U C L A P. Muggli, Paris 2005, 06/09/05 Halo Formation and Emittance Growth of Positron Beams in Long, Dense Plasmas Patric Muggli and the E-162 Collaboration:

U C L AP. Muggli, Paris 2005, 06/09/05

Halo Formation and Emittance Growth of Positron Beams in

Long, Dense PlasmasPatric Muggli

and the E-162 Collaboration:C.D. Barnes, F.-J. Decker, M. J. Hogan, R. Iverson, C. O’Connell, P. Raimondi,

R.H. Siemann, D. Walz

Stanford Linear Accelerator Center

B. Blue, C. E. Clayton, C. Huang, C. Joshi, K. A. Marsh, W. B. Mori, M. Zhou

University of California, Los Angeles

T. Katsouleas, S. Lee, P. Muggli

University of Southern California


• Optical Transition Radiation(OTR)

• CHERENKOV (aerogel)

- Spatial resolution ≈100 µm - Energy resolution ≈30 MeV- Time resolution: ≈1 ps

5 10 15 20 25 30 35 40 45 50

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y

x10 20 30 40 50 60

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x

EXPERIMENTAL SET UP

E-157:

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250

y,E

x10 20 30 40 50 60 70 80 90 100

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y,E

x

E-162:

- 1:1 imaging, spatial resolution <9 µm

e-, e+

N=21010

z=0.7 mmE=28.5 GeV

IonizingLaser Pulse

(193 nm) Li Plasma

ne≈21014 cm-3

L≈1.4 m

CherenkovRadiator

Streak Camera(1ps resolution)

Bending MagnetX-Ray

Diagnostic

Optical TransitionRadiators Dump

∫Cdt

Quadrupoles

Imaging Spectrometer25 m

IP0: IP2:


e-: ne0=21014 cm-3, c/p=375 µm e+: ne0=21012 cm-3, c/p=3750 µm

r=35 µmr=700 µm

• Uniformfocusing force (r,z)

=1.81010

• Non-uniformfocusing force (r,z)

d=2 mm

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

BlowOut

3 beamFront

Back

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

30 beamFront

Back

3-D QuickPIC simulations, plasma e- density:e- & e+ BEAM NEUTRALIZATION

e- e+


e- & e+ FOCUSING FIELDS*

Ex (GV/m)

0

1500

-1500

0-3750 3750

x (µ

m)

z (µm)

e-

Ex (GV/m)

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-700

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x (µ

m)

z (µm)

e+

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Exz=0Electrons1.5e14

x (µm)

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e--0.4

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Exz=0Positrons1.5e14

x (µm)

e+

x0=y0=25 µmz=730 µmN=1.91010 e+/e-

ne=1.51014 cm-3 *QuickPIC

Linear, no abberations

Non-linear,abberations


e- & e+ FOCUSING FIELDS

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-4 -2 0 2 4Er(z)ele1.e15

( )z mm

r=r

r=3r

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-4 -2 0 2 4Er(z)posi1.5e14

( )z mm

r=r

r=3r

QuickPIC x0≈y0≈25 µm, Nx≈39010-6, Ny≈8010-6 m-rad, N=1.91010 e+,

z≈730 µm, ne=1.5 10-6, L≈1.1 cm

• Uniform focusing force (r,z) • Non-uniform focusing force (r,z)

• Weaker focusing force • Stronger focusing force

Front Back Front Back

• e+: focusing fields vary along r and z!


FOCUSING OF e-/e+

0 50 100 150 200 250 300 350 400 450 500

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e-

e+

ne=0 ne≈1014 cm-3

2mm

2mm

• Ideal Plasma Lens in Blow-Out Regime

• Plasma Lens with Aberrations

• OTR images ≈1m from plasma exit (x≠y)

• Qualitative differences


EXPERIMENT / SIMULATIONS

x0=y0=25µm, Nx=39010-6, Ny=8010-6 m-rad, N=1.91010 e+, L=1.4 m

Downstream OTR

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2000

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PE390by80resultsOTR

FWHMx@otr (µm)FWHMy@otr (µm)

ne (×114 cm-3)

• Excellent experimental/simulation results agreement!

SimulationExperiment

0

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2000

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12230cl-n-md4TriangOTR.kg

x-laser OFFy-laser OFFx-laser ONy-laser ON

UV (mJ) OFFUV Energy (mJ)


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12220ce-f-gd4TriangOTR

x-laser OFFy-laser OFFx-laser ONy-laser ON

UV (mJ) OFF

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-0.5 0 0.5 1 1.5 2 2.5

PE115by184largeresults

FWHMx@otr (µm)FWHMy@otr (µm)

ne (×114 cm-3)

Downstream OTR

• Defocusing in x and y “low” in both planes, larger • No distinctive features (-tron oscillations)• Excellent experimental/simulation results agreement!

x0≈65 y0≈48 µm, Nx≈11510-6, Ny≈18410-6 m-rad, N≈1.91010 e+, L≈1.4 m

EXPERIMENTAL/SIMULATION RESULTS

Experiment Simulation

UV Energy (mJ)


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PE390by80results

FWHMx@PlEx (µm)FWHMy@PlEx (µm)

ne (×114 cm-3)

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y,E

x

EXPERIMENTAL RESULTS e+

x0≈y0≈25 µm, Nx≈39010-6, Ny≈8010-6 m-rad, N=1.91010 e+, L≈1.4 m

Cherenkov/Plasma Exit

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12230cl-n-md4TriangCer.kgLaser OFFLaser ON

UV (mJ) OFFUV Energy (mJ)

• Strong focusing in x (large ), defocusing in y (low ) • No distinctive features (-tron oscillations)

Resolution

Limit?


