slide 1 17-19 oct 2005, efda pwi meeting, cea cadarachei.s. landman, fz-karlsruhe fzk investigations...

17-19 Oct 2005, EFDA PWI meeting, CEA Cadarache I.S. Landman, FZ-Karlsruhe Slide 1

FZK Investigations on Wall Surfaces and Tokamak Plasma

1 Forschungszentrum Karlsruhe (FZK), Germany2 Troitsk Institute for Innovation and Fusion Research (TRINITI), Russia3 Kharkov Institute of Physics and Technology (KIPT), Ukraine

Contents

1) Main results on expected consequences of ITER transient events

• Surface melting of tungsten divertor armour and beryllium first wall

• Evaporation and brittle destruction of carbon based materials

• Contamination of the SOL and core plasma after ELMs

2) Objectives

Forschungszentrum Karlsruhein der Helmholtz-Gemeinschaft

FUSION-PL

FZK – EURATOM FUSION ASSOCIATION

I. Landman1, B. Bazylev1, S. Pestchanyi1

with contributions from

V. Safronov2, A. Zhitluckhin2, V. Podkovyrov2 and I. Garkusha3


Main features of FZK PWI activities

• Investigations are carried out for ITER, by means of numerical modelling (because available tokamaks cannot provide required transient loads) and engaging the “ tokamak simulators” - powerful plasma guns

• We develop own codes to apply to ITER predictions -- behavior of fusion materials -- tolerable sizes of off-normal events

• Validations of the codes use mainly plasma guns and electron beams

Current EFDA tasks

TW3-TPP / MATDAM, TW5-TPP / ITERTRAN, TW5-TPP / BEDAM

• Damage to W and CFC ITER divertor materials of EU trademark (with validation by the plasma guns QSPA-T and MK-200UG)

• Damage to beryllium ITER first wall and Be coatings (with validation by a special plasma gun in TRINITI)

• Modelling of damage to ITER divertor target (after ITER disruptions and ELMs)

• Modelling of tokamak plasma contamination following ITER ELMs


Transient energy fluxes expected at the ITER divertor target

ITER Event Repetition Duration Target load Impact energy

Disruption seldom 1 .. 10 ms 10..30 MJ / m2 up to 10 keV

Type I ELMs 1-10 Hz 0.1..0.5 ms 1..3 MJ / m2 1..3 keV

Normal tokamak operation 500 s 10 MJ / m2/ s 1..3 keV

Simulation facilities

Science Centre TRINITI (RUS) and KIPT (UKR) plasma guns FZJ (D) e-beam

Facility name MK-200UG QSPA JUDITH

Pulse duration [ ms ] 0.05 0.2-0.5 1-104

Target load [ MJ/m2 ] 0.3 - 15 0.6 - 30 10

Load spot size [ cm ] 6 – 7 4-5 0.1-0.5

Magnetic field [ T ] 2 0.5 not available

Impact energy [ keV ]

1.5 (ions) 0.2 (ions) 120 (electrons)


FZK codes for consequences of ITER off-normal events

Material surface modelling

MEMOS-1.5D (fluid dynamics)

Melt motion at heated metallic surface

(tungsten and beryllium targets)

PEGASUS-3D (thermomechanics)

Brittle destruction of graphite and CFC

PHEMOBRID-3D (BD threshold model)

Brittle destruction of graphite and CFC

Plasma modelling

FOREV-2D (RMHD)

Plasma shield (disruption, Type I ELM)

SOL contamination (C, W, Be)

Pulse transient loads at targets

TOKES-2D (new MHD code)

Confined plasma equilibrium

Core contamination (by C so far)


Melt motion at ITER ELM conditions

Multiple ELM relevant loads at QSPA-Kh50 for EU W

Deposited energy less than 1 MJ/m2 during 0.2 ms

In 2004 up to 450 shots on one W sample

Damage below melting threshold is very complex:Decrease of melting threshold after many shotsViolent surface cracking of bulk tungstenbelow melting threshold

W cross-sectionafter 1 pulse 30 MJ/m2 0.2 ms

0.9 mm

Impact energy 1.20 MJ/m2

Absorbed energy 0.72 MJ/m2

Pulse duration 0.2 ms

after 100pulses

after 200pulses

after 250pulses

after 370pulsesafter 450

pulses

1.7 mm

after 450pulses

0.5 mm


Simulation of melt motion at ITER ELM conditions

MEMOS calculates melting, resolidification and evaporation

Melt motion is due to 1) p, 2) surface tension, 3) JB force

Multiple ELMs and disruptions

Stochastic separatrix strike positions is important:

• Stochastic changes of SSP affect favourably

• After a few thousand ELMs vaporization becomes dominant

• Multiple ELMs causing melting can significantly decrease the damage caused by rare disruptions

(Particular figures significantly depend on the size of transient event)

ITER transients Kind of damage

Disruption

(10 MJ/m2, 3 ms)

ELM

(3 MJ/m2 0.5 ms)

W vaporization loss

1 m 0.1 m

W melt roughness 5-10 m 1 m

Single ELMs and disruptions

(Simulations with Beare not yet systematic)

Tungsten thresholds as functions of pulse durationThe dependencies Qmelt and Qvap work well

