AAC 2012 TutorialJonathan Wurtele

UCB/LBNL

Principles of Acceleration

How Accelerators Work• Electric fields accelerate particles

• Magnetic and electric fields focus and deflect particles

LULI

"I can see no escape from the conclusion that [cathode rays] are charges of negative electricity carried by particles of matter." But, he continued, "What are these particles? are they atoms, or molecules, or matter in a still finer state of subdivision?"

Accelerator-based energy frontier physics

From Katsouleas and Joshi, Physics Today

Troubles….how to get to the next collider?The problem was realized in 1982, but the solution is elusive.

Always look for newapplications

Particle energy exchange with fields

Design your own accelerator---BUT obey the LAWS:

Maxwell Equations & Lorentz force

Watch out for limits: wakefields, breakdown, phase space and beam brightness

Does anyone want your beam?

Practical issues are important!

Free-Space Acceleration in plane waves

So why not shine laser on electron to get TeV? Diffraction?, dephasing?, depletion? A generic problem?

How well can you do for linear acceleration?

No net linear acceleration by far free space fields

Assume accelerating field is:Free space: no material or particles nearby to create near fields

Net: Energy gain (or loss) outside of finite interaction region

• No other non-acceleration fields (wigglers, bend magnets, …)– Relativistic particle (v ~c) (can be relaxed)– Particle motion in straight line in absence of accelerating field

• Then no linear acceleration is possible (Lawson-Woodward Theorem).

Interaction

Free Space accelerating fields

Particle fields

Collective accelerating fields

Idea of proof

Holds for any superposition of waves

A. Chao online text on beam physics

V

E

Try to ‘get around’ the theorem:

Smooth Waveguide:No diffraction: for long interaction lengthAxial E field (TM-modes)

Bad---quickly dephases.

copper

copper

RF

BEAM

Near field for acceleration- want small bWhat are limits to this?

Self-destructive properties of particle beams, beam qualityThere is always too much of a good thing

“In accelerator jargon,we say that this concept starts to look

iffy.”D. Whittum (Varian)

http://www.slac.stanford.edu/grp/arb/tn/arbvol2/ARDB107.pdf

We will look for better ways to avoid the hypothesis for the theorem

Bend fieldControl the phase velocityLimit the interaction length

Slow wave structuresStanding wave linacsDielectric accelerating structuresPlasma-based accelerators

Dave has nice FEL notes too.

Two-beam accelerators

CLIC

Rk-TBA

Linear acceleration with surface waves

E-field component in direction of particleSlow phase velocity

Finite interaction length:Kicking away particles

B

Kerman/Hartmann

Linear acceleration with dielectrics

copper

Dielectric

Dielectric

copper

Slac pub 8666 (Whittum) also many other groups (this is not a review)

Linear acceleration with dielectrics

copperDielectric

Dielectriccopper

Linear acceleration with dielectrics vph=c

Transverse focusing---Ex is linearSurface field/accelerating field—breakdownNeeds vph=c

From waveguide to….

slow-wave structure

Field has phase velocity ~c and longitudinal component

Closed cavity

http://cas.web.cern.ch/cas/http://uspas.fnal.gov/course-materials/index.shtml

With a mirror:

• Reflect plane wave:

Esarey et at 1995

Novel surface-wave accelerator driven by a high-power CO2 laser

x

z

•Supports w= kc mode can accelerate relativistic particles

•Near field (small gap) attractive ratio Ez/Ex

•Acceleration by surface phonon polaritons (SPP)

SiC/vacuum SPP’s are excitable by a CO2 laser

SiC ε < 0

SiC ε < 0

3 μm

Coupling blues: (a) how do you couple 10.6 μm radiation into a 3 μm hole?? (b) SPP’s group velocity is very small how will they get to the other end??

Shvets and Kalmykov, AAC Conf. Proc. 2004

Vacuum laser acceleration[LEAP E163 SLAC, Colby Talk]

high damage thresholdmaximum couplingsmall beam disruptions(symmetry, smoothness)

Damage ~few J/cm^2, so energy gain~20KeV

Energy exchange between radiation and particles

Particle viewpoint (near field)

Energy balance viewpoint (far field): geometry of interaction must allow for spontaneous emission: the interference of this emission with applied field balances the energy change of particle

Overall energy must be conserved---but how???

The total field energy must be decreased. This can only through the emission of a particleField to inter with the accelerating field.

Only Accelerating fieldParticle moves with constant velocityIs there Linear Acceleration (?)

The energy conservation perspective

Closed Surface A

Field Perspective: Energy Balance

Key points in the derivation

Split the field into various parts

Integrate over time with limits before and after fields have left the interaction region

Fourier Transform the fields

Huang et al 2005; Xie 2004; Zolotorev et al unpublished 2001; Palmer 1995

No Acceleration without Spontaneous Emission

• IFEL• ICARM

Inverse cerenkov• What about plasma-wakefield (Cerenkov in

plasma)—charge must be able to emit a plasma wave if it is accelerated by a wave.

