15
5
Operation
5.1
Suggested operating conditions
Always keep at least 10 cm of liquid in the dewar when the Cryojet is running, as lower
levels could impair the performance.
Never allow the dewar to become empty when
the Cryojet is running.
Keep the plastic cap, the vent valve and the pressure relief valve (or level probe) in place
on the dewar top fitting, to prevent water from the atmosphere entering.
A sample flow rate of about 6 l/min is recommended for most applications. (See 4.1 for
how to set these flow rates.) The lower the flow rate, the higher the base temperature
will be. Lower flow rates may be suitable if very low temperatures are not required,
provided the sample can be placed very close to the nozzle. A flow rate of 4 - 5 l/min is
usually sufficient for the shield flow - lower flow rates can be used if they are sufficient to
stop the sample and nozzle icing up.
For a fast cool-down, set the sample flow rate to 10 l/min initially, and then reduce it to
the desired value when the temperature is close to the set temperature.
5.2
Alignment of Nozzle and Use of Alignment
Tip
The nozzle should be placed as close to the sample as possible to prevent icing. The
limitation on this spacing depends on the diffraction angle required and the angle
between the nozzle and the incoming x-ray beam. In almost every case the nozzle should
be within 10 mm of the sample.
The jet should be centred on the sample as accurately as possible. One way to do this is to
adjust the nozzle first so that the sample is in the plane of the nozzle. This makes it easier
to centre the nozzle. Then move the nozzle back to the desired position using the
micrometer stage. See Figure 8.
Another method is to use the Oxford Instruments alignment tip. Slide the device into the
nozzle, and tighten the knob to clamp it in place. Place a sample mount with no sample
on the goniometer. Adjust the nozzle so that the sharp tip is almost touching the place
where the sample would be. Remove the sample mount. Loosen the knob and remove
the alignment tip. Then place the sample on the goniometer. If required, move the
coldhead forward using the micrometer.
