Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons
The recent experimental results on frontier values of accelerating gradient and energy gain achieved by advanced acceleration methods based on intense plasma wakefields driven by a high-power short laser pulse or a large charge electron bunch are overviewed. Physical principles are considered for...
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Onishchenko, I.N. 2015-05-27T14:34:28Z 2015-05-27T14:34:28Z 2006 Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons / I.N. Onishchenko // Вопросы атомной науки и техники. — 2006. — № 6. — С. 158-162. — Бібліогр.: 17 назв. — англ. 1562-6016 PACS: 41.75.Lx, 41.85.Ja, 41.60.Bq https://nasplib.isofts.kiev.ua/handle/123456789/82288 The recent experimental results on frontier values of accelerating gradient and energy gain achieved by advanced acceleration methods based on intense plasma wakefields driven by a high-power short laser pulse or a large charge electron bunch are overviewed. Physical principles are considered for high-gradient acceleration of charged particles with purpose to elaborate the concept of future compact accelerators, which are called for high-energy physics and high technology applications, and also for creation of contemporary short pulsed radiation sources. The results of investigations on laser plasma wakefield accelerator (LWFA) generating precise monoenergtic beams with a small angle divergence and on plasma wakefield accelerator (PWFA) achieving breakdown through GeV barrier energy gain at SLAC by use wakefield excited by a short intense electron bunch in 1 m length plasma are presented. The possibility of PWFA application to doubling the energy of a future linear collider without doubling its length is considered. Представлены последние экспериментальные результаты по получению высоких ускоряющих градиентов и достигнутых максимальных энергий в новых методах ускорения, основанных на интенсивных кильватерных полях, возбуждаемых в плазме мощным коротким лазерным импульсом или электронным сгустком с большим зарядом. Представлені останні експериментальні результати по отриманню високих прискорюючих градієнтів і досягнутих максимальних енергій в нових методах прискорення, заснованих на інтенсивних кільватерних полях, збуджених у плазмі потужним коротким лазерним імпульсом або електронним згустком з великим зарядом Research supported by Ukr DFFD 02.07/325. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Plasma electronics Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons Прогресс в ускорении плазменными кильватерными полями, возбуждаемыми коротким интенсивным сгустком релятивистских электронов Прогрес в прискоренні плазмовими кільватерними полями, збудженими коротким інтенсивним згустком релятивістських електронів Article published earlier |
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| title |
Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons |
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Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons Onishchenko, I.N. Plasma electronics |
| title_short |
Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons |
| title_full |
Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons |
| title_fullStr |
Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons |
| title_full_unstemmed |
Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons |
| title_sort |
progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons |
| author |
Onishchenko, I.N. |
| author_facet |
Onishchenko, I.N. |
| topic |
Plasma electronics |
| topic_facet |
Plasma electronics |
| publishDate |
2006 |
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English |
| container_title |
Вопросы атомной науки и техники |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Прогресс в ускорении плазменными кильватерными полями, возбуждаемыми коротким интенсивным сгустком релятивистских электронов Прогрес в прискоренні плазмовими кільватерними полями, збудженими коротким інтенсивним згустком релятивістських електронів |
| description |
The recent experimental results on frontier values of accelerating gradient and energy gain achieved by advanced acceleration
methods based on intense plasma wakefields driven by a high-power short laser pulse or a large charge electron
bunch are overviewed. Physical principles are considered for high-gradient acceleration of charged particles with
purpose to elaborate the concept of future compact accelerators, which are called for high-energy physics and high technology
applications, and also for creation of contemporary short pulsed radiation sources. The results of investigations
on laser plasma wakefield accelerator (LWFA) generating precise monoenergtic beams with a small angle divergence
and on plasma wakefield accelerator (PWFA) achieving breakdown through GeV barrier energy gain at SLAC by use
wakefield excited by a short intense electron bunch in 1 m length plasma are presented. The possibility of PWFA application
to doubling the energy of a future linear collider without doubling its length is considered.
Представлены последние экспериментальные результаты по получению высоких ускоряющих градиентов и достигнутых максимальных энергий в новых методах ускорения, основанных на интенсивных кильватерных полях, возбуждаемых в плазме мощным коротким лазерным импульсом или электронным сгустком с большим зарядом.
