US DoE...Field Aligned Antenna Antenna straps, septa, and side protection tiles are normal to the...
Transcript of US DoE...Field Aligned Antenna Antenna straps, septa, and side protection tiles are normal to the...
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Assessment of a Field-Aligned ICRF Antenna*
20th Topical Conference on Radio Frequency Power in PlasmasSorrento, Italy June 25-28, 2013
S.J. Wukitch, D. Brunner, P. Ennever, M.L. Garrett, A. Hubbard, B. Labombard, C. Lau, Y. Lin, B. Lipschultz, D. Miller, R. Ochoukov, M. Porkolab, M.L. Reinke, J.L. Terry, A. Tronchin-James, N.
Tsujii, D. Whyte and the Alcator C-Mod Team
Key Results:
1. Novel, Field aligned ICRF antenna has reduced impuritycontamination, impurity sources, and RF enhanced heat flux.
2. Field aligned antenna has greater load tolerance.3. Measured plasma potentials for Field Aligned antenna are not
remarkably different from plasma potentials associated with toroidallyaligned (TA) antenna.
4. Low heating effectiveness with monopole phasing is a result of poorwave penetration.
I2.2 - Wukitch 120th Topical Conf. RF Power in Plasmas
*Work supported by US DoE awards
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Outline
Description of field aligned antenna.
Impurity contamination and sources
RF enhanced heat flux to antenna and PFCs
Characterize RF enhanced plasma potentials.
Comparison of Dipole and Monopole heating effectiveness
I2.2 - Wukitch 220th Topical Conf. RF Power in Plasmas
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Field Aligned AntennaAntenna straps, septa, and side
protection tiles are normal to thetotal magnetic field, ~10.
Guiding Design Principle is Field Line Symmetry
I2.2 - Wukitch 320th Topical Conf. RF Power in Plasmas
Field AlignedAntenna
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Field Aligned AntennaAntenna straps, septa, and side
protection tiles are normal to thetotal magnetic field , ~10.
Antenna is helical to conform toplasma shape.
Guiding Design Principle is Field Line Symmetry
I2.2 - Wukitch 420th Topical Conf. RF Power in Plasmas
Field AlignedAntenna
B
flux surface
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Field Aligned AntennaAntenna straps, septa, and side
protection tiles are normal to thetotal magnetic field , ~10.
Antenna is helical to conform toplasma shape.
Toroidally Aligned AntennaAntenna straps, septa, and side
protection tiles are normal to thetoroidal magnetic field.
Antenna is cylindrical
Field Aligned Antenna is Normal and Conformal
I2.2 - Wukitch 520th Topical Conf. RF Power in Plasmas
Field AlignedAntenna
Toroidally AlignedAntenna
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Field Aligned Antenna is Normal and Conformal
I2.2 - Wukitch 620th Topical Conf. RF Power in Plasmas
Field AlignedAntenna
Toroidally AlignedAntenna
Field Aligned AntennaAntenna straps, septa, and side
protection tiles are normal to thetotal magnetic field , ~10.
Antenna is helical to conform toplasma shape.
Faraday rods are parallel to the totalmagnetic field.
Toroidally Aligned AntennaAntenna straps, septa, and side
protection tiles are normal to thetoroidal magnetic field.
Antenna is cylindrical.Faraday rods are parallel to the total
magnetic field.
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C-Mod ICRF has Similar Characteristics as ITER
Field aligned antenna
Toroidally Aligned Antennas
Antenna power density exceeds anticipated ITER power density.
Strong single pass absorption (SPA).Metallic PFCs (Mo) that has similar sputtering
characteristics as tungsten.Scrape off layer is opaque to neutrals.
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 7
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Field Aligned Antenna has Achieved Electrical Performance Similar to Toroidally Aligned Antenna
Electrically the Field Aligned antenna hasperformed well.• Antennas conditioned very quickly in plasmas
(~15 discharges) to 2 MW (~6 MW/m2).• Operation over wide range of q95 (3-5.5) has
seen little variation in performance.▪ Misalignment to magnetic field is
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FEM Simulation Utilizes Detailed Antenna Geometry and Simplified Core Wave Propagation
• C-Mod plasma and magnetic data are used in the model.
