ABP Atoms Beams Plasmas Compression of FrequencyModulated Pulses

ABP Atoms, Beams & Plasmas Compression of Frequency-Modulated Pulses using Helically Corrugated Waveguide M. Mc. Stravick, A. W. Cross, W. He, K. Ronald, C. G. Whyte, A. D. R. Phelps, I. V. Konoplev, G. Burt, P. Mac. Innes and A. R. Young SUPA, Department of Physics, University of Strathclyde, Glasgow, G 4 0 NG, Scotland, U. K. 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, 603950, Russia. 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

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

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

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

Helically corrugated waveguide Bragg conditions The helical corrugation m. A=2, m. B=-1 TE 21 TE 11 vg 2 • Corrugation couples a counter rotating TE 11 wave with a corotating TE 21 wave on a 3 -fold helix. Operating eigenwave Dispersion curves of a circular waveguide with a helical corrugation 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 Ø 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; Ø Shorter lengths of waveguide; q Reduced ohmic losses Ø Results in high energy conversion efficiencies at high powers • Operates far from cut-off frequency; Ø Less prone to reflection of the input signal Ø Makes it compatible with amplifier technology q TWT q 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 analyser Method of perturbations Microwave studio Pulse compression ABP

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

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

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

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

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

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

High-power TWT results • Peak power measurement of 2. 73 m. W • Attenuation was 63 d. B • TWT output power into compressor 5. 5 k. W • Peak power of compressed pulse measured to be 135 k. W • Power compression factor 25 • 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 7 k. W 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 30 MHz/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, Mo. D 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 7 k. W TWT amplifier by TMD Ltd which was used to carry out these experiments is gratefully acknowledged Pulse compression ABP