Transcript Slides - Agenda INFN

The 2nd European Advanced Accelerator Concepts Workshop
13-19 September 2015, La Biodola, Isola d'Elba, Italy
Dynamics of Electron Bunches at
Enhancement of Laser Plasma
Wakefield Acceleration by Beam
Plasma Wakefield Acceleration
O.M. Svystun, V.I.Maslov, I.M.Onishchenko, V.I.Tkachenko
NSC “Kharkov Institute of Physics and Technology”
[email protected]
Elena Svystun
The Electron Bunches Dynamics in LPWA
September 13 - 19, EAAC-2015
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Outline
 Introduction
 Parameters of numerical simulation
 Dynamics of electron bunches at enhancement of laser
plasma wakefield acceleration by beam plasma wakefield
acceleration
 Summary
Elena Svystun
Outline of talk
September 13 - 19, EAAC-2015
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Introduction: the advantages of LPA
Laser Plasma Accelerators have well-known advantages:
 LPAs have the ability to sustain accelerating gradients that are several orders of
magnitude greater than those obtained in conventional linear accelerators.
E. Esarey et al., Rev. Mod. Phys. 81, 1229 (2009); V. Malka et al., Science 298, 1596 (2002) ;
W.P. Leemans et al., AIP Conf. Proc. 1299, pp. 3-11 (2010)
Cornell's 7-cell superconducting RF cavity
RF cavity
Electric field < 100 MV/m
Elena Svystun
Introduction: the advantages of LPA
Plasma cavity
Electric field > 100 GV/m
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Introduction: progress of LPA
 LPAs have the potential to produce short electron bunches with high energy for various
applications [E. Esarey et al., Rev. Mod. Phys. 81, 1229 (2009)].
 Over the past decade, due to the rapid development of laser technology LPAs have made
significant progress towards producing high quality beams with higher energy of order
several GeV.
* W.P. Leemans et al., Phys. Rev. Lett. 113, 245002 (2014)
Lawrence Berkeley National Laboratory
* Multi-GeV
electron beams with energy up to 4.2 GeV have been produced from a
9-cm-long capillary discharge waveguide with a plasma density of ≈7·1017 cm−3,
powered by laser pulses with peak power up to 0.3 PW.
Energy spectrum of a 4.2 GeV
electron beam measured using
the broadband magnetic
spectrometer. The white lines
show the angular acceptance of
the spectrometer. The two
black vertical stripes are areas
not covered by the phosphor
screen.
Elena Svystun
Introduction: progress of LPA
September 13 - 19, EAAC-2015
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Introduction
 The main aim of this work is to research the electron bunch dynamics at
enhancement of Laser Plasma Wakefield Acceleration by Beam Plasma Wakefield
Acceleration. For this purpose, the numerical simulation of the plasma wakefield
excitation by a laser pulse in the blowout regime was carried out.
Parameters of the numerical simulation
 Fully relativistic electromagnetic two dimensional particle – in – cell simulation was
performed by the UMKA2D3V code (Institute of Computational Technologies)
S.V. Bulanov et al., Plasma Phys. Rep. 23 (1997) 259
 A computational domain (x, y) has a rectangular shape: 0 < x < 800λ and 0 < y < 50λ,
λ is the laser pulse wavelength, λ = 0.8 µm.
 The computational time interval is τ = 0.05.
 The number of particles per cell is 8 and the total number of particles is 15.96·106.
The simulation was carried out up to 800 laser periods. The period of the laser pulse
t0 = 2π/ω0, where ω0 is the laser frequency.
Elena Svystun
Introduction
September 13 - 19, EAAC-2015
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Parameters of the numerical simulation
 The s-polarized laser pulse enters the computation region filled with uniform plasma
from the left boundary and is incident normally on the plasma.
 The plasma density n0 = 0.01016nc= 1.8·1019 cm-3, where the critical plasma density
nc = meω02/(4πe2), me is the electron mass, e is the electron charge.
 The laser pulse is defined with a "cos2" distribution in its spatial longitudinal
direction and has a Gaussian profile in the transverse direction. FLHM = 2λ. FWHM = 8λ.
 The simulation was performed for the peak amplitude of the normalized vector
potential of the laser field, a0 = eEx0/mecω0 = 5, where e is the electron charge, Ex0 is the
electric field amplitude, me is the electron mass, c is the speed of light.
 The peak laser intensity: I0 = 5.3·1019 W/cm2.
 Coordinates x and y, time t, electric field amplitude Ex and electron plasma density n0
are given in dimensionless form in units of λ, 2π/ω0, mecω0/2πe, meω02/16π3e2,
respectively.
