Signs of trouble with the Oxford Cryosystems Cryostream Cooler include an ice block warning on the cryostream controller display, condensation on the coldhead or transfer line, and ice formation on the crystal or coldhead nozzle. If a problem is suspected with the coldstream, contact beamline personnel.

Contents

• Ice Block Warning
• Bringing the System On-line
• Ice Crystals Forming on Sample
• Aligning the Coldhead
• Optimizing the Laminar Flow
• Advanced Coldstream Troubleshooting

Ice Block Warning

An ice block warning, which reads "Ice Block warning will trip at 2 L/m" on the controller, indicates that the system will shut down eventually because of moisture build-up in the coldhead, but it may not occur for several hours. Since it takes a couple hours to warm up the system to remove the ice block and then to bring it back down to temperature, it is sometimes advantageous to finish collecting a set of data before the ice block is attended to if the nitrogen flow rate has not yet fallen significantly and the unit continues to run well.

Bringing the System On-line

If you find that the system is off-line, first try to reach an operator or a member of the beamline staff. If you cannot locate a staff member, you may try to use the following instructions to bring the cooling system on line.

1. Check that the power is OFF. The switch is located on the back of the controller.
2. Then turn the power ON and wait for the system to complete its self checks. The screen should read "ready for use with cold head #xxx".
3. Press the "program" button. The screen should change. Using the up or down arrow key, choose "RAMP" and press "enter".
4. The cursor should be in the column "rate" now. Set the rate using the "fast arrow" keys to 300 k/hr and press "enter".
5. The cursor should now be in the "temp" column. Using the arrow keys (or fast arrows) adjust the temperature to either 95Kelvin or 100Kelvin, and press the "enter" key.
6. The cursor should be in the "function" column now (below "ramp"). Pressing "start" will make the controller bring the cooler to your set temperature. If you now press "screen" the display will change to normal operational display.

Ice Crystals Forming on Sample

If ice crystals or "snow" begin to accumulate on your crystal, and you do not believe the conditions under which the crystal was frozen are to blame, a likely cause is the misalignment of the coldhead nozzle or the need to adjust the dry air sheath surrounding the nitrogen stream. See "Aligning the Coldhead" and "Optimizing the Laminar Flow" below.

Aligning the Coldhead

A crucial decision is how close to put the snout of the Cryostream to your specimen. We suggest that you bring the cooler down until you can see the shadow of its business end in the crystal-viewing microscope, then back it off until that shadow is just at the edge of the field of view.

If you suspect that the coldhead nozzle is not pointing directly at the crystal, notify beamline staff; they have an alignment tool that can be used to adjust the nozzle accurately.

Optimizing the Laminar Flow

The plume of nitrogen, which is produced by the laminar flow of an outer dry air stream and an innner nitrogen stream, can be optimized with the "flashlight test." The plume is comprised of an "invisible" section (that directly emerges from the coldhead nozzle), followed by a wispy, visible plume. It is desirable to lengthen the invisible section as much as possible. With the lights out in the hutch, shine a flashlight towards the coldstream nozzle to highlight the nitrogen plume. To maximize the length of the invisible section of the plume (within which the crystal will reside), adjust the dry air flow. It is not recommended, however, to adjust the dry air flow to levels much higher than 10 L/min; the proper laminar flow will not be maintained and the crystal could be blown from its support.