[PPT] - Visualising the Dynamics of a Plasma-Based Electron Accelerator PowerPoint Presentation

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Visualising the Dynamics of a Plasma-Based Electron Accelerator

Malte C. Kaluza Institute of Optics and Quantum Electronics, FSU Jena, Germany Helmholtz-Institute Jena

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Thanks to All Collaborators!

Visualising Plasma-Based Acceleration

A. Sävert, M. B. Schwab, M. Leier, M. Reuter, M. Schnell,
A. Kawshik, D. Ullmann, O. Jäckel, F. Ronneberger,
B. Beleites, C. Spielmann, G. G. Paulus, M. Zepf

Institute of Optics and Quantum Electronics, Friedrich-Schiller-University Jena, Helmholtz-Institute Jena

A. Buck, K. Schmid, C.M.S. Sears, J. M. Mikhailowa,
F. Krausz, L. Veisz

Max-Planck-Institute of Quantum Optics, Garching

S. P. D. Mangles, K. Poder, J. Cole, Z. Najmudin

Imperial College London, UK

E. Siminos, S. Skupin

Max-Planck-Institute of the Physics of Complex Systems, Dresden

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Visualising Plasma-Based Acceleration

Motivation and Outline

Compact laser-driven plasma-electron accelerators:
plasma formed and modulated by high-intensity laser pulse
electrons accelerated by fields of laser-generated plasma wave

(„wakefield“)

electron pulse parameters determined by details of interaction
generation and evolution of this wakefield?
acceleration dynamics?
High relevance for future beam-driven plasma-electron accelerators:
research programs started or planned e.g. at SLAC and DESY
first experimental results
Pump-probe geometry well suited for investigation:
accelerator driven by main pulse (“pump pulse”),
can be characterized (“probed“) using synchronized probe pulse
Generate synchronized electro-magnetic probe pulses:
investigate details of interaction with high temporal and spatial

resolution

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High-energy particle accelerators

for protons,
heavy ions,
electrons – linacs,
electrons – synchrotrons

are well established. However, they are large because of limited acceleration field strength to avoid break-through

r ionization.

Conventional Particle Accelerators

CERN GSI SLAC/LCLS Diamond

Visualising Plasma-Based Acceleration

DESY

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High-energy particle accelerators

for protons,
heavy ions,
electrons – linacs,
electrons – synchrotrons

are well established. However, they are large because of limited acceleration field strength to avoid break-through

r ionization.

Conventional Particle Accelerators

CERN GSI SLAC/LCLS Diamond

Visualising Plasma-Based Acceleration

JETI

⇒ use plasma as the medium, high-intensity laser

r electron pulse as the driver!

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What are „High Intensities“?

Visualising Plasma-Based Acceleration

Laser intensity IL ≥ 1019 W/cm2 Intensity of sun @ earth ≈ 103 W/m2 Earth’s cross section ≈ 1014 m2 Total power of the sun reaching the earth ≈ 1017 W

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What are „High Intensities“?

Visualising Plasma-Based Acceleration

Laser intensity IL ≥ 1019 W/cm2 Intensity of sun @ earth ≈ 103 W/m2 Earth’s cross section ≈ 1014 m2 Total power of the sun reaching the earth ≈ 1017 W to (1 mm)2: IL = 1019 W/cm2 to (1 cm)2: IL = 1017 W/cm2 to (0.1 mm)2: IL = 1021 W/cm2

?

Focussingthis power

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What are „High Intensities“?

JETI @ FSU Jena and LWS 20 @ MPQ Garching

Multi-TW OPCPA Laser pulse duration: 8.5 fs pulse energy: 65 mJ focus diameter: <3 µm

max. intensity:

>1×1020 W/cm2 10...30-TW Ti:Sapphire Laser pulse duration: 85 ... 35 fs pulse energy: 750 mJ focus diameter: <3 µm

max. intensity: >1×1020 W/cm2

Visualising Plasma-Based Acceleration

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Plasma Wakefield Acceleration

Visualising Plasma-Based Acceleration

Image courtesy of A.G.R. Thomas

Plasma wave excited by Fpond of high-intensity laser pulse

≡ modulation of ne against ion background (vph,plasma = vgr,laser) ⇒ longitudinal E-fields (~ 0.1…1 TV/m)

injection of electrons into the wave

(e.g. by wave breaking or externally)

