doe facet review february 19, 2008 a plasma wakefield accelerator-based linear collider vision for...
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Doe FACET Review February 19, 2008
A Plasma Wakefield Accelerator-Based Linear Collider
Vision for Plasma Wakefield R&D at FACET and Beyond
e-e+Colliding Plasma WakesSimulation, F. Tsung
Beyond 10 GeV: Results, Plans and Critical IssuesT. Katsouleas
University of Southern California
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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
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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
RAL
LBL Osaka
UCLA
E164X/E-167
ILC
Current Energy Frontier
ANL
LBL
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Research program has put Beam Physics at the Forefront of Science
Acceleration, Radiation Sources, Refraction, Medical Applications
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Charge
Context “…mechanism to elevate some new accelerationtechnologies to the next level of demonstratedperformance.”
1. Evaluate the effectiveness of the anticipated ASF R&D program to confront thecriti cal technical issues for very compact, multi-TeV plasma accelerators.
Advise the HEP program on the anticipated scientifi c impact of FACET, whether theimpact is commensurate with the scale of resources required for construction andoperation; the uniqueness of the facilit y; and the existence of similar capabiliti eselsewhere.
1. Evaluate the effectiveness of the anticipated ASF R&D program to confront thecriti cal technical issues for very compact, multi-TeV plasma accelerators.
2. Advise the HEP program on the anticipated scientifi c impact of FACET, whetherthe impact is commensurate with the scale of resources required for constructionand operation; the uniqueness of the facilit y; and the existence of similarcapabiliti es elsewhere.
#4. Advise the HEP program on the anticipated scientificimpact of FACET, whether the impact is commensuratewith the scale of resources required for construction andoperation; the uniqueness of the facility; and the existenceof similar capabilities elsewhere.
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Particle Accelerators Requirements for High Energy Physics
• High Energy
• High Luminosity (event rate)• L=fN2/4xy
• High Beam Quality• Energy spread ~ .1 - 10%
• Low emittance: nyy << 1 mm-mrad
• Low Cost (one-tenth of $10B/TeV)• Gradients > 100 MeV/m• Efficiency > few %
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Simple Wave Amplitude Estimate
€
∇• E ~ ikp E = −4πen1
kp = ωp Vph ≈ ωp c
n1 ~ no
⇒ eE ~ 4πenoe2c ωp = mcωp
or eE ~no
1016cm−310GeV m
Gauss’ Law
E
1-D plasma density waveVph=c
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Linear Plasma Wakefield Theory
€
(∂t2 + ωp
2 )n1
no
= −ωp2 nb
no
Large wake for a laser amplitude a beam density nb~ no
Requirements on I, require a FACET-class facilityUltra-high gradient regime and long propagation issues not
possible to access with a 50 MeV beam facility
Q/ z = 1nCoul/30 (I~10 kA)
For z of order cp-1 ~ 30 (1017/no)1/2 and spot size =c/p ~ 15 (1017/no)1/2 :
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Nonlinear Wakefield AcceleratorsNonlinear Wakefield Accelerators(Blowout Regime)
• Plasma ion channel exerts restoring force => space charge oscillations
•Linear focusing force on beams (F/r=2ne2/m)
•Synchrotron radiation
•Scattering
Rosenzweig et al. 1990
++++++++++++++ ++++++++++++++++
----- --- ----------------
--------------
--------- ----
--- -------------------- - --
---- - -- ---
------ -
- -- ---- - - - - - ------ - -
- - - - --- --
- -- - - - - -
---- - ----
------
+ + + + + + + + + + ++ + + + + + + + + + + + + + ++ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +-
- --
--- --
EzEz
drive beam
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E+
E-
•Beam propagation• Head erosion (L=• Hosing
• Transformer Ratio:
€
R ≡Δγ load
γ driver
≤E+ ⋅LE− ⋅L
=E+
E−
driver
load
Limits to Energy Gain
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PIC Simulations of beam loading Blowout regime
flattens wake, reduces energy spread
Unloaded wake
Ez
Beam load
U C L A
Loaded wake•Nload~30% Nmax
•1% energy spread
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Emittance Preservation
Plasma focusing causes beam to rotate in phase space
• Emittance n = phase space area:
1/4 betatron period(tails from nonlinear Fp )
Several betatron periods(effective area increased)
x
px
• Matching: Plasma focusing (~2noe2) = Thermal pressure (grad p/3)
• No spot size oscillations (phase space rotations)• No emittance growth
€
2 = εn
2
γ
c
ωp
Fp Fth
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Positron Acceleration -- two possibilities blowout or suck-in wakes
