High radiation scenarios in pronounced detached divertor conditions - - PowerPoint PPT Presentation

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High radiation scenarios in pronounced detached divertor conditions - - PowerPoint PPT Presentation

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High radiation scenarios in pronounced detached divertor conditions at ASDEX Upgrade M. Bernert 1 , F. Reimold 2 , R. Dux 1 , T. Eich 1 , A. Huber 2 , A. Kallenbach 1 , B. Lipschultz 3 , M. Wischmeier 1 , the EUROfusion MST1 team 4 and the ASDEX

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SLIDE 1

High radiation scenarios in pronounced detached divertor conditions at ASDEX Upgrade

  • M. Bernert1, F. Reimold2, R. Dux1, T. Eich1, A. Huber2,
  • A. Kallenbach1, B. Lipschultz3, M. Wischmeier1,

the EUROfusion MST1 team4 and the ASDEX Upgrade Team

1st IAEA TM on Divertor Concepts, Vienna, 29th Sep – 2nd Oct 2015

1Max-Planck-Institut für Plasmaphysik, Garching, Germany 2Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung – Plasmaphysik, Jülich 3University of York, York Plasma Institute, Heslington, York, United Kingdom 4See http://www.euro-fusionscipub.org/mst1.

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SLIDE 2

Motivation

DEMO requirements: – Detached divertor necessary to reduce power and particle flux – 95% of exhaust power needs to be dissipated

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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Only achievable with radiation inside and outside confined region ⇒Core and edge radiators necessary With deuterium: No full / pronounced detachment in H-mode ⇒Seeding impurities necessary for power dissipation

Possible with a conventional divertor using strong impurity seeding

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SLIDE 3

Motivation

DEMO requirements: – Detached divertor necessary to reduce power and particle flux – 95% of exhaust power needs to be dissipated

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

3

Only achievable with radiation inside and outside confined region ⇒Core and edge radiators necessary With deuterium: No full / pronounced detachment in H-mode ⇒Seeding impurities necessary for power dissipation

  • What is the maximum frad?
  • How stable are these regimes?

Match SOL plasma

( Psep/R ≈ 15MW/m, fGW ≈ 1, H98 ≈ 1)

Goal: Test scenarios in present day experiments

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SLIDE 4

The ASDEX Upgrade Divertor

  • Fueling
  • Main fueling and seeding from divertor
  • High-Z seeding from outer midplane
  • Divertor
  • Closed divertor
  • Vertical targets
  • Tungsten coated CFC
  • Solid tungsten tiles (outer target) (qmax > 10 MW/m2 [Hermann, NF 2015])

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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  • Pheat = 27 MW

( available 20 MW NBI, 6 MW ECRH, 6 MW ICRH)

  • R = 1.65 m

Pheat/R ≈ 16 MW/m

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SLIDE 5

Detachment (in H-mode)

  • Inner divertor typically detached
  • Progress of outer divertor detachment:

– Partially – Pronounced – Fully

  • Outer divertor detachment correlated

with increase of plasma density

– Changed fueling?

  • Detachment in H-mode only achieved

with intense seeding, e.g. N

– Full detachment only inter-ELM – ELMs: Complex sequence of detachment states

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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[A.Kallenbach, NF 2015]

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SLIDE 6

The different radiators

Various seeding impurites possible

  • Nitrogen: Divertor
  • Neon: SOL
  • Argon: SOL & pedestal
  • Krypton: Pedestal & core

What is the optimal impurity mix?