Limitations of the model:• RF sheath boundary conditions are not implemented.• Plasma density and temperature do not evolve with application of RF power.• RF potentials are calculated in vacuum region ~1 cm in front of the Faraday
screen.
I2.2 - Wukitch 920th Topical Conf. RF Power in Plasmas
Finite Element Method:• 3-D toroidal FEM• Antenna CAD model is
utilized.• Cold plasma permittivity
tensor rotated alongmagnetic field.
• Use artificial collisionaldamping to modelminority absorption.
M. Garrett et al., Fus. Eng. Design 9, 1570 (2012).
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FEM Simulation show Reduced Integrated E|| for the Field Aligned Antenna
For Field Aligned antenna, the integrated E|| fields are reduced for allantenna phases.• For dipole, estimated integrated E|| is reduced particularly at the peaks.• For monopole, integrated E|| is significantly reduced.
I2.2 - Wukitch 1020th Topical Conf. RF Power in Plasmas
1 2 3−0.3−0.2
−0.1
0
0.1
0.2
0.3
Potential [kV]
Polo
idal
Coo
rdin
ate
[m]
(Pos
ition
alo
ng A
nten
na)
Toroidally AlignedField Aligned
Dipole Phasing
1 2 3 4 5−0.3
−0.2
−0.1
0
0.1
0.2
0.3
Potential [kV]
Polo
idal
Coo
rdin
ate
[m]
(Pos
ition
alo
ng A
nten
na)
Toroidally AlignedField Aligned
Monopole Phasing
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FEM Simulation show Reduced Integrated E|| for the Field Aligned Antenna
For Field Aligned antenna, the integrated E|| fields are reduced for allantenna phases.• For dipole, estimated integrated E|| is reduced particularly at the peaks.• For monopole, integrated E|| is significantly reduced.
▪ Lower than dipole– a surprising prediction.
I2.2 - Wukitch 1120th Topical Conf. RF Power in Plasmas
1 2 3−0.3−0.2
−0.1
0
0.1
0.2
0.3
Potential [kV]
Polo
idal
Coo
rdin
ate
[m]
(Pos
ition
alo
ng A
nten
na)
Toroidally AlignedField Aligned
Dipole Phasing
1 2 3 4 5−0.3
−0.2
−0.1
0
0.1
0.2
0.3
Potential [kV]
Polo
idal
Coo
rdin
ate
[m]
(Pos
ition
alo
ng A
nten
na)
Toroidally AlignedField AlignedField Aligned Dipole
Monopole Phasing
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High Z metallic materials are favored forplasma facing components (PFCs).• Impurity sources and contamination are
more difficult to manage.• Plasma tolerance of high Z materials is
much lower than low Z materials.
ICRF compatibility with high Z PFC hasextensively investigated at C-Mod.• ICRF heated H-mode performance with
high Z PFCs is insufficient.
Challenges for ICRF Utilization: Impurities
0.04
0.08
0.12
1
2
0.5
1.5
2.5
0.6 0.7 0.8 0.9.
1
2
3
951205026
PRAD [MW]
PICRF [MW]
WMHD [MJ]
1.0
H ITER89
Time (s)
bare high Z PFC
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 12
Adapted from Greenwald et al., Nucl. Fusion 37, 793 (1997).
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High Z metallic materials are favored forplasma facing components (PFCs).• Impurity sources and contamination are
more difficult to manage.• Plasma tolerance of high Z materials is
much lower than low Z materials.
ICRF compatibility with high Z PFC hasextensively investigated at C-Mod.• ICRF heated H-mode performance with
high Z PFCs is insufficient.• ICRF impurity contamination has been
can be controlled by boron coatings.
• Low Z film lifetime is limited and doesnot scale to reactor
• Seek to develop ICRF antennas withoutneeding to resort to boronization.
Challenges for ICRF Utilization: Impurities
0.04
0.08
0.12
1
2
0.5
1.5
2.5
0.6 0.7 0.8 0.9.
