IR optimization, DID and antiDID

1
IR optimization, DID and anti-DID

• Brett Parker, Andrei Seryi
• BNL, SLAC
• October 19, 2005

2
From DID to anti-DID

• During ITRP time, suggested DID as a way to
  compensate vertical angle (100mrad) at the IP in
  machines with crossing angle, caused by detector
  solenoid field, to address polarization concerns
  (rotation of spin depolarization)
• the validity of that polarization concerns still
  not obvious, since the spin precession is small
  (a degree) and should be well predictable
• DID field reduces transverse field for incoming
  beam, but about double it for outgoing pairs
  spread out more and background is increased
• especially dramatic effect if outgoing aperture
  not optimized
• With reduced crossing angle, SR effects reduced
  considerably, and can reverse polarity of DID and
  optimize its strength for outgoing beam
  (anti-DID)
• the vertical angle still can be compensated, if
  needed, with less local correction

3
Y orbit in solenoid
5T

• With crossing angle, solenoid cause Y orbit
• ee- beams still collide head-on
• Spin rotation 3 degrees

e-
e
2005 SiD for 20mrad, coordinates at IP y
-20.7mm -- easy to compensate y -97.5 mrad
4
Synchrotron Radiation effects in solenoid

• SR effects vertical orbit cause emission of SR
  photons, growth of energy spread and consequent Y
  beam size growth
• The effect is described by Dssr which behaves as
  Dssr (Bsol Lsol qcross)5/2 and does not depend
  on energy
• The increased vertical IP beam size is to be
  calculated as s (s02 Dssr2 )1/2

Old SiD Dssr 0.3nm (20mrad) 2005 SiD Dssr
0.22nm (20mrad)
5
Standard DID

• Coil wound on detector solenoid, giving
  transverse field, such that combined field from
  solenoid, DID, and QD0 would be result in 0
  vertical angle at the IP

6
Standard DID
e
e-
IP
Dssr 0.19nm (20mrad) y and y at IP are zeroed

• For standard DID, can zero y and y at IP
• Correction is local and very effective
• No increase of SR
• But the post IP field is about doubled by DID, so
  pairs disperse more

IP
7
20mrad 2mrad IR Background Hits in the TPC
with SolenoidDID (Snowmass 2005)
Comparing configurations
Karsten Büßer
Origin of TPC photons pairs hit edge of LumiCal

• Very preliminary, not all details included (e.g.
  QD0 fringe field), apertures may be not
  optimized, could still be OK in comparison with
  detector tolerances to background (W.Kozanecky),
  but anyway, not pleasant

8
DID field and TPC operation

• Second DID topic actively discussed at Snowmass
  was compatibility of DID transverse field with
  Time Projection Chamber
• Traditionally, TPC specify requirements for field
  uniformity with certain high precision
• However, precise 3d field maps used in tracking
  reconstructions anyway
• gt Providing 3d map of solenoid field with DID
  would solve this particular TPC-DID concern
• There is another issue related to TPC track-based
  calibration

9
DID and TPC calibration

• At the last day of Snowmass and after that, in
  discussion of Witold Kozanecki and Dan Peterson,
  the following suggestion was given
• Dan Peterson clarified that a uniform magnetic
  field is required at small z for the purpose of
  performing a track-based calibration the magnetic
  field. The region of uniform field would allow us
  to isolate the effects of the field distortions
  on track trajectories from the effects of field
  distortions on the drift path. I believe that
  uniformity is less important at larger z the
  current DID design field of 0.08T at z 2.2m
  would be acceptable.
• According to Dan, the uniformity requirement is
  dB/B lt 4 10-4 for z lt 50 cm. This is about a
  factor of 10 less than the current DID design at
  z50cm.

10
DID for TPC combine two coils
Single DID. Current Ic11.68 units
Double DID. Currents Ic14.98 units Ic2-2.46
units
Approximate model

• Use two DIDs, placed at different Z, fit the
  currents to reduce the field in the center
• With combined DID, the field within z0.25R
  reduced gt30 times

11
3D calculations of new DID

• Several 3D models of DID, short and long
  versions, with same radius R3.5m were created
• 1.5m, 3.0m, 3.8m length of winding
• In field calculation the effect of detector iron
  is neglected (we checked earlier that this is
  reasonable approximation) but eventually iron
  should be included
• short and long DID combined and current
  adjusted to flatten the field in the center

12
Field of combined DID for detector with TPC

• To flatten the field, current ration short/long
  -1.245, both currents need to be increased 2.5
  times to have the same max field for combined DID
• Reduction of the field in central region (z lt
  0.5m) is about 65 times with respect to the
  single long DID, to ease TPC calibration

13
anti-DID for intermediate crossing angle

• Normal polarity of Detector Integrated Dipole
  (DID) allows to compensate locally the effect of
  crossing the solenoid field for the incoming
  beam, while the field seen by outgoing beam (and
  low energy pairs) about doubles
• Reversing polarity of Detector Integrated Dipole
  (anti-DID) could effectively zero the crossing
  angle for outgoing beam (and pairs) but would
  increase it (1.5-1.6 times) for incoming beam
• Increasing the effective crossing angle for
  incoming beam may create too much synchrotron
  radiation size growth (which depend as DsSRq5/2)
• Smaller initial crossing angle (14mrad) ease the
  use of anti-DID

