The Endcap Muon Alignment System is based on the need to locate each of the 360 Endcap cathode strip chambers (CSC) with respect to the CMS Tracking System with an accuracy ~ 200 µm. It is part of the overall Muon Alignment effort, which also includes the Barrel Muon Alignment System and the Link Alignment System.
The Barrel Muon Alignment System is built around a rigid and dimensionally stable lattice works called MABs (Module for Alignment of Barrel). There are 6 MABs attached to the barrel yoke at each end of the barrel, 60 degrees apart in phi. These outer MAB positions are defined in the CMS tracker coordinate system by the Link Alignment System.
The Link Alignment System will monitor the position of the central Tracker using laser sources and transparent 2D CMOS CCD sensors. Each Link system f plane is defined by measurement of three points in the tracker (via the Link laser and sensors) plus laser levels. This plane is then turned and projected onto two MAB sensors. With these point measurements, MAB laser levels and MAB calibration, the positions of the outer MABs are defined in the Central Tracker system.
The Endcap Muon Alignment System utilizes2D CCD optical Transfer Line reference sensors mounted on these MABs to define six cross hair laser lines which transit across all of CMS from one Endcap to the other. These sensors are our fiducials for position definition in the Tracker system. Laser sources on each end of these Transfer lines operate alternately to provide a total of twelve lines of alignment reference. The system relies on the MABs position and rigidity to align the CSCs in phi, R and Z (Figure 1).
The Endcap Muon Alignment System utilizes an optical sensor composed of four linear CCDs (2048 pixels) in a picture frame configuration to sense the position of two crossed lines of laser light passing through the sensor. These CCDs are perpendicular to and rotated ninety degrees from the laser lines. Through the use of a tapered roof reflector, optical attenuator windows, diffuser and background optical filter; the sensor is capable of detecting laser cross lines from two opposing directions. This provides position measurement from two directions. The readout of the sensor is controlled by a DSP which scans in the double sampling CCD pixel data, stores digital conversions, stores and makes background subtraction to the data, and generates fits to the digital data spectra (means, rms). The system transmits the data (LVDS in CSC region) finally through a sequence of one or more Interface boards onto a RS422 data-control line to a server and host. This system is called DCOPS; digital Cptical position sensor (Figure 2).
The Endcap Muon Alignment System will use the 2D CCD optical sensors attached to the MABs to define twelve Transfer Optical lasers cross hair lines across CMS. The derived Transfer cross hair laser lines will locate endpoint 2D CCD optical Transfer sensors and mechanical Transfer plates on all Endcap Iron discs. See (Figure 1).
(For more detail review see Endcap Muon Alignment System.pdf)
The new Alignment Home page can be found at,
" CMS DCOPS READOUT BOARD".