L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

L. Bobb1, 2, M. Billing3, N. Chritin2, P. Karataev1,T. Lefevre2
1.

2.
3.

John Adams Institute at Royal Holloway, Egham, Surrey,United Kingdom
CERN European Organisation for Nuclear Research, CERN,Geneva, Switzerland
Cornell University, Ithaca, New York, USA

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

 Motivation
 Aim
 Diffraction Radiation
 Experimental preparation for Phase 1
 Simulations
 Vacuum assembly Optical system Future work Outlook for Phase 2
 Diffraction Radiation monitors @LHC

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012 E. Chiadroni, M. Castellano, A. Cianchi, K. Honkavaara, G. Kube, V. Merlo and F. Stella,“Non-intercepting Electron Beam Transverse Diagnostics with Optical Diffraction
Radiation at the DESY FLASH Facility”, Proc. of PAC07, Albuquerque, New Mexico, USA,FRPMN027.
 A.H. Lumpkin, W. J. Berg, N. S. Sereno, D. W. Rule and C. –Y. Yao, “Near-field imaging ofoptical diffraction radiation generated by a 7-GeV electron beam”, Phys. Rev. ST Accel.
Beams 10, 022802 (2007).

 P. Karataev, S. Araki, R. Hamatsu, H. Hayano,
T. Muto, G. Naumenko, A. Potylitsyn, N.
Terunuma, J. Urakawa, “Beam-size
measurement with Optical Diffraction
Radiation at KEK Accelerator Test Facility”,
Phys. Rev. Lett. 93, 244802 (2004).
σy = 14 µm measured
ATF2@KEK

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Motivation
Transverse beam size requirements for the Compact
Linear Collider (Table 5.62 CDR Volume 1, 2012):
Section ofmachine

PDR (H/V)
DR (H/V)

Beam Energy
[GeV]
2.86

Beam size[µm]

Requirement

50/10
10/1

RTML (H/V)

2.86 - 9

10/1

Drive BeamAccelerator

2.37

50 -100

Micron-scale
resolution
Non-invasive
measurement

Baseline high resolution noninterceptive beam profile
monitor:
Laser Wire Scanners
S. T. Boogert et al., “Micron-scalelaser-wire scanner for the KEK
Accelerator Test Facility extractionline”, Phys. Rev. S. T. – Accel. andBeams 13, 122801 (2010)

http://www.clic-study.org/

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Project aim:
To design and test an instrument to measure on the micron-scale thetransverse (vertical) beam size for the Compact Linear Collider (CLIC) using
incoherent Diffraction Radiation (DR) at UV/soft X-ray wavelengths.
Cornell Electron Storage Ring Test Accelerator(CesrTA) beam parameters:

CesrTAE (GeV)σH (µm)σV (µm)

2.1

320

∼9.2

5.3

2500

∼65

D. Rubin et al., “CesrTA Layout and Optics”, Proc. ofPAC2009, Vancouver, Canada, WE6PFP103, p. 2751.

http://www.cs.cornell.edu

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Principle:
1. Electron bunch moves through a high precision
co-planar slit in a conducting screen (Si + Alcoating).
2. Electric field of the electron bunch polarizes
atoms of the screen surface.
3. DR is emitted in two directions: along the particle trajectory “ForwardDiffraction Radiation” (FDR)
 In the direction of specular reflection“Backward Diffraction Radiation” (BDR)

DR Angular distribution

θye-

θ0h

Impact parameter:
𝛾𝜆ℎ≤
2𝜋Generally:
DR intensity ⇧ as slit size ⇩L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

P. Karataev et al.

Vertical polarisation
component of 3-dimensional(θx, θy, Intensity) DR angulardistribution.

PVPC is obtained byintegrating over θx tocollect more photons.

Visibility (Imin/Imax) of
the PVPC is sensitive tovertical beam size σy.

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Measureable visibility for initial test atparameters:
λ = 200 - 400 nm
a = 0.5, 1 mm
σy = 50 µm

To compare with TR
intensities:
𝛼𝛾2TRmax = 2𝜋𝑡𝑦 = 𝛾𝜃𝑦L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

M. Billing, "Introduction to Beam
Diagnostics and Instrumentation for CircularAccelerators", AIP Conference Proc. 281,AIP 1993, pg.75 ff.

atarget ≥ 5∙σy,preferably atarget = 7-10∙σyLarge aperture = low DR intensity
Multiple turns of a single bunch throughthe target aperture
Errors due to beam jitter are reduced byincluding turn-by-turn vertical position
measurements of the bunch in thetarget aperture.

target slitsize[mm]verticalbeam size
[µm]

beam
lifetime
[min]

0.1

9.2

2.40

0.5

30

60 (max)

50

2.22

50

60 (max)

1.0

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012Requirements:
High precision slit size
Coplanarity ≤ 10% ∙ λHigh reflectivity at λAperture sizes a:
0.5 mm, 1 mm
Material: Si

Technical drawings by N. Chritin

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

E = 2.1 GeV
λ = 400 nm
a = 0.5 mm

Source of background

Contribution

SR from beamline optics

HighCamera noise
Residual background

Low

SR + DR
interference

Use a mask upstream of target tosuppress SR contribution.
OTRODRθye-θ0SR
suppression

P. Karataev et al., Proc. of EPAC 2004, THPLT067

MaskTarget

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

A. Cianchi et al., Phys. Rev. ST Accel. Beams 14 (10)102803 (2011)
Aperture sizes

Interferenceamask = atarget

Complete destructive
interference of FDR + BDR(blue)

amask ≈ 2∙atarget

Measureable interference(green)amask ≥ 4∙atarget

Negligible interference (red)Using non-collinear slits(i.e. centres of mask +target do not coincide)allows measurement ofbeam size, beam offset
from the target centre
and angular divergence.

E = 2.1 GeV
λ = 400 nm
amask = 2 mm
atarget = 1 mm
σy = 50 µm

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Electron beam direction

DR experimentTechnical drawings by N. Chritin

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Technical drawings by N. Chritin
Simulations by A. Nosych
E-field magnitude of a single bunch pass in time domain (Gaussian bunch,length = [-4s,4s], s = 10mm)

H-field surface tang complex magnitude (Loss map)
Mode Fr = 1.19 GHz, Q = 3309, Ploss = 0.075 W

Total power loss for single bunch = 0.6 W

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

QuadrupoleSi
1. Alignment of the electron beam with the target
aperture: BPMs for centering (~10 microns resolution)
 Target imaging to look for OTR from beam halo
 Correlate with BLMs:

1Dipole2
3
Virtual BLMs

4
Virtual
Detector 3-400μm off

center+400μm off

Virtual
Detector 4

2. DR vertical beam size measurement

Simulations by A. Apyan

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Far-field Condition:
𝛾2 𝜆𝐋≫
2𝜋• L = distance from source ofDR to detector.
• Compact optical system isin the prewave zone(Pre-wave zone effect intransition and diffraction
radiation: Problems andSolutions -P. V. Karataev).
𝛾2 𝜆2𝜋given γ and λ:Compact optical system (distance to𝜸𝟐 𝝀detector L ≤ 𝟐𝝅 )5 GeV200 nm0.54 m3.18 m

400 nm1.08m

6.37 m𝜸𝟐 𝝀detector L >> 𝟐𝝅 )Bi-convex lens required with camera inback focal plane.

2.

2.1 GeVLong-range optical system (distance toFar-field zone

Dual purpose:
1. Image target
Image DR angular distribution
DR observation wavelengths:
λ = 200 nm, 400 nm

In footprint of target mechanism ( < 1m)

Determined by L and spatial constraints.

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

 DR at soft X-ray wavelengths:
 More complex opticalsystem.
 Grazing target tilt angle
 Aperture size determined by
impact parameter for given
wavelength

E = 5.3 GeV
atarget = 0.2 mm

Main requirement:
Micron-scale resolution

Must use shorter wavelengths

Sensitivity @50 nm ≈ 2x sensitivity @200 nm

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

 LHC also has γ ≈ 4000 (@ E = 4000 GeV)

Main requirement:
Non- invasive measurement

 Using proton beam: Reduced SR background Larger beam size
 Wavelengths in the infrared spectral range

Must use large target apertureL. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

 Simulations have demonstrated the feasibility of vertical beam size measurements atCesrTA. The phase 1 experiment is planned for the end of December 2012 for which
the design and vacuum assembly are close to completion.
 The design must account for the experiment location in a circular machine. This
introduces some advantages and disadvantages not applicable for linacs.
 Preliminary simulations for the phase 2 test aiming for the soft x-ray spectral range
have been presented.
 Feasibility of DR diagnostics on other accelerators has been considered such as
simulations for transverse beam size measurements at the LHC.

I would like to thank J. Barley, J. Conway, J. Lanzoni, Y. Li, T. O'Connell, M. Palmer, D. Rice,
D. Rubin, J. Sexton, C. Strohman and S. Wang (@Cornell) for all technical contributions
and advice. In addition, O.R. Jones and H. Schmickler for organisation of thecollaboration, A. Apyan, E. Bravin, A. Jeff, A. Nosych and S. Vulliez (@CERN) and T.
Aumeyr (@RHUL).

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Thank you for your attention
Questions?

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Extra slides

L. Bobb, IBIC2012, Tsukuba, Japan, Oct 1-4, 2012

Fork OUT, Chamber IN

E-field + B-field magnitude of a single bunch pass in time domain(Gaussian bunch, length = [-4s,4s], s = 10mm)

H-field surface tang complex magnitude (Loss map)

1.017
GHz1.26 GHz

1.19 GHz

Ploss_total = 0.6W

Simulations by A.
Nosych

1.017 GHz

1.19GHz

1.26GHz