In order to install the wiggler it is necessary to introduce some mechanical design details of the wiggler which are relevant to installation. A sketch of the optical bench assembly is shown in figure 1.
The wiggler is made up of two wiggler jaws separated by four gage blocks and supported by two Newport Corporation model X48 optical rails. The gage blocks establish the relative orientation of three of the degrees of freedom of the two jaws (relative tip, tilt and gap). The X48 rails establish the other three (relative transverse position and yaw). When the jaws are installed, bolts holding the jaws together also fix the second three. There are two sets of gage blocks, one for a low field configuration with a gap of approximately 14.4 mm and one for a high field configuration with a gap of 12 mm. The magnetic field of the wiggler is horizontal and the field has a strong focusing sextupole component in this direction. The good field region in the vertical direction is several millimeters so the vertical placement is not critical. The wiggler center is nominally 9 inches above the optical bench on which it will be mounted. This height is set to quite high accuracy by the manufacturer (STI Optronics) and therefore does not have to be adjusted. The wiggler will also be set perpendicular to the optical bench by STI Optronics to very high accuracy. Thus, if the optical bench is level, the magnetic field in the wiggler will be level as well. A pair of stop blocks pinned to the X48 rails determines the transverse wiggler position with respect to the rails. Two sets of pin holes are available for the two gaps. The only wiggler coordinates which must be adjusted when installing the wiggler onto the optical bench is the position on the table. The two adjustment transverse to the beam axis must be very accurate while the adjustment along the axis only needs to be good to about ±0.5 mm. Since it is straightforward to position the wiggler to ±0.005" in both directions, this is what is called for in the procedure.
The wiggler vacuum chamber is supported from the optical bench independent of the wiggler. The two wiggler jaws can be removed and reinserted without affecting the vacuum chamber position.
During initial commissioning, the wiggler jaws will be removed and stored on a 2'x4' optical breadboard with a set of spare X48 rails. Since we want to be able to check the wiggler field quality in this off-line configuration, the X48 rails on the off-line optical bench must be aligned so that the proper relation between the two wiggler jaws is maintained.
The optical bench will have 6 fiducials bolted to it. Four will be near the corners and the other two will be 9.5 inches upstream of the table center. Each will have a standard alignment ball and insert centered over one of the holes in the optical bench. The table is flat to ±0.005" so the fiducials do not need to be carefully measured in the vertical dimension. The wiggler has four alignment balls on each side whose position should be very accurately known with respect to the magnetic center of the wiggler.
I will assume here that the wiggler vacuum chamber is not available until after the wiggler bench is installed on the machine. The following procedure should be used for wiggler installation starting with the presinstallation work in the tunnel:
1. Install four optical bench support bases.
2. Align support bases.
3. Grout support bases.
The following work will be done in the machine shop. When the wiggler and optical bench are received (~Apr. 28):
4. Install the tooling balls on the optical bench. Their nominal positions with respect to the table center should be known to ±0.005" a priori without measurement.
5. Without separating the wiggler jaws , remove the X48 rails from the wiggler and replace with the spare rails.
6. Install the wiggler assembly with the spare rails onto the 2'x4' optical bench and lock down the rails with Loctite or epoxy. The rails now become a reference for the jaw alignment when they are removed from the beamline.
7. Remove the wiggler from the spare rails (again without separating the jaws), replace the original rails, and pin the stop blocks in place using the pin locations appropriate to the gage blocks being used.
8. Place the wiggler on the optical bench and slide into position to an accuracy of better than ±0.2 mm with respect to the bolt hole pattern on the table. Bolt the X48 rail brackets down.
9. If necessary, split the wiggler and install the 12 mm gap blocks. Make sure that the gage blocks are aligned with the gage pads. Pin the stop block in the 12 mm gap position.
10. Install the quadrupoles on the wiggler bench and roughly align them with respect to the wiggler axis.
After the bench is moved to the alignment area:
11. Compare the measured positions with the expected positions of the optical bench fiducials and resolve any discrepancies between the expected positions and the actuall positions.
12. Measure the wiggler position with respect to the table fiducials to the best accuracy possible. The wiggler now becomes the reference for aligning the quads.
