Post on 20-Oct-2019
Lower Hybrid Current Drive Experiments in Alcator C-Mod
Ron ParkerMIT PSFC
Principal Collaborators: Paul Bonoli, John Liptac, Andréa Schmidt, Greg Wallace, Randy Wilson1
Special thanks to: Stefano Bernabei1, Joan Decker2, Bob Harvey3, Amanda Hubbard, Joel Hosea1, Jim Irby, Earl Marmar, Alex Parisot, Yves Peysson2, Miklos Porkolab
Neville Greenough1, Dave Johnson, Atma Kanojia, Patrick MacGibbon, George MacKay, Dave Terry
Alcator C-Mod Physics and Engineering Groups
1Princeton Plasma Physics Laboratory2CEA, Cadarache3CompX, Del Mar, CA
Outline
1. Motivation
2. Lower Hybrid System Description
3. Coupling Measurements
4. Current Drive Results
5. GENRAY/CQL3D Comparisons
6. TRANSP Model of Current Diffusion
7. Summary and Conclusions
Outline - Highlights
1. Motivation
2.2.2. Lower Hybrid System DescriptionLower Hybrid System DescriptionLower Hybrid System Description
3. Coupling Measurements
4. Current Drive Results
5. GENRAY/CQL3D Comparisons
6. TRANSP Model of Current DiffusionTRANSP Model of Current DiffusionTRANSP Model of Current Diffusion
7. Summary and Conclusions
Goal is to use LHCD to supplement boot-strap current and produce high perform-ance steady-state regimes
~ 1 MW net coupled, Γ2 ~ 15%, vacuumgap needed for agreement with model.
Nearly 1 MA driven, n19IR/P ~ 3,sawtooth stabilization, central heating
Good agreement with total current, hardX-Ray and cyclotron emission syntheticdiagnostics. Experimental profiles narrower.
Experimental results in-line with require-ments for high performance SS operation.
Modeling of Lower Hybrid Current Drive in Alcator C-Mod1 Indicates Fully Steady-state High Performance Regimes are Accessible
Ip = 0.98 MA, IBS = 0.7 MA, ILH = 0.28 MAβn = 2.9, HITER-89 = 2.5 (assumed)
PLH = 2.4 MW, ηLHCD = 0.1, n|| = 2.75 PICRF = 4 MW
1P. T. Bonoli, M. Porkolab, J. Ramos, et. al., PPCF 39,(1997)223; P.T. Bonoli, R.R.Parker, M. Porkolab, et.al., Nucl Fus 40,(2000)1251
A 96-Waveguide Grill (4X24) has been Mounted in C-Mod to Implement LHCD Experiments
frontcoupler
vacuumwindow H-taper
3 dB splitter
E-taper
shortor
dump
loadsdiagnostic
probes
diagnosticprobes
C-Mod port flange
C
G
D
The 96 Waveguide Grill is Protected by Moly Limiters and Has ProbesImbedded in it for Measurement of Plasma Parameters at the Grill
Probes
Ti grill as installed in January 2005
This grill quickly deteriorated due torapid formation of titanium hydride.
Formation of TiH could be problematic for ITER.
Stainless steel grill installed in January 2006 as it looked at the end of Alcator C-Mod campaign in July.
Limiters
The LH System is Powered by 12 Klystrons Originally Used in Alcator C
The RF power is furnished by 12 well-traveled Klystronsoperating at 4.6 GHz and up to 250 kW for 5 sec.
Conventional microwave components split the RF power from each klystron 4-ways before entering coupler
The klystrons grouped in banks of 4 in C-Mod Cell
Splitter network used to divide klystronpower
Vector Modulators and I/Q Detectors are Used to control the RF Phases and Amplitudes in Each Pair of Waveguide Columns
Spectra derived from measured amplitudes and phases at the junction between forward and rear waveguide assemblies
Amplitude and Phase of each pair of waveguidecolumns is electronically controlled with responsetime of ~ 1 ms.
Phase between adjacent columns is set manually.
