Getting Started with the iVTI
Important
Before operating the iVTI please familiarize yourself with the principle of operations described in the section iVTI Overview.
The following section provides information about day-to-day operation of the cryostat. If you need assistance troubleshooting iVTI operations, please first consult the manual or contact Bridge12 or CRYOGENIC.
Prior Checks Before Operating the iVTI
Warning
Do not use excessive force or overtighten the needle valve as this can lead to permanent damages of the valve.
Note
If the needle valve is closed and open again, a faint clicking sound is heard as the needle pulls away from the needle valve seat.
Once the magnet has achieved its base temperature the following checks should be performed prior to operating the iVTI:
- Make sure the dry pump bypass valve (V16) is closed.
- Make sure the helium reservoir valve (V12) and the iVTI outlet valve (V11) are open.
- Start the dry pump and adjust the needle valve to a pressure of approximately 5-8 mbar at the head of the iVTI. Please note the needle valve may require several further adjustments as the temperature profile within the flow circuit varies whilst steady-state flow conditions are established in the circuit.
Within a short period of time, the cryostat should reach its base temperature of ~ 1.8 K.
Setting an optimum flow rate requires some experience from the user. The factors that must be considered are:
- If the flow rate is too low the 2 K base temperature of the iVTI may not be achievable, as the available cooling power of the gas may be too low.
- If the flow rate is too high the cryocooler second stage temperature will rise which may affect the maximum ramp rate of the magnet.
- If the flow rate is too high the cryocooler may not condense at a fast enough rate. This leads to rapid boiling of the condensed gas in the circuit and a rapid pressure rise of the circuit.
Typically the iVTI can operate with a single needle valve setting over its whole temperature range. However, if a rapid cooldown is required the user can increase the flow and then subsequently re-adjust the needle valve to give a lower flow setting once the iVTI has cooled close to the required temperature.