Представлені останні експериментальні результати по отриманню високих прискорюючих градієнтів і досягнутих максимальних енергій в нових методах прискорення, заснованих на інтенсивних кільватерних полях, збуджених у плазмі потужним коротким лазерним імпульсом або електронним згустком з великим зарядом
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/82288 |
| citation_txt |
Progress in plasma wakefield acceleration driven by a short intense bunch of relativistic electrons / I.N. Onishchenko // Вопросы атомной науки и техники. — 2006. — № 6. — С. 158-162. — Бібліогр.: 17 назв. — англ. |
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| first_indexed |
2025-11-25T22:31:40Z |
| last_indexed |
2025-11-25T22:31:40Z |
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1850566030735179776 |
| fulltext |
PROGRESS IN PLASMA WAKEFIELD ACCELERATION DRIVEN
BY A SHORT INTENSE BUNCH OF RELATIVISTIC ELECTRONS
I.N. Onishchenko
NSC “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine,
e-mail: onish@kipt.kharkov.ua
The recent experimental results on frontier values of accelerating gradient and energy gain achieved by advanced ac-
celeration methods based on intense plasma wakefields driven by a high-power short laser pulse or a large charge elec-
tron bunch are overviewed. Physical principles are considered for high-gradient acceleration of charged particles with
purpose to elaborate the concept of future compact accelerators, which are called for high-energy physics and high tech-
nology applications, and also for creation of contemporary short pulsed radiation sources. The results of investigations
on laser plasma wakefield accelerator (LWFA) generating precise monoenergtic beams with a small angle divergence
and on plasma wakefield accelerator (PWFA) achieving breakdown through GeV barrier energy gain at SLAC by use
wakefield excited by a short intense electron bunch in 1 m length plasma are presented. The possibility of PWFA appli-
cation to doubling the energy of a future linear collider without doubling its length is considered.
PACS: 41.75.Lx, 41.85.Ja, 41.60.Bq
1. INTRODUCTION
In investigation nature on the smallest scale, which is
composed of the fundamental particles and forces, high
energy particle accelerators play a main role of tools as
microscopes. The energies of most interest for high ener-
gy physics today have reached the multi-TeV level, on
which profound fundamental questions are expected to be
answered on the origin of mass, the predominance of mat-
ter over antimatter and the existence of supersymmetry
and so on.
High energy ion accelerators including proton and
heavy-ion colliders can reveal in-situ synthesis of the nu-
clear matter by producing quark-gluon plasmas at the
quark-hadron phase transition temperature around one-
trillion Ks, which is thought as the high energy density
state at 10-5 seconds after the Big Bang of our universe.
As particle accelerators increased their energy frontier
at an exponential rate and enlarged their applied fields in
the past century, we realize present high-energy accelera-
tors become too large and costly, and possibly they ap-
proach the end of the road. Practical limitations on the
size and the cost of linear colliders can only be overcome
if the acceleration per unit length is significantly in-
creased. By replacing the metallic walls of conventional
structures with “plasma-walls” many limitations are
avoided and very high gradients can be achieved. The ad-
vances of high peak power lasers and intense charged-
particle beams pushed forward many proof-of-principle
experiments of novel laser and plasma accelerator con-
cepts worldwide during the past decade and made tremen-
dous progress in producing the record accelerating elec-
tric field and in achieving breakdown through GeV barri-
er energy gain.
A recent laser-driven plasma wakefield acceleration
(LWFA) experiment has measured an accelerating gradient
of 100 GeV/m [1-4]. Although plasma-based experiments
have shown impressive advances in their accelerating gra-
dients, they are quite short, extending over only a few mm
[5]. For the electron bunch driven plasma wakefield ac-
celeration (PWFA) [6,7] it has been recently demonstrated
the excitation of accelerating gradients as large as 30
GV/m using the ultra-short, 28.5 GeV electron bunches
now available at the Stanford Linear Accelerator Center
(SLAC). As a result, the electrons in the back of the
bunch gained about 3 GeV over the 10 cm-long plasma
with a density of 2.5x1017 cm-3. In recent experiments, en-
ergy gains in excess of 10 GeV, by far the largest in any
plasma accelerators, have been measured over a plasma
length of 30 cm. Moreover, systematic measurements
show the scaling of the energy gain with plasma length
and density. These are key steps toward the application of
beam-driven plasma accelerators to doubling the energy
of a future linear collider without doubling its length.