Principle of the acceleration process

W. Leemans et al., PRL (2014)
A. Pukhov et al., APB (2002)

⇒ quasi-monoenergetic, ultra-short electron pulse

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Plasma Wakefield Acceleration

Visualising Plasma-Based Acceleration

Image courtesy of A.G.R. Thomas

injection of electrons into the wave

(e.g. by wave breaking or externally)

Principle of the acceleration process

M. Litos et al., Nature (2014)

⇒ relativsiticelectron current ⇔ azimuthal B-fields ⇒ quasi-monoenergetic, ultra-short electron pulse

Plasma wave excited by Fpond of high-intensity laser pulse

≡ modulation of ne against ion background (vph,plasma = vgr,laser) ⇒ longitudinal E-fields (~ 0.1…1 TV/m)

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Electromagnetic Probe Pulses

Visualising Plasma-Based Acceleration

Probe-pulse generation

Generation ofsynchronized optical probe pulses:
split off part of

the main pulse

guide it towards

interaction along different path

adjust temporal

delay ⇒ perfect synchronization ⇒ probe pulse duration similar to main pulse ⇒ record movie from subsequent shots at different delays (requires good shot-to-shotstability!)

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Electromagnetic Probe Pulses

⇒ rotation of probe polarization: ⇒ measure φrot to get signature of B-fields, measure ne to get amplitude!

Transverse probing of B-fields in underdense plasma with linearly-polarized

probe pulse: if ⇒ B-field induced difference of η for circularly-polarized probe components

J. A. Stamper et al., PRL (1975)

Measuring B-fields: the Faraday effect

Visualising Plasma-Based Acceleration

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Experimental setup I

JETI parameters: Elaser = 800 mJ, τlaser = 85 fs, f/6 OAP, Ilaser ≈ 3x1018 W/cm2 probe pulse: τprobe ≈ 100 fs @ 1ω

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Two polarograms from two (almost) crossed polarizers: Deduce rotation angle φrot from pixel-by-pixel division of polarogram intensities:

polarogram 2 polarogram 1 560 µm 340 µm

Polarimetry results

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polarogram 2 polarogram 1 560 µm

Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

experimental Faraday feature simulated feature Experimental evidence for B-fields from MeV electrons and bubble!

MCK et al., PRL 105, 115002 (2010)

Polarimetry results

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

JETI parameters: Elaser = 800 mJ, τlaser = 85 fs, f/6 OAP, Ilaser ≈ 3x1018 W/cm2 probe pulse: τprobe ≈ 100 fs @ 1ω LWS-20 parameters: Elaser = 80 mJ, τlaser = 8.5 fs, f/6 OAP, Ilaser ≈ 6x1018 W/cm2 probe pulse: τprobe = 8.5 fs @ 1ω

Experimental setup II

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

polarogram 2 polarogram 1

Electron bunch length: Δz = 4 µm τFWHM= (6±2) fs, τRMS= (2.5±0.9) fs

A. Buck et al., Nature Physics 7, 543 (2011)

Polarimetry results

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Polarimetry:

visualize e-bunch via associated B-fields

change delay between

pump and probe ⇒ movie of e-bunch formation

observe e-bunch formation on-line!
A. Buck et al., Nature Physics 7, 543 (2011)

Polarimetry results

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Shadowgraphy:

visualize plasma wave

change electron density ⇒

change plasma wavelength

A. Buck et al., Nature Physics 7, 543 (2011)

Shadowgraphy results

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Experiments with 30-TW JETI-laser system
Similar resolution, but with 35-fs driver laser:
frequency-broadening of probe pulse

(in gas-filled hollow fiber) ⇒ shorter τprobe ⇒ sub-main pulse temporal resolution, 1.1 µm spatial resolution with optimized imaging system

τprobe = (5.9±0.4) fs

M. Schwab et al., Appl. Phys. Lett. 103, 191118 (2013)

Experimental setup III

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Few-cycle probe pulses

100 µm 10 µm 100 µm 10 µm LWS 20 JETI

Few-Cycle Microscopy

M. Schwab et al., Appl. Phys. Lett. 103, 191118 (2013)

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Probing of plasma wakefield acceleration process

critical power for self injection: for our parameters: ne> 1.5x1019cm-3

S.P.D. Mangles et al., PRSTAB 15, 011302 (2012)

