Aac06 Talk

Progress of the Multibunch Plasma Wakefield Experiments at ATF

Themos Kallos University of Southern California July 2006ad

Presentation Outline  Theoretical Motivation

 Basic Principles of Multiple Bunches  Simulations of 45MeV eBeam into Plasma  Experimental Aspects  CTR Diagnostics for Microbunched eBeam

 Create bunches by selectively blocking eBeam  Gas-Filled Capillary: The road to 1019cm-3 plasma density

 The Double Bunch Experiment  Theoretical Model  Comparison with Experimental Data

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Principles of multiple bunches into a Plasma

Bunched VS Non-Bunched eBeam σr=75μm, σz=1μm Microbunches

13

eBeam Density [cm-3]

x 10

IFEL Microbunched eBeam

3 2 1 0 -1 3.8

4

4.2 4.4 Time [ps]

4.6

Theory & Simulation

Wakefield Evolution @65MeV – Resonant Case 7GeV/m 1

2

Advantages of 1D Code

 1000 times faster than 2D Osiris PIC Code

3

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

 Allows fast plasma density scan  Insensitive to noise (allows longer runs, larger beams)

Predicted Energy Spread After 15mm in plasma

Experiment Overview Electron Beam

Microbunches

Ipeak≈100A σr=75μm

45 MeV

Ipeak≈600A

IFEL Wiggler

Capillary Plasma

Energy Diagnostic

1500μm

Wiggler np=1019 cm-3 Resonant for λp=10.6μm Ppeak≈50MW

10.6μm

λ0=10.6μm, 200ps

Laser Beam  Establish Microbunching (easy)

 Establish 1019 Plasma Density (hard…)

eBeam Diagnostics Coherent Transition Radiation

1μm Ti

To plasma

To energy spectrograph e-

e-

Beamline Window

d 2E1forward e2 2  3 dkd 4  0

 k  c

  sin   1   2 cos 2    

2

Focusing Lens

1 Mirror

IR Detector

eBeam Diagnostics CTR Spectrum Harmonics

13

eBeam Density [cm-3]

x 10

IFEL Microbunched eBeam

3 2 1

FFT

0 -1 3.8

4

4.2 4.4 Time [ps]

4.6

Coherent Transition Radiation (CTR) Data comparison with Theory

Ratio of CTR harmonics

10

Experiment Data Range

8

10

6

10

4

10

2

10

0

0

Ratio of CTR harmonics vs microbunching Ratio of 1st/2nd Ratio of 1st/3rd Ratio of 2nd/3rd

0.5 1 1.5 z of each microbunch [ m]

 All 3 data sets agree around σz=0.7μm

2

Creating Microbunches

By dispersing the eBeam Energy in space 125μm Energy (x)

Half the charge is blocked Time

Energy Slit Closes

At dispersion plane:

250μm

CTR Interferometry Signal for different Slit openings Narrow Slit

Open Slit

1.1

CTR Signal [normalized]

1 0.9 0.8 0.7 0.6 0.5 0.4 14.1

14.15

14.2

14.25

14.3

14.35

14.4

Single Arm Delay [mm]

14.45

14.5

14.55

14.6

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

The Plasma Source Past and Present  Past: Ablative Polypropylene Capillary

 Now: H2 gas-filled Capillary

 20kV, 0.7kA Discharge

 20kV, 1.8kA Discharge

 2.3*1018cm-3 Max Plasma Density

 5.0*1018cm-3 Max Plasma Density

Comparison of Stark Broadening inside and outside the capillary

Plasma light during 20kV discharge

20kV Voltage, 1.3kA Current

FWHM of Ha Line [no back]

Discharge Current Inside

Outside

1 0.9 0.8 0.7

Plasma Density [cm^-3]

Normalized Light Intensity, Discharge Current and Ha Linewidth [au]

1.E+19

0.6 0.5 0.4

1.E+18

1.E+17

0.3 0.2 0.1 0 -100

1.E+16 -200 100

300

500

Time after peak of main discharge [ns]

700

900

0

200

400

600 Discharge Delay [ns]

800

1000

1200

1400

Density with Laser Interferometry # of current oscillations dependence Intereference Pattern, 1.3kA Discharge Trace and Plasma Density 1 cycle = 1.2e18cc

Interference Signal [V], Discharge Current and 1e18cc Plasma Density

Interference Trace

Discharge Current

0

500

1000

1500 Time [ns]

 The phase change introduced from the plasma is   k HeNe L  Np

2

ne 1.2  1018

Plasma Density 1e18cc

1.4 1.2 1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 2000

2500

Double Bunch Experiment 1D Model Prediction for Wakefield

Wakefield Evolution versus Time (5e16 cm^-3 density) eBeam Density

61MeV

200

eBeam Density [1e18 cm^-3] and Wakefield [MeV/m]

Wakefield

59MeV

150 100 50 0 -50 -100 -150 -200 0

1

2

3 Time [ps]

4

5

Double Bunch Experiment Energy Loss and Gain

Double Bunch Energy Loss Experiment First Bunch

Second Bunch

Discharge Current

Energy Loss [MeV]

2 1.5 1 0.5 0 -0.5 -1 -1.5 -2 -1.0

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

120 100 80

With discharge Delay = 1.6 s

No discharge

60 40 20 0 56

58

60

62

Electron Energy (MeV)

64

Spectrometer Output (arb. units)

Spectrometer Output (arb. units)

Discharge Delay [μs]

No discharge

120 100 With discharge Delay = ~2 s

80 60 40 20 0 56

58

60

62

Electron Energy (MeV)

64

Double Bunch Experiment

The 2nd Bunch samples the wakefield of the first Double Bunch In Plasma - 2nd Bunch Data Charge Ratio 300pC:150pC (1st Bunch:2nd Bunch) 2nd Bunch Loss Theory (Peak Wakefield) Theory(Wakefield @Peak of 2nd Bunch 2

Energy Loss [MeV]

1.5 1 0.5 0 -0.5 -1 -1.5 -2 1E+13

1E+14

1E+15

1E+16

Plasma Density [cm^-3]

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

1E+17

1E+18

Experimental Progress Summary  10.6μm

Microbunching confirmed

 HeNe interferometry as a plasma density diagnostic is feasible

 Awaiting for a new 5 kA capillary, aiming for 1019cm-3 plasma density  The wire mesh can seems to be creating microbunches, but will there be enough charge left?  Double Bunch experiment shows dependence on plasma density

Thank you for listening!