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# AAC 2012 Tutorial Jonathan Wurtele UCB/LBNL Principles of Acceleration.

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AAC 2012 Tutorial Jonathan 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?" "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 new applications

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 length Axial E field (TM-modes) Bad---quickly dephases. copper RF BEAM Near field for acceleration-  want small b What are limits to this? Self-destructive properties of particle beams, beam quality There 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 field Control the phase velocity Limit the interaction length Slow wave structures Standing wave linacs Dielectric accelerating structures Plasma-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 particle Slow phase velocity

B B Kerman/Hartmann

Linear acceleration with dielectrics copper Dielectric copper Slac pub 8666 (Whittum) also many other groups (this is not a review)

Linear acceleration with dielectrics copper Dielectric copper

Linear acceleration with dielectrics v ph =c Transverse focusing---Ex is linear Surface field/accelerating field—breakdown Needs v ph =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 CO 2 laser x z Supports  = kc mode  can accelerate relativistic particles Near field (small gap)  attractive ratio E z /E x Acceleration by surface phonon polaritons (SPP) SiC/vacuum SPP ’ s are excitable by a CO 2 laser SiC  ε < 0 3  m Coupling blues: (a) how do you couple 10.6  m radiation into a 3  m 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 threshold maximum coupling small 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 particle Field to inter with the accelerating field.

Only Accelerating field Particle moves with constant velocity Is 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

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 Mass Instabilty A Stable Ring Ring is stable for same reason electron ring 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 frequency Length 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+H+ H+H+ H+H+ H+H+ Snavely et al. (2000) Fuchs et al 2005, Allen et al (2005) Laser: P>10TW 10 18 W/cm 2 Applications Spallation source plasma probe fast ignitor therapy high energy density physics Proper heating of target can accelerate heavy ions Sentoku 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 acceleration Breakout afterburner Radiation Pressure Basic mechanisms are being explored and invented. Mechanisms: Flippo et al Target shaping

But…. LHC …how does Nature do 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 application requirements +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 NEUTRINO FACTORY MUON COLLIDER 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

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