E1/E2 Meeting, 7 April 2011 1 Achievements and open issues in impurity profile control at JET. M. Valisa and Angioni Carraro Coffey Lauro-Taroni Predebon.

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E1/E2 Meeting, 7 April 2011

Achievements and open issues in impurity profile control at JET.

M. Valisa and Angioni Carraro Coffey Lauro-Taroni Predebon PuiattiAlper Belo Corrigan vanEester Garzotti Giroud Lerche Mantica Naulin Tala Tsala et al

JET E1\/E2 meeting - Culham 7 April 2011

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Outline

Background

What we have learnt at JET of the effect of RF on impurity transport

Open Issues

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Impurity accumualtion avoidance may require Active Control to guarantee stationary plasma fusion experiments and optimization of reactor efficiency.

Codes validation is required to include impurities and their control in a ITER/ DEMO flight simulator

RF well know empirical means to pump out impurities in present day experiments. Underlying mechanims still uncertain.

Background 1

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• For core issues, what really matters is the relationship between

D_impurities , D_fuel and e,i , since the relevant parameter is dilution.

• Used impurity density perturbations (= trace impurity )to work out impurity transport as with laser ablation. Modelling of the transient evolutions of the impurities provides an estimate of the transport coefficients.

Background 2

nnD v+ accurate atomic physics

Used 1D transport model with

Main diagnostics for metal impurities: SXR, emission lines , bolometry

At stationarity

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What we have learnt at JET

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Change RF deposition profile (heat modulation to work out heat transport – P Mantica Gas modulation or pellet for DD – L Garzotti)

Shown that D imp and e,i in some situations go together

See ME Puiatti et al PoP 2006

RF (3He minority) deposition radius

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M-E. Puiatti PoP 13 2006 ; C. Angioni et al PRL 2006

RF power on electrons is effective as a means to control heavy impurities in JET low collisionality regimes

eff [=10-14 <ne > <Te >–2 Zeff R ] ≤0.2

MH 58144

MC 58149

Dominant ITG inward v

Subdominant TEM outward v

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RF power as a means to control heavy impurities also in JET Elmy H mode / HIGH DENSITY and Ar puffing in JET

•Core diffusion decreases

•Core convection also decreases and may become outward

NO ICRH

Shot 52136: Strong INward convection

Shots 53548 , 53015 WITH ICRH:

convection may become OUTward

M.E. Puiatti et al .Plas. Phys.Contr. Fus. 44(2002)1863

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LBO & ICRH power scan: Ni and Mo areexpelled from the centre as power increases

H minority / H mode / low collisionality/ about 12 MW NBI, 1.5MA, 3T

= 0.2

Ni and Mo

68383 and 81 – marginal H mode(L-mode, but P>>LH threshold)Low collisonality, Similar triangularity and elongation

Mo( 42) and Ni ( 28):similar behaviour

Open symbols Shots around 58140He3 minority

RF power scan

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GS2 Simulation of the shots with RF power scan

No sign of flow inversion with increaasing RF

Quasi linear, electrostatic

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Mo( 42) and Ni ( 28) have very similar behaviour

= 0.5

Ni and Mo

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Discharges of the RF power scan

= RF Power increase“ “

Target Plasma:

Ip=1.5 MAB= 3TNBI= 12 MWLow triangularityNo sawteethCentral ICRH

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Discharges of the RF power scan

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RF power scan and LBO injection of Ni

= 0.2

Nickel

Out of many correlation attempts ( with rotation, Ti/Te, q and q shear etc ) the best correlation is with R/LTi

Signature of a neoclassical trend?

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= 0.2

Good correlation of v/D with R/LTe

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Correlation with toridal rotation

= 0.2

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Correlation with q and q shear

= 0.2

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= 0.2

Good correlation of v/D with R/LTe

NO RF

1 MW RF

3MW RF

Stationary profiles : extrapolation using evaluated vand D’s

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neoclassical V and D from NCLASS

Neoclassical transport parameters too small:do not macth the experiment

0.05

0.2

0

0.15

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Sensitivity study on neoclassical transport

chord integrated central SXR emission during theinjection of Ni in discharge 74360

ExperimentSimulation - normalized

V neo and D from Exp.

v neo and v/D from Exp

LBO

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D’s and V’s in the ICRH scan database

Impact of RF scan seems to be more on v than on D

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Open issues

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Open Issues

- Role q and q shear? Required shots with similar settings but different timing of LBO during pulseor different timing of ICRH and or NBI

- Role of rotation and shear rotation ? Counter beam or different share of ICRH and NBI keeping total power constant.

1,4

1,6

1,8

2

2,2

2,4

2,6

2,8

44 45 46 47 48 49 50 51

q

74354743557435674360

q(r

ho

=0

.2)

t(s)

ICRH

1) Understand the pump out effect of ICRH

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Open Issues

- Is there a direct role of the RF itself ?

Test different heating schemes – ICRH on fundamental harmonic ,He3 minority heating

-Are neoclassical terms correctly evaluated?

- In/out asymmetries / role of centrifugal forces. Impact on analysis

Can sawteeth be as efficient as RF ? How large and frequent must ST be? Shown in the past that if small their efficiency is smaller than 2MW RF (Puiatti et al PPCF 2003)

2) Issue of poloidal asymmetries

3) Efficiency of RF compared to sawteeth

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Open Issues

4) Effect of ICRF on Zeff In #68383 ( 8 MW ICRH ) Zeff increase from 2 to 4-5 with Zeff from C nearly constant ( L Carraro et al EPS Warsaw) See also JET works by Czarneka where the problem has been investigated in some details. Lot of work also on other machines.

