Growth and Saturation of Large Amplitude
Self-Modulated Wakefield in 60 TW Laser
Plasma and Possible Electron Acceleration
Yoneyoshi Kitagawa*, Michiaki Mori1^ Hisaoki Asatsu**, Shin Akamatsu*,
Ryosuke Kodama*, Kazuo A. Tanaka*, Hidetsugu Yoshida*, Takayoshi
Norimatsu*, Takahisa Jitsuno*, Shuji Sakabe*, Yasukazu Izawa*, Kunioki
Mima*, Tatsuhiko Yamanaka* and Yasuhiko Sentoku*
""Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
^TARA Center, Tsukuba University, Tennodai 1-1-1, Tsukuba 305-8577, Japan
**Osaka Gas Company, Ltd., Hiranocho 4-1-2, Osaka, Osaka 565, Japan
^General Atomics, P.O.Box 85608, San Diego, California 92121-1194, USA
Abstract. A 25 J -1.053 jUm pulse in 0.45 ps (a0= 2.2) was injected into a gas jet. This excited a
large amplitude self-modulated wakefield. By increasing the pulse length from 0.45 to to 1.2 ps, the
wakefield grew close to the wave-breaking limit, which sustained a 350 ±150 GV/m acceleration
field over a 1 mm dephasing distance along the laser axis in a plasma with density 2 x 1019 cm~3.
This resulted in electrons accelerated to 300 MeV. The amplitude saturation of the wakefield is
explained by a pump depletion effect to the large amplitude forward Raman instability.
The Petawatt Laser is completed, which will be used to accelerate electrons above one GeV.
INTRODUCTION
The laser-plasma accelerator concept was first presented in 1979 by Tajima and
Dawson[l]. 10 years later, two frequency CO2 lasers demonstrated the concept[2, 3]
in the laboratory. The laser pulses, however, were as long as nanoseconds and the
intensities were low, resulting in excited plasma wave amplitude of only a few % ,
corresponding to acceleration fields of no more than a few GV/m. The electron gain
was 20 to 30 MeV. A few years later, short-pulse ultra-intense lasers brought significant progress to laser- plasma accelerator studies, especially to the laser wakefield
approach[l, 4, 5]. If the laser intensity becomes so high that the quivering velocity is
larger than the light velocity, the excited wakefield affects the amplitude modulation
on the pump laser at the plasma period[6], which results in extremely high wakefield
generation [7]. In 1995, injecting a 3 TW, 1 ps laser into a helium gas, the ILE group at
Osaka University and the KEK group had obtained an acceleration field of 30 GV/m
and accelerated 1 MeV/c electrons to 18 MeV/c[8]. In this experiment the seed electrons
were generated from an aluminum target illuminated with a 200 ps laser. Also in 1995,
the Rutherford Appleton Laboratory and the UCLA group had injected a 25 TW, 0.8 ps
pulse into a gas jet and had observed forward electrons with energies near 100 MeV [9].
they reported a field of about 150 GV/m. In 2000, we obtained the field of 160 GV/m,
using a 60 TW, 1.053jum, 0.4 ps laser in a hydrogen plasma of 1 x 1019/cm3[10]. Thus,
CP647, Advanced Accelerator Concepts: Tenth Workshop, edited by C. E. Clayton and P. Muggli
© 2002 American Institute of Physics 0-7354-0102-0/02/$19.00
634
an ultra-intense laser was shown to easily excite an accelerating field on order of one
hundred GV/m via the self-modulated wakefield. However, since the self-modulated
wakefield is an instability (that is the forward Raman scattering), it needs a finite time
to overcome any damping mechanism and grow to a saturation level. It is reported that
the wakefield decays into ion acoustic waves in a few ps [11]. Nevertheless, we have no
information about the growth and saturation of the wakefield at early times. It would
be interesting to know what the optimum pulse length for the wakefield growth under a
given plasma density is, or whether it is possible to attain a field larger than the wave
breaking limit.
The wave-breaking-limited field is classically given by E O (W O ) = mQ)pC/e =
30(ft0/1017)2 [GV/m], where nQ is the electron density in cm~3. The ultra-intense
laser, of which the ratio of the quivering velocity to the light velocity, a0 = vosc/c =
(I/(1.23 x 1018W/cm2))! > 1 enhances the field to
(1)
where nl is the perturbed electron density associated with the wave. If a0 > 1.3 and
H-^/HQ = 1, Emax becomes above E O (W O ).
