STFC CLASP Environmental Case Study 2013-2015 Novel Gyrotron Travelling Wave Amplifier for High Power mm-wave Radar Remote Sensing Wenlong He, Craig Donaldson, Liang Zhang, Kevin Ronald, Paul McElhinney, Jason Garner, Colin Whyte, Alan Phelps and Adrian Cross Department of Physics, SUPA-Scottish Universities Physics Alliance University of Strathclyde, Glasgow, G4 0NG, Scotland, UK Duncan Robertson, Robert Hunter and Graham Smith University of St Andrews, SUPA-Scottish Universities Physics Alliance School of Physics & Astronomy, St Andrews, Fife KY16 9SS, Scotland, UK

Introduction Microwave Devices Average or CW Power (kW) 10,000 KLYSTRON FAST WAVE DEVICES 1,000 CFA 100.0 10.0 HELIX TWT CCTWT 1.00 TRIODES 0.10 SOLID STATE EIA, EIO 0.01 MAGNETRON 0.1 1.0 10 100 1000 FREQUENCY (GHz)

Aim of the project To develop a radical new high power amplifier in a mm-wave radar Based on 15 years research at Strathclyde supported by PPARC & STFC PIPPS ST/G003521/1 EPSRC UK Industry (e2v Ltd, TMD Ltd, Elekta Ltd) Gyrotron BWO, (2013) Track record & experience:- 1MW, gyrotron travelling wave amplifier 8GHz to10GHz, (2000) 10kW, gyrotron backward wave oscillator 84GHz to 104GHz, (2013)1 Gyro-travelling wave amplifier (gyro-TWA) offers:- 5X more output power 10X more frequency bandwidth Scalable to higher (sub-mm) frequencies … than existing mm-wave amplifiers 1He W., Donaldson C.R., Zhang L., Ronald K., McElhinney P. and Cross A.W., Phys. Rev. Lett., 110, 165101, (April 2013). Radical: 10 to 50X greater power- bandwidth product

Gyro-TWA Performance Chart 30% efficient & 20% bandwidth 1% bandwidth

Strathclyde Gyro-device 2 key concepts pioneered at Strathclyde:- Helically corrugated interaction region (HCIR) Cusp electron gun HCIR HCIR High power, high frequency, high efficiency Wider frequency tuning range Pure output frequency spectrum Cyclotron Resonance Maser Instability at 2nd harmonic of the electron cyclotron frequency (cheaper) CRM Instability Cusp electron gun Cusp gun Axis-encircling annular electron beam Compatible for CW operation Suitable for energy recovery Better for mode selection (reduced possibility of parasitic modes)

Dispersion diagram Advantages of ideal dispersion w k z Advantages of ideal dispersion Fast wave interaction: high frequency, high power Cyclotron Resonance Maser (CRM) instability: high efficiency Frequency tuneable: with over 20% instantaneous bandwidth Scalable to higher frequencies An ideal dispersion: a constant group velocity in the region of small axial wave-numbers within a broad frequency band

Realization of Favourable Dispersion

Measured Performance of Gyro-BWO (2013) He W., Donaldson C.R., Zhang L., Ronald K., McElhinney P. and Cross A.W., “High Power Wideband Gyrotron Backward Wave Oscillator Operating towards the Terahertz Region” Phys. Rev. Lett., 110, 165101, (April 2013).

HCIR aluminium former manufactured by RAL Gyro-TWA HCIR aluminium former manufactured by RAL CLASP project to demonstrate 94GHz GTWA:- 10% bandwidth kW peak power 2kHz pulse repetition frequency 8% electronic efficiency (50% with depressed collection) For applications in radar (cloud profiling) and magnetic resonance spectroscopy

Gyro-TWA experimental setup Screened box containing: 90 – 96 GHz, 1.5 W Amplifier Paul McElhinney, Craig R. Donaldson, Johannes E. McKay, Liang Zhang, Duncan A. Robertson, Robert I. Hunter, Graham M. Smith, Wenlong He and Adrian W. Cross “An output coupler for a W-band high power wideband gyro-amplifier”, submitted to IEEE Transactions on Antennas & Propagation, (2016).

Amplification signal at 94.5GHz Gyro-TWA (2015) Measured beam properties Amplification signal at 94.5GHz

Environmental Opportunity Clouds strongly affect the earth’s radiation budget but are still little understood Significant role of high altitude cirrus clouds (tenuous clouds of ice particles) Atmospheric climate models require better understanding of clouds Millimetre wavelength cloud profiling radars (CPRs) are optimum tools for probing cloud structure and precipitation Traditional CPRs measure a vertical slice only (zenith or nadir) Desirable to scan 3D cloud volume – requires faster, more powerful CPRs Desirable to improve measurement of cirrus clouds – high altitude ~10-15km, low reflectivity Cirrus reflectivity The gyro-TWA can improve CPR performance Extended range (altitude) Increased sensitivity (cirrus) Faster operation (3D scanning) More data for global climate models

