Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and...

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Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute for Research in Electronics and Applied Physics University of Maryland, College Park, MD Invited Paper #6, May 7, 2008 BIW08, Granlibakken Resort, Lake Tahoe, CA

Transcript of Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and...

Page 1: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Transition, diffraction and Smith-Purcell radiationdiagnostics for charged particle beams

Ralph B. Fiorito

Institute for Research in Electronics and Applied PhysicsUniversity of Maryland, College Park, MD

Invited Paper #6, May 7, 2008 BIW08, Granlibakken Resort, Lake Tahoe, CA

Page 2: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Key Concepts

1) Radiation impact parameter α = γλ/2π range of the radial E field of the charge: Ee ~ K1 (r/α)

TR r >> αDR r <~ α

2) Coherence Length: distance over which phase of E field and photon fieldshift by π radians

Vacuum : Lv ( γ,λ,θ ); Dielectric : LD ( ε,λ )e.g. OTRI, ODTRI, SPR

3) Resonance radiation: I ~ ( N radiators)

resonance condition: Vphoton ( λ,θ ) = Ve = βce.g. XTR from stack of foils, Smith Purcell from a grating

4) Bunch Coherence:

,

2

2

2

,

( 1) ( , ) ( , )

( )

⊥ ⊥

⊥ ⊥

= + −

=

Ω ΩN e

T z z z

z z

N N S kd I d I Nd d d

S k

S

d

F ρ

ωσ

ωσ

Page 3: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Applications of TR, DR and SPR

usual, i.e for rf accelerators where t µbunch >~ ps

Incoherent radiation ( λ << t bunch ) - optical wavelengths

Near Field Imaging (spatial distribution)

• size (x, y) e.g. OTR, ODR

• position (x, y) (offset) OTR, ODR

Far Field Imaging (angular distribution)*• divergence (x’, y’) OTR, OTRI, ODR*, ODTRI

• trajectory angle (X’,Y’) “

• energy (average) and energy spread “* ODR AD can be used to measure beam size as well as divergence

Coherent ( λ ≥ t bunch ) - FIR-mm wavelength• spectrum: direct, autocorrelation technique - bunch length and shape

* angular distribution can also be used

less common: t bunch in optical regime - optical micro bunching, laser plasma interaction - in this regime coherent radiation can be used to diagnose transverse as longitudinal beam properties, e.g. beam size

Page 4: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Spatial resolution (sub micron, independent of energy) < Beam images taken with six different diagnostic screens under the stable experimental conditions (Q ~ 500 pC) at the ATF/BNL 40 MeV linac.

High Linearity :< Electron beam horizontal spot size as a function of charge, measured with scintillating diagnostics and incoherent OTR

Incoherent OTR: well developed; high spatial and temporal resolution

1) imaging: beam profiling + position

Xrms

Page 5: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Highly Relativistic: 30 Gev (SLAC) electron beam120 GeV (FNAL) proton beams

Non Relativistic: 29 MeV protons (Goldsmith and Jelley 1959)(first experiment confirmation of TR)

10 keV (UMER): electron beam50 keV (CLIC) gun test stand: electron beam

OTR Imaging proven useful over very wide range of beam energies

Page 6: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

FNAL NuMI Proton OTR Detector

• OTR foil: 6 µm aluminized Kapton

• Np~6.5e19 protons

• Measure beam shape for every pulse

• Operating at ~2 to 4e13 120 GeV protons per pulse at ~0.5 Hz

– Up to 350 kW beam power

Provided by Vic Scarpine FNAL

Page 7: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Low Energy (10 KeV) electron OTR images of UMER beam using gated ICCD camera

( gun parameters: ∆t =100ns pulse, I ~ 20 mA)

OTR: 0-100ns

0-10ns 10-20ns 20-30ns 30-40ns

40-50ns 50-60ns 60-70ns 70-80ns 90-100ns

OTR: 3ns gate (10-20ns)

36000 frames

OTR: 10ns gate7200 frames

7200 frames1 cm

Page 8: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

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Beam Divergence Diagnostic using Angular Distribution of Single Foil OTR

Θ = 1/γ

e

2 (S) 2 21

2 2 2

d I e1d d c ( )

−−

θθ γ ⇒ =

ω Ω π γ + θ

∆Θ (σ)

A.D. is a function of angle, energy, angle, divergence

and energy spread but is independent of beam size or position

1) Single Foil

Page 9: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Effect of Divergence on OTR Angular Distribution and Horizontal Scans

( 48 MeV CLIC2 Test Facility Beam )

Page 10: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

2) Interference OTR : gives greater sensitivity to beam divergence

V

2 2 1V

2 2 (S)2TOTd I d I4 sin (L / L

where : L

2 )

( / )( )d d d d

− −= λ π γ + θ

=ω Ω ω Ω

Diagnostics:• Center of pattern measures trajectory angle of particle

• Fringe position measure beam energy

• Visibility of OTRI measures beam divergence and/or ∆E/E

• Radial Polarization of OTRI can be used to separate and measure x’ and y’

θx

θy

the “formation” or coherence length,which is common to all relativistic beam radiations.

