Pulse compression ABP Atoms, Beams & Plasmas Compression of Frequency-Modulated Pulses using Helically Corrugated Waveguide S.V. Samsonov, S.V. Mishakin, G.G. Denisov, V.L. Bratman and N.G. Kolganov Institute of Applied Physics, Russian Academy of Sciences, Nizhny Novgorod, , Russia. M. McStravick, A.W.Cross, W.He, K. Ronald, C.G. Whyte, A.D.R. Phelps, I.V. Konoplev, G. Burt, P. MacInnes and A.R. Young SUPA, Department of Physics, University of Strathclyde, Glasgow, G4 0NG, Scotland, U.K.

Pulse compression ABP Compression of frequency-modulated pulses using a helically corrugated waveguide Can be used to generate high-peak-power, short- duration microwave pulses Does not require additional infrastructure beyond the amplifier’s input source requirements: Vacuum pump Power supplies Increased x-ray shielding

Pulse compression ABP In a dispersive medium the group velocity is a function of frequency Sweep-frequency microwave pulse compression in waveguides axial direction in dispersive medium tail of pulse Amplitude of microwave Lower power microwave front of pulse higher power microwave If a pulse is modulated from one frequency to a frequency with a higher group velocity, the pulse will compress

Pulse compression ABP Helically corrugated waveguide Bragg conditions Dispersion curves of a circular waveguide with a helical corrugation m A =2, m B =-1 TE 11 TE 21 The helical corrugation Corrugation couples a counter rotating TE 11 wave with a co- rotating TE 21 wave on a 3-fold helix.

Pulse compression ABP Helically corrugated waveguide Bragg conditions Dispersion curves of a circular waveguide with a helical corrugation m A =2, m B =-1 Operating eigenwave TE 11 TE 21 The helical corrugation Corrugation couples a counter rotating TE 11 wave with a co- rotating TE 21 wave on a 3-fold helix.

Pulse compression ABP Helically corrugated waveguide Bragg conditions Dispersion curves of a circular waveguide with a helical corrugation m A =2, m B =-1 v g1 v g2 Operating eigenwave TE 11 TE 21 The helical corrugation Corrugation couples a counter rotating TE 11 wave with a co- rotating TE 21 wave on a 3-fold helix.

Pulse compression ABP Advantages of a helically corrugated waveguide as compared to a smooth bore waveguide The optimum frequency sweep is from a high frequency to a low frequency  Suitable for use with frequency tuneable BWOs Helically corrugated waveguide can be designed to have a large change in group velocity as function of frequency;  Shorter lengths of waveguide;  Reduced ohmic losses  Results in high energy conversion efficiencies at high powers Operates far from cut-off frequency;  Less prone to reflection of the input signal  Makes it compatible with amplifier technology  TWT  Gyro-TWA

Pulse compression ABP CST Microwave Studio MWS allows dispersion to be calculated without simulating a large number of periods, using periodic boundaries

Pulse compression ABP Dispersion in helically corrugated waveguide Scalar network analyserMethod of perturbations Microwave studio

Pulse compression ABP Group velocity in a helically corrugated waveguide Scalar network analyser Method of perturbation

Pulse compression ABP Experimental set-up of helical waveguide compressor - low power PIN switch Amplifier Low and high-pass filters

Pulse compression ABP Low power experiments with inclusion of amplifier and filters Power compression factor of 18 Input pulseCompressed pulse

Pulse compression ABP Low power experiments with PIN switch Reduced secondary pulses Peak power compression factor of 16 ‘Chopped’ input pulse Compressed pulse

Pulse compression ABP Arbitrary waveform generator and vector signal generator low power measurements Measured peak power in input pulse 4mW Measured peak power in compressed pulse 100mW Peak power pulse compression factor is 25 Input PulseCompressed Pulse

Pulse compression ABP Optimum sweep produced by frequency programmable Agilent Arbitrary Waveform Generator Feed I/Q output to a 40GHz Agilent Vector Signal Generator Used to drive a 7kW X-band TWT amplifier, isolator, directional coupler Microwave signal measured on single shot 12GHz DSO Set-up of compressor experiment using Arbitrary Waveform Generator and Vector Signal Generator with 7kW TWT – high power

Pulse compression ABP High-power TWT results Power compression factor 25 Peak power measurement of 2.73mW Attenuation was 63dB TWT output power into compressor 5.5kW Peak power of compressed pulse measured to be 135kW Energy losses 25%

Pulse compression ABP Future work Year 2 (Present) Construct and assist in the design of a 5-fold helical waveguide CST Microwave Studio modelling of propagation of electromagnetic waves through 5-fold helical waveguide Perform 5-fold compression experiments using Agilent instrumentation and 7kW TWT amplifier

Pulse compression ABP Future work Year 3 Larger diameter 5-fold helical waveguide is needed to compress MW level frequency swept radiation generated by gyro-TWA –Larger diameter prevent RF breakdown Perform frequency swept compression experiments and measure peak power, gain, power and time compression factors and efficiency

Pulse compression ABP Conclusion Optimum faster (up to 30MHz/ns) frequency-modulated pulse produced by the Arbitrary Waveform Generator and Vector Signal Generator resulted in a power compression ratio of 25 with energy losses of 25% Due to its reflection-less properties a helical compressor can be used effectively at the output of a powerful amplifier (TWT), (Gyro-TWA)

Pulse compression ABP Acknowledgements I would like to thank UK Engineering and Physical Sciences Research Council, MoD JGS scheme, Dave Gamble-Dstl and Doug Clunie-Faraday partnership in high power RF, for supporting this work I would like to thank my supervisors; Dr A.W. Cross, Dr W. He and Dr C.G. Whyte and the ABP group The loan of a high power 7kW TWT amplifier by TMD Ltd which was used to carry out these experiments is gratefully acknowledged