On the aspects of quantity and quality of accelerated
particles and radiations, recent experiments succeeded in
demonstrating the remarkable capability for producing
bright high quality particle beams and radiations with a
simple experimental apparatus on a table top, which the
conventional accelerators have been unable to do. These
aspects arouse great interest in applications of the ad-
vanced accelerator technology to many research fields
such as such as material, chemical, biological, medical
and industrial sciences, where a large costly high-energy
accelerator can not be used.
This presentation shows the way from the first ex-
periments in NSC KIPT, Argone Lab., and KEK on plas-
ma wakefield acceleration driven by a single electron
bunch or a sequence of bunches to the great recent results
at SLAC in which energy gains in excess of 10 GeV, by
far the largest in any plasma accelerators, have been mea-
sured over a plasma length of 30 cm. Systematic mea-
surements show the scaling of the energy gain with plas-
ma length and density. The experiments are being pre-
pared with plasma length of about one meter. These are
the key steps toward the application of beam-driven plas-
ma accelerators to doubling the energy of a future linear
collider without doubling its length.
2. MOTIVATION FOR PLASMA ASSISTANCE
Historically the growing scientific interest in the novel
acceleration concepts and advanced accelerator technolo-
gies have been started at the 2nd Geneva Conference in
1956 in three reports presented by V.Veksler [8], G.Bud-
ker [9], and Ya.Fainberg [10]. There the intense fields of
space charge (so called “collective fields”) were proposed
for particle acceleration to high energy at reasonable
158 Problems of Atomic Science and Technology. 2006, № 6. Series: Plasma Physics (12), p. 158-162
length. Simple estimation of the maximum value of such
field excited in plasma of density np can be obtained using
Poisson equation
divE = -4π eδne
and supposing that plasma electrons and ions are fully
separated δne∼ np on a distance of wavelength
λp≡2π/kp=2πc/ωp
Emax [V/cm] ≈ √np [cm-3]
e.g. Emax≈100 GV/m for np=1018 cm-3
Later J.Dawson et. al. proposed to use for excitation
intense plasma field (so called “wakefield”) short high-
power laser pulse [11] (LWFA) or short intense electron
bunch [12] (PWFA). In these two schemes ponderomotive
force of driving laser pulse or space charge of driving
electron bunch displaces plasma electrons. Plasma ions
exert restoring force. Space charge oscillations are excit-
ed. Wake phase velocity is equal to driver velocity (auto-
phase matching). The length of driver (laser pulse/ elec-
tron bunch) should be less than plasma wavelength, at
that wavelength shorter results higher wakefield intensity
due to condition Emax∼np
1/2. According to Wilson theorem
the transformer ratio k=Ez, accel/Ez, decel <2 for symmetric
bunch.
3. PROGRESS IN NEW TRENDS OF PARTI-
CLES ACCELERATION
In the past decade the worldwide experiments of laser-
plasma particle acceleration have boosted their frontier of
particle beam energy and intensity. A trend in experimen-
tal results indicates a rapid increase of electron energies
accelerated by laser-driven plasmabased concepts, whose
rate is three to four orders of magnitude over the past ten
years in coincidence with increase of the laser pondero-
motive energy. A recent laser electron acceleration exper-
iment carried out by using 160 J, 650 fs (~ 250 TW) puls-
es at RAL demonstrated the highest energy laser accelera-
tion at the maximum energy of 350 MeV, though with
100% energy spread, whose energy spectra can be charac-
terized by a power law rather than a Maxwellian distribu-
tion. The highest energy electrons are observed for a fo-
cused laser intensity of 3x1020 W/cm2.
