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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
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
RAL
LBL Osaka
UCLA
E164X/E-167
ILC
Current Energy Frontier
ANL
LBL
Research program has put Beam Physics at the Forefront of Science
Acceleration, Radiation Sources, Refraction, Medical Applications
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.
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 %
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
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 :
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
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
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
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
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
•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
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
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
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
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 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
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
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
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
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
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 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 FFL* =2my*=0.1mm
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