ABP Research Seminar Adams Institute Glasgow, G4 0NG, UK - - PowerPoint PPT Presentation

Research Progress at Strathclyde Research Progress at Strathclyde relevant to Accelerators relevant to Accelerators Alan Phelps Alan Phelps

A.W. Cross, K. Ronald, C.G. Whyte, A.R. Young, W. He, I.V. Konoplev, A.W. Cross, K. Ronald, C.G. Whyte, A.R. Young, W. He, I.V. Konoplev,

• D. Barclay, H. Yin, C.W. Robertson, D.C. Speirs, C.R. Donaldson, P

.

• D. Barclay, H. Yin, C.W. Robertson, D.C. Speirs, C.R. Donaldson, P

. MacInnes, MacInnes, S.L. McConville, K.M. Gillespie, L. Fisher, F . Li, M. McStravick, L. Zhang, S.L. McConville, K.M. Gillespie, L. Fisher, F . Li, M. McStravick, L. Zhang,

• D. Constable, D. Bowes, K.A. Matheson, R. Bryson, M. King, P

.

• D. Constable, D. Bowes, K.A. Matheson, R. Bryson, M. King, P

. McElhinney McElhinney Department of Physics, SUPA, University of Strathclyde, Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, UK Glasgow, G4 0NG, UK

ABP

Research Seminar Adams Institute 17 June 2010 Oxford University

Introduction Introduction

• Strathclyde research group overview

Strathclyde research group overview

• SUPA

SUPA

• Strathclyde research

Strathclyde research High power microwave sources High power microwave sources Examples of modelling and experiments Examples of modelling and experiments

• Conclusions

Conclusions

Strathclyde research group overview Strathclyde research group overview

500km

Strathclyde research group overview Strathclyde research group overview

Strathclyde University Campus Physics Department

Strathclyde research group overview Strathclyde research group overview

• University of Strathclyde ~ 17,000 students

University of Strathclyde ~ 17,000 students

• Physics Department one of 8 within SUPA

Physics Department one of 8 within SUPA

• SUPA graduate school ~ 400 PhD students

SUPA graduate school ~ 400 PhD students

• Microwave & MM-wave research (~ 30 people)

Microwave & MM-wave research (~ 30 people)

Scottish Universities Physics Alliance (SUPA) Members

Aberdeen Dundee St Andrews Edinburgh Heriot Watt Glasgow Strathclyde West of Scotland

Research Themes in SUPA Research Themes in SUPA

• Nuclear and plasma physics

Nuclear and plasma physics

• Particle physics

Particle physics

• Condensed matter & materials

Condensed matter & materials

• Photonics

Photonics

• Astronomy and astrophysics

Astronomy and astrophysics

• Physics applied to the life sciences

Physics applied to the life sciences

• Energy

Energy

Physics Dept

Nano- science Optics Plasma

Biomolecular & Chemical Physics (BCP)

Semiconductor

Spectroscopy & Devices (SSD) Photonics Computational Nonlinear and Quantum Optics (CNQO)

Atoms Beams & Plasmas

Laser- plasma-nuclear

• Cathodes
• Field emission: FEA

Field emission: FEA

• Explosive/plasma flare: Metal & Velvet

Explosive/plasma flare: Metal & Velvet

• Thermionic

Thermionic

• Pseudospark

Pseudospark

• Gun structures
• Pierce, MIG, CUSP
• Coherent h

Coherent high power mm-wave generation

• Slow wave: Dielectric Cherenkov, Cherenkov BWO
• Fast wave: FEL, Gyrotron, CARM, Gyro-TWAs Gyro-

BWOs, Superradiance (CRM & Cherenkov)

Strathclyde research group overview Strathclyde research group overview

Examples of Strathclyde work on high power Examples of Strathclyde work on high power vacuum electronic mm-wave devices vacuum electronic mm-wave devices

• Modelling – using MAGIC, KARAT, SURETRAJ,

Modelling – using MAGIC, KARAT, SURETRAJ, OPERA, MICROWAVE STUDIO, COMSOL, VORPAL OPERA, MICROWAVE STUDIO, COMSOL, VORPAL

• Electron beam research using thermionic, plasma flare,

Electron beam research using thermionic, plasma flare, field emission array and pseudospark cathodes field emission array and pseudospark cathodes

• Design, construction and measuring output of high

Design, construction and measuring output of high power mm-wave vacuum electronic devices. Includes power mm-wave vacuum electronic devices. Includes research, design and construction of couplers, cavities, research, design and construction of couplers, cavities, converters, collectors and windows converters, collectors and windows

• (i) high power mm-wave diagnostics

(i) high power mm-wave diagnostics (ii) power supplies to drive the devices (ii) power supplies to drive the devices

