Plasma Accelerators Bob Bingham Central Laser Facility STFC Rutherford Appleton Laboratory, SUPA University of Strathclyde. HB2016 Malmo 4-8 July 2016
Plasma Accelerators
Bob BinghamCentral Laser Facility
STFC Rutherford Appleton Laboratory, SUPA University of Strathclyde.
HB2016 Malmo 4-8 July 2016
Plasma AcceleratorsLev Landau 1908-1968
Developed theory of wave particle interactions Landau damping 1946. Remained a mystery until John Dawson developed a physical model.
John Dawson 1930-2001Landau Damping first explained by John Dawson 1961originator of plasma wakefield accelerators.
Enrico Fermi 1901-1954
Cosmic ray acceleration Fermi Acceleration 1949
Plasma Accelerators
1) Laser Plasma Wakefield Accelerator LWFA.2) Electron/Positron beam-induced Plasma Wakefield Accelerator PWFA.3) Ion beam-induced Plasma Wakefield Accelerators PWFA.
4) Laser ion acceleration, Sheaths, radiation pressure and shock waves.
Extremely high accelerating gradients:1-100GeV/m
Transient Structures: few ps
Microscopic: 10-100 micron wavelengths
1 EW
1 PW
1 TW
1 GW
1 MW
1 kW
1 W1960 1970 1980 1990 2000 2010
A Brief history of Lasers
Mode-locking (ps)
Q-switching (ns)
Ionisation
1 EW
1 PW
1 TW
1 GW
1 MW
1 kW
1 W1960 1970 1980 1990 2000 2010
A Brief history of Lasers
Mode-locking (ps)
Q-switching (ns)
Ionisation
Limitation due to non-linear processes
Aperture Increase (~ns)
Heating ~ KeV
1 EW
1 PW
1 TW
1 GW
1 MW
1 kW
1 W1960 1970 1980 1990 2000 2010
A Brief history of Lasers
Mode-locking (ps)
Q-switching (ns)
Ionisation
Limitation due to non-linear processes
Aperture Increase (~ns)
Heating ~ KeV
Chirped Pulse Amplification(CPA) (ps, fs)
Relativistic MeV
1 EW
1 PW
1 TW
1 GW
1 MW
1 kW
1 W1960 1970 1980 1990 2000 2010
A Brief history of Lasers
Mode-locking (ps)
Q-switching (ns)
Ionisation
Limitation due to non-linear processes
Aperture Increase (~ns)
Heating ~ KeV
Chirped Pulse Amplification(CPA) (ps, fs)
Relativistic MeV
OPCPA?
Wake Behind a Motor Boat
Light speed surfing on Plasma wakes
Huge gradient (~100GV/m) + Tiny structures (~10-100um)
T.Tajima and J.M. Dawson PRL (1979) LWFAP.Chen, J.M. Dawson et.al. PRL (1983) PWFA
• Laser or beam Pulse
Wake
• Trailing beam
Since 2000 A Plasma Revolution ! ?
evolves to
Laser Wake Field Accelerator(LWFA)A single short-pulse of photons
Self Modulated Laser Wake Field Accelerator(SMLWFA)Raman forward scattering instability
Plasma Beat Wave Accelerator(PBWA)Two-frequencies, i.e., a train of pulses
Laser Wakefield Acceleration
Plasma Wakesphoton beamelectron beamneutrino beamion beams
ne
Plasma Wake
γ , e–+, ν v ≤ c
All very similar
* Drive Plasma Wakes
Tajima and Dawson PRL 1979.
The Bubble Regime
Nature 2004
Courtesy: K. Krushelnick, IC
LBL/Oxford Capillary Guided GeV Laser Plasma Accelerator
• The plasma channel was formed in a hydrogen-filled capillary discharge waveguide (inset). The laser beam was deflected into the capillary using an f/25 off-axis parabola (OAP). Diode 1 and 2 were used to measure the guiding efficiency.
(a) Example of 0.5 GeV bunch. Horizontal axis is beam energy, vertical axis is the beam size in the undeflected plane.
(b) The 0.5 (1.0) GeV beam was obtained in the 225 (310) μm capillary.
(c) and (d) Vertically integrated spectra for the 0.5 and 1.0 GeV beams.
