Beam Imaging with Diffraction Beam Imaging with Diffraction RadiationRadiation

Tanaji SenTanaji SenMay 23, 2007May 23, 2007

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Diffraction RadiationDiffraction Radiation

Radiation emitted when a charged particle passes Radiation emitted when a charged particle passes in the in the vicinityvicinity of a conducting target. of a conducting target.

Two cones (angle ~ 2/Two cones (angle ~ 2/γγ ) of radiation in the forward ) of radiation in the forward and backward directionand backward direction

Key parameters: the impact parameter, beam energy Key parameters: the impact parameter, beam energy and wavelength of radiationand wavelength of radiation

Similar (and different) to transition radiation where a Similar (and different) to transition radiation where a particle passes particle passes throughthrough the conducting target. the conducting target.

Main advantage: Non-invasive (mostly!)Main advantage: Non-invasive (mostly!)

Initial theory developed: ~ 1960sInitial theory developed: ~ 1960s First measurements reported: ~1995First measurements reported: ~1995

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Possible Beam DiagnosticsPossible Beam Diagnostics Diffraction Radiation ObservablesDiffraction Radiation Observables

Near field (at target) and far field intensityNear field (at target) and far field intensityPolarizationPolarizationFrequency spectrumFrequency spectrumFar field angular distributionFar field angular distribution

These can be combined to measureThese can be combined to measureBeam sizeBeam size Beam positionBeam position Beam divergenceBeam divergence EnergyEnergy

Easier with far-field (Fraunhofer diffraction) than with near-Easier with far-field (Fraunhofer diffraction) than with near-field (Fresnel diffraction)field (Fresnel diffraction)

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Diffraction Radiation - LayoutDiffraction Radiation - Layout

FDR

BDR

CCD or PMT

Filter

Polarizer

TargetProton beam

b Impact parameterBeam

Target

2Φ

Φ

Far field imaging at KEKPhys. Rev Letters90, 104801 (2003)93, 244802 (2004)

Near field image at APSPRSTAB:10,022802(2007)

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KEK resultsKEK results

Imin

Imax

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Key parametersKey parameters

TevatronTevatron RHICRHIC LHCLHC

Energy [GeV]Energy [GeV]Imp. par. b [mm]Imp. par. b [mm] Beam size [Beam size [μμm]m]Far-field distance Far-field distance [m] [m]

9809800.170.1711.111.1

0.170.17

2502500.040.042.832.83

0.010.01

700070001.191.1979.279.2

8.868.86

Choose: λ = 1000 nm (near IR); t = 2π b/γλ = 1; Intensity of DR ~ e-t = e-ω/ω

c

Impact parameter b = 15σ (LHC requirement)

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Required beam size Required beam size RHIC: RHIC:

At 4000nm, At 4000nm, σσ ~10 ~10 μμmm. . Not feasible ?Not feasible ?

Tevatron.Tevatron. At 4000nm, At 4000nm, σσ ~45 ~45 μμmm. Within ~0.5m . Within ~0.5m

from B0/D0 from B0/D0 Min σ(arc) ~ 290 Min σ(arc) ~ 290 μμm. m. Far infra-red?Far infra-red?

LHC LHC At 1000 nm, At 1000 nm, σσ ~79. ~79. μμm. Within 20m m. Within 20m

of IPof IP

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Layout in the LHCLayout in the LHCIP5: Horizontal Crossing IP5: Horizontal Crossing

AngleAngleIP1 : Vertical Crossing Angle

b

b

BDR Cone

BDR Cone

Target at 45 to beam direction

Beam 1

Beam 2

Location - Both beams should not arriveat the same time

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Further DevelopmentsFurther Developments

Interference from Interference from multiple aperturesmultiple apertures

Different Target Shapes to remove pre-wave zone effects

Theory needs to be developed for - near field intensity with different aperture shapes - finite target size

Interference pattern is sensitive to beam divergence

Beam

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Criteria for ODRCriteria for ODRWhat diagnostics does it realistically provide?What diagnostics does it realistically provide?

Precision and reliability of measurements Precision and reliability of measurements (understand systematic and random errors)(understand systematic and random errors)

Advantages/disadvantages of ODRAdvantages/disadvantages of ODR

Impact on the machine and detectorImpact on the machine and detector

Does it advance the start of the art?Does it advance the start of the art?

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Next StepsNext StepsExplore the prospects of measuring ODR in a Explore the prospects of measuring ODR in a storage ring: Tevatron, APS, ALS, PEPII, ….storage ring: Tevatron, APS, ALS, PEPII, ….Develop an informal collaboration with US labs Develop an informal collaboration with US labs and CERNand CERNUnderstand better the challenges of near field Understand better the challenges of near field and far field imagingand far field imagingDevelop a proposal for experiments at an Develop a proposal for experiments at an existing facilityexisting facilityPresent proposal to the LARP collaboration for Present proposal to the LARP collaboration for fundingfundingProceed with experiments Proceed with experiments Develop ODR facility for the LHCDevelop ODR facility for the LHC