Cloud Profiling (90-96GHz) Understanding the environment, environmental change and human impacts to inform policy Improving the measurement, observation & monitoring of the earth’s hydrological cycle Improved understanding of fresh water distribution, better flood warnings

Project Partners Prof. Robin Hogan, Professor of Atmospheric Physics Dept. of Meterology, University of Reading International expert in cloud physics and the use of CPR Dr Jon Eastment, Head of Chilbolton Group Mr Darcy Ladd, Chilbolton Station Manager STFC RAL Space Department Operate UK’s only 94GHz CPR ‘Galileo’ System design and operation expertise Dr Jonathan Taylor Head of Observations-Based Research, Met Office Studies microphysics and dynamics of cloud systems Facility for Airborne Atmospheric Measurement (FAAM) Lidar verification of CPR

Upgraded Pulsed Power System Programmable trigger signal generator and optical transmitter circuit Controls an e2v CX1535 Thyratron which switches a cable Blumlein pulsed generator Gyro-TWA modulator generates 40kV, 1.5A, 300ns duration pulses with an increase in the pulse repetition frequency from 100Hz to 2kHz

Radar - Characterisation

Radar Setup Enclosure Duncan A. Robertson, Robert I. Hunter, Thomas F. Gallacher, “94 GHz pulsed coherent radar for high power amplifier evaluation” Proc. SPIE 9829, Radar Sensor Technology XX, Apr. 2016, pp. 1-8

Transmit Pulse Generated by Quinstar to drive Gyro-TWA P_out : P_in at 94 GHz P_out : Freq at +8 dBm drive 1.5 W, 200 ns pulse test

Cloud profiling status Screened lab GTWA Beam transport Lens antenna Plane Mirror The mm-wave beam transport & antenna subsystem were designed and constructed for the 2nd floor Colville building Coupling mirrors, low loss oversized waveguide ~7 m to outside wall Dual lens antennas (Tx and Rx) 0.5m diameter Dual plane mirrors outside on platform

Overall Schematic of 94GHz pulsed radar Colville Building Technology and Innovation Centre EPSRC Grant W. He, EP/K011952/1, “Cyrogenic Free Superconducting magnet” will enable the GTWA to be transportable ABP group moved to a new lab in May 2015 -1 ground level of TiC Suitable for cloud profiling radar and magnetic resonance spectroscopy

Radar Experiment Current Status (2016) Integrating radar transceiver with Gyro-TWA Calibrating receiver in the laboratory using a metal sphere radar target Rx Tx Beam dumps Scattering sphere

Conclusion Converted gyro-BWO to gyro-TWA which included new (Strathclyde) W-band pillbox window and input coupler (Corvtech Ltd) Helically corrugated interaction region, (copper deposition, Thomas Keating Ltd) Vacuum compatible output horn with excellent Gaussian mode content that was matched to the mm-wave beam transport system Broadband output window Upgraded high voltage pulsed modulator to increase pulsed repetition frequency from 100Hz to 2kHz (Strathclyde) Achieved kW, Gyro-TWA operation at 94.5GHz (Strathclyde) Designed and built mm-wave beam transport and antenna subsystem (St Andrews) Developed pulsed radar transceiver (St Andrews) Built & characterised pulsed radar transceiver Developed & tested data acquisition system for pulsed radar experiments Currently performing proof-of-principle mm-wave radar characterisation (Joint) Integrating radar transceiver with gyro-TWA Calibrating receiver in the laboratory using a metal sphere radar target

Future Work The ability of gyro-TWA to scale to operate at higher frequencies via the procurement of a cryo-free superconducting magnet, which also makes the amplifier transportable, opens up a number of important applications including Cloud profiling radar 3D mapping of high altitude cirrus clouds High power (kW) pulsed NMR enhancement via Dynamic Nuclear Polarisation increased sensitivity (660) and faster measurements (hours to minutes) Full excitation of electron spin in Electron Paramagnetic Resonance (EPR) spectroscopy systems and the resulting increased sensitivity will impact on the optimisation of highly polarised biomarkers, characterisation of new biomolecules new drugs in the difficult health areas such as neurodegenerative diseases, cancers, infectious diseases new materials for energy storage & conversion, efficient batteries, solar cells, other smart materials/solid state devices and polymers High power, CW operation will enable long range (km), line of sight, high frequency, broadband communication in adverse weather conditions

Thank you! I’d be happy to answer questions. Acknowledgements I would like to thank STFC CLASP Environmental grant for enabling the interaction of key staff with critical expertise Dr Wenlong He, Strathclyde Design authority for gyro-TWA Dr Duncan Robertson, St. Andrews Expertise in mm-wave radar & EPR Dr Liang Zhang, Strathclyde CUSP gun modelling, pulsed power & mm-wave experiments Dr Craig Donaldson, Strathclyde Mm-wave component design, construction & mm-wave experiments Dr Rob Hunter, St. Andrews Expertise in mm-wave radar instrumentation Thank you! I’d be happy to answer questions.