RECENT PROGRESS AND 2011 PLANS FOR IOS5.3: ASSESSMENT OF LOWER HYBRID CURRENTDRIVE AT HIGH DENSITY FOR EXTRAPOLATIONTO ITER ADVANCED SCENARIOS
G. Wallace for:M. Goniche et al: Tore Supra,
R. Cesario, et al: FTU,
B. Ding, et al:
HT-7/EAST,
S. Shiraiwa, A. Hubbard, O. Meneghini, S.G. Baek, et al:
C-ModBackground and overview






IOS 5.3 is a fairly new JE started in 2010.
Prompted by 2009 results from several devices (C-Mod, FTU, ToreSupra, JET) indicating that LH efficiency drops at a density lower
than would be expected simply from accessibility considerations.
We need a better, common, understanding of the physicalmechanism(s) and validated simulation model(s) in order toextrapolate to the conditions of ITER!
Since previous meeting, C-Mod has been working on improving
analysis techniques and modeling. No new experiments due tomachine shutdown for installation of rotated ICRF antenna.
Tore Supra has some new data and worked on interpretation of pastexperiments.
New data from HT-7.

LHCD modelling
Strongly inductive discharges -> C3PO/LUKE simulations arerather sensitive to E-field and current profile reconstruction byCRONOS Wave is still absorbed at <ne>
~5×1019m-3 (nl= 5.5×1019m-3)
 Large scattering for ILH but
degradation of h (neRILH/PLH)
with density close to ne-2
 Sensitivity studies show lack ofrobustness in LHCD simulations.
However ne-3 scaling is resilient

PLH=2MWM.Goniche et al., EPS2011

Further modelling in progress
ITPA-IOS group, Kyoto, 18-21 October 2011

M.Goniche et al.

HXR vs. ne

Jsat & RMS(Jsat)/Jsatvs. ne

M.Goniche et al., EPS2011• Faster decay of HXR for <ne> > 4×1019m-3 is correlated tostrong increase of jsat fluctuation rate (a=0.72m)• Same result obtained for gas vs. pellet fuelling (PPCF10)
ITPA-IOS group, Kyoto, 18-21 October 2011

M.Goniche et al.

New high density experiments(TS#48233-234-238-239)- Change gas valves (233, 234& 238)
- Change Ip (1.0=> 1.2MA)- More edge diagnostics:
Reflectometer in LH
launcherRF meas. for spectrum
around 3.7GHz
Very fast acquisition(200MHz) for probes#48233

 Reference pulse with fast decay of HXR ( <ne> > 4×1019m-3) not really
reproduced (change of gas injection valves ?) Lower fluctuation rate compared to pulse #45578
 Power in sidebands (f0-(20-40)Mhz) increases with ne up to -50 dB (-60dB on average in the 20-40MHz band) No significant spectral broadening with ne (DF@-10dB ~ 1.2MHz)
ITPA-IOS group, Kyoto, 18-21 October 2011

M.Goniche et al.

Power Spectrum in TL
fc,D@LCFS±5cmP(dBm)

F0-(20-40Mhz)

Pr

RF power in Transmission LineITPA-IOS group, Kyoto, 18-21 October 2011

M.Goniche et al.

Turbulence & Sidebands
Langmuir probe@launcher mouth

RF power inTransmisson Line

+10dB(×10)

×2<ne>(1019m-3)

0.5-3MHzF0 – (20-40MHz)• Level of turbulence & RF power in sidebands very well correlated• Is -60dB (-50dB peak) power level in sidebands (PDI) effective for
reducing CD efficiency ?
ITPA-IOS group, Kyoto, 18-21 October 2011

M.Goniche et al.

Pump width
RF reflected power in Transmisson Line

(width of Pforward 0.2MHz)

Pr1MA<ne>=3x1019

1.2M
A<ne>=5.2x1019• Rather poor resolution (DF=0.2MHz), can be improved in next expt.
 Width @-10dB is ~ 1.2MHz (C-Mod:~2.5MHz, FTU:1=>2.5MHz)
 No significant broadening between nl=3.6 & 5.7×1019m-3 (1MA), nl=3.75& 6.2×1019m-3 (1.2MA)
ITPA-IOS group, Kyoto, 18-21 October 2011

M.Goniche et al.