1
2
3
951205026&960116010
PRAD [MW]
PICRF [MW]
WMHD [MJ]
1.0
H ITER89
Time (s)
bare high Z PFC
boronized high Z PFC
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 13
Adapted from Greenwald et al., Nucl. Fusion 37, 793 (1997).
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Compare Measurements of Core Impurity Contamination, Local Impurity Sources
Compare antenna performancebetween toroidally and field alignedantenna in near axis minority Habsorption scenario with RF powerup to 3 MW.• Magnetic field 5.2-5.4 T with currents
0.6-1.3 MA.
Core impurity content is monitoredusing VUV spectroscopy MoXXXI.
Local impurity (Mo I) sources aremonitored with visiblespectrometer:
• Multiple views of each antennaand poloidal protection limiter.
FA-antTA-ant
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 14
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In L-mode, Field Aligned Antenna has Lower Impurity Contamination
Prior to boronization in L-modedischarges, plasma response is morefavorable for power from FieldAligned antenna.
Impurity contamination is lower.
• Radiated power is 25% lower forcomparable injected power.
• Core molybdenum content issignificantly reduced.
I2.2 - Wukitch 1520th Topical Conf. RF Power in Plasmas
0.03
0.05WMHD [MJ]
1
2Prad (MW)
0.2
0.4Mo XXXI (a.u.)
0.7 0.8 0.9 1 1.1
1
2PRF (MW)
Time (s)
1120
5310
17, 0
20
Toroidally Aligned
Field Aligned
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Core Mo is significantly lower for FieldAligned antenna compared toToroidally Aligned antennas.
• Rise time on the core Mo content issignificantly slower for the Field Alignedantenna than the Toroidally Aligned-antennas.
Field Aligned antenna has lower radiatedpower.
• Radiated power is ~20-30% lower thanfor the Toroidally Aligned antennas inEDA H-mode.
In H-mode, Field Aligned Antenna has Lower Impurity Contamination
0.2
0.4
0.6
P RA
D [
MW
]
0.2
0.4
0.6
Mo
XX
XI [
AU
]
Toroidally Aligned
H-mode0.5 0.6 0.7 0.8 0.9 1.0
Time (s)
0.2
0.6
1.0
1.4
P IC
RF
[MW
]
Field Aligned
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 16
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Toroidally Aligned Antenna Molybdenum Source Correlates with RF Power
Compare the response of the local Mosource for each antenna view when theToroidally Aligned and Field Alignedantenna are powered separately.
Strong Molybdenum source response atthe Toroidally Aligned antenna whenthe Torioidally Aligned antenna ispowered.• Mo source at the Toroidally Aligned
antenna increases with each power step.
I2.2 - Wukitch 1720th Topical Conf. RF Power in Plasmas
1
2
4
3
TA Antenna View
Mo
I Brig
htne
ss [A
.U. 3
86 n
m]
0.6 0.7 0.8 0.9 1.0Time (s)
TA Ant.
.
PICRF [MW]
1
2
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Toroidally Aligned Antenna Molybdenum Source Correlates with RF Power
Compare the response of the local Mosource for each antenna view when theToroidally Aligned and Field Alignedantenna are powered separately.
Strong Molybdenum source response atthe Toroidally Aligned antenna whenthe Torioidally Aligned antenna ispowered.• Mo source at the Toroidally Aligned
antenna increases with each power step.
Weak Molybdenum source response atthe Toroidally Aligned antenna whenField Aligned antenna is powered.
I2.2 - Wukitch 1820th Topical Conf. RF Power in Plasmas
1
2
4
3
TA Antenna View
Mo
I Brig
htne
ss [A
.U. 3
86 n
m]
0.6 0.7 0.8 0.9 1.0Time (s)
TA Ant.
FA Ant.
.
