Progress of the Multibunch Progress of the Multibunch Plasma Wakefield Experiments Plasma Wakefield Experiments

at ATFat ATFThemos KallosThemos Kallos

University of Southern University of Southern CaliforniaCalifornia July 2006adJuly 2006ad

Presentation OutlinePresentation Outline Theoretical MotivationTheoretical Motivation

Basic Principles of Multiple BunchesBasic Principles of Multiple Bunches Simulations of 45MeV eBeam into PlasmaSimulations of 45MeV eBeam into Plasma

Experimental AspectsExperimental Aspects CTR Diagnostics for Microbunched eBeamCTR Diagnostics for Microbunched eBeam Create bunches by selectively blocking eBeam Create bunches by selectively blocking eBeam Gas-Filled Capillary: The road to 10Gas-Filled Capillary: The road to 101919cmcm-3-3 plasma plasma densitydensity

The Double Bunch ExperimentThe Double Bunch Experiment Theoretical ModelTheoretical Model Comparison with Experimental DataComparison with Experimental Data

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Principles of multiple Principles of multiple bunches into a Plasmabunches into a Plasma

Bunched VS Non-Bunched eBeamBunched VS Non-Bunched eBeamσσrr=75=75μμm, m, σσzz=1=1μμm Microbunchesm Microbunches

3.8 4 4.2 4.4 4.6

-1

0

1

2

3

x 1013 IFEL M icrobunched eBeam

eBeam Density [cm

-3]

Tim e [ps]

Theory & SimulationTheory & SimulationWakefield Evolution @65MeV – Resonant Case

The electron beam density x100 (1), the theoretical wakefield (2) and the Osiris simulated wakefield (3) after 1mm of propagation in the plasma. Units: 1=300 GeV/m

1 2

3

7GeV/m

Advantages of 1D Code

1000 times faster than 2D Osiris PIC Code

Allows fast plasma density scan

Insensitive to noise (allows longer runs, larger beams)

Predicted Energy SpreadPredicted Energy SpreadAfter 15mm in plasma

CapillaryPlasma

Wiggler

EnergyDiagnostic

np=1019 cm-3

Resonant for λp=10.6μmPpeak≈50MW

λ0=10.6μm, 200psLaser Beam

Experiment OverviewExperiment Overview

IFEL Wiggler

MicrobunchesIpeak≈600AIpeak≈100A

1500μm

45 MeV

Electron Beam

σr=75μm

10.6μm

Establish Microbunching (easy)Establish Microbunching (easy) Establish 10Establish 101919 Plasma Density Plasma Density (hard…)(hard…)

e-

e-

1μm Ti To energy

spectrograph

To plasma

eBeam DiagnosticseBeam DiagnosticsCoherent Transition RadiationCoherent Transition Radiation

Mirror

FocusingLens

IR Detector

22 2 21 forward

3 2 20

d E e sindkd 4 1 cos

k c 1

Beamline Window

eBeam DiagnosticseBeam DiagnosticsCTR Spectrum HarmonicsCTR Spectrum Harmonics

3.8 4 4.2 4.4 4.6

-1

0

1

2

3

x 1013 IFEL M icrobunched eBeameB

eam Density [cm

-3]

Tim e [ps]

FFT

0 0.5 1 1.5 2100

102

104

106

108

z of each microbunch [

m]

Ratio of CTR

harmonics

Ratio of CTR harmonics vs microbunching

Ratio of 1st/2ndRatio of 1st/3rdRatio of 2nd/3rd

Experiment Data Range

Coherent Transition Radiation Coherent Transition Radiation (CTR)(CTR)

DataData comparison with Theorycomparison with Theory

All 3 data sets agree around All 3 data sets agree around σσzz=0.7=0.7μμmm

Creating Microbunches Creating Microbunches By dispersing the eBeam Energy in spaceBy dispersing the eBeam Energy in space

At dispersion plane:At dispersion plane:

Ener

gy

(x)

Time

250μm125μm

1 microbunch every 30μm (15μm on CTR graph)

Energy Slit Clos es

Half the charge is blocked

CTR Interferom etry Signal for different Slit openings

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

14.1 14.15 14.2 14.25 14.3 14.35 14.4 14.45 14.5 14.55 14.6Single Arm Delay [m m ]

CTR Signal [normalize

d]

Narrow Slit Open Slit

The Plasma SourceThe Plasma Source Past and PresentPast and Present

Past: Ablative Polypropylene Past: Ablative Polypropylene CapillaryCapillary 20kV, 0.7kA Discharge20kV, 0.7kA Discharge 2.3*102.3*101818cmcm-3-3 Max Plasma Density Max Plasma Density

