Spin Tracking Studies for Polarimetry at the ILC Moritz Beckmann - - PowerPoint PPT Presentation

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Spin Tracking Studies for Polarimetry at the ILC Moritz Beckmann DESY - FLC visiting SLAC May-August 2010 IWLC, Geneva October 20, 2010 Moritz Beckmann IWLC Oct 20, 2010 1/ 16 Introduction Polarization is planned to be measured at the

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SLIDE 1

Spin Tracking Studies for Polarimetry at the ILC

Moritz Beckmann

DESY - FLC visiting SLAC May-August 2010

IWLC, Geneva October 20, 2010

Moritz Beckmann IWLC Oct 20, 2010 1/ 16

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SLIDE 2

Introduction

  • Polarization is planned to be measured at the ILC with 0.25 %

uncertainty in the beam delivery system (BDS)

  • Compton polarimeters, beam energy 45-500 GeV
  • Longterm scale calibration of luminosity-averaged polarization

at IP to 0.1% using e+e− collision data

  • Spin diffusion / depolarization must be understood to 0.1%

(further) spin tracking studies required

Moritz Beckmann IWLC Oct 20, 2010 2/ 16

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SLIDE 3

Simulation

  • This study is performed for the ILC
  • Could be used for other projects (e.g. CLIC) as well, if fed

with corresponding lattice / parameters

Moritz Beckmann IWLC Oct 20, 2010 3/ 16

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SLIDE 4

Spin tracking

  • Spin propagation in electromagnetic fields is described by

T-BMT equation d dt s = Ω

  • E(

r, t), B( r, t), p , m , a

  • ×

s

  • Rough approximation (

E = 0, B = 0): Spin precession ∝ orbit bending in magnetic field: θspin = aγ · θorbit ≈ 567 · θorbit for electrons at 250 GeV a: anomalous gyro-magnetic moment, a. k. a. g−2

2

γ = E

m

Moritz Beckmann IWLC Oct 20, 2010 4/ 16

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SLIDE 5

Idealized Lattice

  • Using latest available lattice (ILC2007b), beam parameters

from Reference Design Report (2007)

  • 10 000 particles, spins assumed ∝

ez at the end of the linac

  • Perfect magnet alignment, no collision effects
  • Plot: longitudinal polarization along BDS

UP/DP: positions of up-/downstream polarimeters

  • Dips due to dipoles: polarization vector rotates, but no

significant depolarization

Moritz Beckmann IWLC Oct 20, 2010 5/ 16

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SLIDE 6

Idealized Lattice (cont’d)

UP/DP: positions of up-/downstream polarimeters

Caution: scaling of x-axes varies

Moritz Beckmann IWLC Oct 20, 2010 6/ 16

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SLIDE 7

Idealized Lattice (Zoom)

  • Spin fan-out due to lateral beam size in quadrupoles
  • Red lines: ±0.1% (must know changes to this precision)

Moritz Beckmann IWLC Oct 20, 2010 7/ 16

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SLIDE 8

Special Issues in the Interaction Region

  • Important elements are not yet included in lattice
  • Detector magnets
  • Crab cavities

(give the bunch a transverse kick to compensate for beamline crossing angle)

  • Additional cavity or achromaticity for travelling focus scheme

to achieve higher luminosity

  • Effects of beam-beam collision have to be investigated
  • Disruption of beam (∼ 10−4 rad)
  • Spin flips due to emission of beamstrahlung

Moritz Beckmann IWLC Oct 20, 2010 8/ 16

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SLIDE 9

Alignment / Ground Motion

  • Magnet misalignments between polarimeters contribute to

incomparability of measurements

  • Need to investigate effect of static misalignments and ground

motion:

  • Polarization vector rotation (θspin = aγ · θorbit)
  • Spin fan-out due to poor focussing

Moritz Beckmann IWLC Oct 20, 2010 9/ 16

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SLIDE 10

Alignment / Ground Motion

  • Magnet misalignments between polarimeters contribute to

incomparability of measurements

  • Need to investigate effect of static misalignments and ground

motion:

  • Polarization vector rotation (θspin = aγ · θorbit)
  • Spin fan-out due to poor focussing
  • Compensation by feed-back correctors?