Beam Size=FWHM (BAB’)Charge in the Peak=Area(BAB’)Charge in the Halo=2*Area(CDB)

FIT FOR BEAMS WITH HALO

X-profile

y-profile

Halo


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2 105

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PeakHaloY12230cl-n-md4Triang.qpc

Peak, Laser OFFHalo. Laser OFFPeak, Laser ONHalo. Laser ON

UV Energy (mJ), ne (a.u.)

0

1 105

2 105

3 105

4 105

5 105

6 105

-0.5 0 0.5 1 1.5

PeakHY12230cl-n-md4TrianS.qpc

Peak, Laser OFFHalo. Laser OFFPeak, Laser ONHalo. Laser ON

UV Energy (mJ), ne (a.u.)

HALO FORMATION


• Charge is conserved by the triangular fits• The halo forms at low density


HALO FORMATION


• Very nice agreement

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P390by80PeakHaloFraction

x-Peak Fractionx-Halo Fractiony-Peak Fractiony-Halo Fraction

ne (×114 cm-3)

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P390by80peakHalo5

x-Peak, OFFx-Halo, OFFy-Peak, OFFy-Halo, OFF

x-Peak, ONx-Halo, ONy-Peak, ONy-Halo, ON

mean(UN OFF) (mJ)

Experiment Simulation


0.93 mJ0.01 mJ (OFF)

1mm

OFF ne=21014 cm-3

HALO FORMATION


Experiment

Simulation

• Very similar


BEAM/FIELD EVOLUTION

90 100 110 120 130 140 150 160

P1e14ProfileAndFocZ=6.1

Cell #

Z=0.061 m

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P1e14ProfileAndFocZ=70ad278

Cell #

Z=0.7 mZ=2.78 m

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P1e14ProfileAndFocZ=1.3

Cell #

Z=0.013 m

Radius (cell)

x0=y0=25µm, Nx=39010-6, Ny=8010-6 m-rad, N=1.91010

• Beam becomes non-Gaussian

• Beam size and focusing field “stop” at z≈0.7 m


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Electrons1.5e142SlicesSize.graph

Slce #1

Slce #2

Slce #3

Slce #4

Slce #5

( ) z m

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Positrons1.5e142SlicesSize.graph

1x ( ) µm

2x ( ) µm

3x ( ) µm

4x ( ) µm

5x ( )µm

( ) z m

0 2 4 6 8 10 12 14 16-1.5

-1

-0.5

0

0.5

1

1.5x 10-12

e-/e+: SLICES SIZE IN THE PLASMA

Front Back

e- e+

o=0.34 m, ne matched=1.61013 cm--3

• Head diverges ≈0 • Head diverges ≈0• Coherent betatron motion

of the core• Phase mixing of the

following slices


e-/e+: SLICE EMITTANCE

0 2 4 6 8 10 12 14 16-1.5

-1

-0.5

0

0.5

1

1.5x 10-12

Front Back

e- e+

1.5 10-9

2 10-9

2.5 10-9

3 10-9

0 0.5 1 1.5

Electrons1.5e142SlicesEmit.graph

Slice #1

Slice #2

Slice #3

Slice #4

Slice #5

( ) z m

0

5 10-9

1 10-8

1.5 10-8

2 10-8

2.5 10-8

3 10-8

0 0.5 1 1.5

Positrons1.5e142SlicesEmit.graph

Slice #1

Slice #2

Slice #3

Slice #4

Slice #5

( ) z m• Increase in the head ... • Increase in the head ...• Blow-out, pure ion column

preserves beam emittance• Phase mixing of the

following slices


CONCLUSIONS

• Simulation results show emittance growth, mostly in the front and back of the bunch

• Simulation results confirm the experimental observations

• Simulation results show “hosing” in the back of the bunch

• Focusing of e+ by a plasma is qualitatively different from that of e-:

• Positron bunches are focused without showing betatron oscillations …

• … focusing depends on and at plasma entrance…

• … show formation of a beam halo.

• Focusing force is nonlinear in r and z

• Emittance growth is expected


0.13 mJ 0.23 mJ

0.93 mJ 6.47 mJ

0.01 mJ (OFF)

1mm

EXPERIMENTAL PROFILES @ OTR

y

x

x0=y0=25µm, Nx=39010-6, Ny=8010-6 m-rad, N=1.91010, ne=0.751014 cm-3

• Focusing in x, not in y, ne “independent”• No halo at low ne

• Triangular projected beam profiles (ne≠0)


SIMULATION PROFILES

x0=y0=25µm, Nx=39010-6, Ny=8010-6 m-rad, N=1.91010

• Beam halo, as in experiment• Focusing in x

@ DS OTR

ne=0.751014 cm-3 @ Plasma Exit/Cherenkov @ DS OTR

ne=0

• Triangular projected beam profiles (ne≠0)


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200

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800

1000

1200

1400

1600

0 1 2 3 4 5 6

122300cs-qdTriangxyNe.graph

x-Plasma OFFx-Plasma ONy-Plasma OFFy-Plasma ON

ne (×114 cm-3)

FOCUSING OF e+: HIGH ne

• from OTR images ≈1m from plasma exit

• Focusing limited by emittance growth due to plasmafocusing aberrations?

M.J. Hogan et al., PRL (2003).

• x-size reduction >3, no betatron oscillations

0x=0y=25 µm

N=1.91010 e+

xN≈10yN≈1010-5 m-radL=1.4 m

Documents

U C L A P. Muggli, Paris 2005, 06/09/05 Halo Formation and Emittance Growth of Positron Beams in Long, Dense Plasmas Patric Muggli and the E-162 Collaboration: