Impurity transport characterisation in JET operational scenarios

Carine Giroud 1 E1/E2 meeting 7th April 2011

Impurity transport characterisation in

JET operational scenarios

C. Giroud, C. Angioni, H. Nordman, D. Strintzi, M. Barruzzo, M. Brix, P. Burratti, C. Challis, P. de Vries, J. Hobirk, E. Joffrin, X. Litaudon, A. Meigs, J. Mailloux, M. O'Mullane, V. Naulin, P. Mantica, M. Valisa.

Experimental data collected from 3 dedicated sessions, and parasitic experiments to scenario development sessions in 2007 and 2009.


Motivation

Transport of impurities was probed over a wide range of scenarios • Assess where the transport of impurity is neoclassical ? Is there a radial dependence ? An impurity dependence ?

• How does Dimp/eff vary ?

• Characterisation of the impurity peaking in JET scenarios

• Detailed comparison of impurity transport of L-mode discharges with theoretical models (covered in Emiliano’s talk)

No pedestal impurity transport in this work

Experimental data collected from 3 dedicated sessions, and parasitic experiments to scenario development sessions in 2007 and 2009.


Database of impurity transport

• Reduce error estimation on DZ and VZ by testing the analysis method over a wide range of experimental conditions.• NBI heated discharges are investigated and no Internal Transport Barrier discharges are presented. (data available but not presented here)• MHD has been observed (NTMs) in all discharges, apart from L-mode discharges.• Discharges with weakly ST or ST free ( q0 uncertainty ~ 0.2)

ne(r/a~0.2)<ne> r/a<1.0

In green: discharges discussed in talk


Impurity diffusion: neoclassical?

• NBI heated discharges only

• At r>0.6, impurity diffusion is 2 order of magnitude above neoclassical value for all probed scenarios.

• Region of impurity diffusion reduction varies between scenarios and can be very central r/a<0.2 to r/a<0.4.

• At r>0.6, diffusion of impurity is Z independent.

Look into more details in scenario dependence

Symbolopen neoclassicalfull measured


Dim

p/D

neo

• L-mode: • reduced diffusion within r/a<0.2, Dimp/Dneo~10 for all Z

• H-mode: ( q0~2, H98(y,2)~0.6!) • reduced diffusion within r/a<0.2, Dimp~Dneo but is not characteristic behaviour, and likely to be influenced by presence of MHD.

Ne Ar Ni



Dim

p/D

neo


• H-mode: ( q0~2, H98(y,2)~0.6) • reduced diffusion within r/a<0.2• Dimp~Dneo but not characteristic behaviour MHD presents.

• Hybrid 2007: ( q0~1, H98(y,2)~0.8-0.9, 3/2NTM) • reduced diffusion within r/a<0.4, Dimp~10 Dneo• at r/a~0.6, Dimp~40-50 Dneo

Ne Ar Ni

r/a r/a r/a



Dim

p/D

neo




Ne Ar Ni

r/a r/a r/a

• Steady-state 2007 • reduced diffusion within r/a<0.4, Dimp~ 2-3 Dneo (Ar/Ne)• at r/a~0.6, Dimp~20-40xDneo.

2/1 NTM



Dim

p/D

neo




Ne Ar Ni

r/a r/a r/a

• Steady-state 2007 • reduced diffusion within r/a<0.4, Dimp~ 2-3 Dneo (Ar/Ne)• at r/a~0.6, Dimp~20-40xDneo.

• Hybrid 2009 H98(y,2)~1.37, 4/3 or 5/4 NTM

• reduced diffusion within r/a<0.4, but variation for shot without 3/2 NTM• r/a<0.2 Dimp~ 2-4 Dneo (Ar/Ne/Ni)• r/a~0.35 Dimp~4-10 Dneo (Ar/Ne)

3/2 NTM 3/2 NTM



• Neoclassical diffusion: mostly in high confinement hybrid discharges within r/a<0.2 where Dimp~2-4 Dneo for all impurity.

• Region of reduced diffusion can vary from r/a<0.2 ( L-mode, “H-mode”) to r/a<0.4 for hybrid, SS.

• The diffusion is mainly due to turbulence across the plasma radius

how does Dimp compared to eff?

Impurity diffusion


Dimp vs eff

• eff difficult to determine accurately in r/a~0.15

• At r/a~0.6, on average Dimp/eff ~1. Some doubt on discharges with Dimp/eff~0.4.

• At r/a~0.35, Dimp/eff ~0.4 for hybrid low (no 3/2NTM), Dimp/eff~1. for L-mode and H-mode.

Similar to finding in DIII-D where DHe/eff ~0.5 in core of VH mode

Dim

p


• Due to MHD (mainly NTM at mid-radius), a comparison between neoclassical value and determined convection is only meaningful in the plasma core r/a<0.2.

• In the core (r/a~0.15), Vmeas is mostly of the same sign as Vneo, and vary on average from neoclassical level to within a factor ~4. Vmeas is of the same order as Vneo.

• We do not observe the simple rule V=Vneo for high Z.

Influence of neoclassical pinch ?r/a~0.15

Ne Ar Ni


• Steady-state profile are calculated from the determined transport coefficient with UTC-SANCO assuming a constant source.

• C-profile always less peaked than the electron density and is hollow for electron peaking below 1.3.

• Ne peaking is similar to C but can become more peaked for the electron density above 1.3.