PICRF [MW]
1
2
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Field Aligned Antenna Molybdenum Source Correlates with Toroidally Aligned Antenna Power
I2.2 - Wukitch 1920th Topical Conf. RF Power in Plasmas
1
2
4
3
TA Antenna View
Mo
I Brig
htne
ss [A
.U. 3
86 n
m]
0.6 0.7 0.8 0.9 1.0Time (s)
TA Ant.
FA Ant.
.
PICRF [MW]
1
2
Measurable Mo source response at Field Aligned antenna when ToroidallyAligned antenna is powered.
1
0.5
Mo
I Brig
htne
ss [A
.U. 3
86 n
m] FA Antenna View
0.6 0.7 0.8 0.9 1.0Time (s)
.
PICRF [MW]
1
2
TA Ant.
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Field Aligned Antenna Molybdenum Source has Weaker Response to Field Aligned Power
I2.2 - Wukitch 2020th Topical Conf. RF Power in Plasmas
1
2
4
3
TA Antenna View
Mo
I Brig
htne
ss [A
.U. 3
86 n
m]
0.6 0.7 0.8 0.9 1.0Time (s)
TA Ant.
FA Ant.
.
PICRF [MW]
1
2
Measurable Mo source response at Field Aligned antenna when ToroidallyAligned antenna is powered.
Mo source response is lower at Field Aligned antenna when Field Alignedantenna is active.
1
0.5
Mo
I Brig
htne
ss [A
.U. 3
86 n
m] FA Antenna View
0.6 0.7 0.8 0.9 1.0Time (s)
.
PICRF [MW]
1
2
TA Ant.
FA Ant.
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Challenges for ICRF Utilization: RF Enhanced Heat Flux
RF enhanced heat flux needs to be managed to prevent exceeding thepower handling capability of the antenna and other PFCs.• Steady state operation becomes challenging.
Enhanced RF sheaths are thought to be the underlying physics• Sheaths increase the energy per ion• Radial profile results in convective cells that increase the particle flux.
In ITER, the ICRF antenna design assumes an RF enhanced heat flux of 6MW/m2.• ~125 kW out of 20 MW or 0.625%• JET has measured between 2-10% is found on the septum and antenna limiters• Tore Supra has found ~3.5% for their classical antennas.
I2.2 - Wukitch 2120th Topical Conf. RF Power in Plasmas
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Field Aligned Antenna is Instrumented with Thermocouples
In 5 out of 9 protection tiles, the TZMtiles are instrumented withthermocouples.• Thermojunction is pressed in direct
contact with the TZM tile.• Thermocouple response time is
insufficient to calculate the surfacetemperature or heat flux.
• Use before and after shottemperatures with the tile mass andsurface area to calculate the energyflux for each instrumented tile.
Side protection tiles are expected toreceive the majority of the heatflux.• FS rods, top and bottom tiles are
shadowed by 5 mm and 3 mm,respectively.
1
9
456
1
9
456
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 22
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Total Energy Deposited is Lower with FA Antenna Powered
Analyze the thermocouple data over athree month operational period.• Includes L-mode, H-mode• Current scan Ip=0.6-1.3 MA• Various outer gaps, 0.5-2 cm.• Primarily dipole phase with few monopole
discharges.
Isolated discharges where the FAantenna power (63 discharges) isgreater than 0.7 on injected RF joules(red squares).
Compare with discharges where TAantenna power > 0.9 of the injectedpower (111 discharges).
I2.2 - Wukitch 2320th Topical Conf. RF Power in Plasmas
4
3
2
1
1 21.50.5Injected RF Energy [MJ]
Ener
gy to
RF
Lim
iter [
kJ]
Toroidally Aligned AntennaField Aligned Antenna
Monopole
Discharges heated with the FA antenna have lower total energydeposited.• Monopole phasing has elevated energy deposited – about 3x that of dipole.
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Spatial Distribution of Deposited Energy is Similar
Profile is similar regardless of whichantenna is powered.• Top (#1) and bottom (#9) tiles have
majority of deposited energy.
When field aligned antenna is powered,tile #9 has less the 0.8 kJ depositedenergy.• Data above 0.8 kJ are discharges with
lower hybrid power, locked modedischarges, or increasing power from TAantenna.