A Phenomenological framework of LWFA in the blowout regime and the optimal scaling
W. Lu et al., PR-STAB (2007)
•Laser and plasma matching
•Wake excitation
•Laser guiding (self-guiding or by a plasma channel)
•Local pump depletion
•Wake phase velocity and dephasing
•Self and external injection
•Beam loading
10fs .3nC 1.5GeV electron beam produced by a 200TW 30fs laser pulse
The Blowout/Bubble Regime:
Beam driver:Rosenzweig et al.,P.R.A 1991
Laser driver:W. B. Mori et al., IEEE 1991
Continuous Bubble injection:A. Pukhov et al., A.P. B 2002
Key physics issues for a plasma accelerator
The structure issue:Wake excitation for given drivers ……
The energy spread and efficiency issue:Beam loading, pulse shaping, transformer ratio ……
The stability issue:Driver evolution, matching, guiding, instabilities ……
The injector issue:Self-injection, wave breaking, controlled injection ….
The overall design issue:Parameter optimization for a plasma based accelerator
to match the requirements of beam parameters
Beam-Induced Plasma Wakefield Accelerator (PWA)
• P. Chen, J.M. Dawson et al.
Experiments: E157 Stanford Linear Accelerator SLAC/UCLA 30 GeV driver, 1014 cm-3 plasma
Argonne National Lab (ANL/UCLA) aiming for 1 GeV/m, 1012 particles per
pulse, 100 Hz repetition rate, emittance of 1mm.mrad
plasma
drive beam
driven beam (accelerating
beam)density fluctuations of a plasma
(plasma wave)
Courtesy Chan Joshi
Positron driven wakefields
Courtesy Chan Joshi
Courtesy Chan Joshi
Proton Driven Plasma Wakefield AcceleratorThe CERN AWAKE Experiment
Schematic of experimental area using an available tunnel as the transfer line from the SPS beam. Goal accelerate electron beam to 1GeV. PI A Caldwell
Short Proton DriverGoal to accelerate electrons to TeV in 600m
Caldwell et al Nature Physics 2009
Ion acceleration
• Laser – electrons - ionsDrivelaserbeam
TargetL
Ion acceleration
L < τc/2 ~ 5μmRecirculation, refluxing
• Laser – electrons - ionsDrivelaserbeam
TargetL
t=2L/c
Drivelaserbeam
TargetL
Target NormalSheath acceleration
Fields TV/m
Front surfaceacceleration
21
20
10 ))((5.27)( −− = WcmIVcmE
)()/( 35.0 −≈= cmne
cmcmVE e
peω
At surface of a solid
ne = 1020 cm-3
E ~ 10 GV/cm
Proton efficiency scaling
Laser pulse energy (J)0 100 200 300 400
Con
vers
ion
effic
ienc
y (%
) to
prot
ons
with
ene
rgy
grea
ter t
han
4 M
eV
0
1
2
3
4
5
6
7
810 micron25 micron
• Conversion efficiency scales linearly with laser energy
• Maximum measured conversion efficiency ~6%
• Theoretical limit ~20%
Robson et al, Nature Physics 3, 58 (2007)
∝ EL
Courtesy D Neely
Need 250 MeV protons (ion oncology)
• Hit it harder – generally works.• New laser……
• Try something new• Light pressure
"Please, sir, I want some more." From O Twist, Illustration by George Cruikshank
foto (c) 1997 Fred Espenak
Light Pressure
• At very high intensities a new mechanism can dominate
• The light pressure pushes the whole target forward I/c
• Requires -“perfect” pulse -minimum mass target-very high intensities (> PW)
• Predicted to have -high efficiency-narrow band energy spectrum
250 500 750 1000
102
103
104
105
Energy (MeV)
Pro
ton
Ene
rgy
Spe
ctru
m (a
rb. u
nits
)
250 500 750 1000
102
103
104
105
Energy (MeV)
Circular Polarization Linear Polarization
PIC simulations by Alex Robinson. See New Journal of Physics, 10, 013021 (2008)
Light PressureThe light pressure pushes the whole target forward
Requires -“perfect” pulse -minimum mass target-very high intensities
- Significant advantages
250MeV protons require Intensities of 1022 W/cm2
Laser driven ions (current capability)
Vulcan gives 400J in 600fs ~1 PW = 1013 ions in 2 ps of ion energy 1-60 MeV
Gemini gives 30J in 40fs ~1 PW = few x 1011 ions in 1 ps of ion energy 1-30 MeV
1 shot every 30 mins = 0.2W average laser power
1010 ion/sec = nA
1 shot every 20 secs = 1.5W average laser power
mid 1010 ion/sec = few nA
Laser driven ions (future capability 3-4 years)
High repetition rate Ti:S gives 40-80J in 40fs ~1PW
= 1012 ions in 1 ps of energy 1-30 MeV= 1011 ions in 1 ps of energy 100-200 MeV ?
1 shot every 0.1 secs = 400W average laser power
1013 ion/sec = μA
A Real Challenge for Plasma Based Acceleration
From “Acceleration” to “Accelerator”
A systematic and deep understanding of all therelevant physics is needed to achieve this goal!