• Ar and Ni are generally more peaked than the electron with a discrepancy that seems to increase at high electron density peaking.

what plasma region determine the global peaking ?

Global impurity peaking


The Z dependence of global peaking

is the result of impurity peaking in

central region (r/a<0.4).

Global impurity peaking


• In the core (r/a~0.15), Vmeas is mostly of the same sign as Vneo, and vary on average from neoclassical level to within a factor ~4.

• On average, magnitude of RV is greater than D. As Z increases, magnitude of RV increases in respect to D V plays an important role in central peaking (can be influenced by Vneo).

• The Z dependence of global peaking is the result of impurity peaking in central region (r/a<0.2-0.4).

Comparison experimental results of impurity transport with predictions made with Weiland models and linear GK GS2 for L-mode discharges (no MHD).

Imp. convection and global peaking


Conclusion

• The transport of impurity is rarely neoclassical even in the central region (r/a<0.2)• Dimp~10x Dneo.• one exception: some low hybrid discharge where Dimp~2-4 Dneo.

• Dimp/eff:• at r/a~0.6, Dimp/eff~1• at r/a~0.4, Dimp/eff~0.4 for hybrid discharges at low

• Convection (r/a<0.2)• Vmeas is on average of the same sign as Vneo, and comparable in magnitude.• magnitude of RV is greater than D (more so high Z) V plays important role in peaking.

• Observed Z dependence of global peaking is the result of impurity peaking in

central region. (results from a neo and anomalous contributions).

• Anomalous transport predictions (L-mode) Linear GK and fluid model are in good agreement with experimental impurity peaking with exception of C : this remains an open question ?


What to address in C28C29 ?

• No dedicated experiment on testing exp/theory in C28No dedicated experiment on testing exp/theory in C28 C29: C29:

knowledge of impurity transport in support to scenario development mainlyknowledge of impurity transport in support to scenario development mainly

• Type of discharges to be Type of discharges to be

– OhmicOhmic

– ST L-modeST L-mode

– ST H-mode 2.5MAST H-mode 2.5MA

– Hybrid high Hybrid high /low /low at 1.7T/1.5MA and then increase Ip at 1.7T/1.5MA and then increase Ip

• What problem could be encountered from W point of view ?What problem could be encountered from W point of view ?

– Ohmic: not much expected ?Ohmic: not much expected ?

– ST L-mode: no problem expected ?ST L-mode: no problem expected ?

– ST H-mode: pedestal (elms) + ST activity + W influx ?ST H-mode: pedestal (elms) + ST activity + W influx ? Mainly pedestal, source and MHD activity not so much addressing transport Mainly pedestal, source and MHD activity not so much addressing transport

due to turbulence. due to turbulence. More effect of MHD to be expected than shown in this talk !More effect of MHD to be expected than shown in this talk !


What to address in C28C29 ?

• At some stage during the development need additional information to go forward At some stage during the development need additional information to go forward

– Ar/Ne, Ni injection maybe Af: probe the transport to have a better handle on Ar/Ne, Ni injection maybe Af: probe the transport to have a better handle on

the problemthe problem

– how often can we realistically be expected to do that ? How useful would it how often can we realistically be expected to do that ? How useful would it

be ?be ?

Tools• SANCO with W or STRAHL ? SANCO with W or STRAHL ?

• Reliable W atomic data : how long would that need ?Reliable W atomic data : how long would that need ?

– present W datapresent W data

– future development of W datafuture development of W data

– ionisation, recombinaison, SXR, bolometryionisation, recombinaison, SXR, bolometry

• ccWW at edge and core output in PPF at edge and core output in PPF

• influx output in PPFinflux output in PPF


What to address in C30b ?

• Dedicated experiment on experiment / theory impurity transport:Dedicated experiment on experiment / theory impurity transport:

– He, Be, B: low Z end to be testedHe, Be, B: low Z end to be tested

– high Z end with Whigh Z end with W

– effect of rotation and ICRH effect of rotation and ICRH


Ne Ar Ni

• On average, magnitude of RV is greater than D

• As Z increases, magnitude of RV increases in respect to D.

Convection plays an important role in the central peaking (and as Z increases). Neoclassical

convection is comparable to Vmeas and can have an influence.

r/a~0.15Symbolopen V neoclassicalfull measured

Impurity peaking in central region


• Anomalous transport calculated with Weiland fluid models for ITG/TE modes.(Nordman, EPS 2010) • Predicted Dimp and Vimp are the same for Ne, Ar, Ni.

• At mid-radius, the predicted D and V are in reasonable agreement for Ne, Ar and Ni.

• Dmeas and Vmeas in core not predicted by Weiland model as modes are found stable within r/a<0.4.

• Dmeas/Chi_eff~1. / Weiland model~ 1.5-1.8 GS2 comparison on-going.

Anomalous transport: D and VD

imp

Vim

p


Anomalous transport: peaking

• Additional prediction of anomalous peaking with linear GK GS2 (Angioni, Strintzi). • Agreement between Linear GK code and Weiland model prediction on peaking

• Within errors, the predicted peaking is in agreement with experiment apart from Carbon.

• Carbon is predicted peaked whereas it is measured flat or hollow in the experiments in L-modes at mid-radius thermodiffusion higher than predicted in codes. (Giroud IAEA 2006)

Impurity transport characterisation in JET operational scenarios

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