Now: HNow: H22 gas-filled gas-filled CapillaryCapillary 20kV, 1.8kA Discharge20kV, 1.8kA Discharge 5.0*105.0*101818cmcm-3-3 Max Plasma Max Plasma DensityDensity

Plasm a light during 20kV discharge

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

-100 100 300 500 700 900

Tim e after peak of m ain discharge [ns]

Norm

alize

d Ligh

t Intens

ity, D

isch

arge

Current

and Ha

Linew

idth [a

u]

FW HM of Ha Line [no back] Discharge Current

Com parison of Stark Broadening inside and outside the capillary20kV Voltage, 1.3kA Current

1.E+16

1.E+17

1.E+18

1.E+19

-200 0 200 400 600 800 1000 1200 1400Discharge Delay [ns]

Plasma De

nsity [cm^-3]

Inside O utside

Density with Laser InterferometryDensity with Laser Interferometry # of current oscillations dependence# of current oscillations dependence

eHeNe p 18

nk L N 2 1.2 10

The phase change introduced from The phase change introduced from the the

plasma is plasma is

Intereference Pattern, 1.3kA Discharge Trace and Plasm a Density 1 cycle = 1.2e18cc

-0.6-0.4-0.20

0.20.40.60.81

1.21.4

0 500 1000 1500 2000 2500Tim e [ns]

Interference Signal [V],

Discharge Cu

rrent and 1e18cc

Plasma Density

Interference Trace Discharge Current Plasm a Density 1e18cc

Intereference Pattern for sim ilar param eters1 cycle = 1.2e18cc

00.050.10.150.20.250.30.350.40.45

0 2000 4000 6000 8000 10000Tim e [ns]

Interference S

ignal [V]

Ideal Modulation Depth is 0.2V

1.28kA, 4 osc. 1.28kA, 6 osc. 1.28kA, 3 osc.

W akefield Evolution versus Tim e (5e16 cm ^-3 density)

-200

-150

-100

-500

50

100

150

200

0 1 2 3 4 5Tim e [ps]

eBeam Density [1e18 cm

^-3] and

Wakefield [M

eV/m

]

eBeam Density W akefield

Double Bunch Experiment Double Bunch Experiment 1D Model Prediction for Wakefield1D Model Prediction for Wakefield

61MeV59MeV

Double Bunch Experiment Double Bunch Experiment Energy Loss and GainEnergy Loss and Gain

Electron Energy (M eV)56 58 60 62 64

Spectrometer Output (arb. units)

0

20

40

60

80

100

120

W ith dischargeDelay = 1.6 s

Nodischarge

Electron Energy (M eV)56 58 60 62 64

Spectrometer Output (arb. units)

0

20

40

60

80

100

120W ith dischargeDelay = ~2 s

Nodischarge

Double Bunch Energy Loss Experim ent

-2-1.5-1

-0.50

0.51

1.52

-1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Discharge Delay [μs]

Energy Loss [MeV]

First Bunch Second Bunch Discharge Current

Double Bunch Experiment Double Bunch Experiment The 2The 2ndnd Bunch samples the wakefield of the Bunch samples the wakefield of the

firstfirst

Assume 5*1016cm-3 Plasma Density at 1μs

Double Bunch In Plasm a - 2nd Bunch DataCharge Ratio 300pC:150pC (1st Bunch:2nd Bunch)

-2-1.5-1

-0.50

0.51

1.52

1E+13 1E+14 1E+15 1E+16 1E+17 1E+18Plasm a Density [cm ^-3]

Energy

Los

s [M

eV]

2nd Bunch LossTheory (Peak W akefield)Theory(W akefield @ Peak of 2nd Bunch

Experimental Progress SummaryExperimental Progress Summary 10.610.6μμm m MicrobunchingMicrobunching confirmed confirmed

HeNe interferometryHeNe interferometry as a plasma density as a plasma density diagnostic is diagnostic is feasible feasible

Awaiting for a Awaiting for a new 5 kA capillarynew 5 kA capillary, aiming , aiming for 10for 101919cmcm-3-3 plasma density plasma density

The The wire meshwire mesh can seems to be creating can seems to be creating microbunches, microbunches, but will there be enough charge left? but will there be enough charge left?

Double BunchDouble Bunch experiment shows dependence on experiment shows dependence on plasma plasma density density

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