Monopole phasing causes increaseddeposited energy on top tile.
I2.2 - Wukitch 2420th Topical Conf. RF Power in Plasmas
321Energy to RF Tile [kJ]
4
5
6
1
9
Tile
Num
ber
2
3
7
8
Monopole
Toroidally Aligned Antenna Field Aligned Antenna
Estimate the total power deposited as a fraction of the coupled RF energy• linearly interpolate the energy deposited on tiles #2, #3, #7, and #8 ~ roughly
doubles the measured deposited energy.• Assuming an equal amount on the right set of side protection tiles• the total deposited energy is ~6 kJ for 1.5 MJ injected or 0.4%.
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Challenges for ICRF Utilization: Load Tolerance
88 89 90 91 92
Rmajor [cm]
1018
1019
1020
1021
Cut-off density
LCFS Main Plasma Limiter
Ante
nna
Lim
iter
Scrape-off Layer
Limiter
Shadow
Near
SOL
Far
SOL
ne
[m-3
]
I2.2 - Wukitch
To maintain coupled power to the plasma, an ICRF antenna needs to be load tolerant • either intrinsically • or through external matching.
Edge plasma density profile determines the antenna resistive loading.• Sets the distance to propagation
and • Determines the transmission
impedance.
20th Topical Conf. RF Power in Plasmas 25
Antenna geometry determines antenna reactance.• Modified by plasma which breaks symmetry of the off diagonal terms in the
impedance matrix.
Plasma load variations are encountered during confinement transitions and edge localized mode (ELMs) activity.
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Field Alignment Improves Antenna Load Tolerance
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 26
Field aligned antenna has improved loadtolerance.• Reflection coefficient from Field Aligned
antenna occupies less area thanToroidally Aligned antenna.
• Impedance variation is reduced.
• Q of the antenna, ratio of reactance toresistance, is approximately constant.
• Impedance variation depends primarily onthe real part of the antenna load.
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ELMs Loading Perturbation is Largely Resistive for Field Aligned Antenna
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 27
Field aligned antenna impedance changeis due resistive change.• Toroidally aligned antenna Q and
impedance both vary.
Speculation: antenna impedance matrixbecomes symmetric due to fieldalignment.
Generic antenna impedance matrix:• a11 and a22 are the plasma resistive load• L11 and L22 are the strap self inductance• M12 and M21 are mutual coupling• b12 and b21 represent the coupling through
the plasma – particularly E||
Coupling variation through plasma results in large changes in reflectioncoefficient.
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ICRF interaction with SOL: What is E|| Role?
Oscillating E|| leads to DC sheathrectification.
• I-V curve is highly non-linear andleads to excess electroncollection in presence of RF.
I2.2 - Wukitch 2820th Topical Conf. RF Power in Plasmas
I
V
e- current
i+ current
RF voltage
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ICRF interaction with SOL: What is E|| Role?
Oscillating E|| leads to DC sheathrectification.• I-V curve is highly non-linear and
leads to excess electroncollection in presence of RF.
• DC bias voltage is established onconducting surfaces to maintainambipolarity.
Radial profile of RF enhancedsheaths leads to convection.
E|| interacts with SOL results invariation in off diagonal terms inthe antenna impedance matrix.
Does a field aligned antennareduce RF enhanced sheaths?
I2.2 - Wukitch 2920th Topical Conf. RF Power in Plasmas
I
V
e- current
i+ current
RF voltageDC offset
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GPI
Gas Puff Imaging Monitor Plasma Potential
GPI diagnostic measures the poloidal velocity of the SOL turbulence.• Monitors the radial region between ~1 cm behind the antenna tile radius to the
last closed flux surface.• Maps to the corners of both the Field Aligned and Toroidally Aligned antennas
where the integrated E|| is expected to peak.• Vertical resolution of ~4 cm and radial resolution of ~0.4 cm.
