1 Structured Electron Beams from Nano-engineered CathodesA. Lueangaramwong1, D. Mihalcea1, G. Andonian2, and P. Piot1,2 1 Department of Physics, Northern Illinois University 2 Radiabeam Technologies LLC 3 Fermi National Accelerator Laboratory 17th Advanced Accelerator Concepts Workshop, National Harbor, MD, August, 2016
2 Introduction/MotivationStructured cathodes: cathodes with nano-engineered surfaces → photo or field emission
3 Examples of structured cathodes[ Courtesy from C. Buzzard, NIU] [ R. Li et al., Phys. Rev. Lett. 110, (2013)] [ Radiabeam Technolgies LLC]
4 Simulation of early dynamicsWARP simulation 1 Laser propagating (EM solver)/DC field (ES solver) 2 Multi-photoemission (EM) and Field emission (EM+ES) 3 Output : Beam profiles, Number of charges 4 Analysis 5 Sent to other (fast) tracking programs
5 WARP simulation ES solver: finds static field close to the cathodeEM solver: pro- pagates laser and track macro- particle (PIC) Distribution re- corded 100-nm from cathode.
6 Emission in WARP New emission models implementedFowler-Nordheim's (F-N) law Fowler-Dubridge's (F-D) law
7 Results Plasmonic effect observed (enhanced absorption at resonant wavelength) Field enhancement Distribution for 3-photon emission [A. Seymour et al. AAC2014]
8 [ R. Li et al., Phys. Rev. Lett. 110, 074801 (2013)]Multi beam Practical cathodes → array of beamlets. Run WARP simulation with microparticles. Randomly sample microparticle distribution. build different statistical realization of the distribution at 100-nm from the cathode. Arrange these distributions following the desired array configuration. Injected in a fast PIC code (ASTRA) and track though a given accelerator beamline. Next thing we should do is to consider it analytically [ R. Li et al., Phys. Rev. Lett. 110, (2013)]
9 Multibeam beam ParametersEmittance and Courant-Snyder parameters 1x1 structure M. J. Rhee and K. A. Boulais, “Root-mean-square emittance of multiple beam systems,” Phys. Fluids B 3, 1781 (1991). geometry, pattern, boundary Ex. Focusing condition
10 Structured electron beamsExample : beamlets with rectangular array and hexagonal close packed structure, driven by Gaussian laser pulse distribution Rectangular array triggered by flat top Laser beam size on cathode Example : Unweighted beamlets emitted in rectangular area -> array Cathode with flat top laser
11 Tracking in an RF gun Use WARP-generated in ASTRA:Preserved emittance of a single nanohole segmented beam from an array of 121 holes WARP from cathode ASTRA m from cathode ASTRA
12 Conclusion Engineered cathodes at the nano-scale WARPenhancing quantum efficiency via surface-plasmon excitation, forming ultra-low-emittance beam, or producing structured electron beams. WARP Numerical results of the beam dynamics associated to the cathode in the weak and strong field regimes. Possible applications of some of the achievable cathode patterns when coupled with other phase space manipulations.
13 Thank you for your kind attention