Several different types of electron sources Several different types of electron sources

MM-wave gyrotron driven by a field emission array (FEA) electron gun Physical Review Letters 77, 2320-2323, 1996

MM-wave gyrotron driven by a field emission array electron gun

Plasma flare cathodes

Mm-wave sources using a pseudospark generated electron beam Mm-wave sources using a pseudospark generated electron beam

8

• 30
• 25
• 20
• 15
• 10
• 5

5 10 15 20

• 10

40 90 140 T ime [ns] Discharge Voltage [kV]

• 1200
• 1000
• 800
• 600
• 400
• 200

200 400 600 800 Current [A] Discharge Voltage Discharge Current Beam Current by Rogowski Coil Beam Current by Faraday cup after T ungsten M

Cherenkov maser using high brightness electron beam from pseudospark source

H ollow catho d e A no d e E lectro n beam D ielectric (alum ina) W aveguid e M icrow ave L aun ch in g ho rn S oleno id

Experimental setup of the 14-gap PS powered by a cable pulser and beam-wave interaction investigation

BWO Interaction Region

W-band (75 to 110)GHz Ka-band (26.5 to 40)GHz

Advantages: a) compactness (table-top size); b) simplicity (no B-field); c) flexibility; d) PRF operation W-band Aluminium positive former

• Constructed in University Strathclyde
• Copper is deposited
• Aluminium dissolved in alkali solution

Time-correlated electron beam pulse (green) microwave pulse (red) and applied voltage pulse (blue)

W-band (75-110 GHz) BWO

• 200
• 150
• 100
• 50

50 100 150 200 250

• 100
• 50

50 100 150 200 Time (ns) Voltage (kV)

• 80
• 60
• 40
• 20

20 40 60 80 100 Microwave (mV) Current (A) Applied voltage Beam current Microwave pulse

1mm Aperture, 2 Disk, 10k

• 2

2 4 6 8 10 12

• 178
• 58

62 182 302 Time (ns) Voltage (-kV)

• 1
• 0.5

0.5 1 1.5 2 2.5 3 3.5 4 4.5 Beam Current (A) Voltage Beam Curren

1 mm aperture single gap pseudospark 1 mm aperture single gap pseudospark beam measurements beam measurements M Measured small size (1 mm) beam easured small size (1 mm) beam

Comparison of four types of electron beam source

206 GHz four cavity klystron 206 GHz four cavity klystron

37 GHz Free Electron Laser

Millimetre-wave free electron laser Millimetre-wave free electron laser

37 GHz Free Electron Laser

Model and basic equations of 2D Bragg FEL

• The 2D Bragg corrugation of the

waveguide surface can be defined as: ) cos( ) cos( ) , (

1 ,

ϕ ϕ

m z k a R z r

z

• ut

in

+ =

• EM field can be represented by four

partial waves:

z z

ik z ik z iM iM +

• +
• E

A e A e + B e B e

ϕ ϕ ﾢ − −

= + + r r r r r

• Schematic diagram of two-mirror 2D-1D

FEM interaction region

M m k k k

z z z

= ≅ ′ =

,

M is the number of field variations along azimuthal co-ordinate ϕ . The partial waves A± propagate in ± z direction and B± are near cut-off

• waves. The waves are coupled on the

corrugation if the following conditions are satisfied

• Schematic diagram of 2D distributed

feedback circle

A± B±

k+ k-

B± A± B± A± A± A± B± B±

Physical Review Letters 96, art 035002, 2006

The FEL cavity configuration

Active length 860 mm

Schematic diagram of inner conductor with the corrugated structures (a) 2D-2D (b) 2D-1D

(a) 2D-2D (b) 2D-1D

Photograph of inner conductor

Measurements of 1D and 2D Bragg structures

Frequency [GHz]

• 10
• 20
• 30

35 36 37 38 39

40

TEM↔TEM α≈ 0.08

TEM↔TM01 α≈ 0.11

[dB] Millimetre wave transmission through the 1D Bragg structure of length lz =30 cm

35 36 37 38 39 40

• 10
• 20
• 30

Frequency [GHz] [dB ] Millimetre wave transmission through the 2D Bragg structure of length lz =4.8 cm α≈ 0.12

Co-axial 2D Bragg mirror

• constructed by machining

square chessboard corrugations

• n the outer surface of the inner

conductor

0.2 0.4 0.6 0.8 1 75 80 85 90 95 100 105

Ez Bz

The spectra of a 7ns pump pulse at the input of the structure (thin line) and longitudinal electric fields (solid line) measured on the cavity’s axis in the time frame (10ns – 30ns) having length 4.8 cm. The spikes are associated with cavity eigenmodes having radial indices l=6 and l=7. The contour plots of the longitudinal electric (Ez) and magnetic (Bz) components of the field inside the cavity observed using the 3D code MAGIC.