Results and analyses
ASIPP• No obvious
difference of
HXR between
lithium andboron coatingwall

HT-7

Conclusions

HT-7

ASIPP

• In the limited configuration with wallmaintenance, CD efficiency satisfies the 1/ne
trend as the density is less than 3.5×1019 m-3• There is no obvious difference in CD
between lithium and boron coating wall
• More discharges are needed in EAST at
different configurations, plasma currents andmagnetic to investigate the current drive
efficiency at a large density range

Ray tracing w/ collisional SOL shows
qualitative agreement w/ experiment
GENRAY/CQL3D code
predicts significant drop
in fast electron
population with density
 Model shows higher
non-thermal emission forlimited discharges
 Plan to limit plasma on
different surfaces inupcoming campaign
Limited discharges show narrower
spectrum and more fast electrons
Inner wall limited discharges
exhibit less spectral broadening
at high density (line averaged ne~1.4x1020 m-3)
 Downshifted harmonics due toPDIs are seen, but at -20dB orlower
 Analyzing data to determine if
broadening of main peak is due
to fluctuation scattering or PDIFull wave model with 2-D SOL shows
little collisional absorption on C-Mod2-D SOL model basedon conservation ofpressure along fieldlines Full wave solution
using LHEAF shows
minimal power
absorbed in SOL ( <10 kW at 1.5x1020m-3)
Full wave simulations show very far off axis
absorption  fast electrons not confinedStrong upshift of n|| aswaves reflect from edge
 Effect not produced by ray

tracing

Waves absorbed near
r/a=0.9
 Fast electrons diffuse
across LCFS before slowing
down Stronger absorption ofwaves at smaller r/a
improves current driveIncreasing plasma temperature leads tomore non-thermal emission at high ne
Models predict stronger
single-pass absorption should
mitigate impact of edge/SOLlosses Hotter I-mode discharges showenhanced non-thermal ECE ascompared to L-mode Hot He discharges show
improved HXR emission ascompared to cold Ddischarges


8 T, 1.2 MA, He
5.4 T, 0.8 MA, D

More cross-machine comparisonsneededNeed to determine proper normalized parameters
to compare data from C-Mod, Tore Supra, FTU…
 Density limit does not scale with traditionalparameters of ω/ωLH and n||-n||crit Reducing magnetic field on C-Mod to TS values (~3T) should make comparisons easier with fLHCD asmain difference for wave propagationDensity limit does not scale with ne/nG
across machines

HXR on TS drops at high ne/nG, but C-Mod density
limit is at very low ne/nG

Line averaged density normalized to f2 seems to bereasonable for comparisons between TS, C-modNeed to account for difference in magnetic field?
 B impacts n||crit, ωLH, although density limit does notscale with these parameters on C-Mod Low field experiments on C-Mod will help comparison

TSC-ModOverview of status for IOS-5.3


The variety of new dependences found in independent high density LHCD
experiments makes clear that the physics is complex. Effects in the SOL
and/or plasma periphery (r/a~0.8) appear critical. Likely mechanisms ininclude wave refraction in combination with:Collisional absorption.
Diffusion of fast electrons across LCFSParametric decay, and/or
Scattering from density fluctuations.
Dependence on magnetic configuration (limiter vs divertor, plasma size) again
point to SOL and ray trajectory effects. Would be very helpful to compare
configurations in other divertor devices (eg JET, EAST) to see if the difference
is consistent.
No models currently include all potential effects. Applying all available
models to each machine would be very helpful – can the dependences beunderstood? Some experimental profiles have been shared but modelingwork is not complete.
Equally important in extrapolating to ITER is a reliable prediction of its SOL
profiles! For this we need collaboration with ITPA DIV/SOL group. Errorbars on ITER SOL profiles are large!

Plans for IOS 5.3 in 2011-2012
All devices: Assemble and/or obtain with improved diagnostics, SOL n, T profiles, anddensity fluctuations, and parametric instabilities, for cases with and without
anomalously low ne density ‘limit’. (ie at n < nacc)
Do comparisons reveal common trends, point to causes?
Use in comparisons with (extended, shared) models.
Tore Supra: Continue analyzing existing data.
FTU: Increase/control off-axis Te using ECRH + LHCD. LH power scan at high ne.
C-Mod: Extend configuration studies (limit plasma on upper divertor tiles).
•Higher ICRF power experiments to obtain high single pass absorption.
•Diverted/limited experiments at lower B (~3 T) to get LHCD frequency scaling at TS
field. Also useful for comparing with EAST and JET.
JET: Increase B (N//,acc.) Dedicated density scans in divertor vs limiter could be criticalfor ITER! But run time unlikely until 2012.
EAST: LHCD is operating at 2.45 GHz, not yet at 4.6 GHz. In 2011, plan higherdensity experiments in different configurations, also effect of density fluctuation andparametric instability? Spokesperson will be Bojiang Ding