Smith-Purcell Research Articles

The improved point matching method for triangular metal gratings

In this paper, we present the “point matching method” (PMM) adapted for the calculation of Smith–Purcell (SP) radiation parameters in H-polarization, generated by relativistic electron beams (REB) passing close to a triangular metal grating. A truncated expression H d y, n ( N; β, ω) was used in order to find the coefficients H d y, n ( β, ω) in the infinite Rayleigh expansion of the diffracted field of a moving electron. A linear system of 2 N+1 equations was solved, increasing the number N of harmonics until convergence solutions were achieved. When N→∞ then lim N→∞H d y,n(N;β,ω)=H d y,n(β,ω) and the diffracted field can be calculated. SP radiation factors were calculated using the modified PMM for electron energies in 1–30 MeV domain and metal gratings with period length in 1–10 mm range.

Smith–Purcell radiation experiment using a field-emission array cathode

We have recently started an experiment on visible Smith–Purcell (SP) radiation to examine practical applicability of a field-emission array (FEA) cathode to compact free electron lasers, placing emphasis on safe operation of the cathode as well as beam quality. The electron beam was generated by a 5 cm long triode which employed either a single- or double-gated FEA. Accelerating voltages of up to −40 and −100 kV were applied to the cathode by a regulated power supply and a small Van der Graaff generator, respectively. A 25 μA beam of up to 45 keV was routinely produced and a 5 μA 80 keV beam was also attained. The beam passed through a 1 mm wide slit in the anode and grazed the surface of a 2.5 cm long replica grating with a period of either 0.56 or 0.83 μm. The SP radiation has not been identified owing to irrelevant luminescence caused by the beam at the grating. Still it was confirmed that the FEA cathode is adequately durable and electron beams generated therefrom are sufficiently stable to be used for systematic measurements of radiation.

Smith-Purcell radiation emission in aligned nanoparticles

Smith-Purcell (SP) radiation produced by interaction of fast electron beams running parallel to strings of nanoparticles is investigated. Results for the radiation emission probability and electron energy loss spectra using finite and infinite strings of Al and silica spheres are presented. Both of these quantities are obtained by solving Maxwell's equations exactly using a multipole expansion approach. The response of the spheres is described in terms of their local frequency-dependent dielectric functions. In silica, the emission probability is seen to coincide with the energy loss probability within the gap region, where the solid cannot absorb any energy. Large emission rates are predicted for Al, suggesting its possible application in tunable soft uv light generation. The dependence of the emission on the size of the spheres, the string period, and the electron energy is discussed in detail. Finite size effects are also studied for strings of 1-15 Al spheres.

X-ray generation by the Smith-Purcell effect.

Smith-Purcell (S-P) radiation is produced when electrons graze the surface of a grating. Calculations based on the theory of diffraction radiation show that, given severe restrictions on ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$-beam quality, S-P radiation is highly efficient. Efficient S-P x-ray generation requires relativistic ${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ beams having a transverse momentum and dimension whose product approaches the Heisenberg uncertainty limit.