Cherenkov radiation of Josephson vortices and Cherenkov Josephson 
Microwave oscillators for submm range.

V.V. Kurin *, A.V. Yulin *, M.Yu. Levitchev #

* Institute for Physics of Microstructures, Russian Academy of Science, 
Nizhny Novgorod, Russia

# Research Center Juelich, Juelich, Germany

The report is devoted to theoretical development of the concept of 
Cherenkov radiation of Josephson vortices and experimental 
investigation of characteristics of Cherenkov Josephson Flux-Flow 
oscillators with different designs.
Now it is well known that josephson vortex moving in josephson 
transmission line with dispersion can radiate electromagnetc wave 
when cherenkov condition of equality of  soliton velocity to phase 
velocity of the wave is fulfilled [1]. The scheme of Cherenkov 
oscillator contains Long Josephson Junction (LLJ)(or array of LLJ ) 
electrodynamically built in some wave-guide system which provides 
dispersion to make possible fulfilment of Cherenkov condition. 
This wave-guide system may be simple strip line (even passive edges 
of LJJ may take part of it), periodical inhomogeneous strip lines or 
dielectric wave guide system. Besides, the Cherenkov radiation of 
vortices is possible in 2D Josephson Junctions [2,3]. Due to volume 
nature of interaction between vortices and electromagnetic waves the 
use of Cherenkov radiation will help to improve characteristics of 
existing types of josephson oscillators i.e. expand their frequency 
range and output power, make narrower spectral width of radiation.
Cherenkov oscillators based on single 1D linear and annular LJJ built 
in strip-line with periodical varied width were experimentally tested.
 Some preliminary results regarding these designs of Cherenkov 
oscillators were published earlier [4,5].
I-V curves for external magnetic field applied were measured and 
electromagnetic radiation at the frequency range 80-120 GHz were 
registered by the room-temperature receiver. The new band structure 
of Fiske steps corresponding to band spectrum of eigenmodes of 
periodical transmission line was found and strong radiation with 
frequency and bandwidth depending on biasing current was observed. 
Experimental results are in a good agreement with theoretical 
predictions and simulation. New design of Cherenkov oscillators based 
on parallel array of several LLJs integrated into the only strip-line 
was suggested and preliminary experiments were carried out.


References
 
1. V.V. Kurin, A.V. Yulin, Radiation of Linear Waves by Solitons in a 
Josephson Transmission Line with Dispersion, 
Phys.Rev. B, 55, 9, 11659, (1997)
2. V.V. Kurin, A.V.  Yulin, I.A.  Shereshevskii, and N.K. Vdovicheva,
Cherenkov Radiation of Vortices in a Two-dimensional Annular Josephson
junction, Phys.Rev.Lett, 80, 15, 3372, (1998)
3. A. Wallraff, A. Ustinov, V. Kurin, I. Shereshevsky, N.  Vdovicheva,
Observation of whispering gallery resonances in annular Josephson
junction, Phys.Rev.Lett., v.84, n.1, 151, (2000)
4. V. Kurin, A. Yulin, E. Goldobin, A.  Klushin, H. Kolstedt, 
M. Levichev, and N. Thyssen, Experimental investigation of Cherenkov 
Flux-Flow Oscillators, IEEE transaction on Applied Superconductivity,
9, 2, 3733, 1999
5. A.V. Baryshev, A.V. Yulin, V.V. Kurin, V.P. Koshelets, S.V. Shitov,
A.V. Shchukin, P.N. Dmitriev, and L.V.  Fillipenko, Design and 
Fabrication of Cherenkov Flux-Flow Oscillator, IEEE transaction on 
Applied Superconductivity, 9, 2, 3737, 1999