being used it shouldn t be greater than 20 and there is no real reason for it to be greater than 16 b Type oversamp 16 before starting your acquisition to be safe v Summary 1 Before starting your acquisition with the cold probe you should do the following a dsp 1 or dsp to make sure that it is set to 1 b qcomp y or qcomp to check c oversamp 16 or oversamp to check d rof2 3 4 not gt 5 e gradientshaping y f CHECK your decoupling and spin lock powers decoupling and spin lock times and your acquisition time to be sure that you do not exceed the limits specified for the probe IV b previous page 2 After starting your acquisition CLOSELY monitor the CryoBay Monitor window paying close attention to the Heater power and the Temperature You should monitor this for at least 5 minutes after the acquisition begins a Ifthe heater drops more than 1 5 Watts from the baseline i e if Heater drops from 5 5 to 3 0 ABORT the acquisition aa and check your decoupler powers spin lock powers your decoupling times and spin lock times Section IV above Remember that in most cases your acquisition time at also represents a decoupling time b For long
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