Motion in a plane wave: Nonlinear Acceleration

For particle initially at rest with slow field changes:

Nonlinear Acceleration

no acceleration by plane wave

Ponderomotive push

Stupakov, Zolotorev

Collective Acceleration

Collective Acceleration

• Maxwell Equations (w/w/o sources) for applied fields.• Idea—use the moving fields of a beam or plasma• The concept predates plasma acceleration with lasers,

although beatwave and wakefield accelerators are collective accelerators

• The old ideas have some conceptual similarity with plasma-based ion acceleration

• The old ideas did not work too well. See Sessler’s reviews (http://adsabs.harvard.edu/abs/1982cfac.conf...27S; http://adsabs.harvard.edu/abs/1982AIPC...87..919S).

An old idea: The ERA

• Electron ring accelerator

Ring is unstable—breaks into azimuthal clumps: Negative MassInstabilty

A Stable Ring

Ring is stable for same reason electronring was unstable (Maxwell)

Plasma-based Electron Linac

Broken down medium tolerate(for fs-ps timescales) high E-field

U. Nebraska

Channel has phase velocity ~c, but not so easy to create!

Creation of Accelerating Structures in Plasmas: Femtosecond Engineering

Laser Beatwave

Laser Wakefield

Beatwave

Plasma

Wakefield

Laser or ebeam

Accelerating field

Can also think about counter propagating case

SRS (self-modulated)Timescales set by plasma frequencyLength scale set by skin depth

The realization of collective acceleration:Ion Acceleration in Plasmas

after ?

Main Target (Al)

Contaminants (H2O)

--

--

-

+-

-

- ++

+++

Gitomer et al, 1986

-- --

-

--

-

-

H+

H+

H+

H+

H+

H+

H+

Snavely et al. (2000)Fuchs et al 2005, Allen et al (2005)

Laser:P>10TW

1018 W/cm2

ApplicationsSpallation sourceplasma probefast ignitortherapyhigh energy density physics

Proper heating of target can accelerate heavy ionsSentoku et al. (2003)Hegelich et al. (2002)

Ion and Proton Acceleration

Target properties (curvature, surface treatment, thickness, material)Laser pulse shaping Technology and physics open a new realm of proton/ion acceleration

Target normal sheath accelerationBreakout afterburnerRadiation PressureBasic mechanisms are being explored and invented.

Mechanisms:

Flippo et al

Target shaping

But….

LHC

…how does Naturedo it? Can/should we?

Cosmic Ray Flux

Stochastic Acceleration

• Fields randomly kick particles • Diffusive energy gain (under appropriate

assumptions)• Fermi theory for cosmic rays (complicated and

active area of research). Reflections off of shocks and moving magnetic turning points.

36

“I must confess that one reason we have undertaken this biological work is that we thereby have been able to get financial support for all of the work in the laboratory. As you know, it is much easier to get funds for medical research.”

—Lawrence to Niels Bohr, 1935

Who wants my beam?

Varian Medical Accelerartor (electron, x-ray)PSI Compact Proton Accelerator

37

Who wants your beam? FEL Example

Emittance and energy spread constraints

Six dimensional beam brightness:Conserved (ignoring scattering, nonlinearity/mismatch, CSR, wakefields…)

n

Transverse and longitudinal constraints

Go to board

Electron-positron Colliders

Principle is to understand your applicationrequirements

+constraints on beamstrahlung & background

Slac pub 9914

Concluding Thoughts • Net linear acceleration with a pure vacuum field in free space in the absence of other fields is not possible.

This guides you in inventing new concepts, and in understanding why specific concepts fail or work.• There is no acceleration without spontaneous radiation—a charged particle cannot experience net

acceleration in a system where it will not be able to spontaneously emit photons.• Global energy balance is maintained by the interference of a spontaneously emitted field with an accelerating

field. • Even for a single particle spontaneous emission can set an energy limit. The mass dependence of spontaneous

emission is why high-energy electron colliders are linear, and why a TeV muon collider could be circular. • At high charge collective losses from the accelerated bunch itself must be included. These effects can destroy

the utility of a bunch well before dominating acceleration (e.g., coherent synchrotron radiation in FEL sources).----------------------------• Know the needs of potential users, but do not be a slave to existing technology in envisioning what might be in

the future. Lasers are a great example of technological advances unlocking new physics regimes. • Postdiction is easier than prediction---codes are important but be aware of how you are using them and how

well they perform.• Do not let a theorist ‘prove by intimidation.” Do not immediately believe it when an experimentalist says

something is impossible, has been tried, or is really dumb. Understand why. • Learn to recognize and not engage in hype.• Be careful not to dismiss out of hand someone else’s idea without properly understanding it. You will likely find

yourself right and wrong at times.• Our field uses great technology, is undergoing rapid evolution, and is filled with fun topics—e.g., nonlinear

dynamics, collective motion and instability, fundamentals of radiation emission, particle and nuclear physics, understanding parts of astrophysics, and applications in particle physics, X-ray sources, medicine…

Muon Collider cf. Neutrino Factory

STEVE GEER Accelerator Seminar SLAC 24 March, 2011 40

NEUTRINOFACTORY

MUONCOLLIDER

In present MC baseline design, Front End is same as for NF

The accelerator as seen by… the student:

D. Judd

The accelerator as seen by… The mechanical engineer

D. Judd

The accelerator as seen by… The Electrical Engineer

D. Judd

The accelerator as seen by… the health physicist

The accelerator as seen by… the operator

D. Judd

The accelerator as seen by… the experimentalist

D. Judd

The accelerator as seen by… the lab director

D. Judd

The accelerator as seen by… the funding agency

D. Judd

The accelerator as seen by… the inventor

D. Judd