W-band two-dimensional periodic surface lattice for a surface field Cherenkov maser

Efficient, 0.35-THz Overmoded Oscillator Based on a Two-Dimensional Periodic Surface Lattice

“…It has been assumed that the relative permeability is 𝜇 𝑟 =1. The inner radius of the 'effective metadielectric' is smaller than the minimum radius of the 2D-PSL [22] and the surface field protrudes beyond the lattice. The electron beam can therefore intercept and excite the surface field without touching the walls of the structure.…”

“…The cosinusoidal corrugation on the inner cavity wall is defined: 𝑟 = 𝑟 0 + ∆𝑟𝑐𝑜𝑠(𝑘 ̅ 𝑧 𝑧)𝑐𝑜𝑠(𝑚 ̅𝜑) where ∆𝑟 is the corrugation amplitude and 𝑚 ̅ is the number of azimuthal variations. The azimuthal period 𝑑 𝑚 = 2𝜋𝑟 0 𝑚 ̅ ⁄ is constrained by the wave-beam coupling criterion [22] for the low voltage regime 𝑚 ̅ ≤ 2𝜋𝑟 0 𝜆𝛾 ⁄ , where 𝛾 is the relativistic Lorentz factor. The full set of parameters is given in Table I.…”

“…( 1) and Eq. ( 2) [22] which are linked by matching boundary conditions at the corrugated wall. To ensure continuity of the tangential field and impedance matching at the lattice boundary (r=rw) the following constraints apply: 𝐸 𝑧,1 = 𝐸 𝑧,2 ; 𝐻 𝑧,1 = 𝐻 𝑧,2 ; 𝐸 𝜑,1 = 𝐸 𝜑,2 ; 𝐻 𝜑,1 = 𝐻 𝜑,2 .…”

“…Spanning the 'THz gap' using vacuum electronic sources, whilst maintaining HP output, poses significant challenges, namely: (i) the avoidance of RF breakdown, (ii) the provision of adequate cooling and (iii) manufacturing limitations [8] associated with the small cavity dimensions. One promising type of slow-wave device where these difficulties can be resolved by making the interaction cavity diameter D several times the free space operating wavelength 𝜆, whilst introducing a cosinusoidal corrugation at the inner wall, is a surface wave oscillator (SWO) [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. In contrast to standard sources where 𝐷~𝜆, the interaction cavity of the SWO is oversized and therefore highly overmoded.…”

“…We present theoretical, analytical and numerical results for a SWO with a complex, two-dimensional periodic surface lattice (2D-PSL) interaction cavity and demonstrate high-order mode selection, achieved by coupling volume and surface fields to form a hybrid cavity eigenmode. Slow wave devices based on 2D-PSLs have been the subject of intensive research at the University of Strathclyde [9,[22][23][24][31][32][33][34] and also at the Institute of Applied Physics within the Russian Academy of Sciences [12][13][14][15][19][20][21], where a 32.5 GHz 2D SWO driven by a kiloamp, ~300-600 kV relativistic beam was developed [15].…”