In the plasma wakefied acceleration driven by the in-
tense electron beam, Joshi et al. carried out PWFA experi-
ments at the 30 GeV SLAC FFTB electron beam with
12µ rms bunch length, where the maximum energy gain
of up to 4 GeV was obtained over a 10 cm long lithium
plasma, though the energy spread was 100%. This result
is the first demonstration of the breakthrough of a GeV
barrier in plasma accelerators.
3.1 LASER WAKEFIELD ACCELERATION
(LWFA)
The most prominent experimental results today [2-5]
is the monoenergetic electron beam acceleration in
LWFA, which were presented by Koyama (Japan), Mur-
phy (UK), Malka (France) and Leemans (USA) indepen-
dently. Moreover, their beams have properties of high
quality having a small normalized emittance below 1 π
mm mrad and about 10 femtosecods pulse length with a
charge of the order of 1 nC, making them attractive as po-
tential radiation sources for ultrafast time-resolved studies
in biology and material science as well as an injector for
future FELs and linear colliders.
♦K. Koyama et al. (AIST, Japan) [1]. Ti:sapphire
laser: wavelength-800 nm, power-2 TW, pulse width-50
fs, focus diameter-5µ, focus intensity-1.5×1018 Wcm-2.
Target: supersonic gas (N2, He) jet. Plasma density (0.4…
4.4) ×1020 cm-3 , N2; (0.4-1.3) ×1020 cm-3, He.
Results on electron beam production with energy
7MeV and divergence angle are shown in Fig. 1.
Fig. 1. Spectrum of accelerated electrons in [1]
♦C.D.Murphy et al. (ILC/RAL, UK) [2]. The experi-
ment used the high-power Ti:sapphire laser system at the
Rutherford Appleton Laboratory (Astra). The laser pulses
(λ=800 nm, τ=40 fs with energy approximately 0.5 J on
target) were focused with an f/16.7 off-axis parabolic mir-
ror onto the edge of a 2-mm-long supersonic jet of helium
gas to produce peak intensities up to 2.5×1018Wcm-2. The
electron density (ne) as a function of backing pressure on
the gas jet was determined by measuring the frequency
shift (∆ω=ωpe) of satellites generated by forward Raman
scattering in the transmitted laser spectrum. The plasma
density was observed to vary linearly with backing pres-
sure within the range ne=3×1018 cm-3 - 5×1019 cm-3. Elec-
tron spectra are measured using an on-axis magnetic spec-
trometer. Other diagnostics used included transverse
imaging of the interaction, and radiochromic film stacks
to measure the divergence and total number of accelerated
electrons. The schematic of installation is shown in Fig. 2.
Fig. 2. Scheme of experimental setup in [2]
Measured energy spectrum of accelerated electrons is
shown in Fig. 3.
159
Fig.3. Measured electron spectrum at a density of 2×
1019 cm-3 in [2]. Laser parameters: E=500 mJ, τ=40 fs, I≈
2.5×1018Wcm-2
♦V.Malka et al. (Ecole Polytechnique, France) [3].
Here it was demonstrated that the quality of the electron
beams can be dramatically enhanced. Within a length of 3
mm, the laser drives a plasma bubble that traps and accel-
erates plasma electrons. It leads to the generation of high-
quality electron beams with 10 mrad divergence and 0.5±
0.2 nC of charge at 170±20MeV. From the above, it can
deduced that the electron beam energy was 100 mJ. Thus,
the energy conversion from the laser to the electron beam
was 10%. Contrary to all previous results obtained from
laser–plasma accelerators, the electron energy distribution
is quasi-monoenergetic. The number of high-energy elec-
trons (170MeV) is increased by at least three orders of
magnitude with respect to previous work.
This new regime was reached by using the ultrashort
and ultraintense laser pulse generated in a titanium-doped
sapphire, chirped pulse amplification laser system. The
laser pulse had a 33±2 fs duration (FWHM), and con-
tained 1 J of laser energy at central wavelength 820 nm. It
was focused onto the edge of a 3-mm-long supersonic he-
lium gas jet using a f/18 off-axis parabola. The diffrac-
tion-limited focal spot had a diameter of r0=21µ at
FWHM, producing a vacuum-focused laser intensity of
I=3.2×1018Wcm-2. For these high laser intensities, the he-
lium gas was fully ionized by the foot of the laser pulse
and ionization did not play a role in the interaction. High-
er plasma density was ne =2×1019 cm-3.