5) Analysis Tools for dealing with Tungsten

- Do we have reliable tools for detection and analysis ?- Will W radiation be overwelming to make traditional techniques( such as LBO with Ni and Mo) useless?

6) How to implement a feedback control system on impurity accumulation

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Data available are:• some SXR/VUV spectroscopic lines (KT2 and KT4) with a fairly coarse time resolution. Have lines been identified ? • Soft-X rays: a vertical camera with 34 l-o-s (250μ filter) and a horizontal camera with 17 channels (350μ filter).

Detection and analysis of W on JET

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Heavy impurity transport simulations.Available the predictive impurity transport simulation JETTO/SANCO

The ADAS tables can be used to calculate the local emissivities that integrated along the various l-o-s can simulate the experimental SXR channels

Standard treatment: ZI +1 equations with ionisation and recombination to and from neighbouring ionised states provided by ADAS/adf11 tables.

Superstages treatment: Reduced set of equations each representing a ‘bundle’ of contiguous ionised stages (a ‘superstage’) in coronal equilibrium between each other.

W from 74 to 35 , or more aggressively down to 10 superstages.

Detection and analysis of W on JET

See L Lauro-Taroni H Summers et al presentation at the General Task Force T Meeting 16 February 2009

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Tungsten data available at JET

Most recent W LBOs have been performed during C17 (Nov 2006):68373 3.2T/2.3MA 4.5 MW ICRH, 8.9MW NBI, 0.5 MW LHCD68374 6 MW ICRH, 8.9 MW NBI, 0.8MW LHCD68387 7.7 MW ICRH, 9 MW NBI, 1.1MW LHCD

68373SXR

BOLO

W LBO data available at JET available for testing tools

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SXR Horizontal cameras - B.Alper 68373. W ablation at t=55 s

Example of SXR after LBO of W shwoing central peaking

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SXR Vertical Camera ( B.Alper) 68373 W ablation at t=55

In-Out Asymmetry

Example of SXR after LBO of W showing polidal asymmetry

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Different superstages partitions of W 74 ion (no bundling)35 superstages: natural bundling26 superstages: natural bundling, with 55+ upwards bundled into 2 SS 10 superstages: ions with ionisation potential >800 eV bundled into 1 SS

( for edge plasmas).

But the partition into 10 SS yields a slightly different SXR simulation, with a faster rise in the initial phase. ONGOING WORK

Could be superstage treatment be included in feedback controlled system?

All partitions yield the same nW(x,t), same total number of particles, same Power

Effect of ionization stages partitioning has been tested

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SXR

Black: V Ch. 3 (peripheral)

Red: V Ch 12 (central)

Light blue: H Ch11 (central)

SXR

-500

0

500

1000

1500

2000

2500

3000

3500

4000

54.95 55 55.05 55.1 55.15 55.2 55.25 55.3 55.35 55.4 55.45

time

W/m

2

W source

ΔP bolo

P sim

D (m2/s)

50

100

V (m/s)

Example of ongoing work: simulation of Prad and SXR after W LBO

time

time

ρ Jetto

By L Lauro-Taroni

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Summary and conclusions

• Central ICRH effective on JET to pump out Ni and Mo which feature peaked profiles in JET NBI only H mode plasmas

About 3 MW ICRH required in the analysed shots

• W : only very Preliminary analysis by Lauro Taroni

• Mechanism for impurity pump out? Trends recall neoclassical transport ( proportional to R/LTi) but absolute values do not fit

• Ni (28) and Mo(42) seem to behave similarly , and W?? •ICRH is accompanied by higher Zeff .

• Possibility of treatment of W in superstages successfully implemented in JETTO/SANCO (ADAS files for bundled impurities can be generated )

Simulations of a Tungsten injection in JET started

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SHOT Ip(MA) Bt(T) NBI (MW) ICRH (MW) H/He3

58143 1.8 3.27 13.6 4.7 He3

58149 1.8 3.27 14.6 5.1 He3

66432 1.8 3.35 20 2 He3

66434 1.8 3.35 20 2 He3

68383 2.3 3.2 8.3 8 H

69808 1.8 3.2 11 0 H

74354 1.5 3 12 0 H

74355 1.5 3 12 1 H

74359 1.5 3 12 3 H

74360 1.5 3 10.7 2.9 H

74363 1.5 3 10.5 2.9 H

Ni injections

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68381 2.3 3.2 9 8.45 H

74357 1.5 3 12.5 0 H

74362 1.5 3. 10.5 3 H

Mo injections

SHOT Ip(MA) Bt(T) NBI (MW) ICRH (MW) H/He3

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Soft-X rays:

a vertical camera with 34 l-o-s (250μ filter)

and

a horizontal camera with 17 channels (350μ filter).

E1/E2 Meeting, 7 April 2011 1 Achievements and open issues in impurity profile control at JET. M. Valisa and Angioni Carraro Coffey Lauro-Taroni Predebon.

Documents

jet slide

jet e1e2 meeting culham

mo slide

electrostatic slide

stationarity slide

effect of rf

heavy impurities

impurity profile control