direct laser acceleration of electrons in the corrugated...

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Andrew York Brian Layer John Palastro Thomas Antonsen Howard Milchberg Institute for Physical Science and Technology University of Maryland, College Park, Maryland, 20742 UNIVERSITY OF MARYLAND AT COLLEGE PARK INSTITUTE FOR PHYSICAL SCIENCE AND TECHNOLOGY Direct laser acceleration of electrons in the corrugated plasma waveguide 1.5cm 650 µm 500µm

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Page 1: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Andrew YorkBrian Layer

John PalastroThomas AntonsenHoward Milchberg

Institute for Physical Science and Technology University of Maryland, College Park, Maryland, 20742

UNIVERSITY OF MARYLAND AT COLLEGE PARKINSTITUTE FOR PHYSICAL SCIENCE AND TECHNOLOGY

Direct laser acceleration of electrons in the corrugated plasma waveguide

1.5cm

650 µm

500µm

Page 2: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Laser wakefield acceleration has made GeV electrons available in a compact setup using terawatt lasers

40 terawatt,40 femtosecond

laser pulseElectric discharge plasma waveguide

Page 3: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Laser wakefield acceleration has made GeV electrons available in a compact setup using terawatt lasers

40 terawatt,40 femtosecond

laser pulseElectric discharge plasma waveguide

Page 4: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Laser wakefield acceleration has made GeV electrons available in a compact setup using terawatt lasers

40 terawatt,40 femtosecond

laser pulse

~30 picoCoulombs of ~1 GeV electrons

Electric discharge plasma waveguide

e-

Page 5: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Laser wakefield acceleration has made GeV electrons available in a compact setup using terawatt lasers

But:

This is inherently nonlinear- you need terawatt lasers to do wakefield acceleration

Page 6: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

The SLAC structure is a TM-mode microwave waveguidewith periodic structure to phase-match acceleration.

Ez

Etransverse

Btransverse

EM propagation& particle accel.

‘slow-wave’ structurewave phase velocity < c

A linear process:There's no minimum microwave power

Page 7: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

The SLAC structure is a TM-mode microwave waveguidewith periodic structure to phase-match acceleration.

Ez

Etransverse

Btransverse

EM propagation& particle accel.

‘slow-wave’ structurewave phase velocity < c

internal breakdown (lightning!) and self-destructionif wave fields are greater than ~ 107 Volts/m

accelerator waveguide structure

There is a maximum power, though.

Page 8: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

The SLAC structure is a TM-mode microwave waveguidewith periodic structure to phase-match acceleration.

50 GeV in 3.2 km

50 x109 V/(1.7x107 V/m) = 2 miles

Solution: use ‘milder’ fields over longer distanceview from space

Ez

Etransverse

Btransverse

EM propagation& particle accel.

‘slow-wave’ structurewave phase velocity < c

internal breakdown (lightning!) and self-destructionif wave fields are greater than ~ 107 Volts/m

accelerator waveguide structure

Page 9: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

1.5cm

650 µm

500µm

Another solution: replace the copper tube with a (much smaller) tube made of plasma!

Tube made of plasma. No more “damage threshold”

Now, instead of megawatt microwave klystrons:

You can accelerate with terawatt OR gigawatt optical lasers!

Page 10: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

This might seem a little crazy

Bunch of relativistic electrons

e- Wheee!

But...

Page 11: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

1 mm

Terawatt, femtosecond laser pulse

Microstructured plasma waveguide

PRL 99, 035001 (2007)

We've already done the hardest part:making the plasma tube

Page 12: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

1 mm

The structured plasma can phase-match direct acceleration

e-

Relativistic electron bunch

Radially-polarized femtosecond laser pulse

Our simulations show we can get good acceleration gradients with modest lasers

PRL 100, 195001 (2008)

Page 13: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

1 mm

The structured plasma can phase-match direct acceleration

e-

Relativistic electron bunch

Radially-polarized femtosecond laser pulse

Our simulations show we can get good acceleration gradients with modest lasers

Even small lasers would give big acceleration gradients:

1.9 TW: >80 MeV/cm30 GW: >10 MeV/cm(over many centimeters)

Page 14: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

The structured plasma can phase-match direct acceleration

e-

Relativistic electron bunch

Radially-polarized femtosecond laser pulse

Our simulations show we can get good acceleration gradients with modest lasers

27µm

-27µm

300

0

pz (m

e c)

xi

zi-11 µm -1 µm

Acceleration depends on electron injection:

Page 15: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Total charge and efficiency seem promising. In our 2 TW drive-beam simulations:

-27µm

300

0

pz (m

e c)xi

zi-11 µm -1 µm

About 40 pC of charge can fit in each “bucket”

Each “bucket” absorbs about 1%

of the drive pulse

energy.