Dynamic Phase Control Allows Measurement of Reflection Coefficient in Single Shot
Reflection coefficients havebeen compared to Brambillacoupling code. (Next Slide)
Work is in progress to compare with SWAN code and TOPICAFor LH
0.65 0.7 0.75 0.8 0.85 0.90
50
100
150
60o 90o 120o
150o
180o
90o
0.65 0.7 0.75 0.8 0.85 0.90
1
2
3
0.65 0.7 0.75 0.8 0.85 0.90
1
2
3
4
0.65 0.7 0.75 0.8 0.85 0.90
1
2
3
60 80 100 120 140 160 1800.2
0.25
0.3
0.35
0.4
0.45
0.5
0.55
0.6
0.65
Dtop
Dmid
Dbot
Time (sec)
Time (sec)
Time (sec)
Time (sec)
Co
up
led
Pw
r (kW
)N
e (1
020 m
-3)
Ne
(102
0 m-3
)N
e (1
020 m
-3) Phase (Degrees)
Frac
tio
n P
ow
er R
efle
cted
Reflection Coefficient vs. PhaseLH Power and Probe Densites
Btop
Bmid
Bbot
Comparison of Measured Reflection Coefficient With Brambilla Coupling Code
G. Wallace QP1.00049
0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 1012
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Probe Density cm−3
Fra
ctio
n P
ower
Ref
lect
ed0.08cm Vacuum Gap dn/dx=6*1012cm−4
0.5 1 1.5 2 2.5 3 3.5 4 4.5
x 1012
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
0.5
Probe Density cm−3 or (dn/dx)*.15 cm−4
Fra
ctio
n P
ower
Ref
lect
ed
Variable Density Gradient with No Vacuum Gap
0 0.1 0.2 0.3 0.4 0.50
0.5
1
1.5
2
2.5
3
3.5x 10
12
Den
sity
cm
−3
Distance from Grill cm
Density Profile No Gap
Cutoff Density
Probe Density
0 0.1 0.2 0.3 0.4 0.50
0.5
1
1.5
2
2.5
3
3.5x 10
12
Den
sity
cm
−3
Distance from Grill cm
Density Profile with Gap
Cutoff Density
Probe Density
60o
90o
120o
60o
90o
120o
Ip (MA)
Vloop (V)
ne
(1019 m-3)
Te0 (keV)
PLH (kW)
Vloop (V)
PLH (kW)
Time (sec) Time (sec)
Shot 106061521 Shots 1060615: 5,7,13,21
Increasing Lower Hybrid Power Decreases the Voltage Required to Maintain Constant Current
Change in Loop Voltage (Normalized to Ohmic Value) vs Current Drive Parameteris Nearly Linear Over Range of Densities, Currents and Power
3.5 < ne < 7x1019 m-3
0.5 < Ip < 1 MA
120 < PLH < 830 kW
0
0.2
0.4
0.6
0.8
1
1.2
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35
700kA500kA
Plh/neIpR0(Wm2/Ax1019)
ΔV/V
1 MA
Plh/n19IpR0 (Wm2/A)
The Current Drive Efficiency η = n19I(A)R(m)/P(W) ≈ 3
Ip = IOhmic + Ilh + Ihot
IOhmic = V/ROhmic
ILH = η0Plh/ne19R0
Ihot = V/Rhot
Fit: y = (η0 + η1)x/(1 + η1x)
η0 = n19IR/P =3.1 ± 0.1
η1 = 0.25 ± 0.25
=ROhmicneIpR0/RhotPlh
1Giruzzi, G.,et.al.,NuclearFusion, 37 (1997) 673
R. Wilson, J01.00002
Using method of Giruzzi1:
Note: ne = density @ Te = 2.2 keV
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0.0 0.1 0.2 0.3
Δ V
/ V
PLH / ne Ip Ro (w m2 / 1019 A)
Loop voltage reduction versus normalized PLH
fully non-inductive
Ip > 700 kA
ne = 3.5 - 7 ×1019 m-3
120 < PLH< 830 kW
n|| = 1.6
Plh/n19IpR0 (Wm2/A)
Major Radius (cm)
n e (1
020
m-3
)
During LH pulse (t=1.19s)During LH pulse (t=1.21s)
Before LH pulse (t=0.58s)
TCI nebarThomson
During LH pulse (t=1.19s)Before LH pulse (t=0.58s)
Major Radius (cm)
T e (e
V)
Example of Discharge in Which Sawteeth Were Stabilized and Te0 Increased
Shot 106072029
Phase n||
60º 1.6
90º 2.3
120º 3.1
The Current Drive Efficiency Improves with Decreasing n||
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 0.05 0.1 0.15 0.2 0.25
60 degree90 degree120 degree
Plh/n19IpR0 (Wm2/A)
ΔV
/V
0.6 0.8 1.0 1.2 1.40.0
0.2
0.4
0.6
0.8
1.0
1.2
60º90º
Loop
Vol
tage
(V)
Time (sec)
ne = 5e19 m-3
Ip = 720 kWPLH = 480 kW
LHCD
Two Shots Have Been Modeled with GENRAY and CQL3D
Time (sec) Time (sec)
Ip (MA)
Vloop (V)
ne (1019 m-3)
Teo (keV)
PLH (kW)
1060728011 1060728014
GENRAY and CQL3D Are Used to Model the LHCD Experimental Results
Poloidal and Toroidal Projection of Rays Launched by Antenna (GENRAY) in Ohmic plasma:
rfr
rrp
pfeEppfC
pfpD
ptf e
Fse
ee
rfe
∂∂χ
∂∂δ
∂∂
∂∂
∂∂
∂∂ 1)(+),,()( //
//////
////
//
+Γ++= ⊥
Self-consistent damping of the rays is determined by Fokker-Planck equation containing quasi-linear RF term:
20 40 60 80 100-40-30-20-10
010
20
30
R(cm)
Z(cm)
-100 -50 0 50 100
-50
050
X(cm)Y(cm)
QL RF term FP term E-Field term
Electron Spatialdiffusion
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
r/a
Pow
er D
ensi
ty (
W/c
m3 )
CQL3D Power Depostion Profiles
10607280111060728014
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1−500
0
500
1000
1500
2000
2500
3000
r/a
Cur
rent
Den
sity
(A
/cm
2 )
CQL3D Modeled Current Profiles
10607280111060728014
Experiment Model
Shot/Time Vloop IP(MA) Vloop IP(MA)
106072811t = 1100 ms
0.2 0.53 0.2 0.543
106072814t = 1000 ms
~ 0 1.03 0.1 0.90
Good Agreement Between Measured and Modeled Current and Voltage
A. SchmidtQP1.00050
The Modeled Distribution Function @ r/a =0.6 for 1 MA Shot Has a Plateau Extending to γv||/c ~ 1.2
−1 −0.5 0 0.5 1 1.5 20
0.2
0.4
0.6
0.8
1
Contour plot of distribution function
γ v||/c
γ v pe
rp/c
0 1 2 3 4 5 6 710
9
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
γ v/c
f
Cuts of f(v) at Constant Pitch Angle
θ=0θ=π/4θ=π/2θ=3π/4θ=π
Model includes residual E-field,however its effect on plateau is small.
