Laser wake field acceleration using nano-particles Laser wake field acceleration using nano-particles Department of Physics and Photon Science, Gwangju Institute of Science and Technology Gwangju, Republic of Korea MyungHoon Cho V.B. Pathak, H. T. Kim, Kazuhisa Nakajima, and C.H. Nam th East-Asia School and Workshop on Laboratory, Space, Astrophysical Plasmas In PoHang, Korea

Contents Introduction A New injection method Conclusion Mechanism Model 3D Simulations Electron trapping method

Introduction – laser wake field accelerator 1) Comparison with conventional Cavity method 2) Electron bubble in plasma Laser Wake field

Introduction – Self-injection 1) When the bubble is stationary Trapping condition : It is hard to satisfy ‘trapping condition’ for low plasma density. Kostyukov el al PRL 103,175003(2009) 2) When the bubble is non-stationary Kalmykov el al PRL 103, (2009) Injection is done by ‘bubble expansion’.

Introduction – Injection ponderomotive potential by the laser bubble potential 1) non-trapping 2) self-injection (bubble expansion) 3) controlled injection (artificial)

Introduction – controlled injection 1) Using 2 pulses J.Faure et al nature 444, 737 (2006) a) Colliding M.Zeng et al PRL 114, (2015) b) Copropagating 2 color 2) Using density transition b) Gas jet & capillary a) Sharp density gradient A.J.Gonsalves et al nature phys. 7, 862 (2011) H.Suk et al PRL 86, 1011 (2001) 3) Using B field J.Vieira et al PRL 106, (2011) 4) ionization injection It lowers the trapping barrier, but it is not easy to setup for experiments. A.Pak et al PRL 104, (2010)

A new injection method – Using nano- particle 2) Laser scattering by nano-particle is ignorable.  Wake field is same in both of cases with and without nano-particle. 3) Nano-particle becomes a plus charged sphere forming an electric field. 4) Nano-particle drives electron injection.

Mechanism 1)Electron approaches to nano-particle. Nano-particle generates electric field. 2) Electron goes back to back of bubble. During turning locus, electron gain momentums. 3)Electron meets again nano-particle field. But just passing through without momentum gain.

Model 1)Applying a electric field of charged sphere.

Model 2) Electron motion is 1D or longitudinal.  1D Hamiltonian. 3) Equations of motion well predict the trapping. 4) We derived the trapping threshold for 1D based on stationary bubble. nano- particle

3D simulation – position and density nano-particle position (y)

3D simulation – position and density 1)Depending on position Maximum position for longitudinal injection ※ Case of 3 nano-particles y R nano-particle

3D simulation – position and density 2) Depending on nano-particle density

3D simulation – for a practical example 2) After 1.5mm acceleration, energy=167MeV and energy spread=3%. laser

Conclusion 1.We demonstrated a new injection scheme using nano-particles. 2.The electric field of nano-particle plays a momentum booster of electrons,which follows 1D longitudinal motion. 3.Our 1D model well predicts trapping comparing with 3D PIC simulation. 4.For a practical proposal, we showed various simulations with parameters of position, density and collection of nano-particles.

Add. Aerodynamic focusing lens Aerosol Science and Technology, 39:624–636, 2005 Xiaoliang Wang at al