I2.2 - Wukitch 3020th Topical Conf. RF Power in Plasmas
Field AlignedAntenna
K PlasmaLimiter
A‐B Plasma Limiter
Toroidally AlignedAntenna
LH Coupler
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SOL Potential Profile Estimated from GPI Measurements
In the far SOL, turbulence is convected at the local ExB velocity.• Poloidal velocity and corresponding Er are small in ohmic discharge.
I2.2 - Wukitch 3120th Topical Conf. RF Power in Plasmas
0 1 2Distance into SOL (cm)
-4
-2
0
v(k
m/s
)θ
3
2
4
6
-620
10
0
-10
-20
E r (k
V/m
)
no RF
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SOL Potential Profile Estimated from GPI Measurements
In the far SOL, turbulence is convected at the local ExB velocity.• Poloidal velocity and corresponding Er are small in ohmic discharge.• Dramatic change in Er with application of RF.
I2.2 - Wukitch 3220th Topical Conf. RF Power in Plasmas
0 1 2Distance into SOL (cm)
-4
-2
0
v(k
m/s
)θ
3
2
4
6
-620
10
0
-10
-20
E r (k
V/m
)
no RF
RF
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SOL Plasma Potential Profile Estimated from GPI Measurements
In the far SOL, turbulence is convected at the local ExB velocity.• Poloidal velocity and corresponding Er are small in ohmic discharge.• Dramatic change in Er with application of RF.
Integrate Er profile to deduce potential profile with profile referenced to3Te/e.
• Plasma potential is conserved on a field line.
I2.2 - Wukitch 3320th Topical Conf. RF Power in Plasmas
0 1 2Distance into SOL (cm)
-4
-2
0
v(k
m/s
)θ
3
2
4
6
-620
10
0
-10
-20
E r (k
V/m
)
no RF
RF
0
100
200
Φp profile with ICRFreferenced to 3Te /e
0.5 1.0 1.5 2.0 2.5
(V)
Distance into SOL (cm)
Φ~3Te /e
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Measured Potential for Field Aligned and Toroidally Aligned Antennas are Similar
Impurity contamination differs between the antennas with the Field Alignedhaving lower sources and contamination.• Challenge to hypothesis that lower integrated E|| will lower RF enhanced
sheaths.• Furthermore, difficult to reconcile lower impurity sources and contamination with
E|| unchanged.I2.2 - Wukitch 3420th Topical Conf. RF Power in Plasmas
1120
9040
13
Field Aligned
0.5 1.0 1.5PICRF (MW)
100
200
300
400
φ max
(V)
Toroidally Aligned
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Monopole Phasing does not Perform as well as Dipole
Recall field aligned antenna inmonopole phasing was predictedto have the lowest integrated E||fields.
Heating effectiveness with monopoleis significantly lower than dipolephasing.
Measured plasma potential is higherfor monopole operation than thatmeasured during dipole operation.
0.03
0.05
1
2
WMHD [MJ]
Te0 (keV)
Dipole phasing Monopole phasing
0.6 0.7 0.8 0.9 1
12
1120613007&009
PRF (MW)
Time (s)
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 35
1120
9180
07 &
112
0918
005
Dipole
0.0 0.5 1.0 1.5P ICRF (MW)
0
100
200
300
400
2.0
Monopole
500
600
700
φ max
(V)
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What is Underlying Physics of Poor Performance with Monopole Phasing
Wave spectrum is peaked at longwavelength if one only considers theantenna straps.• Good for coupling at long distances.
• Dipole has peak at shorter wavelength –n~13.
I2.2 - Wukitch 3620th Topical Conf. RF Power in Plasmas
Monopole
Dipole
Pow
er S
pect
rum
(A.U
.)
Monopole
Dipole
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Hypothesis is that Monopole Spectrum Peaks at Short Wavelength
FEM antenna-plasma model indicatesmonopole wave spectrum is peaked atvery short wavelengh.• Wavelength is about half dipole resulting in
high n.
• Image currents on antenna box includingthe septa significantly modify the launchedwave spectrum.
• Dipole phasing image currents on septacancel – little modification of the analyticwave spectrum.
