Two-Color Ionization Injection Experiment Using CO2 Laser-Plasma Accelerator
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Lawrence Berkeley National Laboratory
ATF Users Meeting, BNL, Oct 1-2, 2015
Two-color ionization injection experiment
using a CO
2
laser-plasma accelerator at
ATF II
Outline
•
Concept of two-color ionization injection: <100 nm normalized
transverse
emittance
•
Example of two-color ionization injection using CO
2
drive laser and
Ti:Al
2
O
3
ionization laser
•
Technical/practical considerations: parameter
sensitivity
•
Prospects for
a compact
sub-100 nm emittance diagnostic
L.-L. Yu, E. Esarey, et al., SPIE Conf. Proc. (2013)
L.-L.Yu et al., PRL (2014)
Xu et al., PRST-AB (2014)
C. Schroeder et al., PRST-AB (2014)
C. Schroeder et al., SPIE Conf. Proc. (2015)
Laser field:
•
Ponderomotive force:
•
Ionization rate:
2
-
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Pump laser pulse (circular-polarization):
a
=1.2, 5 um wavelength
92 fs (rms), 36 um spot
Injection laser pulse (linear-polarization):
a
=0.1, 0.4 um wavelength
16 fs (rms), 5 um spot
plasma:
Krypton gas, 2x10
17
cm
-3
C. Schroeder et al., Phys. Rev. ST Accel. Beams.
17
, 101301(2014)
Ultra-low (tens of nm) emittance achievable
using two-color ionization injection
transverse momentum (
p/mc
)
= 2
0
nm
2
0
nm
emittance
Modeled using 3D
PIC
(
WARP
)
2
-
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:
C
O
2
d
r
i
v
e
l
a
s
e
r
CO
2
pump laser puls
e
:
a
0
=2
10 um wavelength
470 fs (FWHM intensity)
155 um spot (ZR = 7.5 mm)
P=20 TW (P/Pc=1) (linear polarization)
10 J
Ti:
Al
2
O
3
(frequency-doubled )injection laser pulse
:
a
1
=0.13
0.4 um wavelength
118 fs (FWHM intensity)
20 um spot (ZR = 3 mm)
114
mJ
delay= 1.
6
ps
Soon to be available at BNL - ATF-II
[
I Pogorelsky and I. Ben-Zvi, PPCF (2014)]
G
a
s
j
e
t
:
(
L
~
0
.
5
-
-
1
c
m
)
K
r
y
p
t
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T
i
:
A
l
2
O
3
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C
O
2
D
r
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v
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l
a
s
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r
n
e
=
10
16
cm
-3
H
s
-
H
i
>0
E
z
/
E
0
a
0
a
1
k
p
(z-ct)
E
0
E
1
Kr
8+
Kr
9+
n
g
=
1.25x1
0
1
5
cm
-3
2
-
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:
C
O
2
d
r
i
v
e
l
a
s
e
r
G
a
s
j
e
t
:
(L~
1
c
m) Kr
C
O
2
D
r
i
v
e
l
a
s
e
r
PIC
PIC
CO
2
pump laser puls
e
:
a
0
=2
10 um wavelength
470 fs (FWHM intensity)
155 um spot (ZR = 7.5 mm)
10 J
frequency-doubled
Ti:Al
2
O
3
injection pulse
:
a
1
=0.13
0.4 um wavelength
118 fs (FWHM intensity)
20 um spot (ZR = 3 mm)
114
mJ
n
e
=
10
16
cm
-3
Normalized emittance (nm)
z (mm)
T
i
:
A
l
2
O
3
I
o
n
i
z
a
t
i
o
n
l
a
s
e
r
2
-
c
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l
o
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o
n
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a
t
i
o
n
i
n
j
e
c
t
i
o
n
:
C
O
2
d
r
i
v
e
l
a
s
e
r
G
a
s
j
e
t
:
(L~
1
c
m) Kr
C
O
2
D
r
i
v
e
l
a
s
e
r
n
e
=
10
16
cm
-3
Normalized emittance (nm)
Propagation distance, z (mm)
Charge [pC]
Energy [MeV]
RMS energy spread
pC
62 MeV
5% (rms)
z
m
CO
2
pump laser puls
e
:
a
0
=2
10 um wavelength
470 fs (FWHM intensity)
155 um spot (ZR = 7.5 mm)
P=20 TW (P/Pc=1) (linear polarization)
10 J
Ti:
Al
2
O
3
(frequency-doubled )injection laser pulse
:
a
1
=0.13
0.4 um wavelength
118 fs (FWHM intensity)
20 um spot (ZR = 3 mm)
114
mJ
delay= 1.
