Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 1 Th Loarer with special thanks to S...

Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 1

Th Loarerwith special thanks to

S Brezinsek, J Bucalossi, I Coffey, G Esser, S GruenhagenPh Morgan, V Philipps, R Stagg, J Strachan.

And alsoEU TF on PWI and JET EFDA contributors

Fuel retention in JETRecent results in L and H-mode


OUTLINE

Recent results in- L mode- Type I ELMy H-mode

Retention- Implantation- Co-deposition: correlation carbon source- EDGE2D

Further plan


Introduction

- Reference in carbon before moving to a full metallic wall: Quantify the benefit (?)

- Validation of the method

- Can we avoid the regeneration?

- Gas balance “on line” for each discharge?

- DT experiments (JET and TFTR) remain very good references for

- Gas balance

- Post mortem

- Fuel removal

- Comparison with other devices: AUG, JT-60U, but also limiter devices

- Extrapolation to ITER


Calibrated Particle Source

(Gas, NBI…)

Divertor cryo-pumps

Wall Retention

Long & Short Term

Gas balance procedure on JETRepeat sets of identical discharges (no intershot conditioning) to avoid history effects Plasma

Injection = Pumped + Short Term Ret + Long Term Ret

Total recovered from cryo-regeneration: Pumped + intershot outgassing over ~800s (assumed equal to Short Term Ret )

Regenerate cryopumps before and after expt. collect total pumped gas (accuracy~1.2%)

Dedicated series of experiments: L and H mode in 2007-2008 as ref for ILW


• 8 repetitive pulses

• Ip/BT=2.0MA/2.4T, 1.8MW ICRH “only”

(42MHz)

• All auxiliary pumps (NBI, LH, main Turbo pumps) off

• Regeneration of divertor cryopump before and after session

“Long Term” retention

Injected – Regenerated

(regeneration about 60 min after last shot)

L mode: short limiter phase

L-mode, HT3 with ~1.7x1022Ds-1 and Early X-point formation

Recent session Evaluate the contribution of the limiter phase


HT3 – Mode B (early X-point) and D

-Mode D “standard X-point” (~9s of limiter start-up phase) # 70534

- Mode B: Early X-point” (~1.3s of limiter start-up phase) # 73654

“Except” the limiter phase Comparable plasma parametersIp, BT, ne, ICRH, Gas rate, recycling…

Ip

ne

ICRH

Gas rate

Total injected

H

Limiter phase

Limiter phase

Ip/BT=2.0MA/2.4T,

1.8MW ICRH “only”


Heating and gas injection ~ 75 s (8 pulses) – Mode B (8th July 2008)

Total divertor time: ~ 170 s, Total limiter time: ~10s

Injection: 24.761 Barl 1.22 1024 D-atoms

Total recovered 21.02 Barl 1.03 1024 D-atoms

Retention 3.741 Barl 1.84 1023 D-atoms (~15%)

Comparison of L-mode experiments

Heating and gas injection ~ 81 s (6 pulses) – Mode D (March 2007)

Total divertor time: ~ 126 s, Total limiter time: ~60 s

Injection: 27.882 Barl 1.377 1024 D-atoms

Total recovered 24.454 Barl 1.208 1024 D-atoms

Retention 3.428 Barl 1.693 1023 D-atoms (~12%)

Detailed analysis of ramp-up and ramp-down phase in progress


Retention in L and H-mode

Pulse type

Injection(Ds-1)

Heating phase (s)

Long term retention (Ds-1)

Divertor phase (s)

Long term retention (Ds-1)

L-modeMode D

~1.8102

2

81 2.041021 126 1.271021

L-modeMode B

~1.7102

2

75 2.401021 170 1.051021

Type III ~1.7102

2

72 2.401021 126 1.371021

Type I ~1.7102

2

32 2.831021 50 1.71021Impact of the limiter phase in the fuel retention experiments with an early X-point (~1.2s of limiter phase) and late X-point formation (~8-10 s of limiter phase) is moderate. Normalisation “Divertor” vs. “Heating time” !

Consistent with the previous results, but “divertor time” and “limiter time” difficult to evaluate with accuracy.