This requires accelerator, plasma and laserphysicists to join forces.
The future looks bright.
Thank you
•Laser driven ions • >10% ion conversion efficiency now possible •Heavy ions, Electrons (>GeV), Gamma rays (0.1-10MeV), neutrons,•Light pressure (250 MeV, 30%?)•Multi pulse offers beam manipulation
Conclusions
Laser and Plasma wakefield accelerators
Laser Plasma Accelerators
• The electric field of a laser in vacuum is given by
• For short pulse intense lasers,
• Unfortunately, this field is perpendicular to the direction of propagation and no significant acceleration takes place.
• The longitudinal electric field associated with electron plasma waves can be extremely large and can accelerate charged particles.
Introduction
• General Principles– Laser-plasma accelerators– Electron-beam-plasma accelerators– Theory – Simulations– Experiments– Future
Spectrum with weak shock. M=1.35 : Te =1 MeV : Ti =2keVPropagating in plasma expanding at 0.1c.
Slice off part of ion distribution -better agreement with experiment
Conclusion• Laser driven ions
• >10% ion conversion efficiency now possible •Heavy ions, Electrons (>GeV), Gamma rays (0.1-10MeV), neutrons,•Light pressure (250 MeV, 30%?)•Multi pulse offers beam manipulation
• Future directions• 10PW, European Laser Infrastructure • New diode drivers increase average power x1000 (3-5 years)• New UK consortium laser ion applications grant 2013-2018• Effect of high dose rates on biological systems• Target technology Cryo Deuterium, liquid targets• Medical ion energies on 4-5 year timescale
Located in the FFTB
FFTB
e-
N=1-2 · 10 10
σz=0.1 mmE=30 GeV
IonizingLaser Pulse(193 nm)
Li Plasmane- 6 · 10 15 cm-3
L- 30 cm
CerenkovRadiator
Streak Camera(1ps resolution)
X-RayDiagnostic
Optical TransitionRadiators Dump
25 m
Cdt
Not to scale!
Spectrometer
PWFA Experiments @SLAC Share Common Apparatus
SLAC Plasma Wakefield Expt.
a,b) Density of electron pulse (brown) and plasma electrons (blue) at two different points in the plasma (12.3 and 81.9 cm). Scalloping features are the result of increasing focusing force.
c) Maximum energy reached after 85 cm. Saturation occurs due to the beam head spreading to the point that it can no longer ionize the lithium vapour.
a) Energy spectrum of electrons in the 30-100 GeV range. Electrons reach 85 GeV (3x106 e/GeV).
b) Experimental (blue) and simulation (red)Reference: Blumenfeld et al. Nature (2007)
Betatron x-ray emission from a LWFA.Electrons trapped at the back of the wakefield are subject totransverse and longitudinal electrical forces; they are subsequentlyaccelerated and wiggled to produce broadband, synchrotron-likeradiation in the keV energy range.
Najmudin et al 2015 Phil. Tran. Royal Soc.
Raw data of electron spectra and corresponding X-ray beams (Astra Gemini laser.)
Betatron Radiation
X-ray energies > 20 keV
Single-shot x-ray phase contrast image of a cricket taken using the Astra Gemini Laser. This 200 TW laser produces 1 GeVelectron beams and very hard x-rays (with critical energy >30 keV).The image shows minimal absorption, indicative of high flux of photons at energies >20 keV, for which the phase-shift cross-section greatly exceeds (>100×) that for absorption.
Betatron Radiation
Najmudin Z et al 2014 Phil. Trans. R. Soc.
Plasma betatronX-rays : source size of few microns.
Divergence < 100mradPulse duration < 100fs.Broadband spectrum keV range
Energy doubling of PWFA: 42 GeV in less than one meter!