6
ps
PIC
simulation
T
i
:
A
l
2
O
3
I
o
n
i
z
a
t
i
o
n
l
a
s
e
r
Propagation distance, z (mm)
points = PIC
ionization
laser spot size (um)
Charge
Q
[pC]
C. Schroeder et al., PRST-AB (2014)
C. Schroeder et al., SPIE Conf. Proc. (2015)
O
p
t
i
m
i
z
a
t
i
o
n
:
c
h
a
r
g
e
v
s
e
m
i
t
t
a
n
c
e
Technical/practical considerations
for 2-color ionization
injection experiment
•
Sensitivity to
plasma
wake
field
amplitude
-
CO
2
laser driver amplitude and duration
•
Sensitivity to timing
/jitter
between
CO
2
and
Ti:Al
2
O
3
lasers
-
Increased ionization
laser duration
(energy) relaxes timing requirements
•
Performance with ioniz
ation
laser
with
0.8 micron wavelength
•
Interaction geometry:
-
c
o-linearity of lasers
-
required pointing
-
required
alignment
•
M
easure
ment of
<100 nm emittance
: single-shot, energy-resolved emittance
diagnostic
Trapping requires weakly-relativistic wakefields
Wakefield amplitude required to trap:
trapping
trapping
Normalized laser intensity,
a
laser energy (J)
FWHM laser duration (fs)
Normalized laser duration
Synchronization and jitter: ~100 fs timing desired
H
s
-
H
i
>0
E
z
/
E
0
a
0
a
1
k
p
(z-ct)
•
Operate at 10
16
cm
-3
with ~500 fs (FWHM) CO
2
pulse
•
~1.6 ps delay between CO
2
and Ti:Al
2
O
3
•
Trapping wake phases:
t
~500 fs
1.6 ps
Optical synchronization achieved by seeding Ti:Al
2
O
3
using solid-state
front-end of CO
2
amplification chain
Longer (more energetic) ionization laser can relax timing/delay sensitivity
~0.5 ps
Performance using 0.8-micron ionization pulse:
larger emittance in laser-polarization plane
Efficiency of 2-
generation (~30-50%) may limit energy in ionization pulse
For fixed gas:
ionization
laser spot size (um)
Charge (pC)
CO
2
pump laser puls
e
:
a
0
=2
10 um wavelength
470 fs (FWHM intensity)
155 um spot (ZR = 7.5 mm)
P=20 TW (P/Pc=1) (linear polarization)
10 J
Ti:
Al
2
O
3
injection laser pulse
:
a
1
=0.
26
0.
8
um wavelength
118 fs (FWHM intensity)
20 um spot
114
mJ
delay= 1.
6
ps
•
90-degree interaction reduces bunch charge: charge = (interaction volume) x (gas density)
-
Co-propagating: (volume)
~ w
2
Z
R
-
90-deg: (volume) ~
w
2
(T
L
c)
Interaction geometry: pointing and alignment tolerances
charge reduced by ~(c
T
L
)/Z
R
Emittance diagnostic: single-shot, energy-resolved
beam size measurement
•
Geometric emittance: ~10
-10
m
•
Consider lens scan for emittance measurement:
m
few um
•
Plasma-based discharge-capillary to provide symmetric, variable, high-field gradient (solenoid) lens
J. van Tilborg et al., PRL (submitted, 2015)
x
m]
y
m]
z[m]
end of LWFA:
27 pC,
62 MeV,
5% (rms) energy
Discharge-cap lens:
1 cm length, 200 micron radius, 46 A,
~230 T/m
Screen
Summary
•
Two-color ionization injection using CO
2
drive laser and Ti:Al
2
O
3
ionization laser
:
produces e-beam with tens of
nm normalized
transverse
emittance
, tens of pC
charge
•
Emittance diagnostic: single-shot, energy-resolved
measurement of beam size
using
plasma-based discharge-capillary lens
•
ATF-II ideal facility to test concept
This experiment conducted at ATF II focused on generating beams with ultra-low transverse emittance utilizing two-color ionization injection with a CO2 laser-plasma accelerator. The technique involves using a pump laser pulse in circular polarization and an injection laser pulse in linear polarization to achieve remarkable results. Technical considerations, parameter sensitivity, and prospects for a compact sub-100 nm emittance diagnostic were explored in detail.