This paper will discuss first the optimum growth and saturation of the self-modulated
wakefield within a strong laser pulse, where a0 reached 2.2. A 60 TW laser was injected
into a hydrogen, helium or argon gas jet and excited a large amplitude self-modulated
wakefield. By increasing the pulse length from 0.45 to to 1.2 ps, the amplitude increased
close to the wave-breaking limit value. 2 x 1019 cm~3 gas plasmas sustained a 350 ± 150
GV/m acceleration field over 1 mm distance along the laser axis. Either the dephasing
or diffraction length seems to determine the distance. Temporal change of the amplitude
of the wakefield was consistent with the idea that the large amplitude forward Raman
scattering rises from a thermal noise and saturates due to a pump depletion effect[12].
The pump depletion length Lp is given by the length over which the laser energy is
transferred to the plasma wave.
The world biggest Petawatt laser (PW laser) was completed [13]. The beam size was
50 cm to extract 1 PW or 500 J in 0.5 ps. The PW Laser will excite the self-modulated
wakefield of 200 GV/m or provide the electron acceleration of 2 GV at 5 mm length.
SELF-MODULATED WAKEFIED EXCITATION USING GAS
PUFF PLASMA
The GEKKO-MII CPA laser, used here, produced 25 J at 1.053 jum with 0.45 (60 TW)
or with 1.2 ps pulse length [15, 16]. The laser beam was focused into a gasjet by an
off axial parabola mirror of f/3.7. 68% of the beam energy was measured to the spot
size of 25 jum in diameter. The intensity on target was 3 x 1018 W/cm2. The prepulse
level was 10~3. Figure 1 shows the experimental setup. The gas jet was formed by a
puff, electro-magnetically switched at 10 kV. At 2 mm above the puff nozzle of 6 mm
aperture, we obtained a gas molecular density of 1019/cm3 over 4 mm long, as shown
635
CCD
D
Sidescattrer
800~1000nm
from Compressor
1053 nm
25 J in 0.4 ~ 1.2 ps
FRS Transmission
to Spectrometers
^^900-1600
410 640 nm
FIGURE 1.
Experimental setup for laser acceleration.
10'
10
n
10 n
-
2
0
2
Radial position from center R (mm)
FIGURE 2.
mm.
Radial distribution of molecular density at 2 mm above gaspuff nozzle. The aperture is 6
in Fig. 2. The figure provides the density scalelength to be 1.5 mm. Twice the Rayleigh
length 2ZR = 2nr^/^ for a given spot radius r0 was also 1 ~ 1.4 mm, which permitted
the wakefield to accelerate electrons over 1 mm. The time in which the gas reaches its
maximum density, is 100 ms for a reservoir pressure of 3000 Torr. The laser was focused
1.75 mm apart from the nozzle center. The intensity was 2.1 x 1018 W/cm2.
The spacial image of the plasma wave was taken by a CCD camera through a bandpass
filter from 800 nm to 1000 nm at!20° backward the laser axis and in the direction of the
laser polarization. The sideview image lengths were 1.1 ~ 1.7 mm either for hydrogen,
helium, or argon gas, close to 2ZR and the plasma scale length. The anti-Stokes line shift
gave the electron density to be 1.1 x 1019/cm3. The wakefield, or excited plasma wave,
becomes a moving grating, scattering the pump laser to Stokes and anti-Stokes satellites.
636
105
(a)
10
4
o
o
100
10
1000
1200
1600
1400
Wavelength (nm)
400
450
500
550
600
650
700
Wavelength (nm)
400
450
500
550
600
650
700
Wavelength (nm)
FIGURE 3. (a) Stokes and anti-Stokes spectrum (shot#13860) at COQ and (b) at 2coQ at for pulse width
1.1 ps and aQ = 1.5. (c)Spectrum at 2o)0 for pulse width 0.4 ps and aQ = 2.2. nQ = 1.1 x 1019/cm3.