γv||/c ~ 1.2 corresponds to n|| =1.3,near minimum n|| of launched spectrum.
An Imaging X-Ray Spectrometer Records Fast Electron Bremsstrahlung Spectrum
D=123cm d=40cm
Spatial resolution:Estimation: Δr ~ 2a / #chords=1.4cm
Geometry: Δr = (1 + D/d)ac ~ 1.7cm
ac=5mmad=5mm
C-Mod Cross section with pinhole camera
B-port
Photon pulses from all 32 channels are stored for post processing
5 10 15 20 25 300
2
4
6
8
10
12
14
16
x 104 Modeled and Measured HXR Spectra
Channel Number
Cou
nt R
ate
(s−
1 keV
−1 )
24 keV (cql3d)34 keV (cql3d)44 keV (cql3d)24 keV (experiment)34 keV (experiment)44 keV (experiment)
X-Ray Profiles and ECE Spectrum Compare Favorably with CQL3D/GENRAY Model
CQL3D/GENRAY profiles are narrow, consistent with narrow current deposition.
X-Rays suggest a broader current profile –spatial diffusion?
A. SchmidtQP1.00050
100 200 300 400 500 600 7000
5
10
15
20
Predicted and Measured ECE Spectra
frequency (GHz)
equi
vale
nt r
adia
tion
tem
pera
ture
(ke
V)
nonthermalfeature
2nd harmonic, R=R0
Measured ECE SpectrumCQL3D ECE Spectrum/5
What is Significance of Negative Loop Voltage in 1 MA Shot?
Time (sec) Time (sec)
Ip (MA)
Vloop (V)
ne (1019 m-3)
Teo (keV)
PLH (kW)
1060728011 1060728014
TRANSP Modeling of Shot 1060728014 Indicates Negative VloopResults From Overdrive In Outer Region of Discharge
RF current overdrive causesa negative E-Field whichdiffuses rapidly to edge,resulting in transient surfacevoltage.
The time for steady-state to develop depends on relativealignment of inductive and RF current profiles.
A. Parisot QP1.00051
0.0 0.2 0.4 0.6 0.8 1.005
101520253035
Cur
rent
den
sity
[MA
m-2]
0.0
0.5
1.0
1.5
2.0
2.5
Loop
vol
tage
[V]
0.4 0.6 0.8 1.0 1.2 1.40
200
400
600
800
LH p
ower
[kW
]
Time [s]
1 MA ohmicbefore LH
Test LH driven current profiles
750 kA
1 MA
Experiment
TRANSP simulation
r/a
Summary and Conclusions (1)
Lower Hybrid Current Drive has been implemented on Alcator C-Mod:
Goal is to use LHCD as a tool to supplement bootstrap current and enable performance optimization studies leading to attractive steady-state regimes.
Results should also inform LHCD decision for ITER
So far ~ 1 MW has been coupled and current drive approaching 1 MA at n ~ 5e19 m-3
has been achieved.
First results indicate current drive efficiency is in line with expectations based onstate-of-the–art models and sufficient to achieve target regimes, although highern|| (lower efficiency) for accessibility and additional power will be required at higher density.
Good general agreement between experiment and both X-Ray and ECE CQL3D-GENRAY synthetic diagnostics. There are indications that j(r) is broader than code predicts – supported by TRANSP modeling.
Summary and Conclusions (2)
In next Alcator C-Mod campaign, emphasis will be on raising absorbed power toward 1.5 MW, increasing density above ne = 1e20 m-3 and exploring interactions with ICRH antenna.
Meanwhile, a second phase incorporating a second launcher and upgrading the source power to 4 MW is underway – operation scheduled for 2009.
With the second phase, sufficient source power will be available for development oftarget AT scenarios.