Introduction
System Overview
Safety  &  Emergency
Controls on the CryoCooling Unit
Instructions for AVIII800/CryoProbe Users

Introduction

The CryoProbes offer a dramatic increase in S/N  by reducing the operating temperature of the NMR coil assembly and the preamplifier. While the sample temperature is stabilized at a user-defined value around room-temperature, the NMR coil assembly -located a few millimeters from the sample- is cooled with cryogenic helium gas.

The most prominent part of the CryoProbes is the cooling unit, in which the so-called ‘coldhead’ expands compressed He and thereby cools it to cryogenic temperatures. Cold He is then circulated through the probe via an insulated He transferline. Vacuum pumps maintain insulation of the probe and the cooler. All operations are supervised by the built-in CryoController unit

System Overview

  CryoProbe
  Cryo-compatible HPPR
  CryoCooling Unit
  He cylinder
  He Compressor
  Water Chiller

Safety  &  Emergency

The main switch of the CryoCooling Unit serves as an emergency OFF:

•   powers down the system
•   all valves are reset to their default positions
•   the system will slowly warm up

This emergency OFF shuts down the supervisor electronics so it should only be used as a last resort.

The system works with helium gas that is pressurized (25 bar) and cooled to ~20K.

Do not disconnect any tube or cable from a running cold system.
If you have to work with an open cabinet, put on protective goggles and gloves (cold burns)
If large quantity of He gas escapes from the He cylinder during a short period, there is a danger of suffocation and one should care for good ventilation, fresh air supply after the incident
If cold He gas comes in contact with eyes or skin, immediately flood the affected area with cold or tepid water.

Controls on the CryoCooling Unit

As indicated, the main switch on the CryoCooling Unit front serves as an EMERGENCY  OFF.
In addition to the main switch on the CryoCooling Unit front,  six additional buttons exist:

•   WARM
•   WARM UP
•   COOL DOWN
•   COLD
•   ERROR
•   UNPLUG

  All buttons and indicators may illuminate to give a status display
  WARM UP, COOL DOWN and UNPLUG buttons can be pressed for input.
  When COLD lights up (green), the system is ready for measurements
  When COLD blinks, the system is slightly overheated- check and reduce decoupling !!
  Whenever other buttons blinks/lights up, pls call immediately an authorized person

Instructions for AVIII800/CryoProbe Users

• Choose the appropriate probe-head, using the  edhead   command (probe #38)
• Due to the sensitivity of the system to the temperature at the sample cavity, load the configuration for the VT unit via  edte:    edte ->  load configuration (choose a configuration file that best matchs your working conditions in terms of probehead (TCI), temperature, flow-rate, BCU unit status -ON or OFF- state etc).
• Use the white (preferably) or blue spinner (never use the ceramic one!!)
• Avoid fast dropping of samples with the sample lift.
• Do not introduce any objects into the sample cavity of the probe (not even soft cotton bud)
• Insert the sample only if the COLD button on the cooling unit is ON, or at least flashing
• The gas flow must be maintained at all times while the CryoProbe is cold- it must not be interrupted before the CryoProbe has been warmed-up
• The sample is subjected to a rather high flow of VT gas (800-935 l/hr).
• Set the max VT heater power limit to 20% (as low as possible)
• Use temperature in the range of 0C to +60C only
• Always keep an eye on the sample temperature (edte)- if the temperature drops, eject the sample to prevent freezing. Never interrupt the VT gas flow !!
• CryoProbe must not be tuned or matched when warm- before attempting to wobb the CryoProbe, the green COLD light should be ON or at least flashing
• Tuning & Matching the CRP:

                      An Automatic Tuning and Matching (ATM) unit was recently installed.
                      The wobbling procedure could be done now either automatically using the atma command, or manually (by clicking the appropriate bottons on the displayed ATM window) using the atmm command.
                      PLS NOTE: For salty samples (>100mM salt) pls use the manual option, atmm.
                      The old wobb command could only be used to view the wobbling signals (no changes could made from that window).

• Verify (via   edasp ) that the RF routing in your file is in accordance with the new HPPR-CRP rules

                                frequency      amplifier        preamplifier
                    F1   1H       FCU1     H 100.0W      1H
                    F2   13C     FCU2     X 500.0W      13C
                    F3   15N     FCU3     X 300.0W      15N
                    F4   2H       FCU4     X 300.0W   locksw 2H 2H

• Excessive RF power can destroy the CryoProbe or its HPPR- obey the limitations.   If in doubt, start with powers that are at least 10 dB below (more positive values) the values you are used to.
• In any case, follow Bruker application-specialist Instructions , found at the folder near the magnet.
• Calibrated pulse lengths values

                          1H         10.12 us  @  +5.0dB
                          13C      12.17 us  @  -1.50 dB
                          15N      39.48 us @    -0.80 dB

• When 2 RF hard pulses are applied to a NMR coil at the same time (e.g. pulsing 13C & 15N), reduce the power of the two pulses by 3 dB each.
• In case of 3 simultaneous hard pulses, the reduction is 10 dB for each.
• The decoupling power required by the CryoProbe is much smaller than a conventional probe- in case the decoupling cases heating of the probe, the COLD button on the cooling unit will start flashing -should this occur, stop immediately the experiment, reduce the decoupling power, and call an authorized person. Do not continue the experiment.
• Since no attenuators are connected to the 3 amplifiers at the console, a special care should be taken regarding excessive pulsing power!!
• A characteristic periodic hiss of the cooling unit is clearly audible at all times
• In normal measuring conditions, the COLD green button lights permanently. In case of blinking, or if other buttons lights/blinks, pls call immediately authorized people.
• All necessary filters are already incorporated in the system- no additional filters are required
• If a large quantity of He gas escapes from the He cylinder during a short period, there is a danger of suffocation- take care for a good ventilation and fresh air supply after the accident
• If cold He gas comes in contact with eyes or skin, immediately flood the affected area with cold or tepid water.