I2.2 - Wukitch 3720th Topical Conf. RF Power in Plasmas
Re(E+) (kV/m)
Monopole
Dipole
MonopoleCurrents Add
DipoleCurrents Cancel
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Test Hypothesis with Mode Conversion Absorption Scenario
Mode conversion heating scenarioenables measurement of corewaves with phase contrastimaging (PCI).• Monopole and dipole should have
similar single pass absorption.
Dipole plasma heating effectivenessis higher than monopole.
Radiated power and core impuritycontamination are similar.• Suggests difference between
monopole and dipole is notdominated by impuritycontamination.
Carbon II responds strongly tomonopole phasing.• Indicates RF power is interacting
with the SOL.I2.2 - Wukitch 3820th Topical Conf. RF Power in Plasmas
0.03
0.05
.4
6
0.2
0.4
0.02
0.06
0.1
0.060.1
0.14
1120905021
0.8 0.9 1.1 1.2.
0.51
1.52
PRAD [MW]
Mo XXXI [AU]
PICRF [MW]
Te0 [keV]
WMHD [MJ]
C II [AU]
Time (s)1.0
DipoleMonopole
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Monopole Spectrum is Inaccessible
PCI measures no waves in theplasma core during monopolephasing.
Full wave modeling shows thatthe monopole spectrumincluding the image currentslaunches waves that remainin the plasma periphery.
I2.2 - Wukitch 3920th Topical Conf. RF Power in Plasmas
-10
-5
0
5
10
0
2
4
6
8
10
12
0.6 0.8 1.0 1.2 1.4Time (s)
1
2
k R (c
m-1
)
PRF (MW)
DipoleMonopole
Inte
nsity
(101
3 m-2
/cm
-1)2
−30 −20 −10 0 10 20−40
−20
0
20
40
V/m/MWabs
−3.7
−1.2
−0.37
−0.12
0.13
0.42
1.3
X = R − R0 (cm)
Z (c
m)
Re(E_)V/m/MWabs
nφ=3
Monopole -(excluding image currents)
−30 −20 −10 0 10 20−40
−20
0
20
40
V/m/MWabs
−3.3−1.1−0.33−0.110.00960.30.96
X = R − R0 (cm)
Z (c
m)
Re(E_)V/m/MWabs
nφ=13
Dipole
−30 −20 −10 0 10 20X = R − R0 (cm)
−40
−20
0
20
40
Z (c
m)
V/m/MWabs
−1.4
−0.44
−0.14
−0.044
1.6
5
16
Re(E_)V/m/MWabs
nφ=26
Monopole -(including image currents)
-
Future Directions
Add plasma response to antenna – plasma model.• Sheath boundary conditions are next physics to be included.• Reconstruct antenna impedance matrix from antenna-plasma model to
investigate role of magnetic field and off diagonal terms.
Investigate relationship between ICRF antenna and plasma potential.• Characterize plasma potential with additional emissive probes - same mapping
as GPI and over wider set of plasma conditions.• Increase poloidal coverage to characterize poloidal profile of plasma potentials.• Does the tile geometry and orientation to the magnetic field play a role?• Can the antenna structure be biased to reduce RF enhanced plasma potential?
Establish relationship between SOL plasma potential and impuritycontamination and sputtering.• Identify impurity source locations.• Is SOL impurity transport modified with RF?
I2.2 - Wukitch 4020th Topical Conf. RF Power in Plasmas
-
Field Aligned ICRF Antenna Results are Promising
Hypothesis: does a field aligned antenna improve ICRF antenna performance?
• reduced impurity contamination and impurity sources,
• has low RF enhanced heat flux, and
• is more resilient to load variations than toroidally aligned antennas.
However, our physics understanding of Field Aligned antenna is incomplete.
• Plasma potentials associated with field aligned antenna operation are similar totoroidally aligned antenna operation.
• Clarification of the underlying physics that influences the SOL plasma potential in thepresence of ICRF is required.
Monopole antenna phasing has poor heating effectiveness due to poor wavepenetration in the plasma core.
I2.2 - Wukitch 20th Topical Conf. RF Power in Plasmas 41