Freiburg 7/07/20001 laser beam lens CCD (long arm) screen + grid CCD (short arm) glass plates at  45° STAMP : Saclay Telescope for the Alignment of Many Points STAMP characteristics (Freiburg/Saclay DATCHA version) : 2 arms (long & short) for the measurement of the laser beam position ( y, z) and direction (  y,  z) Absolute positioning (using fiducial grids) Precision on laser position in the STAMP local coordinate system:  y,z ~ 10  m ;   y,  z ~ 50  rad Dynamical range (mm) : 30*38 with peripheral grids (screen size: 40*45) Transparency ~ 92%  laser = 685 nm (  0.2 mW) Dimensions (mm) : 290 * 100 * 50 z y x

Freiburg 7/07/20002 pixel unit laser spot on CCD (demagnification: g ~ 1/10) reconstructed spot position reconstruction precision on the screen,  = 10  m  on the CCD (  g): 1  m (  13 % of a pixel). reference laser beam (TEM 00 from pigtail) x screen + fiducial grid LEDs for calibration with the grid lens 290 mm 40 mm 100 mm CCD laser spot on screen STAMP top view STAMP PRINCIPLE:

Freiburg 7/07/20003 STAMP CALIBRATION (1) (mechanical reference, spheres - -, not shown ) external camera looking at the grid of the 2 nd arm (long arm) or at the reference grid support cube of the reference grid at the mirrored position of the 2 nd grid (with respect to the reflecting face of the 2 nd glass plate) 2 nd grid (from the long arm) Goal: Correct for the unprecise mechanical positioning of the glass plates and the fiducial grids. Principle: Build a reference STAMP out of 2 precisely known positions of a reference grid (using CMM + optical control) With the same camera, compare the STAMP grid seen by reflection on the glass plate with the reference grid.

Freiburg 7/07/20004 The positions of the reference grids w.r.t. the STAMP support balls of the calibration bench (measured with a CMM and an optical bench) define the reference STAMP (calistamp) with its transfer matrix T : y z yy zz T x y s s x y l l Laser coordinates Spot coordinates on the 2 screens (short and long arms) 2 set of calibration constants (for each arm): Calistamp grid to STAMP grid :  x,  y,  z, scale(x), scale(y) + 5 parameters to account for STAMP screen distortions (photo paper) 4 deviation constants:  x,  y,  x,  y STAMP CALIBRATION (2) T is calculated with a software simulation program. The calibration constants are used for the corrections of the measured spot coordinates. uLong term calibration constants, derived from the ‘ CALISTAMP ’ calibration (done only once).

Freiburg 7/07/20005 mm STAMP deviations Reconstructed grids: Stamp grid (peripheral) Calistamp grid (full) Stamp/calistamp grid fit quality: xx yy 22 Arm nb

Freiburg 7/07/20006 Stability of ‘ CALISTAMP’ calibration constants: Comparison of calibration constants from two calibration runs taken at 2 monthes interval (25/01/2000 and 22/03/2000): The vertical scale shows the maximum effect of the difference (i.e. at the grid edges). The horizontal scale refers to the 12 short arms and the 12 long arms for the 12 DATCHA STAMPs Stamp/calistamp grid position  x,  y Stamp/calistamp grid rotation and x-y scales Stamp deviations  y,  z mm

Freiburg 7/07/20007 STAMP grid to CCD pixels :  x,  y, , demagnifications (x, y) + 5 parameters to account for lens aberrations (identical for all arms) uShort term calibration constants, derived from illuminated screen images STAMP CALIBRATION (3) Present difficulties: Permanent illumination system (red LEDs) not yet installed Calibration done after removal of STAMP from their supports and after removal of a light protection cover made out of scotch tapes: CCDs may have moved during this operation (stability < 1  m required). 22 Stamp grid fit quality: xx yy

Freiburg 7/07/20008 xxx laser ~ 1.7 m fixed Stamp Stamp on a movable platform FREIBURG 4m TEST: Run conditions: No shielding tubes All fans on All light off

