A Plasma Wakefield Accelerator-Based
Linear Collider
Vision for Plasma Wakefield R&D at FACET and Beyond
e-e+Colliding Plasma Wakes
Simulation, F. Tsung
Beyond 10 GeV: Results, Plans and Critical Issues
T. Katsouleas
University of Southern California
Doe FACET Review
February 19, 2008
Outline
•
•
•
•
•
Brief History and Context
Introduction to plasma wakefield accelerators
Path to a high energy collider
Critical issues, milestones and timeframe
What can and cannot be addressed with
FACET
Plasma Accelerators -- Brief History
•
•
•
•
•
•
•
1979 Tajima & Dawson Paper
1983 Tigner Panel rec’d
investment in adv. acc.
1985 Malibu, GV/m unloaded
beat wave fields, world-wide
effort begins
1989 1st e- at UCLA
1994 ‘Jet age’ begins (100 MeV
in laser-driven gas jet at RAL)
2004 ‘Dawn of Compact
Accelerators’ (monoenergetic
beams at LBL, LOA, RAL)
2007 Energy Doubling at SLAC
ILC
Current Energy Frontier
E164X/E-167
LBL
RAL
LBL
Osaka
UCLA
ANL
Research program has put Beam Physics at
the Forefront of Science
Acceleration, Radiation Sources, Refraction, Medical Applications
Charge
Context Ι mechanism to elevate some new acceleration
technologies to the next level of demonstrated
performance.Σ
#3. Evaluate the effectiveness of the anticipated ASF R&D
program to confront the critical technical issues for very
compact, multi-TeV plasma accelerators.
1.
2.
Evaluate the effectivenes s of the anticipated ASF R&D progr am to conf ront the
criti cal techni cal is sue s for very comp act, multi- TeV plasma accelerators.
#4. Advise the HEP program on the anticipated scientific
Advise the HEP program on the anticipated scientifi c im pact of FACET, whether
impact
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theofimpact
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Evaluate
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theof
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els ewhe
operation; the uniqueness of the facility; and the existence
Advise
the HEP capabilities
program on the anticipated
scientifi c im pact of FACET, whether the
of similar
elsewhere.
im pact is comme nsu rate with the scale of resources requir ed for construction and
operation; the uniquene ss of t he facilit y; and the existenc e of simil ar capabiliti es
els ewhe re.
Particle Accelerators
Requirements for High Energy Physics
•
High Energy
•
High Luminosity (event rate)
•
•
High Beam Quality
•
•
•
L=fN2/4psxsy
Energy spread dg/g ~ .1 - 10%
Low emittance: en ~ gsyqy << 1 mm-mrad
Low Cost (one-tenth of $10B/TeV)
•
•
Gradients > 100 MeV/m
Efficiency > few %
Simple Wave Amplitude Estimate
E
Vph=c
1-D plasma density wave
  E ~ ik p E  4 pen1
k p   p Vph   p c
n1 ~ n o
 eE ~ 4 pen oe 2c  p  mc p
or eE ~

no
10GeV m
16
3
10 cm
Gauss’ Law
Linear Plasma Wakefield Theory
(t2   2p )
n1
n
  2p b
no
no
Large wake for a laser amplitude a beam density nb~ no
For sz of 
order cpp-1 ~ 30m (1017/no)1/2 and spot size s=c/p ~ 15m (1017/no)1/2 :
Q/ sz = 1nCoul/30m
(I~10 kA)
Requirements on I, t, s, g require a FACET-class facility
Ultra-high gradient regime and long propagation issues not
possible to access with a 50 MeV beam facility
Nonlinear Wakefield Accelerators
(Blowout Regime)
Rosenzweig et al. 1990
-- -- -- ----- ---------++- ++ ++ ++ ---++-- -+-+------++ ++ ++ ++ ++ --+-+- +--+----+-+- ++
+
+--+ ++ + ++ + +++ ++++ -+++-+------++- ++++ ++++ ++++ ++ ++--++--++++ ++++ ++++ ++
---- ------- --- -- -- - - - -- -- - ---- -- - - - - -- --Ez
• Plasma ion channel exerts restoring force => space charge oscillations
•Linear focusing force on beams (F/r=2pne2/m)
•Synchrotron radiation
•Scattering
Limits to Energy Gain
E-
•Beam propagation
• Head erosion
(L=ps2/e)
• Hosing
load
driver
E+
• Transformer Ratio:
R
g load
g driver
E  L E


E  L E
PIC Simulations of beam loading
Blowout regime
Beam load
flattens wake,
reduces energy spread
Ez
Unloaded wake
Loaded wake
•Nload~30% Nmax
•1% energy spread
U C L A
Emittance Preservation
• Emittance
en = phase space area:
px
s
x
Plasma focusing causes
