1. 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

2. 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)

3. 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, , (April 2013).
Radical: 10 to 50X greater power- bandwidth product

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

5. 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)

6. Dispersion diagram Advantages of ideal dispersionw 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

7. Realization of Favourable Dispersion

8. 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, , (April 2013).

9. 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

10. 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).

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

12. 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

13. 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

14. 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

15. 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

16. Radar - Characterisation

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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.