1. LumiCal mechanical design, integration with LDC and laser alignment
Wojciech Wierba
Institute of Nuclear Physics PAN
Cracow, Poland
IRENG07, SLAC,

2. Outline of talk Mechanical design: Integration with LDC:
dimensions, space for FE electronics, cables & cooling.
Integration with LDC:
LumiCal fixing, cables & cooling patch, beam pipe shape, opening scenario.
LumiCal alignment:
requirements, solutions, problems

3. Mechanical design Very challenging project
Two half barrels to clamp LumiCal on the beam pipe
30 tungsten/silicon detector layers
Odd/even planes rotated by 7.5 degree
Total weight of ~250 kg (one LumiCal)
Self supporting design of the tungsten structure
„C” frames for supporting cables, cooling, alignment
Movable support to open LumiCal – temporary support necessary
Very challenging project
Accuracy in Si sensors placement in order of a few micrometers

4. Mechanical design „C” frame Cables, cooling FE electronics Si detector
Inner det. radius
Inner mech. radius
Barrel closing
Movable support

5. LumiCal mech. dimensions
Inner mech. radius (96 mm) has to be smaller by ~4 mm than inner det. (100 mm) radius because of straight line cutting of Si wafer.
Outer det. radius is limited by the 6”
Si wafer size.

6. LumiCal cross section Si detectors glued to ceramic
support or directly to tungsten
absorber.
Si detectors glued to each
tungsten plate (better energy
resolution) or to every second
tungsten plate on both sides
(very precision machining of
a half of tungsten plates.
The gap between plates
should be reduced from 1.5 mm
to ~1 mm (or less) using bump
bonding (better energy res.).

7. Water cooling Power dissipation ~20 W with cycled electronics
Water used for cooling and temperature stabilization
Underpreasure
cooling system to
avoid leakages

8. Integration with LDC How to fix LumiCal? (~250 kg)
Where to put signal, power cables and cooling pipes? (~10-20 cm2)
Beam pipe shape – minimize the material in front of LumiCal
Opening scenario (Vertex, TPC maintenance)

9. LumiCal inside LDC
LumiCal can be mounted to special support fixed to the square ‘construction’ pipe.
Cables and cooling water pipes can be feed out in the gap between TPC and ECal endcap.
Space for connectors
Access to connectors
LumiCal has to be centered on the outgoing beam.

10. Auxiliary systems
Output digital links: max. 360 TP cables LVDS (estimated 180)
Power cables: 6 power lines ~5-10 mm2
Control cables (+clock): a few TP cables coax cables
Water cooling: ~4 copper pipes ~10 mm dia.
Thermal insulation of the LumiCal to prevent temperature changes

11. Beam pipe centered on detector axis
Solution not convenient for BeamCal and vacuum (to small pipe diameter)

12. Beam pipe centered on outgoing beam
Better for BeamCal and vacuum, the LHCal has to be centered on
the outgoing beam. The beam pipe diameter between LumiCal and BeamCal
has to be discussed more carefully.

13. Opening scenario
It is not necessary to open and take out LumiCal for Vertex and TPC maintenance.
But, to pull out TPC, it is necessary to disconnect cables and cooling pipes.
Need space for connectors and access to cables and pipes.
For LumiCal maintenance (beam pipe exchange) it is necessary to install temporary support with movable cars.
Disconnect cables and cooling pipes
Unscrew halfbarrels and move both LumiCal parts out.

14. Two LumiCal’s alignment
LumiCal x, y position with respect to the beam (incoming) should be known with accuracy better than ~700 µm (better ~ µm) (LumiCal’s will be centered on outgoing beam)
Distance between two LumiCal’s should be known with accuracy better than ~ µm (14 mrad angle)

15. Alignment measurement based on beam pipe and BPM.s
Reflective laser distance measurement – accuracy ~1-5 µm, resolution ~ µm
Mirrors glued to beam pipe
Calibration of sensors procedure – detector push-pull solution (?)
Calibration of sensors procedure after power fault (?)
Beam pipe (well measured in lab before installing, temperature and tension sensors for corrections) with installed BPM
(BPM’s also on outgoing beam?)
Laser beams inside ‘carbon’ pipe (need holes, but possible)

16. LumiCal laser displacement measurement
Two laser beams, one perpendicular, second with the angle of 45˚ to the CCD/CMOS sensor surface, are used to calculate the position shift.
The CCD camera and lasers can be fixed to the LumiCal and beam pipe.
We foresee 3 sensors (or more) to measure tilt of each LumiCal.
Six (?) laser beams from one to another LumiCal passing inside the ‘carbon support’ pipe can be used to measure the relative position shift (the method described above can be used) and the distance between two LumiCal’s (very challenging, not solved yet).
The measurements were performed on a proof-of-principle basis and achieved the accuracy of about ± 0.5 μm in x, y and ± 1 µm in z direction. Thermal stability of the prototype is ~0.7 µm/ºC

17. Summary Very challenging project:
precisely positioned Si sensors (inner radius accuracy < ~4 µm), x & y alignment with respect to the beam < ~700 µm, distance between Calorimeters < ~100 µm, tilts < ~10 mrad.
Alignment is a crucial task:
distance between LumiCals (z) should be known better than ~100 µm over 4.5 m.
A lot of problems to be solved, a lot of work to be done…