1. Structured Electron Beams from Nano-engineered Cathodes
A. 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/Motivation
Structured 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 dynamics
WARP 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 cathode
EM solver: pro- pagates laser and track macro- particle (PIC)
Distribution re- corded 100-nm from cathode.

6. Emission in WARP New emission models implemented
Fowler-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 Parameters
Emittance 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 beams
Example : 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 WARP
enhancing 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