beam to rotate in phase
space
1/4 betatron period
(tails from nonlinear Fp )
Several betatron periods
(effective area increased)
• Matching: Plasma focusing (~2pnoe2s) = Thermal pressure (grad p~e2/s3)
s  en
2
2 c
g p
• No spot size oscillations (phase space rotations)
• No emittance growth
Fp
Fth
Positron Acceleration -- two possibilities
blowout or suck-in wakes
e+
ee+ load
• Non-uniform focusing force (r,z)
• Smaller accelerating force
• Much smaller acceptance phase for acceleration and focusing
Ref. S. Lee et al., Phys. Rev. E (2000); M. Zhou, PhD Thesis (2008)
Accelerator Comparison
•On ultra-fast timescales, relativistic plasmas can be robust, stable and
disposable accelerating structures
•No aperture, BBU
TESLA structure
l ~ 30cm
Plasma
l ~ 100mm
2a
Path to a TeV Collider
from present state-of-the-art*
•
Starting point: 42 --> 85 GeV in 1m
– Few % of particles
•
Beam load
– 25-50 GeV in ~ 1m
– 2nd bunch with 33% of particles
– Small energy spread
•
Replicate for positrons
•
Marry to high efficiency driver
•
Stage 20 times
* I. Blumenfeld et al., Nature 445, 741 (2007)
CLIC-like PWFA LC Schematic
~120 MW
AC power
per side
12 usec trains of e- bunches accelerated
to ~25 GeV
Bunch population ~3 x 1010, 2 nsec
spacing
100 trains / second
Drive Beam Accelerator
~2 km
~60 MW drive
beam power
per side
~20 MW main
beam power per
side
PWFA Cells:
DR 25 GeV in ~ 1 m, 20 per side Beam Delivery System,
~100 m spacing
IR, and Main Beam
Extraction / Dump
Main Beam e- Source:
~ 4 km
500 nsec trains of e- bunches
Bunch population ~1 x
spacing
100 trains / second
1010,
2 nsec
1TeV CM
DR
Main Beam e+ Source:
500 nsec trains of e- bunches
Bunch population ~1 x 1010, 2 nsec spacin
100 trains / second
Drive Beam Source
• DC or RF gun
mini-train 20
mini-train 1
• Train format:
• With 3 x 1010 /bunch @ 100Hz:
• ~2.3 mA average current,
~2 A beam current, similar to
beam successfully accelerated
in CTF3
500ns:
250bunches
2ns spacing
100ns
kicker gap
12ms train
•Compress bunches to ~30 m RMS length
• SPPS achieved much smaller RMS lengths
• Accelerate to 25 GeV
• Fully-loaded NC RF structures, similar to CLIC / CTF 3
• Inject into “Drive Beam Superhighway” with pulsed extraction for each PWFA cell
• Both e+ and e- main beams use e- drive beam
See slide notes for additional background
Drive Beam Superhighway
•
Based on CLIC drive beam scheme
– Drive beam propagates opposite direction wrt main beam
– Drive mini-train spacing = 2 * PWFA cell spacing i.e, ~600 nsec
Drive Beam Distribution
• Format options
– Mini-trains < 600 nsec
• NC RF for drive beam
• Duty cycle very low
– Individual bunches > 12 μsec
• SC RF for drive beam
• Duty cycle ~100 %
Main Beam Source and Plasma Sections
• Electron side:
•DC gun + DR
•Compress to 10m (achieved in SPPS)
•20, +25GeV plasma sections, each 1E17 density, <1.2 meters long
• Gaussian beams assumed
-shaped beam profiles => larger transformer ratio, higher efficiency
• Final main beam energy spread <5%
• Positron side:
• conventional target + DR
• Positron acceleration in electron beam driven wakes (regular plasma or
hollow channel)
• Will have tighter tolerances than electron side
Matching / Combining / Separating Main and Drive Beams
•
•
•
Must preserve bunch lengths
Preserve emittance of main beam
~100 μm spacing of main and drive
bunches
– Time too short for a kicker – need
magnetostatic combiner / separator
– Need main – drive bunch timing at μm
level
•
Different challenges at different
energies
– High main beam energy: emittance
growth from SR
– Low main beam energy: separation
tricky because of ~equal beam
energies
•
Need ~100 m between PWFA cells
“First attempt” optics of 500 GeV / beam separator.
First bend and first quad separate drive and main
beam in x (they have different energies); combiner
is same idea in reverse. This optics needs some
tuning and ~2 sextupoles. System is isochronous
to the level of ~1 μm R56. Assuming that another
~50 m needed for combiner, each PWFA cell needs
~100 m of optics around it.
