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PLASMA WAKEFIELD ACCELERATION

PLASMA WAKEFIELD ACCELERATION. Pisin Chen Kavli Institute for Particle Astrophysics and Cosmology Stanford Linear Accelerator Center Stanford University Introduction A Brief History of Plasma Wakefields Plasma Wakefield Excitation by Alfven Shocks Simulations on Alfven Plasma Wakefields

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PLASMA WAKEFIELD ACCELERATION

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  1. PLASMA WAKEFIELD ACCELERATION Pisin Chen Kavli Institute for Particle Astrophysics and Cosmology Stanford Linear Accelerator Center Stanford University • Introduction • A Brief History of Plasma Wakefields • Plasma Wakefield Excitation by Alfven Shocks • Simulations on Alfven Plasma Wakefields • Possible Applications to the Knee? • Summary Workshop on Physics at the end of the Galactic Cosmic Ray Spectrum Aspen, April 26-30, 2005

  2. A Brief History of Plasma Wakefields Motivated by the challenge of high energy physics • Laser driven plasma wakefield acceleration T. Tajima and J. M. Dawson (1979) • Particle-beam driven plasma wakefield accel. P. Chen, J. Dawson, et al. (1984) * Extremely efficient: eE ≥ √ n [cm-3] eV/cm For n=1018 cm-3, eE=100 GeV/m → TeV collider in 10 m! * Plasma wakefield acceleration principle experimentally verified.

  3. Cosmic Acceleration Mechanisms Addressing the Bottom–Up Scenario for Acceleration of Ordinary Particles: • Conventional cosmic acceleration mechanisms encounter limitations: - Fermi acceleration (1949) (= stochastic accel. bouncing off B-fields) - Diffusive shock acceleration (1970’s) (a variant of Fermi mechanism) Limitations for UHE: field strength, diffusive scattering inelastic - Eddington acceleration (= acceleration by photon pressure) Limitation: acceleration diminishes as 1/γ • Examples of new ideas: - Zevatron (= unipolar induction acceleration) (R. Blandford, astro-ph/9906026, June 1999) - Alfven-wave induced wakefield acceleration in relativistic plasma (Chen, Tajima, Takahashi, Phys. Rev. Lett. 89 , 161101 (2002).)

  4. Alfven Wave Induced Wake Field Simulations Work done by K. Reil (SLAC) and R. Sydora (U of Alberta) Dispersion relation for EM waves in magnetized plasma: Simulation parameters for plots: • e+ e- plasma (mi=me) • Zero temperature (Ti=Te=0) • Ωce/ωpe = 1 (normalized magnetic field in the x-direction) • Normalized electron skin depth c/ωpe is 15 cells long • Total system length is 273 c/ωpe • dt=0.1 ωpe -1 and total simulation time is 300 ωpe -1 • Aflven pulse width is about 11 c/ωpe • 10 macroparticles per cell ωpe2= 4πe2n/m Ωc= eB/mc y Ey Simulation geometry: Alfven pulse vA~ 0.2 c x Bz z

  5. Start with a (1D) Plasma in a Boxrmass=2.0

  6. Slowly Grow By and Ez

  7. Particle Velocities Follow

  8. Bz and Ey develop Self Consistently

  9. Wakefield Develops

  10. All Fields “Released”

  11. Traveling

  12. End of Show…

  13. Particle momentum gain from Ex follows pulse Alfven pulse (Bz, Ey) 120 230 c/ωpe 120 230 c/ωpe VA ~ 0.2 c Longitudinal fields created by transverse Alfven pulse 120 230 c/ωpe 120 230 c/ωpe Particle acceleration in the wake of an Alfven pulse

  14. Momentum gain follows pulse Alfven pulse (Bz, Ey) 120 230 c/ωpe 120 230 c/ωpe VA ~ 0.2 c Longitudinal fields created by transverse Alfven pulse 120 230 c/ωpe 120 230 c/ωpe Particle acceleration in the wake of an Alfven pulse (later time)

  15. c/wpe=15 rmass=1 (e-e+plasma) B0/Bperp=10 Width=90 t=10 valf=0.66 Run_6300

  16. c/wpe=15 rmass=1 B0/Bperp=10 Width=90 t=35 valf=0.66 Run_6300

  17. c/wpe=15 rmass=1 B0/Bperp=10 Width=30 t=10 valf=0.66 Run_6302

  18. c/wpe=15 rmass=1 B0/Bperp=10 Width=30 t=35 valf=0.66 Run_6302

  19. c/wpe=15 rmass=1 B0/Bperp=1 Width=30 t=10 valf=0.66 Run_6341

  20. c/wpe=15 rmass=1 B0/Bperp=1 Width=30 t=35 valf=0.66 Run_6341

  21. c/wpe=15 rmass=1 B0/Bperp=1/4 Width=90 t=10 valf=0.9 Run_6344

  22. c/wpe=15 rmass=1 B0/Bperp=1/4 Width=90 t=35 valf=0.9 Run_6344

  23. c/wpe=15 rmass=1 B0/Bperp=1/4 Width=30 t=10 valf=0.9 Run_6345

  24. c/wpe=15 rmass=1 B0/Bperp=1/4 Width=30 t=35 valf=0.9 Run_6344

  25. Possible Applications to the Knee • Is alternative acceleration mechanism necessary? -- Exisitng Diffusive shock acceleration paradigm appears to work well. • But, -- Can Emax go beyond 1017eV? -- What is the mechanism that accelerates e- or e+ to very high energy in order to induce the observed TeV photons?

  26. Pulsar wind nebulae Crab (Weisskopf et al 00) B1509 (Gaensler et al 02) Vela (Pavlov et al 01) Our main source of information about the wind is Pulsar Wind Nebulae in young supernova remnants. Box calorimeter for the wind. shock Properties of pulsar winds: Highly relativistic (~106) upstream, ~c/2 downstream Kinetic energy dominated at the nebula  = B2/(4nmc2) ~10-3 Pole-equator asymmetry and collimation Produce nonthermal particles A. Spitkovsky (2005) v<<c Kennel & Coroniti 84 Rees & Gunn 74 What are pulsar wind properties at the source?

  27. CRAB NEBULA SN1054 Radio Infrared Optical X-ray -ray Synchrotron emission: Lifetime: X-rays -- few years, -rays -- months. Need energy input! Crab pulsar: erg/s, 10-20% efficiency of conversion to radiation. Max particle energy > eV, comparable to pulsar voltage. Nebular shrinkage indicates one accelerating stage: require /s PSR also injects B field into nebula (~10-4 G) <100MeV S   -0.3 (radio);  -1.0 (X-ray) A. Spitkovsky (2005) Radio mystery:lifetime > nebular age. Need /s

  28. Summary • Plasma wakefields induced by Alfven shocks can in pirnciple efficiently accelerate UHECR particles. • Preliminary simulation results support the existence of this mechanism, but more investigation needed. • In addition to GRB, there exist abundant astrophysical sources that carry relativistic plasma outflows/jets. • Its application to CR around the knee is unclear. • Pulsar winds are highly relativistic, and may perhaps serve as the site for such acceleration for e.

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