Effect of MDI Design on BDS Collimation Depth

1
Effect of MDI Design on BDS Collimation Depth

• Frank Jackson
• ASTeC Daresbury Laboratory
• Cockcroft Institute

2
Contents

• Collimation depth and method
• RDR collimation depth (SiD MDI)
• Other MDIs (GLD, GLC)
• Other parameter sets

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Collimation Depth Philosophy

• Halo synchrotron radiation (SR) from final
  doublet must pass cleanly through interaction
  region (IR)
• Small apertures in the IR include vertex
  detector, masking, forward calorimetry,
  extraction quadrupoles
• Halo size divergence at final doublet entrance
  must be constrained to collimation depth
• Effective collimation depth (actual spoiler gaps)
  may need to be tighter to compensate for
  spoiler?FD transport

4
Collimation Depth Method

• Possible to solve problem analytically
• SR fan profile through detector depends on halo
  size in FD
• Halo size in FD depends on collimation aperture
• Constrain SR fan size to solve for collimation
  depth
• Many SR emission points
• No unique solution solution ellipse in x, y

IR Aperture
SR fan profile
y
s
Collimated beam halo
x
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Implementing the Method

• Analytical method implemented by O. Napoly
  (Saclay) for TESLA TDR (2001)
• Calculates the solution ellipses from very many
  SR emission points through whole FD
• Halo phase space at each emission point is
  reverse-traced (linear, on-energy optics) from
  IP.
• Repeat analysis for each small IR aperture
• Find global collimation depth

vtx beamcal mask
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RDR collimation depth

• IR design assumes SID-like detector, L 3.51
• Collimation depth constraint comes from first
  extraction quad (R 15mm)
• Beamcal mask (r12mm) comes close to SR fan
• 11.9?x , 70.7?y ? spoiler full gaps 2.7mm (x)
  1.3mm (y)

2006e
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MDI Impact on Collimation Depth

• MDI depends on final detector concept
• Effect of changing MDI on IR parameters
• L
• Forward calorimetry geometry
• Extraction line design
• (possibly) final quad changes
• Difficult to evaluate the effect of change in MDI
  on collimation depth
• Complete MDI designs dont exist for all the
  concepts

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MDI parameter space

• Need complete MDI parameter set to calculate each
  collimation depth
• Used detector outline docs to get information
  (red means guess)
• Extraction quad QEX is the limiting aperture in
  all cases
• But my QEX guesses are very uncertain for LDC and
  GLD
• Results show expected - SR fan size at a fixed
  point from IP increases with L (for fixed FD)

Concept L Beamcal mask r, z (mm) Beamcal r, z (mm) QEX r, z (mm) FD params Collim depth x, y
SID 3.51 12, 331 15, 334 15, 656 2006e 11.9, 70.7
LDC 4.05 13, 355 13, 375 15, 656 2006e 10.5, 55.6
GLD 4.50 20, 430 20, 450 15, 656 2006e 9.5, 46.7
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Parameter Sets

• Calculation has been done for nominal parameter
  set
• Other parameter sets have smaller ?? larger IP
  angles ? tighter collimation
• Low P high lumi, ? twice as small as
  nominal
• Reduced collimation depth by factor 1/?2
• 8.5?x , 50?y

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Alternative Crossing Angles?

• 2mrad remains alternative small angle option
• Lack of symmetry in problem, shared magnets for
  incoming/extracted beam
• Force symmetry by using virtual apertures that
  ensure SR clearance

incoming beam axis
detector axis
1.0mrad
2.0mrad
outgoing beam axis
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Conclusion

• Latest extraction line design now constrains
  collimation depth
• Impossible to say which is the best detector
  concept for collimation, without complete MDI
  design (inc. extraction line) for each concept.
• Greater L will probably lead to tighter
  collimation
• Philosophy has been for perfect clean SR passing
  through IR
• More sophisticated analysis
• Can we tolerate SR on the extraction quads and
  beamcal and so relax collimation depths
• The answer to those questions will be strongly
  affected by MDI design.

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Backup Slides
13
SID Concept Geometry

• L3.51 m
• BeamCal inner radius 15mm (p28, last para)
• BeamCal Beampipe inner radius 12 mm (Fig 80,
  p131)
• BeamCal LowZ covering mask radius 12mm (for 20
  mrad, p160)
• BeamCal Z location 321-334 (Table 1, p13)
• Vertex beampipe radius 12mm (fig 29, p 53)
• Much of the beamcal geometry worked out for 20
  mrad, hope it is same for 14 mrad

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GLD Concept Geometry

• L 4.5 m (first para, p96)
• BeamCal inner radius 20mm (Tab 2.13, p 97)
• BeamCal Beampipe inner radius 15mm (Tab 3.1,
  p104)
• BeamCal LowZ covering mask radius 20mm (Tab 2.13,
  p 97)
• BeamCal Z location 430-450 (2nd para, p73)
• Vertex beampipe radius 15mm (first para, p 96)
• Much of the beamcal geometry worked out for 20
  mrad, hope it is same for 14 mrad

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LDC concept

• L 4.05 m (p98)
• BeamCal inner radius 13mm (Tab 6, p 9)
• BeamCal Beampipe inner radius ???
• BeamCal LowZ covering mask ????
• BeamCal Z location 355-375 (Tab 6, p 9)
• Vertex inner radius (not beam pipe) 16mm (Table
  1, p8)
• Much of the beamcal geometry worked out for 20
  mrad, hope it is same for 14 mrad

16
GLD extraction geometry

• Justification for my guess at extraction line
  params on slide 8.
• Slide from Valencia meeting T. Tauchi Background
  Study at GLD-IR

• Has used 2006c deck designed for L3.51
• Changed QD0 position to L4.5,
• But no changes to extraction quads position
  aperture

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Off-Energy Halo?

• DBLT routine uses linear, on-energy beam
  transport
• Can cross check with BDSIM simulation
• Off-energy, collimated halo (?p 1 Gaussian),
  at FD entrance, track and plot resulting SR fan
• Plot below are for 2006c lattice

SR profile at 1st Extraction Quad (r18mm)
?p1, Gaussian
On-energy, ?p1 Gaussian
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1TeV Parameters

• IP angle Sqrt(e/b)
• From 500GeV to 1TeV, e?2e, bx?1.5bx, by?0.75by
• IP angle in y more than doubles
• Collimation depth twice as tight in y.