Palastro et al., PRE 77, 036405 (2008)

Page 16: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Cluster Jet (Ar, H2,N2)

How we made the plasma tube:

Spatially modulated 500mj 100ps Nd:YAG

laser pulsePeriodically Modulated

Plasma Waveguide

Axicon

Breakdown in atmosphere, mm-scale corrugations

1.5cm

Diffractive optic to shape the waveguide

creation pulse

We have a lot of control over the shape and density

of the plasma tube.

Page 17: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Cluster Jet (Ar, H2,N2)

Spatially modulated 500mj 100ps Nd:YAG

laser pulsePeriodically Modulated

Plasma Waveguide

Axicon

Diffractive optic to shape the waveguide

creation pulse

1.5cm

Breakdown in argon clusters, 100's μm-scale corrugations

We have a lot of control over the shape and density

of the plasma tube.

How we made the plasma tube:

Page 18: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Cluster Jet (Ar, H2,N2)

Periodically Modulated

Plasma Waveguide

Axicon

1.5cm

Diffractive optic to shape the waveguide

creation pulse

Spatially modulated 500mj 100ps Nd:YAG

laser pulse

35µm

50µm

Small corrugations are crucial if we're going to

extend this technique to ion acceleration

Breakdown in atmosphere, 10's μm-scale corrugations

How we made the plasma tube:

Page 19: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Cluster Jet (Ar, H2,N2)

We've demonstrated terawatt guiding in these tubes*. They're corrugated optical waveguides!

Periodically Modulated

Plasma Waveguide

Axicon

100mj 50-70fs Ti:sapphire laser pulse

(delayed ~2ns relative to YAG pulse)

1.5cm

Diffractive optic to shape the waveguide

creation pulse

Spatially modulated 500mj 100ps Nd:YAG

laser pulse

13 µm

So far we've demonstrated guiding of a linearly polarized laser pulse.

We need to guide a radially polarized pulse (a TM waveguide mode) for effective acceleration.

*PRL 99, 035001 (2007)

Page 20: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

•Use a ‘Ring Grating’ (RG)- a transmissive diffraction grating lithographically etched into a fused silica disk

•Image the RG through an axicon to the line focus

•Creates a modulated plasma spark that evolves into a modulated channel

•Different ring gratings give us different modulation periods

100ps pulse

Pulse images the RG from 60cm upstream

The ring grating

In the lab, it looks like this:

Page 21: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Second method- tailored cluster flow

Ar or N2

Cluster Jet

100ps Nd:YAG laser pulse

Modulated Plasma Waveguide

Axicon

60fs Ti:Al2O3 laser pulse

60 fs transverse interfer. probe

1.5 cm

1030 µm

330µm

Page 22: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Cluster flow can be tailored to make extremely small features in the plasma channel

Transverse Phase Shift

Nitrogen cluster target @

-150 deg C

Argon Cluster target @ 22 deg C

200 μm

50 μm

600 μm

(200 consecutive shot average)

Radial Electron Density

60 μm dia.

Abel Inversion

Abel Inversion

5*1018 cm-3

at wall

9*1018 cm-3

at wall

~3*1018 cm-3

on axis

~2*1018 cm-3

on axis

Page 23: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Conclusions

•Optical-frequency linac with no damage threshold•Simple, unoptimized model shows strong acceleration•Plasma structures are under control•Need radial polarization: diffractive optics?

•Need an injector: solid target? wakefield acceleration?•Extension to ions needs study

Page 24: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Guiding in corrugated hydrogen plasma channels

• H2 jet cryogenically cooled to enhance clustering• Electron densities of ~1.5*1018 cm-3 on axis and ~3*1018 cm-3 at channel wall for a delay of 1ns

15µm

1017 W/cm2

(b) (i) (ii) (iii)

700 µm

500 µm

200 mJ 300 mJ 500 mJ+ misalign.

Waveguide generation pulse energyand alignment controls modulation features

Page 25: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Why use a 100ps laser pulse and clusters?

