Cheryl, Rodica

On Monday we started aligning the TGG crystals inside the Faraday magnet, and found that we could not get the same rotation as at LLO. The single TGG crystal was rotating properly 22.5 deg, but the double crystal system was rotating the difference instead of sum of the individual rotations. We realized that the magnetic field orientation inside the magnet is OPPOSITE to the one in the LLO magnet, for the same mechanical orientation (end cap to right as described in E0900301 assembly document). We decided to rotate the magnet so that now the configurations/rotations at LLO and LHO are the same, even if the mechanical assembly shows now the LHO magnet reversed.

Once the magnet was rotated and we re-centered the beam through, was very easy to position the crystals  for the optimum rotation.

Next we hit another snag - we noticed that one of the threaded rods used to lock the crystal holders in place on each side of the magnet would be interfering with the heat sink, since the holes in the magnet housing were too low. We removed the crystals again, and unbuckled the omega-shaped straps and rotated the magnet about its axis to clear the bottom space for the heat sink.

At this moment we re-inspected the crystals under bright light and they still look nice and clean. A couple of tiny spots which didn't blow off, but we assesed they did not need recleaning. 

We firmly retighten the cap on the quartz crystal, which surprisingly was slightly loose, probably from twisting/untwisting the holder to insert inside the dust sleeve in the magnet. We also wiped again the inside of the dust shield with IPA.

Finally we inserted the crystals back in the magnet and optimized the positioning:

TGG+QR

TGG+QR+TGG