SSRL Cryo-Cooler


Instructions for Operation of the Cryo-Cooler

Normal Operation of the Cryo-Cooler:

  • The cryo-cooler system runs continuously at a nitrogen gas flow rate of ~1 SCFH when the cold stream is not in use for flash-cooling. Do not completely shut off the nitrogen gas flow.
  • The 40 liter Dewar (inside the hutch) is automatically filled.
  • The large 160 liter Dewar (outside the hutch) is filled by technicians on a weekly basis, however, you may have to fill it, if for some reason the Dewar becomes empty (see instructions below).
  • The Dewar resides behind the beam line control rack at BL 7-1.
  • A heated deflector shield, provided at the beamlines, prevents the goniometer and phi shaft from getting cold; it plugs into a socket attached to the side of the lead shielding screen and the heating is automatically regulated.
  • When the goniometer shield is removed reduce the flow rate to ~1 SCFH.
  • Do not let the cold stream strike the phi axis mount; this will eventually cause the phi axis to loose steps!

Mounting and Aligning the Cryo-Transfer Line:

  • Move the scanner to a crystal-to-film distance of at least 400 mm.
  • Insert the transfer line into the V-bracket minimizing flexing by simultaneously rotating the Dewar slightly.
  • Tighten the screw with the nozzle positioned ~7 mm from the centered crystal by aligning the mark on the transfer line to the edge of the V-bracket (on 9-1 simply lock the relocating clamp in place).
  • Set the nitrogen flow rate for ~16 SCFH.
  • Center the cold stream about the crystal position using the translations (positioning can be tested with an aligned fiber or loop). There should be absolutely no build up of ice at the crystal position.
  • Select a crystal-to-film distance and reoptimize the beam intensity.
  • Make sure the temperature is stable (~ 90 K); the temperature is displayed on a LED in the beamline control rack. Add 267 to the temperature readout to calculate the calibrated temperature at the crystal position in Kelvin.

Flash Cooling and Crystal Manipulation:

  • For flash-cooling directly in the cryo-stream, use the transfer line spring deflector.
  • Cryo-tongs for the SSRL or the "original style" Hampton Research cryo-pins are available for transferring crystals to the cold stream that have been flash-cooled directly in liquid nitrogen.
  • The transfer tongs will keep samples cool for ~10 seconds.
  • The required cryo-tools and Dewars are provided at the beamlines for proper removal and storage of samples at liquid nitrogen temperature.
  • If propane/ethane is used at SSRL, users are required to read and strictly abide by the SSRL Propane/Ethane Protocol.

Cryo Cooler Alarm Systems

There are two alarm systems which involve the cryo-cooler, the LN2 fill alarm and the house gas alarm.

The LN2 Fill Alarm

  • The LN2 fill alarm will sound when the liquid nitrogen level in the hutch dewar falls to a low level. This usually means that the 180 L dewar needs to be filled. After the alarm sounds, the 180L dewar should be filled within an hour or two or the sample will be lost.
  • The LN2 fill alarm is located on the control panel (blue rack). It is connected to a sensor located in the hutch dewar that detects if the nitrogen level is too low. A buzzing noise will occur when this happens.

The House Gas Alarm

  • The house gas alarm will sound if the house nitrogen gas pressure falls below a safe level. When this happens the nitrogen gas for the cryo-stream is taken from the 180L dewar rather than the house gas system.
  • If this alarm sounds or the light is lit, your crystal is in danger and should be removed and safely stored until the house gas system is repaired.
  • Please contact support staff if this alarm sounds.
  • The alarm is located above the 180 L dewar.

Directions for filling the 180 Liter Dewar:

  • The 180 liter Dewar is normally filled by a technician, however, if the auto fill alarm sounds, the tank may have to be filled.
  • Before you remove the tank, check the house gas switch alarm located above the dewar tank or in the hutch. If the orange light is on or the alarm is sounding, your crystal will be damaged when the tank is removed.
  • Switch off the auto fill system before filling the tank.
  • After closing the gas and liquid valves, disconnect the liquid fitting marked in red (a wrench is located near the tank).
  • Disconnect the gas connection by pushing up the lever, and then pulling out the gas hose.
  • Moving carts are stored in building 131 just past the nitrogen fill station near a group of nitrogen tanks. (contact the duty operator if you can not locate a cart.)
  • Disconnect the earthquake brace.
  • The liquid nitrogen fill station is located in building 131 just past beam line 9, find the room by looking for the big beige doors.
  • Detailed directions for filling the tank are posted in filling room. Remember to rotate the valves back a quarter turn, or the valves may be difficult to close.
  • To disconnect the tank after filling, you may need to warm up the connections with a heat gun.
  • When you return the tank to the beam line make sure to reattach the earthquake bracing.
  • Reconnect the fittings, but do not over tighten them.
  • Open the liquid and gas supply valves.
  • Switch the auto fill system back to auto.
  • Check the fittings for leaks.

Shutting Down the Cryo-Cooler:

  • Reduce the nitrogen gas flow to ~1 SCFH, however, do not turn off the gas flow.
  • Move the scanner to a crystal-to-film distance of 400 mm.
  • Carefully remove the transfer line limiting flexing by rotating the 40 liter Dewar.
  • The transfer line rests just upstream of the V-block assembly.
  • Select a crystal-to-film distance and reoptomize the beam intensity.
  • The power supply and auto fill system should remain on.
  • Please report any missing or broken items.

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