S

Pulsed power systems that drive Pulsed power systems that drive the 600 MW electron beam the 600 MW electron beam

Assembly of the Marx pulsed power supply and the transmission line Connection of the transmission line to the diode cathode via pressurised spark gap and matching resistors

The FEL experiment

FEL apparatus to produce mm-waves

• co-axial output horn and Mylar window of diameter 0.2m
• matching resistors for capacitor bank powering solenoid
• ignitron switch and fibre optic controlled trigger unit
• solenoid of length 2.55m, diameter 0.3m with undulator inside
• 3D X-ray shielded enclosure

0.5 1 36 36.5 37 37.5 38

Srf

f (GHz)

Measured spectrum of the output radiation from the FEL 60 MW at 37.2 GHz

Heterodyne Frequency Diagnostics

High power mm-wave amplifiers High power mm-wave amplifiers

• High power broadband mm-wave

High power broadband mm-wave amplifiers are generally more difficult amplifiers are generally more difficult to achieve than the single frequency to achieve than the single frequency mm-wave oscillators mm-wave oscillators

• A solution Strathclyde has been

A solution Strathclyde has been working on is the helical waveguide working on is the helical waveguide gyro-TWA (a type of gyro-TWT) gyro-TWA (a type of gyro-TWT)

Where s is an integer, ωc is the cyclotron frequency and ωco is the cut-off frequency of the waveguide.

e c

m eB ere wh γ = ω

2 / 1 2 2

) c v 1 (

−

− = γ

Use of dispersion graphs to design new RF sources

Use of dispersion graphs to design new RF sources

Ideal dispersion can be realized by using a helically corrugated interaction waveguide It changes the dispersion diagram such that an eigenwave of a constant group velocity (Vg=Vb) exists in the near-infinite phase velocity region (kz=0) for a very wide frequency band. k

z

Conventional Gyro-TWT

ω

Ideal Gyro-amplifier dispersion

ω kz

High power mm-wave amplifiers High power mm-wave amplifiers

Synthesis of Ideal mode to create new sources

Gyro -TWA amplifier schematic Gyro -TWA amplifier schematic

Kicker Helical waveguide with tapers Main solenoid

High power mm-wave amplifiers High power mm-wave amplifiers

Physical Review Letters 81, 5680-5683, 1998 Physical Review Letters 84, 2746-2749, 2000 Physical Review Letters 92, art 118301, 2004

Modelling of a cusp gun for 390GHz gyrotron Modelling of a cusp gun for 390GHz gyrotron

Cusp gun

• Axis-encircling,

annular electron beam

• Better for energy recovery

& mode selection

• Measurement agrees

with simulation: 40kV 1.5A

Wideband W-band gyro-device Wideband W-band gyro-device

Helical interaction waveguide

• High power, high frequency, high efficiency
• Wide frequency band

W-b a n d Gy ro

• BWO Dis

p e rs io n d ia g ra m

7 5 8 5 9 5 1 5 1 1 5

• 1
• 5

5 1

Wa ve num be r [1 /m ] Fre que nc y [GHz ]

Wave A Wave B Beam W1 W1 Measured Magic W

• b

a n d Gy ro

• TW

A D is p e rs io n D ia g ra m

70 80 90 100 110

• 10
• 5

5 10

Wa v e n u m b e r (1 /cm ) Fre q u e n cy (GHz

Magic TE21 TE11 W1 e-beam

Predicted Performance Predicted Performance

Gyro-BWO Gyro-BWO

Centre freq. ≈ 94 GHz Tuning range ≈ 20% Maximum power ≈ 10 kW Efficiency ≈ 15% Centre freq. ≈ 95 GHz

• Freq. bandwidth ≈ 10%

Maximum power ≈ 10 kW Efficiency ≈ 15% Gain = 40dB

S aturate d pow e r and gain

2 4 6 8 1 0 9 0 9 2 9 4 9 6 9 8 1 0 0

F re q (G H Power (kW)

2 5 2 8 3 1 3 4 3 7 4 0

Gain (dB) P ower (k W ) G ain (dB

Gyro-TWA Gyro-TWA

390 GHz Harmonic Gyrotron 390 GHz Harmonic Gyrotron

Design and simulation of a CW source based on a Design and simulation of a CW source based on a cusp gun and working at the 7 cusp gun and working at the 7th

th harmonic number

harmonic number

390 GHz 7th harmonic at TE71 mode

Growth rate at 7th harmonic resonance

Cavity & Cold Test Cavity & Cold Test

Cavity designed

& manufactured

Average Losses:

Spark Erosion:

• 0.5 dB

Drilled Cavity

• 3.1 dB

Cold tested with 300-500 GHz VNA

Co-harmonic gyrotron using a Co-harmonic gyrotron using a novel corrugated cavity novel corrugated cavity

Mean radius, r Mean radius, r0

0 = 8 mm

= 8 mm Corrugation depth, l = 0.7 mm Corrugation depth, l = 0.7 mm Length, L = 39 mm Length, L = 39 mm Modes excited: Modes excited:

2 2nd

nd harmonic, TE

harmonic, TE2,2

2,2 (37.5 GHz)

(37.5 GHz) 4th harmonic, TE 4th harmonic, TE4,3

4,3 (69.7 GHz & 75 GHz)

(69.7 GHz & 75 GHz)

Suggested beam parameters: Suggested beam parameters:

Beam voltage, 60 kV Beam voltage, 60 kV Beam current, 5 A Beam current, 5 A Pitch angle, 45 degrees Pitch angle, 45 degrees Magnetic field, 0.7 T Magnetic field, 0.7 T Axis-encircling beam Axis-encircling beam

( ) ( )

sin 8 r r l φ φ = +

Advantages of depressed collector

• Improve the overall tube efficiency
• Decrease cooling requirement
• Decrease x-ray emission

Depressed collector

collected beam

• utput
• verall

P P P − = η

Depressed collector research

Depressed Collector Simulation Depressed Collector Simulation

Simulation uses 3D PIC code MAGIC Genetic algorithm used to optimize geometry Effect of secondary electrons, including true secondary electrons and rediffused electrons Heat power density distribution on electrodes Simulation of X-band Gyro-BWO and W-band Gyro-BWO

• L. Zhang, et al, IEEE Trans. Plasma Sci.,

37, 390-394, 2009

• L. Zhang, et al, IEEE Trans. Plasma Sci.,

37, 2328-2334, 2009

Primary True secondary

Rediffused

SUPA II project to apply plasma-based accelerators

Auroral Kilometric Radiation - AKR Auroral Kilometric Radiation - AKR

Aurora Borealis – Northern Lights

Planetary Magnetospheres Planetary Magnetospheres

Planetary Aurora

Animation courtesy of NASA

Jupiter’s aurora

Solar wind electron beams Radio emission region

All solar system planets with strong magnetic fields (Jupiter, Saturn, Uranus, Neptune, and Earth) also produce intense radio emission – with frequencies close to the cyclotron frequency.

Natural radiation sources – formation of an Natural radiation sources – formation of an electron horseshoe distribution electron horseshoe distribution

(a) Electron beam enters increasing axial magnetic field (a) Electron beam enters increasing axial magnetic field (b) Electrons gain transverse velocity at the expense of axial velocity. (b) Electrons gain transverse velocity at the expense of axial velocity. (c) Beam distribution function develops horseshoe-like profile. (c) Beam distribution function develops horseshoe-like profile.

• positive gradient

positive gradient in in transverse velocity transverse velocity near the tip of the distribution. near the tip of the distribution.

1

0 = z z B

B 8

0 = z z B

B 17

0 = z z B

B

30

0 = z z B

B

ve v f

+ = ∂ ∂

⊥

ve v f

+ = ∂ ∂

⊥

v⊥ v



v



v⊥ v⊥ v 

B

AURORAL KILOMETRIC RADIATION

THE AURORAL DENSITY CAVITY

VISIBLE AURORA

IONOSPHERE

AURORAL ELECTRON FLUX

Bz

Bz0

B

CATHODE ELECTRON BEAM

LABORATORY EXPERIMENT TERRESTRIAL AURORAL PROCESS

AKR Strathclyde Laboratory Experiment AKR Strathclyde Laboratory Experiment

Solenoid 1 Solenoid 2 Solenoids 3,4,5 and 6

• 4 0
• 2 0

2 0 4 0 6 0 8 0 1 0 0 1 2 0 2 4 6 8 10 1 2 14

F re q u e n c y (G

R e l a t i v e a m p l i t u d e ( d B )

Frequency (GHz)

Measured RF spectrum

Conclusions Conclusions

• Particle-wave interaction synergy of sources & accelerators

Particle-wave interaction synergy of sources & accelerators

• High power mm-wave oscillators achieving MWs

High power mm-wave oscillators achieving MWs

• High power mm-wave amplifiers – novel solutions

High power mm-wave amplifiers – novel solutions

• MM-wave research moving into THz range

MM-wave research moving into THz range

• Microwave/RF ultra-high power sources ~1GHz

Microwave/RF ultra-high power sources ~1GHz

• Laser plasma accelerators for applications

Laser plasma accelerators for applications

Acknowledgements Acknowledgements

Support from EPSRC, STFC, RSE, RS, EU, Dstl, The Faraday Partnership, e2v & TMD