=0.3 ms

++


Simulation of W-brushe with MEMOS

Validation by QSPA-T

• The complicated profile of W-brushe is implemented

• Validation by QSPA-T is carried out

• The depth of W melting and resolidification profile is rather similar to that of bulk W target however melt velocity is less by a factor 0.3 - 0.5

Optimization of W macrobrush design

optimization of inclination of brushes top surfaces

• Shadowing of brush edges may decrease melt roughness

• Optimal surface inclination angle / 2

Damage to the dome gapsand the divertor cassette gaps

• the melting of copper at the W-Cu adjoins is significant

• protective tungsten aprons of the gaps may be necessary


2 mm

Brittle destruction of CFC

Main results from plasma guns MK-200UG and QSPA-T

CFC NB31 and NS31 were exposed to 200 shots 15 MJ/m2

Both CFC behaved similarly (regime with vapour shield)

Maximum erosion rate is proportional to pulse duration

PAN fibres max. erosion rate is of 20 m/ms

pitch fibres max. erosion rate is of 3 m/ms (evaporation)

Graphite particles of sizes of 1 to 102 m are collected

Now investigations for EU trademark CFC at 0.5-1.5 MJ/m2in frame of the EFDA task MATDAM started

• Start of vaporization: Qmin=0.3 MJ/m2 for 0.05 ms (MK-200UG) (Qmin: at 0.5 ms would be Qmin = 1 MJ/m2) CFC surface after 150 shots at QSPA-T

CFC NS31 and NB31 have been developed for ITER

CFC have a 3D structure of fibres and a matrix

At stationary tokamak regime CFC behaves good

At the transient loads anticipated in ITER high erosion rates are discovered


CFC brittle destruction simulation using PHEMOBRID and PEGASUS

The PEGASUS model:

3106 cells of 1 m represent CFC 3D structure

Thermal- and mechanical bonds between the grains

Anisotropic heat transport through grain boundaries

Stress due to anisotropy and temperature gradients

Cracking of the bonds above elasticity threshold

The crack interrupts connection between grains

PEGASUS works on “microscopic” scale (weeks of running)

PHEMOBRID works on “macroscopic scale”(BD threshold of CFC (10 KJ/g) is like melting point of W)(PHEMOBRID: 3D code also but only a few hours of running)

PHEMOBRIDresults

Simulation: 0.8 MJ/m2 0.5 msExperiment 0.3 MJ/m2 0.05 ms(data for the emissivity 0.9)

Value of thermal conductivity is importantPulse shape is also important ( and 50%)


PEGASUS: BD damage to a standard CFC structure

PEGASUS: BD damage to improved CFC structure

New CFC structure is suggested

The PAN fibres are inclinedunder 45 deg to the pitch fibres

In PEGASUS simulationsBD erosion rate has decreasedsignificantly (~ 5 times)

Experiments at MK-200 UGto proof this qualitative predictionare set up (the CFC is to be cut as [111])

The CFC erosion is due to preferential crackingon the surfaces of PAN fibres

erosion depth 30 um, 4000 K at the boundary

This simulation only tried to discoverBD erosion features but not the scale

Validation is necessary

CFC simulations using PEGASUS


Development of FOREV-2D

• magnetic toroidal geometry of ITER and JET are available

• multi-fluid SOL plasma description (ions of D, T, He, C)

• radiation transport in toroidal geometry for C is implemented

Results obtained with upgraded FOREV-2D

• radiation load of the first walls in ITER and JET

• a rough validation by JET was carried out (20 versus 35 MW)

SOL contamination by carbon impurity after Type I ITER ELMs

For Q1MJ/m2, carbon ions fill SOL for several ms

The density up to 1021m3, thus DT is dissolved in C

In few ms SOL is cooled down to a few eV by radiation losses.

Influx of carbon impurity into the pedestal after ELM: 31017 m-2

Modelling of ELM-induced SOL contamination


Contamination of ITER core after ELMS

(first simulations with the new code TOKES)

Main Features of TOKES• The Grad-Shafranov equation is solved at each time step (2D magnetic field evolves together with plasma)

• Multi-fluid plasma, Pfirsch-Schlüter cross transport so far (now D, T, He and C ion species are available)

• Poloidal field coils automatically control plasma boundary• D- and T beams heat and feed, radiation cools• D+T He + n reaction produces burning by alphas

First preliminary result

Whole ITER confinement of 500 s was simulated

Tolerable ELM size 1 MJ/m2 for ELM frequency 0.5Hz

Rather uncertain implications have still been used:(plasma fraction dumped out in ELM burst assumed 0.5)

We see that ELMs do not clean the plasma of impurities

Carbon impurity propagationinto the core after ELM (TOKES)


Objectives

Up to now mainly carbon transport in SOL was simulated (W and Be not)Therefore we will develop tungsten impurity transport in SOL and the core

Radiation transport also for tungsten impurity

Further material investigations (CFC, W, Be) with PEGASUS and MEMOSin particular, aiming impurity influxes into SOL

Main future activities are going to be devoted for ITER transients

Further quantification of the heat fluxes to ITER divertor and first

Quantification of ELM size threshold for radiation collapse caused by the impurities

Lifetime prediction for CFC, W and Be

Theoretical support of ongoing experiments with EU materials for ITER

Continue W-O-H chemical erosion with MD code CADAC

slide 1 17-19 oct 2005, efda pwi meeting, cea cadarachei.s. landman, fz-karlsruhe fzk investigations...

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