637
According to the Bragg scattering theory, we estimated the wakefield amplitudes from
the intensity ratio of the Stokes to pump wave intensities [14]. The second harmonics of
the pump laser is also scattered from the same plasma wave. For the pump power P0, the
scattered m-th Stokes harmonic powers Pm are given as
nnmn0Lz]2\sin(MIz)
where nm is the m-th harmonic density perturbation and Lz is the distance over which
the plasma wave is excited. A& shows a phase mismatch of three wave mixing. The
momentum conservation between the electromagnetic and electrostatic wave requires:
0
s
p
~ 2 c nc'
Now A&= 3 mm"1 for nG = 1019/cm3. In the case of Lz ~ mm, it is difficult to
fix the last bracket value in the right hand term in Eq. 2. Thus this term can reduce
the data reliability. The line ratio between the first and second Stokes harmonics was
then used to cross check the absolute amplitude[17]. The line ratio between Stokes
harmonics provided an absolute amplitude without any assumption on the three wave
phase mismatch between the pump, scattered and plasma waves. In addition, the second
harmonic of a large amplitude plasma wave is given by [18]: n2/nQ ~ [nl/n()] .
Combining this result with Eq. 2, we obtain a relation between the second Stokes
scattering P2 and the density fluctuation due to the plasma wave as follows:
P
•*• 1
1
P IP
•*• 1I '/ •*• f\
U
in
/n \j'}I2
V\ 'M
1'/ **f\
(n
In \j }'2I
\\ ''1
I' / f*(\
(4)
Thus by measuring the Stokes harmonics, we obtain the wakefield amplitude as a
function of the electron density. The electron density is obtained from the Stokes shift
from the pump frequency.
Figure 3 (a) shows the first Stokes Pl and the second Stokes P2 spectrum around the
co0 pump PQ for the pulse length of 1.2 ps and at a0 = 1.5(Shot # 13860). The Stokes
shift k(Pi) — A(P0) = 16 nm gives an electron density of nQ = 2 x 1019/cm3. Equation 4
predicts the density fluctuation nl/n^ to be 44 %, and Eq. 1 predicts Emax to be 230
GV/m. Since the indium-gallium-arsenide (InGaAs) array limits the detection range
from 900 nm to 1600 nm, no anti-Stokes line was detected. Figure 3(b) is the same shot
as (a), but the Stokes satellites Pl and P2 can be observed around the second harmonic
pump PQ. For this case, n^jn^ is 77 % and Esat is 490 GV/m. In this case, the antiStokes peak /*_! can clearly be seen. We found that the 2co light is also scattered by
excited plasma wave. Consequently, we can get the density and its fluctuation both from
co Satellites and from 2co satellites.
Figure 3(c) shows the Stokes satellites Pl,P2,P_l,P_2 around the second pump for a
0.45 ps pulse width. Although the density is nearly the same as for the above cases (1.1
x 1019 /cm3 and a0 even increases to 2.2) nl/nQ decreases to 20 % and Esat drops to 126
GV/m. Figures 3 (b) and (c) suggest that the wave grows with increasing pulse width
from 0.45 to 1.2ps.
638
[ps]
Pla
sm
a
De
ns
ity
ne
e
[cm
]
-3
]
/m]
de [GV
Amplitu
Pul
se w
idth
τ
1.5
FIGURE
FIGURE 4.
4. Acceleration
Acceleration field
field of
of self-modulated
self-modulated wakefield E
Emax
max is plotted for pulse length in x axis
and
and electron
electron density
density in
in yy axis.
axis.
SELF-MODULATED WAKEFIELD GROWTH
ESTIMATION OF SELF-MODULATED
AND SATURATION
Since the wakefield is forward Raman scattering,
scattering, the wave must grow with time. The
Since
initial density fluctuation nn1l/n
initial
/nQ0 may arise from a thermal noise nth
/nQ0 as the Raman
th/n
instability grows. However, since
since the simple exponential growth model is too sharp
instability
explain the experimentally measured growth between 0.4 and 1.2
1.2 ps, we introduce
to explain
characteristic damping terms, such
such as pump depletion, dephasing, and Rayleigh lengths.
characteristic
The dephasing
dephasing length
length is aa phase slip
slip distance between the laser and the wakefield as well
The
as aa slip
slip distance
distance between the wakefield and the electrons. Assuming that the damping
as
is in
in the
the form of aa phase velocity divided by the characteristic length, then
is
n1 nth
11
11 1I
—- =
= -^ exp
exp γ − c( + + ) τ .
