joint sewgs-tfe meeting s. brezinsek22/07/2008 tf e impact of n 2 on carbon chemistry in jet s....

Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008

TF E

Impact of N2 on carbonchemistry in JET

S. Brezinsek, Y. Corre

and TFE


TF E

JET experiments associated with N2 injection

High density divertor operation to approach type III ELMy H-mode: integrated scenario development for ITER Hybrid scenario studies with impurity seeding type I ELMy H-mode: operation window with small ELMs in perspectives for ITER Compatibility of advanced tokamak scenarios with the ITER like-Wall: power load reduction and (semi-detached) divertor operation for JET

Benefit: High density divertor operation at „acceptable“ divertor conditionsPenalty: Reduction of the confinfement

Study of the N2 scavenger effect: avoid carbon in remote areas

Good compromise needed!


TF EType III ELMy H-mode experiment

N2 blow

GIM10

GIM10

GIM11

gas form Observation and configuration

NII light

TFE 2005


TF EFirst observation of CN molecules in JET

Two spectra: prior and post injection Difference spectrum

CN bands appear only directly at the wall Nitrogen and oxygen remain also on inner viewing lines Minor reduction of Carbon lines at this injection level and location Increase of high-n Balmer lines => increase of local density This line-of-sight shows no signifcant recombination (~ 5-10 eV)


TF E

JET: N2+ could not be found in the spectrum!

No N2 and N2+ spectral lines observed

TEXTOR: N2+ spectra could be well identified (local gas blow )

JET and TEXTOR: N2 could not be observed!


TF E

Type III ELM regime with N-seeding:

Integrated scenario: hybrid type III ELM

- High N (>2.5) and low Ip (1.7MA) at q95~3.2

- self-generated non-inductive current

- stability properties (q close to unity)

Hybrid scenario:

Reference Hybrid D-fuel. Hybrid type III with N seeding

N~2.6

frad~50%

P=22MW

H98(y,2)*0.83

N~2.6

frad~25%

P=20MW

H98(y,2)*1.05

- High radiative fraction (75% for ITER)

- Reduced heat load (transient and stationary)

- Reduced erosion (PFC lifetime)

Hybrid Scenario with N2 seeding


TF E

Radiative Feed-back N-seeded

Type III

Feed-forward

100% deutérium

#68505

#68532

#68747

#68515

#68739

#68746

N=0.75x1022

N=1.58x1022

N>2.1x1022

N>2.1x1022

N-seeding Feed-forward

Type III

Type I

#68743

#68742

drops ~

10%

Hybrid type III(best pulse)

frad (baseline in between ELMs)

H98

(y,2

) *

Maxim

um f

rad with

D-fuelling

Type III ELM regime (frad>40%)

N-seeding enables to reach higher frad for similar H98*

Conclusion:

achieve hybrid type III ELM

Operational space


TF ECN emission

Far SOL Near SOL


TF ECN distribution

#68515 CN pattern #68532 CN pattern

Reference N2 injection

CN appears with some delay


TF E

Reduction due to N2 injection

#68515 CD pattern #68532 CD pattern


Hydrocarbon chemistry (outer divertor)

Hydrocarbons reduced during strong D2 and N2 injection


TF ECarbon ion flux (total sputtering yield)

Reduction due to N2 injection

#68515 CII pattern #68532 CII pattern


Carbon reduced during strong D2 and N2 injection


TF E

Wrong orientation#68515 D pattern #68532 D pattern


Incident deuterium flux

D remains almost constant => no strong sign of recombination


TF E

#68515 NII pattern #68532 NII pattern


Nitrogen flux during injection

Certain amount of nitrogen from previous discharges (at SP) 2 cleaning discharges performed


TF ESummary

CN observed in different experiments N2 and N2

+ not observed in any experiment Hybrid scenario:

Reduction of chemical sputtering (CH) observed at high D2 and N2 fluxes Reduction of total carbon yield (CII) observed at high D2 and N2 fluxes Strong emission of CN observed in the SOL (away from the N2 injection)

Role of local plasma temperatures (experiments close to detachment) Role of local surface temperatures (experiments cool down the target) Scavenger of hydrocarbons?

joint sewgs-tfe meeting s. brezinsek22/07/2008 tf e impact of n 2 on carbon chemistry in jet s....

Documents

n seeding n

tfe slide

joint sewgstfe meeting

brezinsek22072008 tf

nseeded type

injection slide

elm high n

different experiments