up 1 ITPA Naka meeting 2009 Transport simulation of current ramp-up & ramp-down by F. Imbeaux* presented by X. Litaudon* F. Imbeaux, F. Köchl, V. Basiuk, J. Fereira, J. Hobirk, D. Hogeweij, X. Litaudon, J. Lönnroth, V. Parail, G. Pereverzev, Y. Peysson, G. Saibene, M. Schneider, G. Sips, G. Tardini, I. Voitsekhovitch On behalf of : JET-EFDA contributors, Tore Supra work programme, ITER Scenario Modelling group (ITM-TF) Association Euratom-cea i a c a r m f c a r e d h i a c a r m f c a r e d h *
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Transport simulation of current ramp-up & ramp-down by F. Imbeaux* presented by X. Litaudon*
Transport simulation of current ramp-up & ramp-down by F. Imbeaux* presented by X. Litaudon*. Association Euratom- cea. *. - PowerPoint PPT Presentation
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ISM Working Group 1 ITPA Naka meeting 2009 31st March 2009
Transport simulation of current ramp-up & ramp-down
by F. Imbeaux* presented by X. Litaudon*
F. Imbeaux, F. Köchl, V. Basiuk, J. Fereira, J. Hobirk, D. Hogeweij, X. Litaudon, J. Lönnroth, V. Parail, G. Pereverzev, Y. Peysson, G. Saibene, M. Schneider, G. Sips, G. Tardini, I. VoitsekhovitchOn behalf of : JET-EFDA contributors, Tore Supra work programme, ITER Scenario Modelling group (ITM-TF)
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ISM Working Group 2 ITPA Naka meeting 2009 31st March 2009
Modelling of current ramp
2
• Aim of the working group: model current ramp-up (and down) in ITER
– Implications on PF system design,
– H&CD methods for current profile shaping
– flux consumption
• Main issues are related to the transport model
try to validate a model against present experiments
• Validation: li , Vloop, Te, Ti test against several JET, Tore Supra AUG, experiments (ohmic, NBI, LHCD, ECCD)
• Up to now, energy and current diffusion are modelled
• L mode edge plasmas
ISM Working Group 3 ITPA Naka meeting 2009 31st March 2009
Consideration on current ramp transport modelling
3
• Choice of the transport model : scaling-based, empirical, 1st principles
– Li prediction and Flux consumption strongly depend on the Te at >0.5
– Model has to predict Te up to = 1 with L-mode edge
– Scaling-based transport model are
• a priori less sensitive to the assumptions on the boundary conditions (stiffness issue, drift wave models not accurate close to the edge)
• Have hopefully a correct dependence on Ip and machine size for extrapolation
• May miss several physical effects try to validate on extensive range of machines / heating schemes
– empirical models: Bohm/gyro-Bohm and Coppi-Tang have been tried as well
• Validation on existing experiments is essential
• Excellent opportunity for code-to-code benchmarking :
– Jetto and Cronos used in comparison with experimental data
– Astra, Jetto, Cronos used in ITER predictions
ISM Working Group 4 ITPA Naka meeting 2009 31st March 2009
Database from JET, Tore Supra, AUG with various H&CD mix
4
• Current ramp-up for base-line (q95~3) & AT scenario (q95~5) :
• Current ramp-down from base-line scenario (2.4T/2.7MA, q95~3):
Pulse ramp-down additional heating
JET 72200 slow noneJET 72202 fast noneJET 72210 fast NBI heating until ramp-downJET 72241 fast NBI heating after ramp down (in low Ip phase)
TORE SUPRA
AUG 22110 (ohmic) just added last week
To be transferred to ITPA database }
ISM Working Group 5 ITPA Naka meeting 2009 31st March 2009
Scaling-based model
5
• Scaling-based model: energy content of ohmic or heated Ip ramps with L-mode edge correctly modelled by either
– H mode scaling with H98 = 0.4 – 0.5
– L mode scaling with H97 = 0.6
• i = e, renormalised so that
• Fixed () shape : power balance chi’s during ramp-up tend to be rather flat, then strong increase towards the plasma edge : (,t) = A(t)(1+6 2 + 80 20)
• Boundary Te ( = 1) taken from experiment (guessed from ECE)
• Ne profile taken from experiment (JET: inversion of interferometry data)
• Flat Zeff assumed, <Zeff> taken from experiment (Bremsstrahlung)
thlossth WPHW 9898
ISM Working Group 6 ITPA Naka meeting 2009 31st March 2009
Calibration on JET shot 70497 (constant q95 ~3 ohmic ramp-up)
6
• Model i = e, renormalised to IPB98 scaling, H98 = 0.5 (mimics L mode), radial shape 1+6 2 + 80 20 (adjusted to fit experimental Te profile peaking).