Page 11: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Far Field PatternCamera

Image PlaneCamera

Θobserv ∼ 10/γ

Pellicle BeamSplitter

Lens focused to Infinity

mirror

BandpassFilter

Beam

Experimental Setup for OTR RMS Emittance Measurement

OTR interferometer

Beam magnetically focused to x or y waist condition at mirror

εrms,n = βγ<x>1/2<x’>1/2

Page 12: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Y waist λ=650nm

Y width (um)

0 200 400 600 800 1000 1200 1400 1600 1800

Inte

nsity

AU

0

50

100

150

200

250

300

DataDouble Gaussian fitσ1 = 56.36 +/−.59µmσ2 = 410.67 +/− 10.94µm

Example: OTR Images and OTRI at JLAB Show Two Beam Components and provide x, y rms emittances at x,y beam waists:

Y waist λ=650nm

Angle in units 1/ γ

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Inte

nsity

AU

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Calculated Fitσ1 = 0.54+/- 0.01mradσ2 = 2.3+/-0.08 mradData

Page 13: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Optical phase space mapping

Concept: Optical beam radiation e.g. OTR, and an optical mask can be used to map the transverse phase space of the beam (measure localized beam divergence and trajectory angle:analogous to standard pepper pot method)

Electron beam

Camera 2

Camera 1

MaskPolarizer

BandpassFilter

Page 14: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

DIFFRACTION RADIATION(produced by interaction of the field of a constant velocity charge with a

boundary)

1) when a ∼ γλ, DR is produced and AD is frequency dependent

a

e

Forward DR

Backward DR

Impact Parameter: α = γλ/2π ,

is the range of the radial field of the charge: Εe ∼ Κ1 (r/α)

2) When a << γλ DR = TR; particle doesn’t see hole and no diffraction wings

Diffraction fringes

Shift of peaks fromθ = 1/γ

Page 15: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

DR and TR from Finite Screens are Related Phenomena

~b γλ b

DR from holeFinite Screen TR

Babinet’s Principle applies:TR DR TRScreen Hole FiniteScreenE E E∞ = +

Page 16: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Optical Diffraction-Transition Radiation Interferometry

(extends OTRI diagnostics to low energy and/or low emittance beams)

Perforated first foil

Beam

mirrored foil (OTR source)

perforated foil (ODR source)

ODR

ODR+OTR

Page 17: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Angle, 1/γ0.0 0.5 1.0 1.5 2.0

Inte

nsity

, OTR

uni

ts

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Calculation ( σ = 0.3+ - 0.03 )Data

Angle, 1/γ0.0 0.5 1.0 1.5 2.0

Inte

nsity

, OTR

uni

ts

0.0

0.5

1.0

1.5

2.0

2.5

Calculation ( σ = 0.35 + - 0.03 ) Data

Example: Comparison of Horizontal Divergence Measurementsusing ODTRI and OTRI on the 50 MeV ATF Electron Beam

( λ = 600 x 10 nm )

ODTRI τ = 480s OTRI τ = 360s

Page 18: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

1) Near field intensity surrounding aperture sensitive to distance from centroid position of beam and its spatial distribution

Resolution of ODR BPM : 40 um measured

10 um (estimated)

[see contributed talk P. Evtushenko,

#5 today]

Offset beam passing through slit

Non Interceptive ODR BPM and size monitors

under intense development in Japan (KEK), Russia (TPI) Italy,(INFN), USA (APS, SLAC, JLAB

Page 19: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Near Field ODR - 7-GeV Beam at APS

ODR offers the potential for nonintercepting, relative beam-size monitoring with near-field imaging. This is an alternate paradigm to far-field work at KEK and INFN.

A.H. Lumpkin et al., Phys. Rev. ST-AB, Feb. 2007

Page 20: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

ODR Has Good Beam-Position Sensitivity Using Vertical (y) Polarization Component

OTR and ODR Image Centroid versus Horizontal rf BPM values linear.

A.H. Lumpkin et al., Phys. Rev. ST-AB Feb.2007

rf BPM x-position (mm)

-4 -2 0 2 4

Imag

e x

cent

roid

(mm

)

-4

-3

-2

-1

0

1

2

3

4

OTR centroid ODR centroid

y

x

beam

edge

ODR

Page 21: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Farfield ODR Beam Size Monitor

0.5 mm

1 mm

An experiment based on the detection of Optical Diffraction Radiation has been set up at DESY FLASH Facility to measure the transverse electro beam size.

M. Castellano, E. Chiadroni (INFN - LNF) A. Cianchi (INFN - Roma2)

K. Honkavaara (HH University)G. Kube (DESY)

Page 22: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Preliminary Results

Beam transport optimization0.7 nC25 bunches2 s exposure timeEbeam (nominal) = 680 MeV800 nm filter and polarizer in

Simulation parameters:

Gaussian distributed beamσy = 80 µmσ’y = 125 µrad -5 -4 -3 -2 -1 0 1 2 3 4 5

0.0

0.2

0.4

0.6

0.8

1.0

Inte

nsity

[a.u

.]

