1. LC Interaction Region Magnet Issues
Tom Markiewicz/SLAC
Snowmass 2001
11 July 2001

2. Issues Interaction with detector solenoid Dealing with beam extraction
Orbit and spot size effects
1 external forces on Q1
Longitudinal and Transverse fields in Q1
Dealing with beam extraction
Apertures
Input Quads: Stay free set by SR from orbit
Ext Quads: SR sets min; Beam dump backshine sets max
Flexibility/Adjustability
Mechanical Stability: O(1nm) control of Field Center
Field Stability: ~5 x 10-6 (NLC)
Thermal Effects
Power Supply Stability
Radiation resistance

3. Magnet Technology Choices
Permanent Magnets (NLC)
Compact, stiff, few external connections, no fringe field to affect extracted beam
Adjustment more difficult
Superconducting (TESLA)
Adjustable, big bore
Massive and not stiff, would require windings to eliminate fringe field affecting extraction line
Iron (JLC)
Adjustable, familiar
Massive, shielded from solenoid, extraction in coil pocket seems daring

4. Crossing Angle Considerations Interaction with Detector’s Solenoid
Beam Steering before IP:
Transverse component of solenoid changes position and angle of beams at the IP
1.7 mm , 34.4 mrad at 1 TeV, L*=2m, Bs=6 T, qC=20mrad
Dispersion and SR cause spot size blow up
3.1 mm added to vertical spot size
Handle with clever upstream beam steering gymnastics and by moving QD
So NOT a problem (unless SR term a (L*BsqC)5/2 grows too large)
Beam Steering after IP:
Energy dependence of angle of extraction line
Steering: position (410 mm) & angle (69 mrad) different from B=0 case at 1 TeV
Only run with solenoid ON and Realign extraction line when necessary

5. “Large” and “Silicon” Detectors (same scale)
3 Tesla
5 Tesla

6. LD and SD Detector Masking
30 mrad
32 mrad

7. JLC IR 8 mrad Design Iron magnet in a SC Compensating magnet
Elevation View
Iron magnet in a SC Compensating magnet
8 mrad crossing angle
Extract beam through coil pocket
Vibration suppression through support tube

8. TESLA IR

9. TESLA Extraction at 0º
Vertical extraction with electrostatic separators, septum, and dipoles to dump at z=240m
Beams separated by ctB/2=50m (800 GeV)
Beamstrahlung photons to separate dump at z=240m

10. e+,e- pairs from beams. gg interactions
At NLC-1000B:
44K per bunch per side
<E>=10.5 GeV
0.85 W

11. e,g,n secondaries made when pairs hit high Z surface of LUM or Q1
High momentum pairs mostly in exit beampipe
Low momentum pairs trapped by detector solenoid field

12. TESLA IR

13. Neutron Backgrounds The closer to the IP a particle is lost, the worse
e+/e- pairs and radiative Bhabhas hitting the Pair Lum-Mon, beam-pipe and magnets in the extraction line.
Disrupted beam lost in the extraction line.
0.25 % beam loss in recent redesign
Disrupted beam and beamstrahlung photons in the dump
Neutron hit density in VXD
NLC-LD-500 GeV Tesla-500 GeV
Beam-Beam pairs x 109 hits/cm2/yr O(109 hits/cm2/yr)
Radiative Bhabhas x 107 hits/cm2/yr < x 108 hits/cm2/yr
Beam loss in extraction line x 108 hits/cm2/year
Backshine from dump x 108 hits/cm2/yr negligible
TOTAL x 109 hits/cm2/yr
Figure of merit is 3 x 109 for CCD VXD

14. Neutrons from the Beam Dump Controlled by Shielding and Geometry
Geometric fall off of neutron flux passing 1 mrad aperture [parent distribution for next slide]

15. Dump-produced Neutron flux at z=0 as a function of radius
1.2E10 neutrons hit the beampipe within +/-5cm at r>1.0 cm
30% scatter into VXD
Divide by area of VXD L1 to get quoted hit density = 0.25E9/cm^2/y
Fall off for r>1.0 cm due to limiting aperture of EXTRACTION LINE QUAD DOUBLET (currently mm from L= m from the IP; SR concerns MAY require larger aperture)
Fall off as r -> 0cm comes from reduced solid angle view of the dump
As r is reduced need to integrate more of this curve.
Limiting Aperture

16. Integrated Dump Neutron Flux vs. Radius
Detector Group Constantly Asking why inner VXD radius can’t be x2 SMALLER
As Beampipe radius is reduced by x2
Flux from dump up x10
Hit density up by x40
dump becomes equal to pairs as source of neutron hits
SR issues (S. Hertzbach talk)

17. (Similar plots for TESLA)
HALO Synchrotron Radiation Fans with Nominal 240 mrad x 1000 mrad Collimation
(Similar plots for TESLA)