(5)
n0
n0
L p Ld ZR
√
2
2 /2] is the pure growth rate of the
Here γ7 =
=ω
co^/(\/8a)
<z0 /[1
+ aa^/2]
the forward
forward Raman
Raman
Here
0 /[l +
p /( 8ω00)) ·•a
0
scattering (FRS)
(FRS) [19],
[19], L pp =
= (a
(a0Q/3
/3n)(ric/n^)k
scattering
π )(nc /n0 )pλ p is the damping rate due to
to pump
pump depletion
depletion
of the
the laser
laser and
and Ldd =
= 6a0QL pp is the damping due to dephasing
[12].
dephasing[12].
of
The thermal noise nnthth/n
/nQ0 could be on the order of vv^/c,
The
th /c, since the equation of
continuity can
can be
be written
written as
as −
—con
+ kvfhthnnQ0 =
continuity
ω nthth +
= 0 and the FRS phase velocity
velocity co/k
ω /k ~
∼ c,
where cc is
is the
the light velocity. The
The electron
electron temperature of
of 11keV
keV provides nnthth/n
/nQ0 =
= 0.04.
where
If we
we assume
assume that the density fluctuation nn1l/n
If
/nQ0 in Eq. 11 obeys the above-mentioned
growth, we can simply
simply substitute
substitute Eq. 5 into Eq. 1,
1, which
which leads
leads to
to the
the saturated
saturated field
field
growth,
£maxThe
E
E
.
The
temporal
behavior
of
E
is
plotted
in
Fig.
4.
One
horizontal
axis
is
the
max
max
max
plasma density nw00..
639
FRS Field [GV/m]
1000
800
3x1019 /cm3
3x1019/cm
2x1019
600
1.3x1019
400
1x1019
200
1x1019
0.2
0.4
0.6
O.S
1
Pulse width τ [ps]
1.2
1.4
Pulse width t [ps]
FIGURE 5. Emax as a function of the pulse length.
FIGURE 5. Emax as a function of the pulse length.
Figure 4 shows that the amplitude saturates between 0.5 ps and 1ps for the densities on
19 /cm
3 . Since
shows
that
the amplitude
0.5 ps and the
Ipssaturation
for the densities
on
the Figure
order of4 10
L p Ldsaturates
∼ ZR forbetween
these parameters,
is mainly
19
3
the
order
of
10
/cm
. Since The
Lp<^L
for these
parameters,
the saturation
d~ ZR pulse
ps at ne =is2mainly
× 1019
due to the pump depletion.
optimum
length
is τ ∼ 1.2
19
−3to
due
the pump
depletion.
The3 optimum
pulse
~ 1.2
ne = 2 xof10the
cm
. Both
the data
from Fig.
(b) and (c)
are length
plottedisinx Fig.
5 ps
as aatfunction
3
3 . The of
cm~ width.
. BothLines
the data
Fig.from
3 (b)Fig.
and4(c)
plotted
Fig. 519asW/cm
a function
the
pulse
are from
replotted
for are
n0 =
1, 1.3,in
2, 3×10
results
19
3
pulse
width.
Lines
are
replotted
from
Fig.
4
for
n
=
1,1.3,2,3
x
10
W/cm
. The
results
seem to show that the amplitude saturates due toQ the pump depletion and 1.2
ps is
close
to show that
thewidth
amplitude
due to the
pump
andis 1.2
ps is
close
toseem
the optimum
pulse
in thesaturates
present system.
The
best depletion
fitted curve
at the
electron
19
−3
to
the
optimum
pulse
width
in
the
present
system.
The
best
fitted
curve
is
at
the
electron
density n0 = 1.3 × 10 19cm 3.
density
nQ = 1.3
x 10 density
cm~ . for hydrogen, helium and argon gas is shown in Fig.
Emax versus
plasma
18
2 . Data
£max
versus
plasma
density
hydrogen,
helium
andW/cm
argon
gas ispoints
shownfrom
in Fig.
??, where the laser intensity wasfortaken
to be 2.5
×1018
2ω0
2
??,
where
the
laser
intensity
was
taken
to
be
2.5
x
10
W/cm
.
Data
points
from
2coof
0
Stokes seem to be 1 ∼ 2× higher than the ω0 Stokes. Since the P2 spectral width
Stokes
seem
to
be
1
~
2x
higher
than
the
co
Stokes.
Since
the
P
spectral
width
of
0
2
ω0 Stokes is twice the P1 width in Fig. ??(a), if we compare not the peak ratio but
co0 integrated
Stokes is twice
the ratio,
Pl width
in Fig.
??(a),
if we compare
not the
peak 1.5
ratiotimes,
but
the
intensity
the data
from
ω0 Stokes
will increase
at least
the integrated
ratio,
from Between
co0 Stokesthewill
increase
at
leastis 1.5
times,
Stokes.
gas
species,
there
not
a
clear
which
is closer intensity
to the data
fromthe
2ωdata
0
which is closer
to the
data from
the gas
thereisisfrom
not aFig.
clear4,
0 Stokes. Between
difference
of either
density
or its2co
perturbation
amplitude.
