Fully predictive modelling of H-L transitionin ITER and present day tokamaks
V. Parail , P. Belo, G. Corrigan, F. Koechl, C. Labate, A.
Loarte, M. Mattei, G. Saibene, R. Sartori and ISM
Working Group.

Outline:• Modelling of H-L transition in ITER – why it is important?

•Models for L-H and H-L transition, type-III ELMs and pass to andfrom high performance;• Role of impurities;• Summary.
V.
Parail,IOSMeeting,
ITPAKyoto,Meeting,
October 2011
V. ParailIOS ITPA
OctoberKyoto,
2011

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Coupled JINTRAC/CREATE-NL simulation of H-L transition in

ITER Scenario-2– can ITER PF system cope with it?

*p (top) and Inner gap (bottom) time evolution following ”expected ” fast(blue/green), slow (black) and “unexpected” fast H-L transition (red)*)”expected”=highest gain and ideal controller

0.6

p0.4
0.2

m

0.2

0.1

V. Parail IOS ITPA Meeting, Kyoto, October 2011

Reference safe gap

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Transport models for L-H and H-L transition
Two models for L-H and H-L transitions were used in simulations- “global”
and ”local” models;•In “global approach” the code compares total heat flux through theselected magnetic surface (either top-of-barrier or deeper inside, forcode stability) with most recent parametric fits for L-H transition power
threshold from Martin et al. J. Phys 2008 (including an atomic massdependency):

PL H
•

717
0.0488 ne0,.20
Bt0.803 S 0.941 M 2

1

In “local approach” the code compares electron temperature at the
selected magnetic surface (normally on top-of-barrier or anticipated
top-of-barrier) with the “local” parametric fits for the electron
temperature at L-H transition (from E. Righi et al, Plasma Phys.
Control. Fusion 42 (2000) A199–A204):

Tcrit ,keV

0.39ne,20 0.64 B1.69 M 0.14 q95 0.86

V. Parail IOS ITPA Meeting, Kyoto, October 2011

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Transport models for L-H and H-L transition
After either comparing the heat flux Q with the power threshold PLH in“global” approach or Te,top with the critical temperature in “local” approachtransport within edge barrier is modified in 3 possible ways:
 Plasma stays in L-mode if Q< PLH or Te,top< Te,crit; Plasma enters H-mode with type-III ELMs if PLH<Q<or Te,crit<Te,top< Te,crit ,.

PLH, 1.5> >1

Transport within edge barrier is reduced to neo-classical level
between ELMs.
Type-III ELMs are similar to type-I ELMs (with Gaussian increase inedge transport coefficients) but with lower value of critical pressure
gradient cr-III<1 Plasma enters H-mode with type-I ELMs if Q> PLH or Te,top>
Te,crit with type-I ELMs having higher value of critical pressure gradientcr-I~1.8
V. Parail IOS ITPA Meeting, Kyoto, October 2011

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Transport models for L-H and H-L transition•We simulate all main plasma profiles including ion density and, in somesimulations, impurity;• Modelling of ion density (and impurity) is probably the most difficult task

since it involves modelling of cold neutrals, which originate in the SOL;
• Modelling on density pump out following H-L transition is even moredifficult as it involves not only SOL physics but also plasma-wall interaction

and neutrals removal by the cryopumps;• Since we do not include SOL modelling in simulations presented here, we
assume that all neutrals and impurities originate at the separatrix;•We also assume that outgoing ions are recylced from the separatrix withREC<1.
V. Parail IOS ITPA Meeting, Kyoto, October 2011

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A typical JET H-mode plasma with composite ELMs and fast H-L transition,
which is used as a template in our simulations (note a significant increase inline radiation after each ELM).

WTH
nedl

coreedge

PNBI
PradD

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“Non-local” model (1)• Discrete ELM model
undergoes a series ofrepetitive L-H-L transitions
caused by sudden energy flux
drop after L-H transition,
which are not usuallyobserved in experiment
V. Parail IOS ITPA Meeting, Kyoto, October 2011

Wth [MJ]•Discrete ELM model( = 0.95) PNBI [MW] <ne> [1019 m-3]

• Density trend is not so well
reproduced (adjustment ofrecycling could help);•JET #72207: preliminary data

64208
6
4
2015
10
50
1,51,0crit.