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Presentation Transcript
Two-color ionization injection experiment using a CO2 laser-plasma accelerator at ATF II C. Schroeder, C. Benedetti, J. van Tilborg, C. Geddes, E. Esarey, W. Leemans Lawrence Berkeley National Laboratory ATF Users Meeting, BNL, Oct 1-2, 2015 Office of Science UNIVERSITY OF CALIFORNIA 1 1
Outline Outline Concept of two-color ionization injection: <100 nm normalized transverse emittance Example of two-color ionization injection using CO2drive laser and Ti:Al2O3ionization laser Technical/practical considerations: parameter sensitivity Prospects for a compact sub-100 nm emittance diagnostic Office of Science UNIVERSITY OF CALIFORNIA 2 2
Laser field: Ponderomotive force: Ionization rate: L.-L. Yu, E. Esarey, et al., SPIE Conf. Proc. (2013) L.-L.Yu et al., PRL (2014) Xu et al., PRST-AB (2014) C. Schroeder et al., PRST-AB (2014) C. Schroeder et al., SPIE Conf. Proc. (2015) Office of Science UNIVERSITY OF CALIFORNIA 3 3
2-color ionization injection generates beams with ultra-low (tens of nm) transverse emittance Pump laser pulse (circular-polarization): a=1.2, 5 um wavelength 92 fs (rms), 36 um spot Injection laser pulse (linear-polarization): a=0.1, 0.4 um wavelength 16 fs (rms), 5 um spot plasma: Krypton gas, 2x1017 cm-3 Modeled using 3D PIC (WARP) 20 nm emittance C. Schroederet al., Phys. Rev. ST Accel. Beams. 17, 101301(2014) transverse momentum (p/mc) = 20 nm Ultra-low (tens of nm) emittance achievable using two-color ionization injection Office of Science UNIVERSITY OF CALIFORNIA 4 4
2-color ionization injection: CO2 drive laser ng = 1.25x1015cm-3 Gas jet: (L~0.5--1 cm) Krypton ne = 1016 cm-3 Ti:Al2O3 Ionization laser a0 Hs-Hi >0 Ez/E0 CO2Drive laser a1 Soon to be available at BNL - ATF-II [I Pogorelsky and I. Ben-Zvi, PPCF (2014)] CO2pump laser pulse: a0=2 10 um wavelength 470 fs (FWHM intensity) 155 um spot (ZR = 7.5 mm) P=20 TW (P/Pc=1) (linear polarization) 10 J Kr9+ Kr8+ E1 E0 Ti:Al2O3(frequency-doubled )injection laser pulse: a1=0.13 0.4 um wavelength 118 fs (FWHM intensity) 20 um spot (ZR = 3 mm) 114 mJ delay= 1.6 ps kp (z-ct) Office of Science UNIVERSITY OF CALIFORNIA 5 5
2-color ionization injection: CO2 drive laser Gas jet: (L~1 cm) Kr CO2pump laser pulse: a0=2 10 um wavelength 470 fs (FWHM intensity) 155 um spot (ZR = 7.5 mm) 10 J frequency-doubled Ti:Al2O3injection pulse: a1=0.13 0.4 um wavelength 118 fs (FWHM intensity) 20 um spot (ZR = 3 mm) 114 mJ Ti:Al2O3 Ionization laser CO2Drive laser ne = 1016 cm-3 final emittance in laser polarization plane (~ thermal emittance): Normalized emittance (nm) PIC = 80 nm PIC final emittance out of laser polarization plane: = 42 nm z (mm) Office of Science UNIVERSITY OF CALIFORNIA 6 6
2-color ionization injection: CO2 drive laser Gas jet: (L~1 cm) Kr PIC simulation Normalized emittance (nm) Ti:Al2O3 Ionization laser CO2Drive laser ne = 1016 cm-3 CO2pump laser pulse: a0=2 10 um wavelength 470 fs (FWHM intensity) 155 um spot (ZR = 7.5 mm) P=20 TW (P/Pc=1) (linear polarization) 10 J Propagation distance, z (mm) RMS energy spread Energy [MeV] Ti:Al2O3(frequency-doubled )injection laser pulse: a1=0.13 0.4 um wavelength 118 fs (FWHM intensity) 20 um spot (ZR = 3 mm) 114 mJ delay= 1.6 ps Charge [pC] pC 62 MeV 5% (rms) z = m Propagation distance, z (mm) Office of Science UNIVERSITY OF CALIFORNIA 7 7
Optimization: charge vs emittance C. Schroeder et al., PRST-AB (2014) C. Schroeder et al., SPIE Conf. Proc. (2015) charge: points = PIC Charge Q[pC] wi (mm) ionization laser spot size (um) Office of Science UNIVERSITY OF CALIFORNIA 8 8