Ref. S. Lee et al., Phys. Rev. E (2000); M. Zhou, PhD Thesis (2008)
• Non-uniform focusing force (r,z)• Smaller accelerating force
• Much smaller acceptance phase for acceleration and focusing
e- e+
e+ load
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•On ultra-fast timescales, relativistic plasmas can be robust, stable and disposable accelerating structures
TESLA structure
Plasma
2a~ 30cm
~ 100m
Accelerator Comparison
•No aperture, BBU
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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)
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CLIC-like PWFA LC Schematic
Drive Beam Accelerator
12 usec trains of e- bunches accelerated to ~25 GeVBunch population ~3 x 1010, 2 nsec spacing100 trains / second
Main Beam e+ Source:
500 nsec trains of e- bunches Bunch population ~1 x 1010, 2 nsec spacing100 trains / second
DRPWFA Cells:
25 GeV in ~ 1 m, 20 per side~100 m spacing
DR
Main Beam e- Source:
500 nsec trains of e- bunches Bunch population ~1 x 1010, 2 nsec spacing100 trains / second
Beam Delivery System, IR, and Main Beam Extraction / Dump
~2 km
~60 MW drive beam
power
per side~20 MW main
beam power per side
~120 MW AC power
per side
~ 4 km
1TeV CM
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Drive Beam Source• DC or RF gun
• Train format:
• With 3 x 1010 /bunch @ 100Hz:• ~2.3 mA average current, ~2 A beam current, similar to beam successfully accelerated in CTF3
•Compress bunches to ~30 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
100nskicker gap
mini-train 1 mini-train 20
500ns:250bunches2ns spacing 12s train
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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
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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 %
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Main Beam Source and Plasma Sections
• Electron side:•DC gun + DR•Compress to 10 (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
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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.
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TeV Beam Parameter Summary
IP Parameters* e+ e-
h.e. bunch gamepsX [m] 2.0E-06
h.e. bunch gamepsY [m] 5.0E-08
beta-x [m] 5.0E-02
beta-y [m] 2.0E-04
sigx [m] 3.2E-07
sigy [m] 3.2E-09
sigz [m] 1.0E-05
Dy 5.6E-01
Uave 2.81
delta_B 0.14
P_Beamstrahlung [W] 2.9E+06
ngamma 0.79
Hd 1.2
Lum. [cm-2 s-1] 2.4E+34
Int. Lum. [fb-1 per 2E7s] 474
Coherent pairs/bc 2.2E+07
E CM at IP [GeV] 1000
N, drive bunch 2.9E+10
N, high energy bunch 1.0E+10
n h.e. bunch/sec [Hz] 25000
Main beam train length [nsec] 500
Main beam bunch spacing [nsec] 2
Main beam bunches / train 250
Repetition rate, Hz 100
PWFA voltage per cell [GV] 25
PWFA Efficiency [%] 35
# of PWFA cells 20
n drive bunch/sec [Hz] 500000
Drive bunch energy [GeV] 25
Power in h.e. beam [W] 2.0E+07
Power in drive beam [W] 5.7E+07
Avg current in h.e. beam [uA] 40.05
Avg current in drive beam [mA] 2.29
Modulator-Drive Beam Efficiency [%] 54
Site power overhead [MW] 71
Total site power [MW] 283
Wall Plug Efficiency 14%
*If DR emittance is preserved
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Other Paths to a Plasma-based Collider
• Hi R options --> 100 GeV to TeV c.m. in single stage – Ramped drive bunches or bunch trains – Plasma question: hose stability– RF Driver questions: pulse shaping techniques, drive charge is 5x larger
• SRF Driven Stages– 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/) needs to increase by 102-104
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Critical Issues
System Req. Issue Tech Drivers
N Load 2nd bunch Chicane+chirp
photocathode
Load 2nd bunch Bunch shape
Phase control
nMatching
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
Red=FACET onlyBlue=FACETGreen=Facet partial
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R&D Roadmap for a Plasma-based Collider
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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
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Backup and Extra
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Future upgrade or alternative paths• PWFA can be an upgrade path of e-e- or options• The following flow corresponds to the afterburner path
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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 FFL* =2my*=0.1mm
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1 TeV Plasma Wakefield Accelerator
5, 100 GeV drive pulses, SC linac
Trailing Beam
~10 µs+
Trailing Beam
Ref.: V. Yakimenko and R. Ischebeck, AIP conference proceedings 877, p. 158 (2006).
~1 ns
PWFA Modules
P