18. Basic Issue #3 Colliding Small Beam Spots at the IPQ1 Q1
Relative Motion of two final lenses e+ e-
sy ~ 3 nm
Dy = sy/4 ~ 1 nm
Control position & motion of final quads and/or position of the beam to achieve/maintain collisions
Get a seismically quiet site
Don’t screw it up: Pumps, compressors, fluids
Good magnet and detector engineering: Light, stiff Q1 in a rigid detector
Tie to “bedrock”: get lenses outside detector as soon as possible

19. Luminosity Loss vs. Position & Angle Jitter
NLC
TESLA
Larger Dy leads to
sensitivity ~0.1s ~0.5nm

20. Luminosity Stabilization
Performance of ALL LCs based on feedback systems such as that developed at SLC
“SLOW” feedback based on machine rep rate f and can handle motion of frequencies up to ~f /20 to f /60
0.1-1 Hz at TESLA where f = 5 hz
2-5 Hz at NLC where f = 120 Hz
TESLA’s long (2820) train of widely (337ns) spaced bunches allows the extension of the technique to frequencies up to ~100 kHz and should handle all correlated noise sources with minimal luminosity loss and little impact to the detector
NLC relies on a variety of techniques to stabilize the collisions against jitter above the 2-5 Hz range

21. Sensor Driven Active Vibration Suppression at NLC
Inertial Capacitive Sensors QD
Carbon fiber stiffener
Piezo mover
Interferometric Sensors: Optical anchor
FFTB style cam movers
Cantilevered support tube

22. Optical Anchor R&D
rms = 0.2nm
Measured Displacement over 100 seconds

23. Detector Solenoid Field Effects
Detector size and field limits magnet technology choices
Solenoid field effects:
Steel pole magnets
Saturates steel pole magnets; requires a flux excluder
Saturates steel shielding
Permanent magnets(PM)
Axial field rotates magnetization vector reducing strength; dependent on PM anisotropy energy
Radial field contributes to demagnetizing force on PM
Superconducting magnets(SC)
Reduces achievable critical current in SC wire
Develops large forces in SC coil

24. 4 Tesla Large Detector Field Map

25. LC Small Detector Field Map
Uniform Current Density Coil B
versus z, NLC IR Solenoid 1 z 6 L* L* 5 4
Bz, T B z
, T 3 2 1
0.5 1
1.5 2
2.5 3
3.5 4
z, m

26. Q1 Hallbach Quadupole Andy Ringwall

27. 1996 NLC Magnet Engineering Scheme
Final Doublet Magnet Technology Choice
Q1: Rare Earth Cobalt (REC: Sm2Co17 or Sm1Co5)
Smaller mass works better with active vibration stabilization
Compact: Not much transverse space available
No fluids
BUT: can it survive B|| (reduces max. pole tip field) and B (demagnetizes over time)?
For small detector Bz(2m) < 3 T and Br(2m) < 500 G
Q1 SC for tune-ability: can we engineer this away?
Must be self-shielded to not affect the out-going beam
Q2A & Q2B iron (if it will fit)
Sm2Co17 :
Higher Remnant Field: Br=1.2 T
Sm1Co5 :
Lower Remnant Field
More magnet rigidity
Better radiation resistance

28. NLC Quad Strengths and Dimensions
Magnet
Radial Aperture
Gradient
Rmax
Z_ip
Length
QD0
1.0 cm
144 T/m
288 T/m
4.6 cm+3/8”=5.6cm
XXXXX
3.81 m
2.0m
QF1
36.4 T/m
72.8 T/m
1.2cm+3/8”=2.2cm
1.7cm+3/8”=2.7cm
7.76 m
4.0 m
c1=0.923
(M=32 blocks, N(harmonics)=2)
c2=0.95
Bremnant=1.05 T (Sm1Co5)

29. LCD-L2 (3T) with 3. 8m L. Optics Separate (Easier
LCD-L2 (3T) with 3.8m L* Optics Separate (Easier?) Extraction Line qC=20 mrad
52 mrad Cal acceptance
32 mrad M1 acceptance
Calorimeter
SF1 M2
QF1 M1
SD0
QD0
Feedback BPM & Kicker
6.3 mrad Lum-Mon acceptance
Low Z shield
Beampipe
Pair LumMon
1 mrad exit aperture
Support Tube

30. Q1 End View

31. Q1 with stiffener & movers

32. Q1 in Detector

33. Self Shielded SC Quad for NLC Gordon Bowden

34. TESLA SC FD Quad & Cryostat
QD0:
L=2.7m
G=250 T/m
Aperture=24mm
QF1:
L=1.0m

35. Tesla Final Quads In Detector

36. TESLA Quads in Detector