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