research progress at strathclyde relevant to acceleratorsjaiweb/slides/2010_phelps.pdf · research...

Research Progress at Strathclyde Research Progress at Strathclyde

relevant to Acceleratorsrelevant to Accelerators

Alan PhelpsAlan 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. McElhinneyMcElhinney

Department of Physics, SUPA, University of Strathclyde, Department of Physics, SUPA, University of Strathclyde,

Glasgow, G4 0NG, UKGlasgow, G4 0NG, UK ABP

Research Seminar Adams Institute 17 June 2010 Oxford University

IntroductionIntroduction

Strathclyde research group overviewStrathclyde research group overview

SUPA SUPA

Strathclyde researchStrathclyde research

High power microwave sourcesHigh power microwave sources

Examples of modelling and experimentsExamples of modelling and experiments

ConclusionsConclusions


500km


StrathclydeUniversityCampus

Physics Department


University of Strathclyde ~ 17,000 studentsUniversity of Strathclyde ~ 17,000 students

Physics Department one of 8 within SUPAPhysics Department one of 8 within SUPA

SUPA graduate school ~ 400 PhD studentsSUPA 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 SUPAResearch Themes in SUPA

Nuclear and plasma physicsNuclear and plasma physics Particle physicsParticle physics Condensed matter & materialsCondensed matter & materials PhotonicsPhotonics Astronomy and astrophysicsAstronomy and astrophysics Physics applied to the life sciencesPhysics applied to the life sciences EnergyEnergy

Physics

Dept

Nano-science

Optics Plasma

Biomolecular & Chemical

Physics (BCP)

Semiconductor Spectroscopy

& Devices (SSD)

Photonics

Computational Nonlinear

and Quantum Optics (CNQO)

AtomsBeams

& Plasmas

Laser-plasma-nuclear

Cathodes Field emission: FEAField emission: FEA Explosive/plasma flare: Metal & VelvetExplosive/plasma flare: Metal & Velvet ThermionicThermionic PseudosparkPseudospark

Gun structures Pierce, MIG, CUSP

Coherent hCoherent high power mm-wave generation Slow wave: Dielectric Cherenkov, Cherenkov BWO

Fast wave: FEL, Gyrotron, CARM, Gyro-TWAs Gyro-BWOs, Superradiance (CRM & Cherenkov)


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

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

Electron beam research using thermionic, plasma flare, Electron beam research using thermionic, plasma flare, field emission array and pseudospark cathodesfield 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 sourcesSeveral 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 beamMm-wave sources using a pseudospark generated electron beam

8

-30

-25

-20

-15

-10

-5

0

5

10

15

20

-10 40 90 140

T ime [ns]

Discharge Voltage [kV

]

-1200

-1000

-800

-600

-400

-200

0

200

400

600

800

Current [A]

Discharge Voltage

Discharge Current

Beam Current by Rogowski Coil

Beam Current by Faraday cup aft er T ungst en Mesh

Cherenkov maser using high brightness electron beam from pseudospark source

H o llowca th o d e

A n o d e

E le c tro n b e am D ie le c tr ic(a lum in a )

W av eg u id e

M ic row av e s

L au n ch in g h o rnS o le n o 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

0

50

100

150

200

250

-100 -50 0 50 100 150 200

Time (ns)

Vo

ltag

e (

kV)

-80

-60

-40

-20

0

20

40

60

80

100

Mic

row

ave

(m

V)

Cu

rre

nt

(A)

Applied voltage Beam current Microwave pulse

1mm Aperture, 2 Disk, 10kV

-2

0

2

4

6

8

10

12

-178 -58 62 182 302

Time (ns)

Vol

tage

(-kV

)

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Bea

m C

urre

nt (A

)

Voltage

Beam Current

1 mm aperture single gap pseudospark 1 mm aperture single gap pseudospark beam measurementsbeam measurements

MMeasured small size (1 mm) beameasured small size (1 mm) beam

Comparison of four types of electron beam source

206 GHz four cavity klystron206 GHz four cavity klystron

37 GHz Free Electron Laser

Millimetre-wave free electron laserMillimetre-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, ϕϕ mzkaRzr zoutin +=

• EM field can be represented by four partial waves:

z zik z ik z iM iM+ - + -E A e A e + B e B eϕ ϕﾢ− −= + +

r rr r r

• Schematic diagram of two-mirror 2D-1D FEM interaction region

Mmkkk zzz =≅′= ,

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]

0

-10

-20

-30

35 36 37 38 39 40

TEM↔TEM

α≈ 0.08TEM↔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 on the outer surface of the inner conductor

0

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 beamthe 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

0.5

1

36 36.5 37 37.5 38

Srf

f (GHz)

Measured spectrum of the output radiation from the FEL60 MW at 37.2 GHz

Heterodyne Frequency Diagnostics

High power mm-wave amplifiersHigh 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 oscillatorsmm-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.

ec m

eB ere wh

γ=ω 2/1

2

2

)c

v1( −−=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 waveguideIt 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.