• Non-local model can be tuned
to give the temporal evolution
in Wth qualitatively in line withexperiment;

0,50,051,552,052,553,053,554,054,555,0Time [s]7/13

“Non-local” model (2)It is important to stress that description of H-L transition, which includes
transition to type-III ELMs (two broken lines, one with discrete and one withcontinuous ELMs), matches experimental observation much better than
Instant H-L transition
instant transition to L-mode.

V. Parail IOS ITPA Meeting, Kyoto, October 20118/13

“Local” model (1)BIII I

Local model
type-III H-mode

BIII I6

Wth [MJ]

Te 0.91TcritJET #72207: preliminary dataL-mode

1

Te 0.9Tcrit

type-I H-mode

PNBI [MW]Te 0.9Tcrit

2<BIII-I<4( = 0.95)

0.39ne,20201510
501.69

BM

0.14

q95

0.86

crit.

Tcrit ,keV

0.64

41,51,00,50,052,0

Righi PPCF (2000)

V. Parail IOS ITPA Meeting, Kyoto, October 2011

52,553,053,554,0Time [s]9/13Comparison between “Global” and “Local” model

particle transport withinbarrier;• Include radiation;• No validated multi-machine
local model exists!

Local model
Non-local model

PNBI [MW]Wth [MJ]

6420151050( = 0.95)• Fine tuning of heat andJET #72207: preliminary datacrit.

• Local model avoids nonphysical dithering transitionsof the non-local model• Reasonably good descriptionof the L-H transition• Fails to describe the fast fallin energy and density during
H-L transition• Possible ways to improvemodel include:

1,5
1,00,50,052,052,553,053,554,0Time [s]V. Parail IOS ITPA Meeting, Kyoto, October 2011

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Role of radiation (1)(note a significant increase in line radiation after each ELM).

WTHnedlcoreedge

PNBI
Prad
D

V. Parail IOS ITPA Meeting, Kyoto, October 2011

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Role of radiation (3)• Recent example of selfconsistent predictivemodelling of impurity
redistribution on top ofmain ion density and ionand electron
temperature simulation;• Note significant
temporary rise in line
radiation following each
type-I ELM (as observedin experiments)

WthPnbi, Prad

NNe

Zeff

L-modeType-III ELMs
V. Parail IOS ITPA Meeting, Kyoto, October 2011

Type-I ELMs
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Summary and unresolved issues

 Global model describes better H-L transition but fails to reproduce LH transition due to persistence of strong dithering; On the other hand, local model reproduces the dynamics of L-H
transition reasonably well but fails to reproduce fast H-L transition;
 Much more work is needed to bring density evolution in better

agreement with experiment; Impurity radiation might play an important role in the dynamics of H-Ltransition;
Systematic comparison with experimental results are needed before
applying either model to ITER.
V. Parail IOS ITPA Meeting, Kyoto, October 201113/13

backup

V. Parail IOS ITPA Meeting, Kyoto, October 2011

“Non-local” model (1)Ploss 0.8
PMartin 08

type-I H-mode•Discrete ELM model
Wth [MJ]AIII I

type-III H-mode

19

AIII I•Continuous ELM model
76543210-31

Ploss 0.8
PMartin 08•JET #72207: preliminary dataL-mode

1<ne> [10 m ]Ploss 0.8
PMartin 08

1<AIII-I<1.58642

PMartin 08

0.0488ne,20 0.717 B 0.803 S 0.941
Martin PPCF (2008)

Ploss 0.8

loss power at =0.8

V. Parail IOS ITPA Meeting, Kyoto, October 2011

PNBI [MW]015
105051,552,052,553,053,554,054,555,0Time [s]15/16

Role of radiation (2)• Adding some impurity radiation after big ELM crash helps to bring plasma toa long type-III period even with local H-L transition model;

PNB, PNB, PRAD

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