13. Lock down the wiggler support rails with Loctite or epoxy.
14. Align the quadrupoles with respect to the wiggler and each other so that they are all collinear to within ±100 µm and collinear with the wiggler in the horizontal direction to within ±100 µm.
When resources are available:
15. Install optical bench on bases.
16. Align bench with floor grid in the FEL vault to ±0.5 mm accuracy using the table fiducials.
17. Check relative alignment of quadrupoles and wiggler. This ends the responsibility of the alignment crew until step 31. All alignment of the viewers and vacuum chamber is done by the FEL team using a boresighting telescope provided by the alignment group.
When the two optical cavity benches and their optical components are installed and aligned and the vacuum chamber and support are fabricated, cleaned and assembled:
18. Remove front wiggler jaw and the gage blocks and install wiggler vacuum chamber and support with 0.002" shim between the wiggler and the vacuum chamber. The vacuum chamber should be blanked off on all ports. Make sure that the vacuum chamber support is not tied down to the table yet. Loosen all bolts which establish the positin of the wiggler vacuum chamber with the exception of the vertical position which should be good to high precision.
19. Reinstall front jaw and gage blocks with 0.002" shim between the wiggler and the vacuum chamber. If necessary, shim the feet of the vacuum chamber support so that it lays flat on the optical bench (or loosen the screws which tie the vertical legs to the rest of the system and take up any slack). Tie the vacuum chamber support down to the table securely and tighten all the support bolts. Measure the relative position of the vacuum chamber and the wiggler using non-magnetic feeler gauges.
20. Back off the wiggler jaws and remove the shims. Replace the wiggler jaws. Verify using feeler gauges that the vacuum chamber is in the same position it was in previously with respect to the jaws.
21. Split the first and last QBs. Install alignment fiducials in the first and last QBs on the optical bench and install mirrors upstream of the first OTR viewer which allow sighting down the axis of the wiggler from the upstream end.
22. Under a clean hood, remove the blank-off flanges from the wiggler vacuum chamber and any upstream and downstream flanges. Seal the open pipes with Saran wrap and fix in place with rubber bands.
23. Using the turnbuckles on the viewer actuator assemblies, align four OTR viewers on the wiggler girder (Note that the shielded viewer cannot be adjusted) along the line defined by the first and last QBs on the optical bench. Adjust the center turnbuckle first and then the side turnbuckle.
24. Install a permanent monument on the downstream optical bench (just downstream of the exit window) which is centered on the line defined by the two quads. Note that the optical cavity mirrors must be removed for this step.
25. Install mirrors which permit one to view from the downstream end through the wiggler. Look down the center of the two quads.
26. Align an aperture on the upstream optical bench which is centered on the line defined by the two quads. This may be the MPS shutter.
27. Match the HeNe into the beam pipe from the upstream end (it may be inserted via the Brewster window or through the collimator) and align with the LSS shutter on the upstream end and the monument on the downstream end. View the laser image on each of the five viewers.
28. Retroreflect the HeNe off a spare cavity mirror and center on the center wiggler viewer. Check the position on the upstream fiducials.
29. At this point the rest of the vacuum chamber may be installed or the blank-offs may be reinstalled.
30. When the entire vacuum chamber is installed between the two fiducials on the two optical benches at either end of the FEL, slowly evacuate the chambers while monitoring the position of the intervening viewers. Correct the viewer positions if necessary.
After the vacuum chamber is in position and all elements are boresighted:
31. Measure the positions of the flanges for the five OTRs and the BPMs.
Figure 1. Sketch of elements mounted on wiggler optical bench. Electron beam enters from the right and passes in order, an OTR viewer, QB quadrupole #1, SEE BPM #1, QB quadrupole #2, the wiggler, including three OTR viewers, QB quadrupole #3, SEE BPM #2, QB quadrupole #4, and the final OTR viewer. The BPMs are aligned coarsely with the quadrupoles. The viewers are aligned via boresighting, and the quadrupoles and the wiggler are aligned using fiducials. OTR viewers actually enter from above but are shown entering from the side for clarity.