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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N Ar Kr

[T.Pütterich, EPS 2015]

Ne

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SLIDE 7

High radiation scenarios

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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Nitrogen:

Pheat = 21 MW

Pheat/R = 12.7 MW/m

  • Pronounced

detachment

fGW ≈ 0.95 H98 ≈ 0.9

  • Small reduction of

confinement

cN,core ≈ 2-3% frad ≈ 90%

  • Dominant radiation from

inside confined region

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SLIDE 8

High radiation scenarios: Nitrogen

  • Strong radiator at X-point

⇒ MARFE-like radiation condensation

  • With ongoing detachment:

Radiator moves at X-point from outside to inside of confined region

  • Time evolution of several seconds

⇒ RT control possible

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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Constant N puff

  • > increasing N density
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SLIDE 9

High radiation scenarios: Nitrogen

  • Radiator can be reproduced by SOLPS
  • Temperature reduction within confined region
  • Te < 5eV
  • D line radiation observed

⇒ Parallel temperature gradients inside confined region!

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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[F.Reimold, PSI 2014]

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SLIDE 10

High radiation scenarios: Nitrogen

  • Radiator can be reproduced by SOLPS
  • Temperature reduction within confined region
  • Te < 5eV
  • D line radiation observed

⇒ Parallel temperature gradients inside confined region!

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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[F.Reimold, PSI 2014]

  • Pedestal top pressure reduced at

similar core performance

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SLIDE 11

High radiation scenarios

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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Krypton:

Pheat = 19 MW

Pheat/R = 11.5 MW/m

  • Pronounced

detachment

fGW ≈ 0.8 H98 ≈ 0.9

  • Small reduction of

confinement

cKr < 0.1%

  • Low impact on dilution

frad ≈ 75%

  • Radiating ring around

pedestal top

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SLIDE 12

High radiation scenarios: Krypton

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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  • Krypton radiates in ring at

pedestal top

  • Nonlinear response to Kr

seeding level ⇒poloidally symmetric radiation condensation?

  • Discharges only quasi-stable

(stable for less than 10 τE )

  • Kr modulated by ELMs
  • ELM frequency reduces

Kr replaces (RT controlled) N

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SLIDE 13

High radiation scenarios:

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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Reducing (AUG #31648)

Pheat = 10.5 MW

  • Radiation moves inside
  • Density increase too small

Stable (AUG #30503)

Pheat = 19 MW

  • Radiation within pedestal
  • Temperature reduction

compensated by density increase

⇒ Radiation outside pedestal top

Krypton: Confinement

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SLIDE 14
  • Poloidally localized radiation

(above X-point) ρpol ≥ 0.985

  • Radiating ring

0.8 ≤ ρpol ≤ 1

  • Small reduction of confinement

(<10%)

  • Impact on confinement

varying

  • fELM increases
  • fELM decreases
  • Quasi-stable for more than 2s
  • Stable vs ELMs, full stability

not shown yet

Zeff(3%N) ≈ 1.91, dfuel(3%N) ≈ 6%

  • Lower impact on fuel dilution

Zeff(1‰Kr) ≈ 1.91, dfuel(1‰Kr) << 1%

High radiation scenarios: Comparison

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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Nitrogen:

  • Pronounced detachment of outer divertor

at highest heat fluxes

  • Most radiation inside confined region

Krypton:

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SLIDE 15

JET

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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SLIDE 16

Summary

Detached divertor possible at high heating powers using N and/or Kr – Conventional divertor – Pheat/R ≈ 12 MW/m (Demo: Psep/R=15MW/m) – frad ≤ 90% – Dominant radiation inside the confined region – Scenarios quasi-stable (N) – Real time control most likely possible – Impact on confinement differs with radiation location (Kr) – A possible solution for DEMO and ITER? Outlook

  • Stability (Kr) and controllability (N) to be tested
  • Where do Ne and Ar radiate in AUG?

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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SLIDE 17

Open questions, points of discussion

  • What is the stabilizing mechanism for the X-point radiator?
  • Why didn’t it work for carbon walls?
  • How does the radiation influence the H-mode threshold?
  • Does maybe Pped matter instead of Psep?
  • How to estimate Psep?
  • What is the best impurity mix?
  • Do future machines need other impurities (e.g. xenon)?
  • Impurity behaviour with pellet fueling?
  • Increased impurity divertor compression?

1st IAEA TM on Divertor Concepts, 29th Sep 2015

  • M. Bernert

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