TeV Beam Parameter Summary
E CM at IP [GeV]
N, drive bunch
N, high energy bunch
n h.e. bunch/sec [Hz]
Main beam train length [nsec]
Main beam bunch spacing [nsec]
Main beam bunches / train
Repetition rate, Hz
PWFA voltage per cell [GV]
PWFA Efficiency [%]
# of PWFA cells
n drive bunch/sec [Hz]
Drive bunch energy [GeV]
Power in h.e. beam [W]
Power in drive beam [W]
Avg current in h.e. beam [uA]
Avg current in drive beam [mA]
Modulator-Drive Beam Efficiency [%]
Site power overhead [MW]
Total site power [MW]
Wall Plug Efficiency
1000
2.9E+10
1.0E+10
25000
500
2
250
100
25
35
20
500000
25
2.0E+07
5.7E+07
40.05
2.29
54
71
283
14%
IP Parameters*
h.e. bunch gamepsX [m]
h.e. bunch gamepsY [m]
beta-x [m]
beta-y [m]
sigx [m]
sigy [m]
sigz [m]
Dy
Uave
delta_B
P_Beamstrahlung [W]
ngamma
Hd
Lum. [cm-2 s-1]
Int. Lum. [fb-1 per 2E7s]
Coherent pairs/bc
e+ e2.0E-06
5.0E-08
5.0E-02
2.0E-04
3.2E-07
3.2E-09
1.0E-05
5.6E-01
2.81
0.14
2.9E+06
0.79
1.2
2.4E+34
474
2.2E+07
*If DR emittance is preserved
Other Paths to a Plasma-based
Collider
•
Hi R options --> 100 GeV to TeV c.m. in single stage
–
–
–
•
SRF Driven Stages
–
–
–
•
Ramped drive bunches or bunch trains
Plasma question: hose stability
RF Driver questions: pulse shaping techniques, drive charge is 5x larger
5 stage example of Yakimenko and Ischebeck
Plasma question: extrapolate to 2m long 100 GeV
SRF questions: 3x5 +1 times the power/m and loading of ILC, wakes and
BBU
Laser drivers
–
–
–
Extrapolate 1 GeV experiments to 25 GeV
• Scale up laser power x25, pulse length x5, density x0.04, plasma
length x125
• 20 Stages
Plasma questions: channel guiding over 1m; injected e-; e+ behind bubble
Laser questions: Avg. laser power (20MW/h) needs to increase by 102-104
Critical Issues
System Req.
N
Red=FACET only
Blue=FACET
Green=Facet partial
Issue
Tech Drivers
Load 2nd bunch
Chicane+chirp
photocathode
g/g
Load 2nd bunch
Bunch shape
Phase control
en
Matching
hosing
Scattering
Ion motion
Plasma sources
Plasma channels
plasma matching sections
Combiner/separators
e+
Gradients
Nonlinear focusing
Accel on e- wake
Plasma channels
e+ sources
phase control
E
Beam propagation
Synchrotron losses
Staging or shaping
Simulation modeling
to guide designs
Laser jitter stabilization
f
Power coupling
RF stability w/ hi load,
short bunch (CSR)
Gas removal & replenish
Klystron power
CLIC
DoD Gas laser program
L
Final Focus-Plasma lens’
Pointing stability
Plasma sources
Ultra-fast feedback
R&D Roadmap for a Plasma-based Collider
Summary
• Recent success is very promising
• No known show stoppers to extending plasma
accelerators to the energy frontier
• Many questions remain to be addressed for realizing
a collider
• FACET-class facility is needed to address them
– Lower energy beam facilities cannot access critical
issues in the regime of interest
– FACET can address most issues of one stage of a 5-20
stage e-e+ TeV collider
Backup and Extra
Future upgrade or alternative paths
• PWFA can be an upgrade path of e-e- or gg options
• The following flow corresponds to the afterburner path
Beam delivery
• NLC style FF with local chromatic correction can be a starting point
• ~TeV CM required just ~300m
• Energy acceptance (full) was about 2% – within a factor of two from what
is needed for PWFA-LC (further tweaking, L* optimization, etc)
• Beam delivery length likely be dominated by collimation system (could be
+1.0-1.5km/side) – methods like crystal collimation and nonlinear
collimations to be looked at again
An early (2000)
design of NLC FF
L* =2m
by*=0.1mm
1 TeV Plasma Wakefield Accelerator
PWFA Modules
P
~10 µs+
Trailing
Beam
~1 ns
Trailing
Beam
5, 100 GeV drive pulses, SC linac
Ref.: V. Yakimenko and R. Ischebeck, AIP conference proceedings 877, p. 158 (2006).