Measuringthe length of the 2nd plasma wave period (at fixed position in the plasma) and the electron charge:

A. Sävert et al., Phys. Rev. Lett. 115, 055002 (2015)

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Results from Few-Cycle Microscopy

injection transverse focussing acceleration

A. Sävert et al., Phys. Rev. Lett. 115, 055002 (2015)

Plasma wave evolution above injection threshold: ne=1.6x1019cm-3

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Results from Few-Cycle Microscopy

Bubble expansion starts before injection. No beam-loadingbut amplificationofpump pulse: λp for ne=1.6x1019 cm-3 „well behaved“ beam-loadingdominated single-bubble regime multiple-bubble regime wavebreaking radiation

A. Sävert et al., Phys. Rev. Lett. 115, 055002 (2015)

Measuringlength of 1st plasma wave period (at ne=1.6x1019 cm-3) at different positions: After injection: strongly non-linear evolution

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Comparison with numerical simulations

electron density & pump pulse intensity computed shadowgrams experimental shadowgrams 3D PIC simulation (EPOCH), 150x70x70 µm3 sliding box, 2700x525x525 cells

E. Siminos et al., submitted (2015)

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Probing Laser-Driven Wakefields

Visualising Plasma-Based Acceleration

Comparison with numerical simulations

A. Sävert et al., Phys. Rev. Lett. 115, 055002 (2015)

Bubble expansion starts before injection. No beam-loadingbut amplificationofpump pulse.

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Probing Beam-Driven Wakefields

Visualising Plasma-Based Acceleration

consequences for probing?
Energy gain:

Probing of plasma waves at lower background densities

when reducingne
W. Lu et al.,

PRSTAB 10, 061301 (2007)

plasma wave length λpl increases

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Probing Beam-Driven Wakefields

Visualising Plasma-Based Acceleration

Probing of plasma waves at lower background densities

ne = 1.7×1019 cm-3, 𝜇plasma = 9 µm 1 ne = 4.8×1018 cm-3, 𝜇plasma = 17 µm 2 probing image, simulated for λprobe = 750 nm plasma wave, simulated with 3D-PIC probing image, simulated for λprobe = 1.4 µm 4 3 5

E. Siminos et al., submitted (2016)
Sensitivity/contrast depends on 𝜇probe/𝜇plasma (~1/12 optimal)

⇒ increase 𝜇probe to mid-IR (8...10 µm for ne ≤ 1017/cm3)

Space and time scales of plasma wave increase similarly

⇒ few-cycle probe pulse in mid-IR gives similar relative resolution!

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Probing Beam-Driven Wakefields

Visualising Plasma-Based Acceleration mid-IR: 2 µm ≤ λpr≤ 10 µm near-IR: λpr @ 800 nm

spectral broadening + compression shift λpr (+ amplification in an OPA) + spectral broadening + compression

synchr. few-cycle, near-IR probe
synchr. few-cycle, mid-IR probe

works @ ne = 0.5...1×1019cm-3 works @ ne = 3×1016...1×1018cm-3

M. Schwab et al., APL 103, 191118 (2013)

Probing of plasma waves at lower background densities

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Probing Beam-Driven Wakefields

Visualising Plasma-Based Acceleration

when reducing ne

⇒ use synchronizedfew-cycle mid-IR pulses, adapt diagnosticcomponents (lenses, cameras, polarizers,...)

Probing of plasma waves at lower background densities

⇒ probe electrons‘ B-fields in plasma using Faraday-effect: ⇒ High-resolution diagnostic for visualization of wake field and for synchronization of e-bunch and driver for external injection

A. Buck et al., Nature Phys. 7, 543 (2011)
Energy gain:
W. Lu et al.,

PRSTAB 10, 061301 (2007)

plasma wave length λpl increases
consequences for probing?

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Conclusions

Visualising Plasma-Based Acceleration

Probingdiagnostics reveal detailed insight

into plasma-based electron accelerators

Few-cycle optical pulses can be used to

deduce densityand acceleratingfield distributions in the plasma

Study non-linear evolutionofplasma wave

⇒ quantitative information about acceleration details

Use of these diagnostics might help to
vercome current issues of plasma

accelerators (stability/reproducibility) in the future ⇒ Further improve plasma diagnostics, their sensitivity and their resolution in the future! ⇒ Adapt probing wavelength to match requirements for high-energy plasma electron accelerators!