θy [mrad]

Experimental data Simulation

0.5 mm slit

OD

R S

igna

ture

-0.004 -0.002 0.000 0.002 0.0040.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Inte

nsity

θy [rad]

OTR angular distribution

Bea

m a

nd O

TR

Opt

imiz

atio

n

800 nm filter in800 nm filter and polarizer in

Center of the slit100 µm with respect tothe center of the slit

Approaching one edge of the slitFrom

OTR

to

OD

R

σy ≈ 70 µmσx ≈ 10σy

Page 23: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Radiation Based Bunch Length Diagnostics

Standard :

1) Streak camera using incoherent OTR (limited to about 1ps resolution)2) Direct spectral measurements using CSR, CTR, CDR (difficult to

implement, limited band width)3) Autocorrelation of CTR, CDR using Michelson interferometer (Barry

and Lihn, Faraday Cup 1996) (no phase info. must be added)4) E-O Sampling techniques (see review by van Tilborg -invited talk #4 )

Relatively new: CDR angular distribution method and CSPR method

Page 24: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

2( , ) ( , )e

TOTJ p E pω ω∝

CDR ANGULAR DISTRIBUTION BUNCH LENGTH MONITOR

1. For small target: D < γλ , Angular Distribution of DR depends on frequency

2. OPTIMUM SIZE OF RADIATOR FOR GIVEN ENERGY PRODUCES CDR IN FREQUENCY BAND APPROPRIATE TO BUNCH WIDTH ∆f ~ 1/∆t

Calculation of Radiated CDR Power for single electron*

V

CDR

*A. G. Shkvarunets and R.B.Fiorito, PRSTAB , January (2008)

For a bunch*:2

1

( ) ( , ) ( )zW p J p S dω

ω

ω ω ω= ∫

Page 25: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

DR/TR from a disc D=8mm, Ψ=450

Horizontal scan, X [mm]-150 -100 -50 0 50 100 150

Inte

nsity

[NTR

]

0.0

0.2

0.4

0.6

0.8

1.0

1.2F=50GHz 150GHz250GHz 350GHz 450GHz 600GHz 800GHz 1200GHz 1800GHz

Example: CDR from 8 mm disk produced by a 10 MeV ebeam(optimized for a 2ps bunch observed at a distance of 300mm)

Horizontal distribution of CDR

Horizontal scan X [mm]-150 -100 -50 0 50 100 150

Inte

nsity

x ∆

F / A

[N

TR x

GH

z]

0.0

0.2

0.4

0.6

0.8

1.00.5ps, A=317 1ps, A=76 1.5ps, A=28

Formfactor of a relativistic Gaussian bunch.Peak DR distribution.

Frequency [THz]0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

K

0.0

0.2

0.4

0.6

0.8

1.0

0.5ps 1ps 1.5ps Peak DR

Page 26: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Y [mm]-60 -40 -20 0 20 40 60

Det

ecto

r Sig

nal

[V]

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7experimenttheory

PBU 0Pulse=0.69psRMS=5%

Y [mm]-60 -40 -20 0 20 40 60

Det

ecto

r Sig

nal

[V]

0.00

0.05

0.10

0.15

0.20

0.25

0.30experiment theory

PBU 0Pulse=0.78psRMS=8.6%

Proof of Principle Experiment at the PSI 100 MeV linacfor two bunch compressor tunes

CDR slit

Single Gaussian bunch fit

0.69ps bunch, RMS=5%

0.78ps, RMS=8.6%

Double Gaussian bunch fit, RMS=1.26%,

-3.2ps time 3.2ps

0.57ps, Am=1; 2.84ps, Am=0.2, Shift=1.53ps

* Shkvarunets, Fiorito, paper WEPC21, Proc. of DIPAC 07

CDR plate

Page 27: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Coherent Smith Purcell Radiation Bunch Length Monitor

*S. Korbly, et. al., PRSTAB, 9, 022802 (2006) and PRL 94, 054803

Some (not all) Labs developing CSPR diagnostics:

TPU 6 MeVMIT-Dartmouth*: 15 MevUniversity of Mainz: 900 MeVOxford, Essex, SLAC: multi GeV (up to 30 GeV)

Page 28: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Smith-Purcell radiation is produced when a charged particle beam interacts with a periodic metallic structure. (spatially coherent DR)

The structure, or ‘grating’, causes an angular dispersion of wavelengths according to the relationship (radiation resonance condition):

where l is the period of the grating, n is the emitted order of radiation, β = v/c and θ is the observation angle.

The wavelength range depends upon the grating period, and can be selected.

Coherent enhancement occurs for bunch lengths shorter than, or equal to, the emitted wavelengths.

Smith-Purcell Radiation:

Fig. 1

Page 29: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Intensity per unit frequency for nth order for single electron

For bunch of N electrons

Longitudinal bunch form factor

Page 30: Transition, diffraction and Smith-Purcell radiation diagnostics ......Transition, diffraction and Smith-Purcell radiation diagnostics for charged particle beams Ralph B. Fiorito Institute

Experiment: Measure CSPR AD for two different bunch lengths