GeV LWFA in cm scale plasma
Snapshot of wakefield Controlled injection by colliding laser pulse
”Dream Beam“ Multi-GeV energy gain of PWFA
Ionization induced injection Boosted frame simulation:Full scale modeling of 10-100GeV stages
2GeV LWFA in a gas cell
Simulations (from above paper)
Shock Mach number 2 – broader spectrum than experiment
Another experiment – Najmudin et al PoP 18, 056705 (2011)
Broader spectrum – more like simulations
Proton scaling with laser parameters
Robson et al, Nature Physics 3, 58 (2007)
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model
•Mora PRL 90, 185002 (2003): isothermal expansion model provides good fit:• Fuchs et al Nat. Phys. 2, 48 (2006):• Scaling study up to ~5×1019 W/cm2;
Proton scaling with laser parameters
Robson et al, Nature Physics 3, 58 (2007)
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model10 micron (1 ps)25 microns (1ps)25 micron (various)
• Scaling study up to ~6×1020 W/cm2
• Isothermal model overestimates energies
•Mora PRL 90, 185002 (2003): isothermal expansion model provides good fit:• Fuchs et al Nat. Phys. 2, 48 (2006):• Scaling study up to ~5×1019 W/cm2;
Proton scaling with laser parameters
Robson et al, Nature Physics 3, 58 (2007)
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model10 micron (1 ps)25 microns (1ps)25 micron (various)
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model10 micron (1 ps)25 microns (1ps)25 micron (various) isothermal model • Scaling study up to ~6×1020 W/cm2
• Isothermal model overestimates energies
•Mora PRL 90, 185002 (2003): isothermal expansion model provides good fit:• Fuchs et al Nat. Phys. 2, 48 (2006):• Scaling study up to ~5×1019 W/cm2;
Proton scaling with laser parameters
Robson et al, Nature Physics 3, 58 (2007)
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model10 micron (1 ps)25 microns (1ps)25 micron (various)
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model10 micron (1 ps)25 microns (1ps)25 micron (various) isothermal model
Laser intensity (W/cm2)1019 1020 1021
Max
imum
pro
ton
ener
gy (M
eV)
0
10
20
30
40
50
60
70Fuchs et al Nat Phys 2006isothermal model10 micron (1 ps)25 microns (1ps)25 micron (various) isothermal model2-phases model2-phases with 3-D effects
• Scaling study up to ~6×1020 W/cm2
• Isothermal model overestimates energies
• Model revised to include dual temperature phase; Mora, PRE 72, 056401 (2005)
250 MeV Protons require ~ mid 1022 Wcm-2
•Mora PRL 90, 185002 (2003): isothermal expansion model provides good fit:• Fuchs et al Nat. Phys. 2, 48 (2006):• Scaling study up to ~5×1019 W/cm2;
Shock wave Ion accelerationHaberberger et al (Nature Phys. 8, 95 (2012))used multiple pulses to produce accelerated ions with narrow energy spread.
Note sawtooth shape.
The Blowout/Bubble Regime
The challenges:
Ion channel formed by crossing (fluid model breaks down) Multi-dimensional (2D/3D) Electromagnetic in nature Highly relativistic plasma motion Trapping and crossing are different
Trajectory crossing
Driven by an electron beam: nb>np Driven by a laser pulse: a0>~2
Full scale 3D PIC simulations of LWFA:From GeV to 100GeV
Channel-guided LWFA with external injection (.5-100GeV)
M. Tzoufras et al., JPP 2012
Boosted Frame simulation for 10-100GeV:
S. Martins et al., Nature Physics (2010)
Proton scaling with intensity
• Defocus results in •Reduced intensity•Lower maximum proton energy
•Vulcan PW 1 ps 1054 nm illumination• 2 micron think Al targets
• Lower energy protons suited for•Fast Ignition•Secondary heating
Conversion EfficiencyComparison with previous studies
• Defocus reduces intensity - proton energy
•Defocus enables thin targets – higher efficiency
Robson et al, Nature Physics 3, 58 (2007)
P(PW) τ(fs) np (cm-3) w0 (μm) L(m) a0 ∆nc/np Q(nC) E(GeV)
0.020 30 1×1018 14 0.016 1.76 60% 0.18 0.99
0.040 30 1.5×1018 14 0.011 2.53 40% 0.25 0.95
0.100 30 2.0×1018 15 0.009 3.78 0% 0.40 1.06
0.200 100 1.0×1017 45 0.52 1.76 60% 0.57 9.9
2.0 100 3.0×1017 47 0.18 5.45 0% 1.8 10.2
2.0 310 1.0×1016 140 16.3 1.76 60% 1.8 99
40 330 4.0×1016 146 4.2 7.6 0% 8 106
20 1000 1.0×1015 450 500 1.76 60% 5.7 999
1000 1000 6.5×1015 460 82 12.1 0% 40 1040
Note: Channel guiding: 60% and 40%; Self-guiding: 0%; external injection: 60%; self-injection: 40% and 0% P/Pc=0.7 for 60% case, and 2 for 40% case
A road map of single stage LWFA
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
J Hollaway 2012
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
J Hollaway 2012
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
J Hollaway 2012
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
J Hollaway 2012
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
J Hollaway 2012
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
J Hollaway 2012
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
+
++
+
+
+---
J Hollaway 2012
The Self-Modulation Instability
Long proton beam Neutral plasma
Affects long drive beams.
+
++
+
+
+---
+
++
+
+
+---
Neutral plasma
Self-modulated driver beamJ Hollaway 2012