♦W.P.Leemans et al. (LBNL, USA) [4]. In the works
mentioned above, however, acceleration distances (the
diffraction or Rayleigh length) have been severely limited
by the lack of a controllable method for extending the
propagation distance of the focused laser pulse. The ensu-
ing short acceleration distance results in low-energy
beams with 100 per cent electron energy spread, which
limits potential applications. Here it was demonstrated a
laser accelerator that produces electron beams with an en-
ergy spread of a few per cent, low emittance and in-
creased energy (2×109 electrons at 80±1.8MeV). Bunches
with energy up to 150MeV have been observed on sepa-
rate shots. Applied technique involves the use of a pre-
formed plasma density channel to guide a relativistically
intense laser, resulting in a longer propagation distance.
In the channel-guided laser wakefield accelerator, the
plasma channel was formed in a supersonic hydrogen gas
jet by two pulses fired 500 ps before the drive pulse. The
supersonic gas jet was 2.4 mm long at an atomic density
of 4.5×1019 cm-3. A cylindrical filament of plasma was
ionized by an intense (60 fs, 15 mJ) igniter pulse,
collinear with the pulse that drives the plasma wave and
focused at f/15 near the downstream edge of the gas jet.
The plasma was subsequently heated to tens of eV by in-
verse bremsstrahlung, using a long (250 ps, 150 mJ) pulse
incident from the side for efficient heating. The resulting
hot plasma filament on axis expanded outward, driving a
shock wave. This shock resulted in a density depletion on
axis and a nearly parabolic transverse density profile
which was tuned by adjusting the timing and energies of
the beams.
The plasma wave was driven by a 500 mJ pulse of
55 fs FWHM, focused at the upstream edge of the channel
to an 8.5µm FWHM spot by an f/4 off axis parabola giv-
ing an intensity of 1.1×1019 Wcm-2. Propagation of the
laser was monitored with a side interferometer (using a 2
ω probe laser) and mode imager CCD. The electron beam
accelerated by the plasma wave was analyzed using an in-
tegrating current transformer, a phosphor screen, and a
magnetic spectrometer. The laser mode at the channel exit
is a well defined spot of 24mm FWHM containing 10%
of the input energy. This indicates the effectiveness of the
channel in maintaining the drive beam intensity and mode
over many diffraction lengths.
A high-quality electron bunch is formed when the ac-
celeration length is matched by plasma density changing
to the dephasing length, and when the laser strength is
such that beam loading is sufficiently strong to turn off in-
jection after the initial bunch of electrons is loaded.
The results open the way for compact and tunable
high-brightness sources of electrons and radiation.
These four experiments have shown the possibility of
realization high gradient of accelerating field of order
100 GeV/m. The problem is to enlarge the length of ac-
celerating process and hence the final energy of accelerat-
ing particles. The maximal record energy at laser-plasma
acceleration is above 300 MeV [5].
♦ K.Krushelnick et al. (Imperial College London,
UK) [5]. The experiment was performed using the Vul-
can Petawatt Nd:glass laser system, which produced puls-
es of 160 J in a duration of τ=650 fs (FWHM). The laser
was focused to a 6 µ diameter spot at the edge of a super-
sonic 2 mm diameter helium gas jet using an f=3 off-axis
parabolic mirror. This produces peak intensities in excess
of 3×1020 Wcm-2 in vacuum.
The spectrum recorded at np=7.7 × 1018 cm-3 shows the
highest observed electron energies. The signal descends
into the background at 300 MeV. The beam divergence
measurements show that close to the optimum density the
beam divergence was approximately 50 mrad for
electrons above 1.5 MeV.
There are two explanations of the processes of trap-
ping and accelerating of plasma electrons resulting in pro-
duction of precise monoenergetic electron beams with a
small divergence and a short duration - transverse wave
breaking injection [13] and bubble acceleration [14].
