PPT Slide
Why not use wake field suppressor strips ?
- design very difficult (we could not find, so far, a satisfactory solution)
Remember: four 130 cm long, very thin strips which must
(a) be connected to exit foil
(b) put under tension (thermal expansion and inward motion of exit foil, few mm)
(d) not touch the detector boxes
- even assuming unrealistic† thickness of 10 ?m (stainless steel), then
? multiple scattering corresponds to about
(3.4 - 83) ? 10 ?m ? 8.9/1.76 ? 170 - 4200 ?m of “perpendicular” Al foil
†Due to resistive overheating. Compare to HERA-B case:
current Iherab = Ilhcb /10 (and only one beam),
resistance Rherab = Rlhcb ? 10?m/5?m ? 7mm/12.7mm ? Rlhcb ? 1.1
? heat load Plhcb = Pherab ? 102 ? 2 / 1.1 ? 180 .
(and HERA-B observed already a strip temperature increase)
- have to come closer to the beams than the detector boxes
r ? 4 mm ? more background, reduced efficiencies
- introduce a risk: what if the aperture requirements at startup are worse than currently assumed ?
- WF calculations showed that, in “open” position, strips do not shield sufficiently (few kW of WF losses)
- what if one strip breaks at runtime? (and, in fact, a strip did broke at HERA-B)