Thespecies,
solid curve
difference
of
either
density
or
its
perturbation
amplitude.
The
solid
curve
is
from
Fig.
4,
which is larger than the classical wave breaking limit E0 (n0 ), as shown by a dashed line,
which is larger than the19classical
wave
breaking
limit
E
(/Z
),
as
shown
by
a
dashed
line,
O
O
−3
19
−3
between n0 = 1.4 × 10 19cm−33 and 3.2 × 1019
19 cm 3. At 2.4 × 10 19 cm 3 , the predicted
between
nG =800
1.4GV/m,
x 10 cm~
x 10some
cm~experimental
. At 2.4 x 10points
cm~seem
, the to
predicted
field
reaches
1.8 × and
E0 (n3.2
)
and
exceed
0 ) and some experimental points seem to
field
reaches
800
GV/m,
1.8
x
£
(ft
0
the wave breaking limit. The data0 points
are averaged to be 350 ± 150 GV/m exceed
around
The data points are averaged to be 350 ±150 GV/m around
19 W/cm3limit.
nthe
=wave
2 × 10breaking
.
ft0 0 = 2x!019W/cm3.
W/cm3 , but it is smaller for 1019 W/cm3 or more. If
Ld is larger than 2ZR for n0 1019
Ld is larger than 2ZR for rc0 < 1019W/cm3, but it is smaller for 1019W/cm3 or more. If
we take the acceleration distance to be Lz = min[Ld , ZR ], the energy gain Wa = Emax · Lz ,
we take the acceleration distance to beL z = mintL^Z^], the energy 3gain Wa = Em3X-Lz,
W/cm , L is estimated to
which is plotted in Fig. 6 as dotted curve. At n0 = 2 × 1019
which is plotted in Fig. 6 as dotted curve. At nQ = 2 x 1019W/cm3, Lzz is estimated to
be 0.5 mm, giving Wa = 300 MeV. If the acceleration
distance is the full plasma column
be 0.5 mm, giving W = 300 MeV. If the acceleration distance is the full plasma column
length ∼ 2 mm and Eamax = 350 GV/m, then Wa is 700 MeV. The electron spectrometer
length ~ 2 mm and E
= 350 GV/m, then Wa is 700 MeV. The electron spectrometer
points up to 22 MeV, max
although there are no more
data points, suggests that the slope
points up to 22 MeV, although there are no more data points, suggests that the slope
temperature
of
the
accelerated
electrons
is
35
MeV
and
the maximum
maximumenergy
energyisisover
over100
100
temperature of the accelerated electrons is 35 MeV and the
MeV,
as
shown
in
Fig.
7.
The
self
focusing
of
the
laser
beam
in
plasma
will
suppress
the
MeV, as shown in Fig. 7. The self focusing of the laser beam in plasma will suppress the
640
10 3
10 3
103
103
Cal.Field
Cal.Field
g limit
reakin
I
10 22
10 2
102
10
Energy gain [MeV]
FRS Field [GV/m]
ave b
I
Cal.gain
H- 1
He-1
Ar-1
H- 2
He-2
Ar-2
10 1
10 1
0.6
0.6
19
0.8 10
10
0.8
2 10
19
3 10
19
cm -33]]
nn [[cm0
2
18 W/cm2 . Solid circle is from ω Stokes and open
FIGURE
versus electron density at 2.5 ×1018
FIGURE6.6. EEmax
max versus electron density at 2.5 x 10 W/cm . Solid circle is from (O0 0Stokes and open
circle
from
2
ω
Stokes.
Solid
line
is
from
Eq.
1
and
dashed
line
the classical
classical wave-breaking
wave-breaking limit.
limit.
circle from 2o)00 Stokes. Solid line is from Eq. 1 and dashed line is
is the
=35MeV
€>.,.
Noise level
10
20
40
60
80
100
Energy (MeV)
19
◦ direction.
FIGURE7.7. Electron
Electron spectrum
spectrum to
to 43
43°
direction. Solid point:Laser 1.2 ×
x 1019
W/cm
FIGURE
W/cm22 and
and 1^=1.3
ne =1.3x×
19 −3 3
18
2
18
3
19
18
2
18
−3
10
cm,
Open
point:
5.1
x
10
W/cm
and
3.0
x
10
cm.