•The far leading edge of the 100ps beam disassembles / ionizes the clusters, leaving a cold plasma that the remainder of the pulse heats.•Much more efficient than heating an unclustered gas (for same average Z in a plasma, 3x-10x less pump energy required)

50 Å ~ 600 ÅSingle Ar cluster

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Critical density layer

Under-dense plasma

Sub-critical plasma−ξ Eint/4π < 0

Super-critical plasmaa

H. Sheng et al, Phys. Rev. E 72, 036411 (2005)

Page 26: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Our next project: generating a radially polarized femtosecond-scale, multi-millijoule pulse.

Page 27: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Corrugated guide: simple estimates of dephasing lengths and acceleration gradients

n1 > n2One full dephasing cycle

Estimate acceleration gradients using index modulation toy model:

Accelerating-phase region: low index

Decelerating-phase region: high index

λ = 800nmNe1 = 3*1018 cm-3

Ne2 = 6*1018 cm-3

wch = 12μm

p = 1, m = 0

} Ld1= ~260 μm

Ld2=~165 μm

For P = 1 TW, Ez =0.55 GV/cm, giving an effective gradient of 77 MV/cm (14% “efficiency”)

Wakefield comparison: Malka et al. used a 30 TW laser at λ = 0.8 μm to produce an acceleration gradient of ~0.66 GV/cm

This is a linear process with no threshold.

1 mJ regenerative amplifier alone P = 20GW Effective accel. gradient: 11 MV/cm

Page 28: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Accelerating-phase region: low plasma density (high index)

Decelerating-phase region: high plasma density (low index)

n1 > n2Mod period d

Ld1 Ld2

Simplified density modulation:

So, what's the gradient? A toy model:

The driving wave speeds up and slows down in successive portions of the modulation so that the acceleration in the first part is not completely cancelled by deceleration in the second part.

Energy gain per cycle: adeELELEeU dzdz 02211 )( −≈−−≈∆ where 1<a

Model this real waveguide:

As this simplified

waveguide:

Page 29: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

Lucky for us, there's already a proof-of-principle experiment for electron acceleration by a radially polarized laser pulse

580-MW peak power gave 31 MeV/m.

10 TW peak powers are now routine, but neutral-gas phase matching limits peak intensities for ICA.

Page 30: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

A more realistic model: FDTD simulations*

3000 μm

130 μm

*Using MEEP, http://ab-initio.mit.edu/wiki/index.php/Meep

Plasma density vs. r and z

Electrons per cm3

Plasma density vs. r and z

e-

Page 31: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

A more realistic model: FDTD simulations*

3000 μm

130 μm

*Using MEEP, http://ab-initio.mit.edu/wiki/index.php/Meep

Plasma density vs. r and z

Electrons per cm3

Plasma density vs. r and z

e-

Page 32: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

A more realistic model: FDTD simulations*

3000 μm

130 μm

*Using MEEP, http://ab-initio.mit.edu/wiki/index.php/Meep

Plasma density vs. r and z

Electrons per cm3

Plasma density vs. r and z

e-

Page 33: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

A more realistic model: FDTD simulations*

3000 μm

130 μm

*Using MEEP, http://ab-initio.mit.edu/wiki/index.php/Meep

Plasma density vs. r and z

Electrons per cm3

Plasma density vs. r and z

e-

Page 34: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

A more realistic model: FDTD simulations*

3000 μm

130 μm

*Using MEEP, http://ab-initio.mit.edu/wiki/index.php/Meep

Plasma density vs. r and z

Electrons per cm3

Plasma density vs. r and z

e-

Page 35: Direct laser acceleration of electrons in the corrugated ...fsc.lle.rochester.edu/pub/HEDLP/presentations/York.pdf · Andrew York Brian Layer John Palastro Thomas Antonsen Howard

A more realistic model: FDTD simulations*

One full dephasing cycle Accelerating-phase region: low index

Decelerating-phase region: high index

λ = 6.4 μmNe1 ~=0.5*1017 cm-3

Ne2 ~= 0.5*1018 cm-3

wch ~= 40μm

tpulse ~=300 fs

3000 μm

130 μm

*Using MEEP, http://ab-initio.mit.edu/wiki/index.php/Meep

Plasma density vs. r and z

Electrons per cm3

Plasma density vs. r and z

Simulation includes: Plasma dispersion Finite pulse duration Leakage effectsCylindrical coordinates

-25

+33

-38

+59

Accelerating field Ez seen by a relativistic electron vs. propagation distance

-64

+93

-92

+123

Ez

-111

+138

-113

+130

-98

+103

-72

+69

-45

+39

Net gain!

(~3% “efficiency”, room for optimization)