→ Requirements on alignment and BPM precision Need for additional correctors?

Moritz Beckmann IWLC Oct 20, 2010 9/ 16

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SLIDE 11

Static Misalignments

  • Initial sample, each element randomly misaligned

(Gaussian-distributed random numbers, σx,y = 2 µm)

  • σx,y = 2 nm in final focus region (0-50m in front of IP)
  • Plots shows three exemplary samples

distance from IP [m]

20 40 60 80 100 120 140

  • long. polarization

0.78 0.785 0.79 0.795 0.8 0.805

IP DP

not misaligned misaligned Moritz Beckmann IWLC Oct 20, 2010 10/ 16

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SLIDE 12

Static Misalignments

  • Initial sample, each element randomly misaligned

(Gaussian-distributed random numbers, σx,y = 2 µm)

  • σx,y = 2 nm in final focus region (0-50m in front of IP)
  • Plots shows three exemplary samples
  • No feed-back correctors implemented yet
  • Dashed: after rotation of the momentum vectors at the IP

such that < pt >= 0; spins rotated accordingly (aγ)

  • Orbit correction at IP: ∆Pz

Pz (IP,DP) < 0.1% distance from IP [m]

20 40 60 80 100 120 140

  • long. polarization

0.78 0.785 0.79 0.795 0.8 0.805

IP DP

not misaligned misaligned misaligned, corrected Moritz Beckmann IWLC Oct 20, 2010 10/ 16

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SLIDE 13

Static Misalignments (cont’d)

  • Collimators in BDS absorb up to 1000 particles due to missing
  • rbit correction (will be moved in front of upstream

polarimeter according to SB-2009 proposal)

  • Observed changes in polarization consistent with statistical

effects (≤ 2σ)

  • ∆Pz of corrected beams = ∆Pz from collimators

⇒ Orbit correction at IP: ∆Pz

Pz (UP,IP) < 0.1% distance from IP [m]

  • 1800
  • 1700
  • 1600
  • 1500
  • 1400
  • 1300
  • long. polarization

0.78 0.785 0.79 0.795 0.8 0.805

UP

not misaligned misaligned

collimators

distance from IP [m]

10 20 30 40 50 60 70 80 0.78 0.785 0.79 0.795 0.8 0.805

IP

not misaligned misaligned misaligned, corrected Moritz Beckmann IWLC Oct 20, 2010 11/ 16

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SLIDE 14

Static Misalignments: IP

[rad]

  • rbit

θ

0.05 0.1 0.15 0.2 0.25 0.3 0.35

  • 3

10 ×

[rad]

spin

θ

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 20 40 60 80 100

  • rbit

θ ⋅ γ = a

spin

θ

[rad]

  • rbit

θ

0.05 0.1 0.15 0.2 0.25 0.3 0.35

  • 3

10 ×

[rad]

spin

θ

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 5 10 15 20 25 30 35 40

  • rbit

θ ⋅ γ = a

spin

θ

  • Orbit and helicity

vector rotation are strongly correlated

  • Provisional

feed-back (lower plot) recovers longitudinal polarization

  • Assumption: Spins

∝ ez at the end of the linac

Moritz Beckmann IWLC Oct 20, 2010 12/ 16

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SLIDE 15

Ground motion

  • A. Hartin, PST 2009
  • Plot: IP beam y-position and helicity with ground motion