160
3.2 BEAM PLASMA WAKEFIELD ACCELERA-
TION (PWFA)
Inspired by the ideas stated in [8-12] the first proof-of-
principle experiments have been performed in many labo-
ratories (see Table), including KIPT (Ukraine), ANL
(USA), KEK (Japan), Novosibirsk INI (Russia).
Parameters and results of the first proof-of-principle
experiments
KIPT,
Ukraine,1971
ANL,
USA,1988
KEK,
Japan,1990
Energy, MeV 2 21 250(500)
Bunch duration, ps 57 7 10
Length, mm 17 2.1 3
Diameter, mm 10 2.8 2-3
Charge, nC 0.32 4 5-10
Number of bunches 6⋅ 103 1 6
Plasma density,cm-3 1011 4-7⋅ 1010 4⋅ 1011
Plasma length , cm 100 33 20
Wake field, MV/m 0.2 5.3 60
Experiments at SLAC on advanced acceleration meth-
ods aim at demonstrating high gradient acceleration in a
1 m long plasma cell. Plasma modules of this length
would be well suited for building a future linear collider.
The intended use of the existing SLAC linac for the pro-
posed experiment limits the achievable gradient to about
1 GeV/m. Though not as high as achieved by other plas-
ma-based experiments, this gradient is much larger than
in any metallic structure. The basic idea for these experi-
ments is to use a single SLC bunch to both excite the
plasma wakefield (head of the bunch) and to witness the
resulting acceleration (tail of the bunch).
The E-157 experiment at SLAC has aimed to extend
high-gradient plasma wakefield acceleration from the mm-
scale to the m-scale. An accelerating gradient of up to 1
GeV/m was induced in a 1.4 m long plasma module. The
experiment measures deceleration, acceleration and trans-
verse focusing of the high power SLAC linac electron beam.
The E-162 experiment at SLAC was a continuation of
the E-157 experiment. It aimed to extend high-gradient
plasma wakefield acceleration from the mm-scale to the
m-scale and to expand measurements on positron beam.
E157/E162 experiments have successfully observed
many of the predicted phenomena: multiple betatron oscilla-
tions of the beam as the plasma density is increased; propa-
gation of a matched beam through the plasma; sloshing of
the tilted beam and the electron hosing instability in an ion
column; dynamic focusing of the beam; X-ray emission due
to betatron motion in the ion column; focusing of a positron
beam; acceleration and deceleration of the drive beam.
The E-164 experiment at SLAC on high gradient plas-
ma-wakefield acceleration using ultrashort electron bunch
with number of electrons Nb (shortening of electron bunch
length from σz = 0.6 mm (E157/E162) to 100µ (E164) by
means of ultra-short bunch facility (USBF)) aimed in-
crease the intensity of plasma wakefield 36 times taking
into account the 1/ σz
2 bunch length scaling of the acceler-
ating gradient accordingly to the dependence
Elinear = 240 MV/m⋅ [Nb/4×1010]⋅ [0.6/σz(mm)]2
The physical scheme of PWFA is presented in Figure 4.
In a plasma wake field accelerator, the space charge of a par-
ticle bunch displaces the electrons of a preformed quiescent
plasma to produce a large plasma wake field that can accel-
erate a subsequent bunch at a very high rate.
Fig. 4. Physical mechanism of the PWFA
Simulation of nonlinear wakefield excitation shows essen-
tial enhancement of the peak accelerating gradient (Fig. 5).
Epeak ≈ 3-4 Elinear
Fig. 5. 2D simulation results from OSIRIS code of a 100µ
bunch containing 2×1010 electrons propagating through a
5.6×1015 cm-3 plasma. The peak accelerating gradient is
14GeV/m
In Fig. 6 the results of simulation of energy loss of the
bunch head and energy gain of the bunch tail is presented for
the parameters of E-164 experiment with 100µ length bunch.
It is seen maximum energy gain 4.4 GeV over 30cm long
plasma.
Fig. 6. Energy loss and gain of bunch electrons from
head to tail of the 100µ length bunch
The latest new result at SLAC [6,7] on electrons ac-
celeration in plasma wakefield excited by intense rela-
tivistic electron bunch is the first demonstration of the
breakthrough of a GeV barrier in advanced accelerators
promising to leave behind conventional colliders, includ-
ing planned ILC, before 2020 year.