Freiburg 7/07/20009 y3y3 y1y1 x1x1 o1o1 y o1 y2y2 x2x2 o2o2 x3x3 o3o3 sag y y o3 Measured quantities in the 4m test: Support 1 Support 3 Support 2 The local support coordinate systems are defined from the 3 balls (cone/slot/flat) positions.  y1  y3 Quantities measured by the STAMP and the CMM: Sagittas : sag y, sag z Coordinates of the external frames in the local coordinate frame of the central support: y o1, z o1, y o3, z o3,  y1,  z1,  y3,  z3 ( For the STAMP: assume that the axis o 1 y 1 and o 3 y 3 are parallel to the x 2 o 2 y 2 plane) cone slot flat

Freiburg 7/07/ Results of the 4m test: 9 data sets: 7 different positions of support 2, 2 runs per data set pos 0_1 : Reference positions pos 0_2 : STAMP 2 removed and remounted pos 1 : 12 mm shift in z (laser moved) pos 2 : add a 10 mrad tilt around y axis (images mixed up > missing) pos 3 : remove the 12 mm z shift pos 4 : add a 10 mm shift in y (laser moved) pos 5 : remove the tilt around y pos 6_1 : back to the reference position pos 6_2 : laser moved

Freiburg 7/07/ Measured quantities in the 14m test: STAMP 1 STAMP 3 STAMP 2 Quantities measured by the STAMP : Coordinates of the external frames in the local coordinate frame of the STAMP 2 support: y o1, z o1, y o3, z o3, y o4, z o4,  y1,  z1,  y3,  z3,  y4,  z4 ( assuming that the axis o 1 y 1, o 3 y 3 and o 4 y 4 are parallel to the x 2 o 2 y 2 plane) y2y2 x2x2 x y1y1 x1x1 x y3y3 x3x3 x y4y4 x4x4 x STAMP 4 mirrors 3390 mm 5630 mm 4260 mm Quantities measured by the CMM : Coordinates of the balls which defines the local coordinate frame of the STAMP 2 support. Spot at 14 m

Freiburg 7/07/ Present problems: Nices features: Use commercial products (CCD, glass plates, lenses). No precision mechanics required. Can easily be improved with new CCDs ( larger CCD => shorter device). Large range (from 30x38 mm to 40x40mm with the LED scheme shown below). Can work with visible laser light. Fast and simple calibration (1 week for 180 STAMPs). Radiation hardness (same technology as the TC255 tested at Prospero). High transparency : 56% of intensity left after 7 STAMPs (intermediate  ray with 4 MDT and 3 TGC layers). The DATCHA/Freiburg STAMP has been built with a too soft aluminium alloy with ball inprints larger than 10  m. When working with visible laser, some light protection (short tubes ) may be needed to protect from parasitic light. May be solved by using a pulsed laser and background image subtraction (not done in the Freiburg test). Bad laser optics used for the Freiburg test (problem at 14 m). Size (length = 290mm). With a twice as large CCD (presently 4 x 3.5 mm for the TC237), the demagnification can be reduced to 1/5 and the length decreased down to 200 mm. The thick glass plate (5mm) can possibly be replaced by a thin mylar foil (10  m) canceling the secondary reflection and the beam deviation. The LED system for illumination of the grid during the runs for the control of the lens-CCD positions w.r.t. the screen has not yet been tested). Simulation shows that the grid can be replaced by 4 LEDs at the screen corners (see figure). and potential improvements:

Freiburg 7/07/ Integration inside the ATLAS spectrometer : The principle of the STAMP implementation in the End Cap spectrometer is shown on the sketch on the right. The laser can be placed either at the EI or at the EO layer. No STAMP size problem is expected st the EM and EO layers. At EI, it is possible to replace the STAMP by the laser itself. This may even simplify the system implementation with the intermediate polar beam (large distance between the bar and the beam, which requires a periscope system when optical sensors are used. EI bar platform Laser head Piezo aiming system ( mm, remote control) Laser fiber

Freiburg 7/07/ STAMP cost table : Mechanics 2000 FF glass plates 300 x FF CCD TC x FF lenses 50 x FF TOTAL 3300 FF (500 Euros)