• Te is correctly reproduced.
• CRONOS simulation
t = 0.5 s
red - : Simulation
blue * : ECE
Purple * : Thomson scattering
t = 4 s t = 5 st = 2 s
2.6T/2.6MA, q95~3
ISM Working Group 7 ITPA Naka meeting 2009 31st March 2009
• Model i = e, renormalised to IPB98 scaling, H98 = 0.5 (mimics L mode), radial shape 1+6 2 + 80 20 (adjusted to fit experimental Te profile peaking).
• Te is well reproduced for > 0.6. Even if larger deviations occur inside = 0.6, they almost do not affect the li evolution.
• Li slightly overestimated, li ~ 0.08, ~ measurement accuracy.
• Vloop good, slightly underestimated
Apply same model on another ohmic ramp for AT scenario (JET #72818)
7ITPA meeting Milan, October 2008, F. Imbeaux
t = 6 s
Simulation
ECE
Thomson scattering
3 6 5 4
time (s)
4 5 5.5 3.5 4.5
time (s)
2.7T/1.8MA, q95~5
ISM Working Group 8 ITPA Naka meeting 2009 31st March 2009
Ohmic Ip Ramp-down (JET 72202)
8
• Both models follow equally well li and the volume averaged Te
Experimental
Bohm/gyro-Bohm*
Scaling, H98 = 0.5
JETTO
*without non-local Bohm multiplier
2.4T/2.7MA down to 1.0MA
14 16 18 20 22 24
time (s)
ISM Working Group 9 ITPA Naka meeting 2009 31st March 2009 9
• Comparison of the two models : some difference in Te profile peaking, that Bohm/gyro-Bohm provides a better agreement (for JET)
• A possible approach consists in combining: profile dependence as B/gB + scaling renormalisation for multi-machine capability ?
Ohmic Ip Ramp-down (JET 72202)
Experimental
Bohm/gyro-Bohm
Scaling, H98 = 0.5
JETTO
ISM Working Group 10 ITPA Naka meeting 2009 31st March 2009
LHCD assisted ramp-up in AT scenario (JET 72823)
• Scaling base model, H98 = 0.4
• LHCD calculated during interpretative run
• Li slightly overestimated, li ~ 0.1
3 6 5 4
time (s)
3 6 5 4
time (s)
3 6 5 4 2
2.7T/1.8MA, q95~5
ISM Working Group 11 ITPA Naka meeting 2009 31st March 2009
t = 3 s t = 4 s t = 5.5 s
Excellent fit of the volume averaged temperatures, both electron and ion
LHCD assisted ramp-up for AT scenario (JET 72823)
Simulation
ECE
Thomson Scattering 2.7T/1.8MA, q95~5
ISM Working Group 12 ITPA Naka meeting 2009 31st March 2009
Ion temperatures from CXS
LHCD assisted ramp-up for AT scenario (JET 72823)
Simulation
* CXS
NBI blips (MSE & CXS) during current rise : • CXS & MSE measurements
t = 4 s t = 5 s
TI TI
2.7T/1.8MA, q95~5
ISM Working Group 13 ITPA Naka meeting 2009 31st March 2009
LHCD assisted ramp-up for AT scenario (JET 72823)
t = 4.5 s
NBI blips (MSE & CXS) during current rise : • CXS & MSE measurements
t = 5.5 s
• Comparison to MSE q-profile (EFTM)
2.7T/1.8MA, q95~5
ISM Working Group 14 ITPA Naka meeting 2009 31st March 2009
First attempts to test GLF23 in JET ramp-up phase
• When applied from the edge at high q (JET 71828, ohmic, 1 s after breakdown, 5 < q < 15 )
• Very low transport predicted near the edge ( = 1) barrier forms and non monotonic Te profiles appear
• When trying to patch the edge (impose = 10 m2/s from = 1 to = 0.75), the same problem appears at = 0.75
• Possibility to use GLF23 ? : on the whole radius ? At high q ?