Elena Svystun
The parameters of the numerical simulation
September 13 - 19, EAAC-2015
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Self-injection of three short electron bunches
The plasma density: n0 = 0.01016nc= 1.8·1019 cm-3
The peak normalized laser field strength : a0 = 5
The peak laser intensity: I0 = 5.3·1019 W/cm2
FLHM = 2λ and FWHM = 8λ, the laser pulse wavelength: λ = 0.8 µm
bunches
3rd 2nd 1st
Wake perturbation of plasma electron
density excited by one laser pulse at the
time t = 105t0
Elena Svystun
The Electron Bunches Dynamics in LPWA
Longitudinal component of the
wakefield Ex excited by one laser
pulse with intensity at the time
t = 105t0
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Self-injection of three short electron bunches
Wake perturbation of plasma electron
density and off-axis (y = 25.5) radial
wake force Fr (red line) excited by one
laser pulse at the time t = 105t0
 The 2nd bunch is decelerated
and it is close to the area of a
strong defocusing field.
bunches
rd
3
2nd 1st
 The 3rd bunch is accelerated.
Wake perturbation of plasma electron
density and longitudinal component of
the wakefield Ex (red line) excited by
one laser pulse at the time t = 105t0
Elena Svystun
The Electron Bunches Dynamics in LPWA
September 13 - 19, EAAC-2015
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Evolution of the wake perturbation of plasma electron density
Wake perturbation of plasma electron density and longitudinal component of the
wakefield Ex (red line) excited by one laser pulse
time t = 125t0
time t = 130t0
time t = 115t0
bunches
3rd 2nd 1st
time t = 135t0
 The 2nd self-injected bunch approaches
the area of a strong defocusing field.
 The 2nd bunch continues to decelerate
and enhances the field which accelerates
the 3rd bunch.
Elena Svystun
The Electron Bunches Dynamics in LPWA
September 13 - 19, EAAC-2015
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Defocusing of the 2nd self-injected electron bunch
bunches
3rd 2nd 1st
Wake perturbation of plasma electron
density and longitudinal component of
the wakefield Ex (red line) excited by
one laser pulse at the time t = 135t0
 The 2nd bunch is located in
the region of defocusing field
 and the 2nd bunch approaches
the region of defocusing field
with higher amplitude.
Wake perturbation of plasma electron
density and off-axis (y = 25.5) radial
wake force Fr (red line) excited by one
laser pulse at the time t = 135t0
Elena Svystun
The Electron Bunches Dynamics in LPWA
September 13 - 19, EAAC-2015
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Wake perturbation of the plasma electron density excited by one laser pulse
at the time t = 140t0 and
longitudinal component of the wakefield Ex
off-axis (y = 25.5) radial wake force Fr
bunches
2nd 1st
3rd
 The 2nd bunch is affected by the defocusing field. Therefore, when the 2nd bunch
further approaches the 1st wakefield steepening (the 2nd front of the 1st bubble), its selfcleaning becomes faster due to defocusing.
 The other bunches are in focusing fields and oscillate along the radius.
 The 1st dense accelerated bunch has been focused to the axial region, so the field of its
space charge has exceeded the field of bubble. Hence at the next time the 1st bunch will be
periodically expanded.
Elena Svystun
The Electron Bunches Dynamics in LPWA
September 13 - 19, EAAC-2015
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Wake perturbation of plasma electron density excited by one laser pulse
time t = 145t0
time t = 150t0
time t = 155t0
bunches
2nd 1st
3rd
time t = 160t0
 The 2nd self-injected electron
continues to defocus and self-clean.
bunch
 Thus the 2nd witness bunch becomes driver
and transfers its energy to the next witness
bunch.
 Finally this driver bunch is completely selfcleaned due to defocusing by radial fields of the
bubble.
Elena Svystun
The Electron Bunches Dynamics in LPWA
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Transformation of the 1st witness bunch to the driver
 The 1st witness bunch becomes driver together with the partially
dissipated laser pulse.
 They provide further acceleration of witness.
time t = 435t0
time t = 490t0
time t = 490t0
1st witness bunch
Wake perturbation of plasma electron density and longitudinal component of the
wakefield Ex (red line) excited by one laser pulse
Elena Svystun
The Electron Bunches Dynamics in LPWA
September 13 - 19, EAAC-2015
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Summary
 It has been shown that the Laser Plasma Wakefield Acceleration
Scheme changes with time into combined Laser Plasma Wakefield
Acceleration Scheme and Beam Plasma Wakefield Acceleration Scheme.
This leads to the transformation of the 2nd witness bunch behind the laser
pulse to the driver. Hence combination of the laser pulse, the 1st and the 2nd
bunches behind the laser pulse provide further acceleration of witness (the
3rd bunch behind the laser pulse).
 Thus the numerical simulation demonstrates that the transition from the
laser-wakefield acceleration mechanism to extra beam-plasma-wakefield
acceleration mechanism provides additional acceleration of the short
electron bunches.
Elena Svystun
Summary
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Thank you for attention !
Elena Svystun
Thank you for attention!
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