Cryostat Assembly

The Assembly of Michelle requires the lifting and handling of heavy assemblies and usually requires the presence of at least two and preferably 3-4 people. All such staff should be conversant with safe handling procedures and be equipped with safety boots and helmets, at least one should have had appropriate slinging training.  The assembly is based on the use of the Michelle Handling Manipulator and an associated hoist (at UKIRT the jib crane).The whole process is also eased by ready access to storage facilities for the unassembled modules and appropriate (wheeled) methods of moving these modules within range of the lifting facilities.

Durations:
A complete assembly from scratch as described below will take several days. As a planning guide I have given an estimated time for each major subsection at the heading level.

2.   Installing the Cryogenic Cabling (300K to 80K)

3.   Installing the Support Trusses and Radiation Shield

Figure 4.1   Lowering the main optical bench into the vacuum vessel, with the fill tubes being guided through the radiation shield.

4.2  Fit the collet clamps to the nitrogen fill tubes and push them into the holes in the radiation shield.

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Figure 4.3 Tightening the bolts holding the MOB onto the truss.

Figure 4.4 Bolting down the collet clamps from the MOB nitrogen fill tubes. Note that the Radiation Shield Heater panel shown here now has clamping bars across the backing plate.

Figure 4.5   Installing the support collars on the nitrogen fill tubes.

Figure 5.1a. Lowering the CTI1020 cold head in the vacuum vessel. (Note that the copper wick assembly has now been replaced by a solid copper sleeve)

Figure 5.1b. Bolting the CTI1020 cold head onto the vacuum vessel.

5.2  Tighten the eight screws which mount the the copper collar on the radiation shield to the copper sleeve attached to the 1st stage of the coldhead. These should be torqued to M6 setting.

(NEW PHOTO REQD)

Figure 5.2.  The second stage adapter plate can be seen at the end of the 2nd stage column, protruding through the radiation shield. The wicking bundles go from the adapter plate to the copper block which is bolted to the main optical bench at the bottom of the picture. The circular collar at the top clamps the radiation shield onto the sleeve from the first stage. The first and second stage temperature sensors are shown.

5.3  Install the Radiation Shield temperature sensor on the copper plate behind the field rotator motor and attach connector.  (This may have not been removed as now clear of area.)

5.4  Tighten the six 6-32UNC screws and their invar spacers which hold the 2nd stage adapter plate onto the end of the 2nd stage pillar (to required torque setting). This is an awkward operation requiring a short Allen key.

5.5  Install the temperature sensor on the second stage adapter plate and attach connector.

5.6  Install the 2nd stage wicking between the adapter plate and the main optical bench (see Figure 7). The screws are M5 with a torque setting of ...

Figure 6.1.   Installing the Joule-Thomson cooler in the centre section of the vacuum vessel. Note that it now comes fitted with it's own Radiation Shield which will obscure the inner pipework. This operation will be done in Hawaii using the Handling Trolley.

Figure 6..2. The electrically insulating inserts which screw the Joule-Thomson cooler into the centre section of the vacuum vessel.

Figure 6.3 The interface between the J-T cooler first stage and the radiation shield. The green circle marks the position of the electrically insulating moat. (NEW PHOTO req'd)   Check that the J-T cooler is electrically isolated from the cryostat.  Fit the small flat shield to the end of the J-T radiation shield.

7   Installing the Slit wheel/Field Rotator Assembly (20 mins)

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Fit tape along gaps at the rearmost of the motor plate as this is a known light leak area.

Figure 8.1   Lowering the filter wheel assembly into the front optical bench. (Alignment features highlighted)

Figure 8.3. Mounting the Front Optical Bench onto the Main Optical Bench.

Figure 8.4. Aligning the FOB to the MOB. The three reference pads are circled in green in the lower picture; the filter wheel assembly and fore-optics are not shown for clarity.

10.   Installing the Detector Box and array

The detector in its gold coloured box should normally be mounted as late as possible in the assembly procedure to avoid damage. It should be stored in a protected, dry atmosphere and carried in a container that keeps it electrically contacted to ground through an approximately 1 million Ohm resistance (to prevent fast changes in potential difference and hence high instantaneous current flow).

1. To the top of the Joule-Thomson cooler, which should in turn be connected to the telescope ground.
2. To a conducting mat placed on which the person installing the detector box should stand.
3. To a wrist strap on the installer.
4. To the grounding stud on the gold detector box.

   

   Figure 10.1. The detector box and translation mechanism grounding scheme for electrically safe installation.

Figure 10.2. Detail of the mounting screw arrangement for the detector box.

Figure 10.5. Grounding the detector box when the detector cables are not connected.

Figure 10.6. Installing the Detector Box's 25K Radiation Shield

Figure 10.7. The copper arm from the J-T Cooler to the detector box.

Figure 10.8. The detector cable assembly mounted on the copper cooling arm.

Figure 10.9a and 10.9b. The double layer aluminium 4K radiation shield foil radiation.

Figure 10.10. The assembled detector box, with the 4K cooling circuit installed.

11.2  Mechanism Check
Using CCS dm screens do a force datum on the mechanisms in turn.   One person should observe the mechanism itseld for motion, noise etc., whilst the other should observe the dm screen for datum switch operations etc.
Before driving the motors remove all perspex films used to cover the motor shafts.

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11.3  Temperature Sensor Check

Indicate temperature reading either directly from scanners or from CCS

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11.8   Dismount the front section of the vacuum vessel (mass = 220kg) from its storage plate and lower it onto the centre section. This is best done with the interfacing surface tilted approx 17 deg (top of Radiation Shield horizontal).   Fit the two alignment dowels that fit the front cover (and hence the calibration unit) to the centre section.

Figure11.8. Installing the front cover of the cryostat (UKIRT configuration).

Figure 12.4. Rotating the grating drum.

Figure 12.6. Lowering the grating drum onto the main optical bench.

The wick attached to the motor which rotates the drum is tricky to access (see Figure 12.9).

Figure 12.9 The thermal wicks on the grating drive motors. The hand is pointing to the wavelength drive wick at the left (note the grey snubber bar on the radiation shield). The right hand picture shows the difficult to access grating exchange motor wick.

Grating Assembly Mechanism Check

Before closing the grating vacuum cover the system should be connected to the Cryostat Control system to confirm the performance of the Grating mechanism and status switches. The connection to the Grating temperature sensor should also be checked. (A complete status switch check can be performed using the Status cable break-out box if desired). Before driving the motors remove all perspex films used to cover the motor shafts.

Grating Assembly Status Switches

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Grating Assembly Temperature Sensor Check

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Figure 12.13. Installing the grating drum vacuum cover.

Figure 13.1 The Calibration Unit (The Integrating Sphere is not fitted)

Figure 14.1 Mounting the On-Cryostat Detector Control Electronics Rack