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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
Strathclyde research group overviewStrathclyde research group overview
500km
Strathclyde research group overviewStrathclyde research group overview
StrathclydeUniversityCampus
Physics Department
Strathclyde research group overviewStrathclyde research group overview
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)
Strathclyde research group overviewStrathclyde research group overview
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
High power mm-wave amplifiersHigh power mm-wave amplifiers
Synthesis of Ideal mode to create new sources
Gyro -TWA amplifier schematicGyro -TWA amplifier schematic
Kicker
Helical waveguide with tapers
Main solenoid
High power mm-wave amplifiersHigh power mm-wave amplifiers
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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