Joint SEWGs-TFE meeting S. Brezinsek22/07/2008 TF E Impact of N 2 on carbon chemistry in JET S....
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Transcript of 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
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
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!
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
TF EType III ELMy H-mode experiment
N2 blow
GIM10
GIM10
GIM11
gas form Observation and configuration
NII light
TFE 2005
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
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)
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
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!
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
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
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
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
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
TF ECN emission
Far SOL Near SOL
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
TF ECN distribution
#68515 CN pattern #68532 CN pattern
Reference N2 injection
CN appears with some delay
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
TF E
Reduction due to N2 injection
#68515 CD pattern #68532 CD pattern
Reference N2 injection
Hydrocarbon chemistry (outer divertor)
Hydrocarbons reduced during strong D2 and N2 injection
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
TF ECarbon ion flux (total sputtering yield)
Reduction due to N2 injection
#68515 CII pattern #68532 CII pattern
Reference N2 injection
Carbon reduced during strong D2 and N2 injection
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
TF E
Wrong orientation#68515 D pattern #68532 D pattern
Reference N2 injection
Incident deuterium flux
D remains almost constant => no strong sign of recombination
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
TF E
#68515 NII pattern #68532 NII pattern
Reference N2 injection
Nitrogen flux during injection
Certain amount of nitrogen from previous discharges (at SP) 2 cleaning discharges performed
Joint SEWGs-TFE meeting S. Brezinsek 22/07/2008
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?