model for “noisy” site without correction

  • Nominal beam size σy at IP: 5.7 nm

Moritz Beckmann IWLC Oct 20, 2010 13/ 16

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SLIDE 16

Summary

  • A spin tracking framework for high energy linear colliders has

been set up

  • First studies have been performed for the ILC, where an

understanding of polarisation to the permille-level is required

Moritz Beckmann IWLC Oct 20, 2010 14/ 16

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SLIDE 17

Summary

  • A spin tracking framework for high energy linear colliders has

been set up

  • First studies have been performed for the ILC, where an

understanding of polarisation to the permille-level is required

  • Alignment in whole BDS is crucial, but causes mainly helicity

vector rotation → reversible

  • Provisional orbit correction at the IP

⇒ same Pz at polarimeters and IP w. r. t. tolerances

  • Need to specify the polarization requirements on beam

position monitors and alignment systems → more investigations

Moritz Beckmann IWLC Oct 20, 2010 14/ 16

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SLIDE 18

Outlook

  • Include more details into the simulation
  • Detector magnets
  • Crab cavities
  • Travelling focus scheme
  • Collision effects
  • Ground motion
  • Feed-back systems in lattice
  • Interface to polarimeter simulations
  • Develop calibration strategies

Moritz Beckmann IWLC Oct 20, 2010 15/ 16

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SLIDE 19

Thanks for your attention!

Moritz Beckmann IWLC Oct 20, 2010 16/ 16

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SLIDE 20

Backup slides

Moritz Beckmann IWLC Oct 20, 2010 17/ 16

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SLIDE 21

Static Misalignments: Upstream Polarimeter

θorbit: angle between reference orbit and actual particle orbit

  • Effects from misalignments are small, though visible

(distribution offset from zero)

  • Depolarization ∼ 10−7

Moritz Beckmann IWLC Oct 20, 2010 18/ 16

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SLIDE 22

Static Misalignments: Downstream Polarimeter

[rad]

  • rbit

θ

0.01 0.02 0.03 0.04 0.05 0.06 0.07

  • 3

10 ×

[rad]

spin

θ

0.02 0.04 0.06 0.08 0.1 0.12 2 4 6 8 10 12

  • rbit

θ ⋅ γ = a

spin

θ

[rad]

  • rbit

θ

0.01 0.02 0.03 0.04 0.05 0.06 0.07

  • 3

10 ×

[rad]

spin

θ

0.02 0.04 0.06 0.08 0.1 0.12 2 4 6 8 10 12 14 16 18 20 22 24

  • rbit

θ ⋅ γ = a

spin

θ

  • Less correlation than

at the IP, effect of extraction line quadrupoles?

  • needs further

investigation

Moritz Beckmann IWLC Oct 20, 2010 19/ 16

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SLIDE 23

Effects of Energy spread

  • Sample as in the beginning, no misalignments
  • No difference due to energy spread visible

Moritz Beckmann IWLC Oct 20, 2010 20/ 16

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SLIDE 24

Effects of Energy spread

  • Sample as in the beginning, no misalignments
  • No difference due to energy spread visible

Moritz Beckmann IWLC Oct 20, 2010 21/ 16

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SLIDE 25

Detector magnets

  • Detectors contain
  • solenoid for tracking devices
  • dipole (anti-DID) to compensate for (detector) effects of

crossing angle

Moritz Beckmann IWLC Oct 20, 2010 22/ 16

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SLIDE 26

Detector magnets

  • Detectors contain
  • solenoid for tracking devices
  • dipole (anti-DID) to compensate for (detector) effects of

crossing angle

  • Additional correction kickers required to align beam at IP and

behind detector

  • Parameters (solenoid field etc.) vary for different detector

concepts

Moritz Beckmann IWLC Oct 20, 2010 22/ 16

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SLIDE 27

Detector magnets: Orbit Correction

Simple model of SiD, first-order orbit correction

  • Mean x position < 0.03 mm
  • Plot for polarization not available due to technical problems

Moritz Beckmann IWLC Oct 20, 2010 23/ 16

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SLIDE 28

Detector magnets: Polarization

  • Technical problem: Spin tracking through kickers not

implemented yet

  • Tracked spins: do not include kickers and anti-DID
  • Orbit angles: approximation θspin = aγ · θorbit not valid in and

around solenoid ( B ≫ B⊥)

  • Tracked spins: visible effect from solenoid expected

Moritz Beckmann IWLC Oct 20, 2010 24/ 16