Technical/practical considerations for 2-color ionization injection experiment Sensitivity to plasma wakefield amplitude - CO2laser driver amplitude and duration Sensitivity to timing/jitter between CO2 and Ti:Al2O3lasers - Increased ionization laser duration (energy) relaxes timing requirements Performance with ionization laser with 0.8 micron wavelength Interaction geometry: - co-linearity of lasers - required pointing - required alignment Measurement of <100 nm emittance: single-shot, energy-resolved emittance diagnostic Office of Science UNIVERSITY OF CALIFORNIA 9 9
Trapping requires weakly-relativistic wakefields Wakefield amplitude required to trap: Normalized laser intensity, a trapping trapping laser energy (J) Normalized laser duration FWHM laser duration (fs) Office of Science UNIVERSITY OF CALIFORNIA 10 10
Synchronization and jitter: ~100 fs timing desired 1.6 ps a0 Hs-Hi >0 Ez/E0 Operate at 1016 cm-3 with ~500 fs (FWHM) CO2 pulse ~1.6 ps delay between CO2 and Ti:Al2O3 a1 Trapping wake phases: t~500 fs ~0.5 ps kp (z-ct) Optical synchronization achieved by seeding Ti:Al2O3 using solid-state front-end of CO2 amplification chain Longer (more energetic) ionization laser can relax timing/delay sensitivity Office of Science UNIVERSITY OF CALIFORNIA 11 11
Performance using 0.8-micron ionization pulse: larger emittance in laser-polarization plane Efficiency of 2- generation (~30-50%) may limit energy in ionization pulse For fixed gas: CO2pump laser pulse: a0=2 10 um wavelength 470 fs (FWHM intensity) 155 um spot (ZR = 7.5 mm) P=20 TW (P/Pc=1) (linear polarization) 10 J Ti:Al2O3injection laser pulse: a1=0.26 0.8 um wavelength 118 fs (FWHM intensity) 20 um spot 114 mJ delay= 1.6 ps Charge (pC) ionization laser spot size (um) Office of Science UNIVERSITY OF CALIFORNIA 12 12
Interaction geometry: pointing and alignment tolerances Ti:Al203 C02 Gas jet 90-degree interaction reduces bunch charge: charge = (interaction volume) x (gas density) - Co-propagating: (volume) ~ w2 ZR - 90-deg: (volume) ~ w2 (TLc) charge reduced by ~(cTL)/ZR To avoid injection over larger transverse area (proportionally increasing emittance): - Pointing tolerance: mradfor 20 micron spot, 0.4 micron wavelength Alignment tolerances: - xm< 4 um Office of Science UNIVERSITY OF CALIFORNIA 13 13
Emittance diagnostic: single-shot, energy-resolved beam size measurement Geometric emittance: ~10-10 m Consider lens scan for emittance measurement: m few um Plasma-based discharge-capillary to provide symmetric, variable, high-field gradient (solenoid) lens J. van Tilborg et al., PRL (submitted, 2015) Weingartner et al., PRST-AB (2012) x m] Dispersed beam at screen x m] y m] Screen y m] dipole z[m] Energy [MeV] (transverse position on screen) end of LWFA: 27 pC, 62 MeV, 5% (rms) energy Discharge-cap lens: 1 cm length, 200 micron radius, 46 A, ~230 T/m measurement requires ~micron resolution at screen -wave-plate for Ti:Al2O3 to vary laser polarization and measure x, y-planes Office of Science UNIVERSITY OF CALIFORNIA 14 14
Summary Summary Two-color ionization injection using CO2 drive laser and Ti:Al2O3 ionization laser: produces e-beam with tens of nm normalized transverse emittance, tens of pC charge Emittance diagnostic: single-shot, energy-resolved measurement of beam size using plasma-based discharge-capillary lens ATF-II ideal facility to test concept Office of Science UNIVERSITY OF CALIFORNIA 15 15