kz

Conventional Gyro-TWT

ω

Ideal Gyro-amplifier dispersion

ω

kz


Synthesis of Ideal mode to create new sources

Gyro -TWA amplifier schematicGyro -TWA amplifier schematic

Kicker

Helical waveguide with tapers

Main solenoid


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

Modelling of a cusp gun for 390GHz gyrotronModelling 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-deviceWideband W-band gyro-device

Helical interaction waveguide

- High power, high frequency, high efficiency

- Wide frequency band

W-band Gyro-BWO Dispersion diagram

75

85

95

105

115

-1000 -500 0 500 1000

Wavenumber [1/m]

Freq

uency

[G

Hz]

Wave A Wave BBeam W1W1 Measured Magic

W-band Gyro-TWA Dispersion Diagram

70

80

90

100

110

-10 -5 0 5 10

Wavenumber (1/cm)Fre

quen

cy (G

Hz)

Magic TE21TE11 W1e-beam

Predicted PerformancePredicted Performance

Gyro-BWOGyro-BWO

Centre freq. ≈ 94 GHzTuning range ≈ 20%

Maximum power ≈ 10 kWEfficiency ≈ 15%

Centre freq. ≈ 95 GHzFreq. bandwidth ≈ 10% Maximum power ≈ 10 kW

Efficiency ≈ 15%Gain = 40dB

S atu ra te d p o w e r an d g a in cu rv e

0

2

4

6

8

1 0

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

F re q (G H z )

Pow

er (k

W)

2 5

2 8

3 1

3 4

3 7

4 0

Gai

n (d

B)

P o w e r (k W ) G a in (d B )

Gyro-TWAGyro-TWA

390 GHz Harmonic Gyrotron390 GHz Harmonic GyrotronDesign 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 7cusp gun and working at the 7thth harmonic number harmonic number

390 GHz 7th harmonic at TE71 mode

Growth rate at 7th harmonic resonance

Cavity & Cold TestCavity & 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 cavitynovel corrugated cavity

Mean radius, rMean radius, r00 = 8 mm = 8 mm

Corrugation depth, l = 0.7 mmCorrugation depth, l = 0.7 mmLength, L = 39 mmLength, L = 39 mm

Modes excited:Modes excited:22ndnd harmonic, TE harmonic, TE2,22,2 (37.5 GHz) (37.5 GHz)

4th harmonic, TE4th harmonic, TE4,34,3 (69.7 GHz & 75 GHz) (69.7 GHz & 75 GHz)

Suggested beam parameters:Suggested beam parameters:Beam voltage, 60 kVBeam voltage, 60 kVBeam current, 5 ABeam current, 5 APitch angle, 45 degreesPitch angle, 45 degreesMagnetic field, 0.7 TMagnetic field, 0.7 TAxis-encircling beamAxis-encircling beam

( ) ( )0 sin 8r r lφ φ= +

Advantages of depressed collector Improve the overall tube efficiency Decrease cooling requirement Decrease x-ray emission

Depressed collector

collectedbeam

outputoverall PP

P

−=η

Depressed collector research

Depressed Collector SimulationDepressed Collector SimulationSimulation 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, 2009L. 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 - AKRAuroral Kilometric Radiation - AKR

Aurora Borealis – Northern Lights

Planetary MagnetospheresPlanetary 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 distributionelectron 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 gradientpositive gradient in in transverse velocitytransverse velocity near the tip of the distribution. near the tip of the distribution.

10 =zz BB

80 =zz BB

170 =zz BB

300 =zz BB

vev

f +=∂∂

⊥

0

vev

f +=∂∂

⊥

0

v⊥

v

v

v⊥

v⊥

v

B

AURORAL KILOMETRIC RADIATION

THE AURORAL DENSITYCAVITY

VISIBLE AURORA

IONOSPHERE

AURORAL ELECTRON FLUX

Bz

Bz0

B

CATHODE ELECTRONBEAM

LABORATORY EXPERIMENTTERRESTRIAL AURORAL PROCESS

AKR Strathclyde Laboratory ExperimentAKR Strathclyde Laboratory Experiment

Solenoid 1

Solenoid 2Solenoids 3,4,5 and 6

-4 0

-2 0

0

2 0

4 0

6 0

8 0

1 0 0

1 2 0

0 2 4 6 8 1 0 1 2 1 4

F r e q u e n c y (G H z )

Re

lati

ve a

mp

litu

de

(dB

)

Frequency (GHz)

Measured RF spectrum

ConclusionsConclusions Particle-wave interaction synergy of sources & acceleratorsParticle-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 solutionsHigh power mm-wave amplifiers – novel solutions

MM-wave research moving into THz rangeMM-wave research moving into THz range

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

Laser plasma accelerators for applicationsLaser plasma accelerators for applications

AcknowledgementsAcknowledgements

Support from EPSRC, STFC, RSE,

RS, EU, Dstl, The Faraday Partnership,

e2v & TMD

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