BCAM Development

© 2020, Kevan Hashemi, Brandeis University




Starting in September 2020, we record here our day-to-day work on BCAM cameras, sources, and electronics. Refer to the BCAM User Manual for a description of the BCAM.


[02-SEP-20] The source plates we made for the ATLAS New Small Wheel (nSW) hole the ferrules at the end of four optical fibers, with two facing one way and two the other. We have the plates made, insert 2.5-mm zirconia ferrules, measure the center-line of the ferrules with respect to the plate's BCAM-like kinematic mounting balls, intersect the center-line of each ferrule with a plane a set distance from the front or back face of the plate, and so obtain four points in mount coordinates that represent the centers of the polished ends of the fibers when we later install fiber-loaded ferrules in the source plates. The distance from the fiber tip to the face of the plate is not critical, because it is parallel to the axis of the viewing BCAM. The fiber ferrules we push all the way into their mounting hole and by construction the tip is within ±100 μm of the correct distance from the face.

Figure: nSW Wide Source Plate with Fibers Loaded. Each pair of sources is separated by 60 mm. In the narrow plates, the separation is 30 mm.

We made two types of source plate: wide and narrow. The wide plates have the sources on each face separated by 60 mm in the direction perpendicular to the fiber axis, while the narrow plates have their sources separated by 30 mm. We are installing roughly 2000 wide source plates and 200 narrow plates in the nSW.

We translate source plates across our granite beam, using the method we describe in BCAM Calibration on the Granite Beam, and so obtain a measurement of the separation of the two sources. We fasten the source plate to a kinematic mount and displace the mount perpendicular to the axis of a BCAM camera, at a range of one or two meters, with gauge blocks to set the displacements. We move 35-mm in 5-mm steps. We compare the separation we measure on the granite beam with that which we obtained with the CMM.

Figure: nSW Wide Source Separation Measured by CMM and Granite Beam, Comparison. By Xinfei Huang.

The granite beam measurement of separation is roughly 0.05% smaller than the CMM measurement. We repeat these measurements for BCAM sources, which are lasers mounted on the front face of a BCAM. We measure the separation of source on ten BCAMs, first with the sources separated in the horizontal direction while we translate them horizontally, then with the sources separated vertically while we again translate horizontally. Once again, the granite beam measurement is 0.05% smaller, and we are pleased to note that the vertical and horizontal measurements give the same result on the beam. Our calibration of magnification by horizontal displacement gives us ±0.01% accurate calibration in the vertical direction as well.

Figure: N-BCAM Source Separation Measured by CMM and Granite Beam, Comparison. With sources arranged horizontally (left) and vertically (right). By Xinfei Huang.

Meanwhile, we are constructing the alignment system of the nSW at CERN, and we look at the self-consistency of the instruments on a partially-constructed wheel. We have alignment bar measurements by the CMM at Freiburg, BCAM calibrations made at Brandeis and checked at CERN, and source plate measurements made at Brandeis. We take images of all sources with all cameras that view the sources, and run ARAMyS to reconstruct the bar positions and chamber positions. In ARAMyS Source Plate Calibration Study, we find that the optical location of the sources appears to be 0.7 mm inside the ferrule.

[07-OCT-20] We have a new Azimuthal BCAM adaptor plate, shown below, that brings the azimuthal BCAM pivot point to the axis of the roll cage.

Figure: Azimuthal Adaptor Plate on Front Mount of Backward-Facing Roll Cage. Use this arrangement for Black Azimuthal BCAMs. Blue and Black Azimuthal BCAMs shown next to roll cage.

We say the base plate is forward-facing when the arrow made by its kinematic mounting balls points towards the source block, which is to the right in the view above. We say it is backward-facing when this same arrow points away from the source block, as shown above. When we place the roll cage on the base plate, regardless of the orientation of the base plate, the kinematic mount closest to the source block is the front mount and the one farthest from the source block is the rear mount. The front and rear mounts share the two middle balls on the roll cage.

Figure: Small Source Block for BCAM Camera Calibration. Laser diode sources on 16-mm square, as required by the 50-mrad field of view of Azimuthal and Polar BCAMs.

We have two source blocks for BCAM camera calibration. A large one with optical fiber sources on a 50-mm square, and a small one with laser diode sources on a 16-mm square. Both are shown below.

Figure: Large Source Block for BCAM Camera Calibration. Optical fiber sources on 52-mm square, as required by the 100-mrad field of view of N, D, and H-BCAMs.

With the base plate in the backward direction, the plate on the forward mount, we can calibrate the Black Azimuthal BCAM, so long as we use the small source block. We calibrate Blue Azimuthal BCAMs with the base forward using the front mount.