Compression of pulses from a relativistic bwo using helically corrugated waveguides

The use of an overmoded circular waveguide with helical corrugations (HC) of its inner surface as a dispersive medium enables compression of monotonously frequency modulated microwave pulses. The region of operating parameters (frequency range, input pulse duration, sweep interval) in conjunction with low reflection and high RF electric strength makes the HC-waveguide compressor attractive for increasing the peak power from relativistic non-resonant electron devices such as BWOs up to an extremely high power level. The principle of BWO operation allows for sufficiently broadband smooth frequency tuning by varying the accelerating voltage so that frequency-swept pulses at GW powers can be produced. A higher-order mode compressor waveguide having sufficient power handling capabilities was designed and tested at low and GW powers. The waveguide has a 5-fold HC coupling TE_2,2 and TE_3,1 modes. The designed BWO was tested at the IAP using SINUS-6 high-current accelerator. Due to special arrangement of a coaxial diode, a voltage drop from 600 kV to 400 kV with a beam current of 4-5 kA during about 15 ns was achieved resulting in BWO output signal with a power of about 0.6 GW with a frequency sweep from 10 GHz down to 9.6 GHz. The use of an HC-waveguide compressor of about 0.6 m in length with appropriate mode converters in front of the BWO resulted in the pulse compression with the peak power increase up to 1.8 GW. The simulations show that an increase in length of the HC waveguide by another 0.4 m may result in additional power increase up to 3-3.5 GW which is expected to be realized in the next few months.