1. New ATLAS VI Mechanical Tolerances and Aperture Approvals1

2. Mechanical Tolerances for New Layout
Gap between supports and IST to allow sliding and thermal expansion
Sag of IST and beam pipe when installed
IST
Beam Pipe
Installation survey for global position
Survey for straightness of IST
Circularity 2

3. New Mechanical Tolerances
Mechanical group
Sub-group
Radial tolerance (mm)
Construction
Circularity
0.1
Gap for sliding and thermal expansion
0.45 (0.2 for sliding radial clearance and 0.25 for thermal expansion during bake-out)
Installation
Alignment of installed IST
1.0 (Ref: EDMS )
Sag of IST/beam pipe package when installed
0.4
Construction and Deflection
Total
1.95 3

4. Summary for ATLAS Aperture Tolerances
Radial Tolerance
Value (mm)
Mechanical Tolerances
1.95 mm
Survey and alignment case 1
2.6 mm at a 2σ, 95 % confidence level when installed with reference to the low beta magnets [NOTE: this will be checked relative to the old beam position and this precision is actually 1 mm, but take worst case for a factor of safety]
Stability
2.5 mm= (1.25 mm x 2 FOS) – [NOTE: this assumes 5 years between realignments with a factor of safety of 2. In reality it has been shown from LEB meeting 4 Feb 2011 that the beam is stable to mm over the year and that the Q1 magnets likely move with the ATLAS cavern]
Beam stay clear aperture
15.45 mm
Total
22.5 mm 4