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

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

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

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

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

LD and SD Detector Masking 30 mrad 32 mrad

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

TESLA IR

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

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

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

TESLA IR

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 1.8 x 109 hits/cm2/yr O(109 hits/cm2/yr) Radiative Bhabhas 1.5 x 107 hits/cm2/yr < 0.5 x 108 hits/cm2/yr Beam loss in extraction line 0.1 x 108 hits/cm2/year Backshine from dump 1.0 x 108 hits/cm2/yr negligible TOTAL 1.9 x 109 hits/cm2/yr Figure of merit is 3 x 109 for CCD VXD

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]

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 10-11 mm from L=6-10.8 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

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)

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

Basic Issue #3 Colliding Small Beam Spots at the IP Q1 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

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

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

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

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

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

4 Tesla Large Detector Field Map

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

Q1 Hallbach Quadupole Andy Ringwall

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

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)

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

Q1 End View

Q1 with stiffener & movers

Q1 in Detector

Self Shielded SC Quad for NLC Gordon Bowden

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

Tesla Final Quads In Detector

TESLA Quads in Detector