The experiment described in [6-7] uses an ultrarela-
tivistic electron bunch to create plasma in lithium vapor
and to drive a large amplitude plasma wave. When the
electron bunch enters the lithium vapor, the electric field
of the leading portion of the bunch ionizes the valence
electron of each lithium atom in its vicinity leaving fully
ionized neutral plasma for the remainder of the bunch.
The plasma electrons are then expelled from the beam
volume and return one-half plasma period later. The re-
turning plasma electrons form density concentrations on
axis behind the bunch leading to a large accelerating field
for the particles in the back of the bunch.
161
http://www.slac.stanford.edu/grp/arb/e157/old_home.html
A single 28.5 GeV bunch of 1.8×1010 electrons from
the Stanford Linear Accelerator Center linac was com-
pressed to the length of 12µ (rms). There are no tech-
niques available to time resolve the spectrum of 12 µ
(40 fs) bunches; consequently, the energy changes from
the plasma are measured by comparing the time integrat-
ed energy spectrum of the bunch with and without the
plasma (Fig.7). The neutral lithium vapor is fully ionized
by the large radial electric field of the compressed elec-
tron bunches and the plasma density is then equal to the
lithium vapor density (10 cm long 2.8×1017 atoms/cm3).
Fig. 7. Single bunch energy spectra downstream from the
plasma for (a) the case of no plasma and (b) a 10 cm long
2:8×1017 e/cm3 lithium plasma
In the recent experiments [7], submitted to EPAC-
2006, energy gains in excess of 10 GeV, by far the largest
in any plasma accelerators, have been measured over a
plasma length of 30 cm. Demonstration the scaling of the
energy gain with plasma length allows applying beam-
driven plasma accelerator to doubling the energy of future
linear collider without doubling its length.
Future two-bunch plasma accelerators will use one bunch
to drive the wake and accelerate a second bunch with narrow
energy spread. Provided the intrabunch spacing and plasma
density are adjusted accordingly, the measured accelerating
gradient in a two-bunch scheme should continue to increase
as the drive bunch length is shortened.
This experiment has verified the dramatic increase in
accelerating gradient predicted for short drive bunches
and has reached several significant milestones for beam-
driven plasma-wakefield accelerators: the first to operate
in the self-ionized regime, the first to gain much more
than 1 GeV energy, and the largest accelerating gradient
measured to date by 2 orders of magnitude. It is a crucial
step in the progression of plasmas from laboratory experi-
ments to future high-energy accelerators and colliders.
Research supported by Ukr DFFD 02.07/325.
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ПРОГРЕСС В УСКОРЕНИИ ПЛАЗМЕННЫМИ КИЛЬВАТЕРНЫМИ ПОЛЯМИ, ВОЗБУЖДАЕМЫМИ КО-
РОТКИМ ИНТЕНСИВНЫМ СГУСТКОМ РЕЛЯТИВИСТСКИХ ЭЛЕКТРОНОВ
И.Н. Онищенко
Представлены последние экспериментальные результаты по получению высоких ускоряющих градиентов и достигну-
тых максимальных энергий в новых методах ускорения, основанных на интенсивных кильватерных полях, возбуждаемых в
плазме мощным коротким лазерным импульсом или электронным сгустком с большим зарядом.
ПРОГРЕС В ПРИСКОРЕННІ ПЛАЗМОВИМИ КІЛЬВАТЕРНИМИ ПОЛЯМИ, ЗБУДЖЕНИМИ КОРОТКИМ ІН-
ТЕНСИВНИМ ЗГУСТКОМ РЕЛЯТИВІСТСЬКИХ ЕЛЕКТРОНІВ
І.М. Онищенко
Представлені останні експериментальні результати по отриманню високих прискорюючих градієнтів і досягнутих
максимальних енергій в нових методах прискорення, заснованих на інтенсивних кільватерних полях, збуджених у плазмі
потужним коротким лазерним імпульсом або електронним згустком з великим зарядом.
162
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3.2 Beam Plasma Wakefield Acceleration (PWFA)
References
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