Te
Ti
Normalised radius
(2.6T/2.6MA, q95~3 at flat top )
5.5sJET 77251JET 71828 t=1s
ExpAfter breakdown
ISM Working Group 15 ITPA Naka meeting 2009 31st March 2009
Tore Supra ramp-up experiments
• Fast current ramp (0.7 MA/s), plateau Ip = 0.9 MA reached at t = 1 s
• off-axis co-ECCD (.7 MW) and/or LHCD (.8 MW) during ramp at t = 0.25s
• Same li evolution, but different Te evolution & time of first sawtooth
TS40679 : LH+ECCD
TORE SUPRA
TS40676 : ECCD
Blue : usual scaling-based model H98 = 0.5
Green / red: two experimental measurements of li
ISM Working Group 16 ITPA Naka meeting 2009 31st March 200916ISM Working group
1st set of simulation: ITER ramp with constant boundary shape
• L-mode transport model: (r) validated on JET & TS with H98 = 0.5.
• The edge temperature set to Tb=20*Ip[MA] eV, although with the chosen transport model Tb assumption is not that important.
• Use a formula for Zeff (used by the ITER team):
– Zeff = (1.7+2.3x(0.5/ne)2.6)), Carbon is main impurity
• The current ramp follows the ITER reference one with 15MA at 100s:
• The simulations start at 3MA (t=8s), with an initial condition for the q-profile (li=1) and a temperature profile.
• ITER divertor shape from Ip3MA: full bore plasma.
• densities <ne>/nGW = 0.15; 0.25; 0.4 (low to medium density).
• Use a variation of heating: Ohmic, 10MW and 20MW of ECRH with power deposition at mid-radius (heating only, no current drive).
ISM Working Group 17 ITPA Naka meeting 2009 31st March 2009
Modelling of ITER ramp with various heating
& densities
17Working group D. Hogeweij et al, EPS 2008
<ne>/nGW = 0.25
<ne>/nGW = 0.4
<ne>/nGW = 0.15
10 MW ECRH <ne>/nGW = 0.25
20 MW ECRH <ne>/nGW = 0.25
ISM Working Group 18 ITPA Naka meeting 2009 31st March 2009
Modelling of ITER ramp with various heating at <ne>/nGW = 0.15
18Working group
Te profile evolution. Hollow profiles achieved transiently with off-axis ECRH, still present at the end of the ramp
Te ITB may be obtained with such hollow q-profiles (not in the model)
D. Hogeweij et al, EPS 2008
ISM Working Group 19 ITPA Naka meeting 2009 31st March 200919ISM Working group
2nd set of simulation: ITER ramp with evolving boundary shape
ASTRA
CRONOS
JETTO
Tore Supra like
JET like
ISM Working Group 20 ITPA Naka meeting 2009 31st March 200920
• Ohmic ITER ramp-up, time-dependent plasma boundary (preset), using the same model as before, H98 = 0.5
• Code comparison: rather close agreement between CRONOS and JETTO, in spite of the differences in the treatment of equilibrium, transport coefficient renormalisation, …
• Detailed code comparison starting from basic simulations going on between ASTRA and JETTO
Working group
2nd series: ITER with prescribed evolving boundary shape
ISM Working Group 21 ITPA Naka meeting 2009 31st March 2009
• Up to now, mainly the scaling-based model was used, work being extended to empirical models like Bohm/gyro-Bohm and Coppi-Tang
– Test on multiple machine data : JET, Tore Supra and Asdex Upgrade
– Rather good agreement with experimental data (on Te, li and Vloop prediction) has been found in several cases. None of these models can be ruled out yet.
– Analysis still in progress, more detailed trends / observations to be given when the full database analysis will be completed
– Multiple transport codes working on the same dataset allow detecting bugs / sensitivity to unexpected parameters / assumptions
– Coppi-Tang implementation : still doubts on a few details (definitions of some quantities) need to have the same as in TSC
• Extend data base to other heating schemes, other machines (ITPA) should contribute to further validate the models
• Continue testing other models : – introduce more sophisticated radial dependence in scaling-based ? Try further
GLF23, through first attempt was quite unsuccessful
• Include free-boundary equilibrium calculations : try for the end of 2009
Perspectives
ISM Working Group 22 ITPA Naka meeting 2009 31st March 2009