10 cm , Open point: 5.1 × 10 W/cm and 3.0 × 10 cm
diffraction and
and make
make 2Z
2ZRR longer[20].
longer[20]. However,
However, Ldd will not become longer,
diffraction
longer, unless
unless we
we
useaatapered
taperedplasma
plasma duct,
duct, thus
thus compensating
compensating the phase shift[21].
shift[21].
use
PETAWATT LASER
LASER COMPLETION
PETAWATT
Theworld
world biggest
biggest Petawatt
Petawatt laser
laser (PW
(PW laser)
laser) was
was completed
completed [13].
[13]. The
The
The beam
beam size
size was
was
50
cm
to
extract
1
PW
or
500
J
in
0.5
ps.
The
design
parameters
of
the
PW
Laser
50 cm to extract 1 PW or 500 J in 0.5 ps. The design parameters of the PW Laser are
are
641
TABLE 1. PW Laser Design Parameters
Front out Amp. out Comp. out
Spectrum
Pulse length
Beam diam.
Inner diam.
Energy
6nm
3ns
10mm
10 ml
32cm
13 cm
800 J
3.0 nm
500 fs
50cm
20.3 cm
500 J
On target
14/un(2/A)
> 1019W/cm2
listed in Table 1. Figure 8 shows a diagram of its configuration. The front end includes
a Ndiglass oscillator, a stretcher, and an optically parametric chirped pulse amplifier
(OPCP Amplifier), which provides 20 ml with a 6 nm bandwidth.
The main amplifier consists of eight glass disks in Cassegrain geometry. Since the
spectral width of the amplifier output limits the pulse width of the compressed beam,
we made the preamplifier gain low and the main one high, which results in getting the
spectral width larger than 3 nm for a 1 kJ output. As a result, we obtained a pulse shorter
than 1 ps. The output beam is transported to the Target I room, where a deformable
mirror compensates for phase distortions on the wave front. A pair of 1-m diffraction
gratings, grooved at 1485 lines per mm and set in double path configuration, compresses
the pulse length to 500 fs in vacuum. Though the amplifier provides output up to 1.1
kJ, the damage threshold of the grating limits the current output to below 500 J. The
compression chamber, shown in Fig. 9 is placed on iron frames at the heigh of 7.16 m
from the floor. The focusing system consists of two plain mirrors and a 21-degree offaxial parabola mirror of 3.8 m focal length (f-number is 7.6). The chamber is connected
through a gate valve to the horizontal port of the target chamber. The pointing accuracy
is about 10 juradian at the focusing point. A 1-ns/l-nm chirped light, partially sliced
from the front end, directly drives the GEKKO XII laser system. Therefore the PW laser
beam can illuminate the imploded core plasma within ± 10 ps accuracy.
The PW Laser can excite the self-modulated wakefield of 200 GV/m or provide the
electron acceleration of 2 GV at 5 mm length, which is plotted on the progress curve of
the acceleration field, as shown in Fig. 10.
CONCLUSION
A 60 TW Laser has excited a self-modulated wake field via forward Raman scattering in
1019 cm~3 plasma column. The laser intensity is 3 x 1018 W/cm2, one order higher than
the self focusing threshold. The self-modulated wakefield grows from thermal noise and
saturates due to pump depletion. The optimum pulse length is 1.2 ps at nQ = 1.3 x 1019
cm~3. The plasma wave (self-modulated wakefield) amplitude is > 70%, corresponding
to an accelerating field of 350 ± 150 GV/m. The field can exceed the wave breaking
limit. Plasma waves were likely excited over the Rayleigh length (1~ 2 mm axial length)
which can accelerate electrons to energies > 300 MeV. The PW Laser will excite the
self-modulated wakefield of 200 GV/m or provide the electron acceleration of 2 GV at
5 mm length.
642
OSCILLATOR ROOM
GEKKO XII
COMPRESSOR
FIGURE 8.
Diagram of the PW Laser configuration.
ACKNOWLEDGMENTS
The authors would like to thank the GMII laser operation member for their technical
supports and all the PEII members for their encouragements. The authors also thank the
Petawatt Laser construction project member.
S. Wilks, LLNL, C. Joshi and C. Clayton, UCLA, are acknowledged for their kind
and useful discussions. This work was partially supported by the Ministry of Education,
Science, Sports and Culture, the Grant-in Aid for Scientific Research (B) 09480092.
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