Retention closely linked to the carbon source


Type I ELMy H-mode

ne~0.7nGW

PTOT (MW)NBI+ICRH~13MW

D(in) D (out)

Time (s)

#69260

Ip = 2.0 MA, B = 2.4 T

- Short term retention: “limited” to “fast” reservoir and recovered in between pulses (outgasing)- Long term retention: Co-deposition and implantation : Slow process compared to short term over 5-10 sec

WELM ~100 kJ ~ 60 Hz

Heating phase

Injection

Exhausted

Retention


High power discharge in JET

Ip=3.5MA, BT=3.2T

ne

Ptot (NBI + ICRH) ~ 23-24MW

Wdia~9.5MJ

Gas: 5.0x1022Ds-1

ELMs600-700kJ per ELM

Gas balance “on line”, w/o regeneration


Gas balance High power discharge

Using the same pumping speed Retention as high as ~3.3x1022Ds-1

Consistent with strong carbon erosion from recycling and ELMs Increase by ~10 of the retention To be confirmed by dedicated exp


C source for High power discharge

Type I ELMs (600-700kJ)

L mode

Type I ELMs (100kJ)


Carbon production and scenario

J Strachan et al. Nuc. Fus. 2003

L mode(3-4MW)

Type IH mode

10-15MW

- Increase of carbon source depends on scenario (ELMs, recycling flux…) enhanced retention by co-deposition

- Increase by a factor of ~2 of carbon source from L to type I ELMy H-Mode


Carbon production and scenario

J Strachan et al. PSI 2008

Carbon ionisation rate in the SOL as a function of D ionisation rate


D,T

Wall

Mechanisms for fuel retention

Two basic mechanisms for

Long term fuel retention

Deep Implantation, Diffusion/Migration, Trapping

C, Be C, Be, D ,T

Codeposition

Short term retention (Adsorption: dynamic retention)

~ Recovered by outgassing

Separate the contribution of implantation and co-deposition?


DT experiments in JET

Retention by implantation and co-deposition

“Same” retention although different scenario

TFTR

Phase 1 (June 1997)

Gas injection only 11.4g 2.34x1024T

injected

1.0x1024T retained (~40%)

80 pulses in L modePhase 1

Phase 2 (End 1997-Early 1998)

Both NBI and Gas injection

23g

~40% retained

High power discharges in H mode

Phase 2


Implantation and co-deposition

2.5x1024

2.0

1.5

1.0

0.5

0.0

Par

ticl

es

4176041740417204170041680Pulse Number

T Injected Cryopump regeneration

50-50% D/T 100% T

Early phase of DT experimentsRetention~100% for the 10 first discharges (~4x1023T)

Retention deduced fromCryo regeneration

Injection


Implantation

JET DT experiments- Implantation dominates in phase 1- Co-deposition main process in phase 2

- JET ~ 200 m2 : maximum retained fluence ~1021m-2 reservoir of ~ 2 1023 T consistent with implantation of particles with incident energy of ~ 200eV.


Summary…and further plans!

- No impact of the limiter phase in the gas balance analysis

- Retention linked to carbon production

- Implantation

Dominant process in early phases

Later co-deposition

- Further plans

Dedicated session with high power (ELMs) /injection

- Modelling correlate the retention with carbon

source (EDGE2D)


Retention: Short and long term

Short term retention- Depends on plasma scenario, wall conditioning and Material (Be, C)…-“Limited” to “fast” reservoir and recovered in between pulses (outgassing)

Actively cooled device Steady state operation-->Long term retention

Long term retention

- Co-deposition Correlated to C production

- Implantation Edge plasma, material structure…

Long term retention

Short term retention

5

4

3

2

1

0

1020

Ds-1

4003002001000

Time (s)

# 32299 # 32300

TS

Dynamic retention: ≈ 5 x1021D JET ≈ 2.5 1022 D ~ wall area ratio


Gas Balance (1/2)From cryo-pump regeneration (~1%) and calibrated gas injection

Evaluation of the pumped flux

- During the plasma

- Between pulses

0 10 100 1000 100001min 1hour 1day 1week

Plasma

During plasmainj>pump

Retention>0Short & Long term

Between pulses, session, days…inj=0

pump= OutgasingRetention<0

Short term retention only(dynamic retention)

Evaluation of Short and Long term retentionInjection = Long Term Ret + Short Term Ret + Pumped flux


Gas balance (2/2)

Two complementary methods to measure the pumped flux

2 – Collection of all the total particles pumped (Tbo, Cryo…) into a separate calibrated volume (equivalent to the AGHS used at JET)

- Accurate neutral pressure measurement in volume (Temperature)- Analysis of the gas composition collected (H, D, T and Impurities)

1 – Neutral pressure and Pumping speed

Pumped flux = PDiv*SDiv + PNBI* SNBI + PDiag*SDiag

- Require enough pressure gauges located in the “pumping pipes”, regular calibration of both pressure gauges and pumping speeds.

- These 2 methods are complementary; the second method gives the equivalent of the integral of the first one.- Allow to check/limit/evaluate the possible drift of the neutral pressure measurements over long periods (days, weeks…).- These two methods are “technically easy” to be implemented.

Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 1 Th Loarer with special thanks to S...

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Transcript of Th Loarer - SEWG on Fuel retention – JET, 22-23 July 2008 1 Th Loarer with special thanks to S...