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Concept of the (pre) alignment of the QD0 magnets HvdG, Dec 2010

Concept of the (pre) alignment of the QD0 magnets HvdG, Dec 2010. Each quadrupole is equipped with two X&Y reference-defining-rings (hard steel, roundness better than 1 μm, diameter precision better than 10 μm), at both ends of the magnet.

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Concept of the (pre) alignment of the QD0 magnets HvdG, Dec 2010

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  1. Concept of the (pre) alignment of the QD0 magnets HvdG, Dec 2010

  2. Each quadrupole is equipped with two X&Y reference-defining-rings (hard steel, roundness better than 1 μm, diameter precision better than 10 μm), at both ends of the magnet.

  3. 8 radial spokes are facing each of the ring’s outer surface, transferring the radial reference to a larger radius

  4. The radial alignment of the tips of a set of four spokes (two inner and two outer spokes). Rasnik optical path well (temperature) shielded. Alu tubes foam shield

  5. Spoke: principle Two types: inner and outer Spoke core: options:Alu, StainlessSteel, Zerodur, Invar Core temperature sensors Core: heated by resistive wire Core is only loosely attached to outer tube Outer tube: has shielding and protection function. It may consists of two coaxial tubes with foam insulation in between.

  6. Calibration: • On calibration station, measure (1D) alignment by means of • the rotation of gauge blocks equipped with Rasnik components • After that, place two outer and two inner spokes: record Rasnik/RasDif • readings, and correct readings with the station’s alignment data • Exchange one by one the inner and outer spokes: read Rasnik/RasDif • data. • The only precision parts are: • the four reference rings: roundness better than 1 micron • the gauge blocks: dimension better than 1micron • The connection of the spoke and ring should be precise better than a micron • The (effective) dimension of the spoke should not change more than one • micron. This can be realised by monitoring its temperature, and by taking care • that there are no external forces acting on it. Only differences in temperature • of the pokes within a spoke wheel matter. Since the average radial value of 8 • alignment systems corresponds with the magnet alignment, the latter can • be measured with 1 micron precision (in terms of the position of the ring centers). • We assume that the shielding of the Rasnik systems is adequate.

  7. image pixel sensor light source diffraction plate hole outer spoke inner spoke

  8. Fig. 2. The position of a QD0 face center, with respect to its RR, is monitored by four Rasnik Proximity systems. The axii of all four systems are parallel to the beam direction (Z).

  9. Fig. 3. The RR-side tip of a spoke. Fig. 4. The spoke is pressed onto its reference plane by means of a fitting.

  10. not for the record: Can we have a pencil line-of-sight along the beam pipe, inside of the vertex detector, of only 1 mm diameter?

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