14
Fields FDs
GLD field and FD with L4.5m
SiD field and FD with L3.5m

• Use 2005 field maps for SiD and GLD and older
  TESLA field for LDC
• Use 14mrad total crossing angle, L3.51m for
  SiD detector and L4.51m for GLD and LDC
• Use same FD structure, with FD quads and
  sextupoles rematched

LDC field and FD with L4.5m
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anti-DID for SiD

• Use Guinea-pig pairs and track in solenoid and
  anti-DID field
• With optimal anti-DID, more than 60 of pairs are
  directed into the extraction aperture

Optimal anti-DID
DID OFF
Normal DID
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SiD anti-DID

• High energy pairs follow initial beam trajectory,
  and go to extraction aperture
• Low energy pairs follow the field line, and also
  go to extraction aperture

Use Guinea-pig pairs for nominal ILC parameters
17
Normal DID SiD

• With normal DID, which is optimized for incoming
  beam, the high energy pairs go to extraction
  aperture, but low energy pairs directed away from
  extraction aperture

18
Incoming beam in SiD with anti-DID
QD0

• Anti-DID increase SR effects for incoming beam,
  but for 14mrad the impact is negligible ( 0.2
  on Lumi)

19
Optimal anti-DID for SiD

• Note that strength of anti-DID is smaller than
  nominal DID
• For 14mrad
• The optimal anti-DID max field is 0.0205 T
• The nominal DID max field is 0.036 T
• Thus, normal DID is 1.75 times stronger than
  anti-DID for SiD

20
anti-DID for GLD

• With optimal anti-DID, more than 50 of pairs are
  directed into the extraction aperture

Normal DID
DID OFF
Optimal anti-DID
21
GLD
Normal DID
Optimal anti-DID
reduced number of pairs plotted
22
Incoming beam in GLD with anti-DID
QD0

• Anti-DID does increase SR effects for incoming
  beam, but for 14mrad the impact is minor (less
  than 1 on Lumi)

23
Optimal anti-DID for GLD

• Field in the central region is flattened with two
  DID coils (short and long) whose currents are
  properly adjusted
• In comparison with air coil calculated field,
  this field takes into account an approximate
  effect of detector iron

24
anti-DID for LDC

• With optimal anti-DID, more than 60 of pairs are
  directed into the extraction aperture
• SR effects are larger in LDC than in GLD.
• One can use 30 weaker antiDID to reduce SR, but
  still gt50 pairs will go to extraction aperture

Optimal anti-DID
DID OFF
Normal DID
25
Optimal anti-DID
LDC
Normal DID
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Incoming beam in LDC with anti-DID
QD0
Pictures for anti-DID at 0.0235 T

• SR is larger in LDC. Can use reduced anti-DID
  strength to minimize impact on Lumi.

27
Optimal anti-DID for LDC

• Field in the central region is flattened with two
  DID coils (short and long) which current are
  properly adjusted
• Shown the field for the optimal case for pairs.
  May want to work 30 below the optimum to reduce
  SR

28
Incoming beam with anti-DID, example for SiD

• Only y at IP compensated with QD0 dipole
  corrector
• Angle y zeroed w QD0, y is free
• Both y and y zeroed with QD0 and QF1 correctors
  (difficult)

Dssr 0.37nm (14mrad) gt DL/L 0.27
Dssr 1.2nm (14mrad) gt DL/L 2.8
this picture is without anti-DID number for Dssr
is with anti-DID
Dssr 6.6nm (14mrad) gt DL/L 40
(Orbits shown are for 20mrad and for anti-DID
larger than optimal)
29
14 mrad crossing Geant model of SiD

• Takashi Maruyama modeled SiD with anti-DID
• Results already shown in Toms talk. Included
  here for completeness

QD0
QFEX2A
QDEX1B
QDEX1A
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VXD Hit comparison
Takashi Maruyama
2, 14, 20 mrad
14 mrad crossing DID/Anti-DID

• DID or anti-DID almost no effect on VXD hits

ILC 500 GeV Nominal beam parameters
31
Photons into Tracker
Takashi Maruyama

• Pair energy into BeamCal is smaller in 14 mrad
  crossing.
• Anti-DID can further reduce the energy to the 2
  mrad crossing level.
• of secondary photons generated in BeamCal is
  also smaller.

photons/BX into Tracker
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Conclusion

• Application of anti-DID was considered for SiD,
  GLD, LDC for intermediate crossing angle 14 mrad
• With optimal anti-DID, the number of pairs
  directed to extraction aperture is more than 50
• The max field of optimal anti-DID is about 0.6 of
  DID
• With anti-DID, the IP angle still can be zeroed
  or decreased, with less local correction
• The modified DID with flattened field in the
  central region was created for GLD and LDC, to
  ease TPC calibration
• Background simulations with anti-DID show that
  photon flux toward TPC region is decreased and is
  same as in 2mrad