Principles of Acceleration AAC 2012 Tutorial Jonathan Wurtele UCB/LBNL
LULI How Accelerators Work • Electric fields accelerate particles • Magnetic and electric fields focus and deflect particles "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 Troubles….how to get to the next collider? The problem was realized in 1982, but the solution is elusive. Always look for new applications From Katsouleas and Joshi, Physics Today
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 Collective accelerating fields Particle fields
E Idea of proof V Holds for anysuperposition of waves Chao online text on beam physics
Try to ‘get around’ the theorem: copper BEAM Smooth Waveguide: No diffraction: for long interaction length Axial E field (TM-modes) RF copper Bad---quickly dephases. 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
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 copper Dielectric Dielectric copper
Linear acceleration with dielectrics vph=c Transverse focusing---Ex is linear Surface field/accelerating field—breakdown Needs vph=c
From waveguide to…. Closed cavity slow-wave structure http://cas.web.cern.ch/cas/ http://uspas.fnal.gov/course-materials/index.shtml Field has phase velocity ~c and longitudinal component
With a mirror: • Reflect plane wave: Esarey et at 1995
SiC ε< 0 SiC ε < 0 Novel surface-wave accelerator driven by a high-power CO2 laser x •Supports w= kc mode can accelerate relativistic particles •Near field (small gap) attractive ratio Ez/Ex •Acceleration by surface phonon polaritons (SPP) 3 μm z SiC/vacuum SPP’s are excitable by a CO2 laser 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 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) 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. 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
Field Perspective: Energy Balance Only Accelerating field Particle moves with constant velocity Is there Linear Acceleration (?) The energy conservation perspective Closed Surface A
Key points in the derivation Integrate over time with limits before and after fields have left the interaction region Split the field into various parts Fourier Transform the fields Huang et al 2005; Xie 2004; Zolotorev et al unpublished 2001; Palmer 1995
No Acceleration without Spontaneous Emission • IFEL • ICARMInverse 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:
Ponderomotive push Nonlinear Acceleration no acceleration by plane wave 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’sreviews (http://adsabs.harvard.edu/abs/1982cfac.conf...27S; http://adsabs.harvard.edu/abs/1982AIPC...87..919S).
An old idea: The ERA • Electron ring accelerator A Stable Ring Ring is stable for same reason electron ring was unstable (Maxwell) Ring is unstable—breaks into azimuthal clumps: Negative Mass Instabilty
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!
Wakefield Beatwave Creation of Accelerating Structures in Plasmas: Femtosecond Engineering Laser Beatwave Laser or ebeam Plasma Can also think about counter propagating case Accelerating field Laser Wakefield SRS (self-modulated) Timescales set by plasma frequency Length scale set by skin depth
The realization of collective acceleration:Ion Acceleration in Plasmas Applications Spallation source plasma probe fast ignitor therapy high energy density physics Contaminants (H2O) - - - - H+ Laser: P>10TW 1018 W/cm2 + + - H+ - - + H+ - - H+ - H+ - + - + H+ - - + - H+ - - Snavely et al. (2000) Fuchs et al 2005, Allen et al (2005) Gitomer et al, 1986 Main Target (Al) Proper heating of target can accelerate heavy ions Sentoku et al. (2003) Hegelich et al. (2002) after ?
Ion and Proton Acceleration Target shaping Mechanisms: Target normal sheath acceleration Breakout afterburner Radiation Pressure Basic mechanisms are being explored and invented. Target properties (curvature, surface treatment, thickness, material) Laser pulse shaping Technology and physics open a new realm of proton/ion acceleration Flippo et al
Cosmic Ray Flux But…. …how does Nature do it? Can/should we? LHC
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.
“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
Who wants your beam? FEL Example Emittance and energy spread constraints Transverse and longitudinal constraints Six dimensional beam brightness: Conserved (ignoring scattering, nonlinearity/mismatch, CSR, wakefields…) Go to board n
Electron-positron Colliders Slac pub 9914 Principle is to understand your application requirements +constraints on beamstrahlung& background
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 TeVmuon 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 NEUTRINOFACTORY MUONCOLLIDER In present MC baseline design, Front End is same as for NF Accelerator Seminar SLAC 24 March, 2011