EU PWI TF Meeting Nov. 4 – 6, 2009, Warsaw

EU-PWI TaskforceEU-PWI Taskforce

Report on the F4E W Task Force to Report on the F4E W Task Force to ‘‘Assess Assess the Option to Start Operation the Option to Start Operation

in ITER with a full W Divertor’in ITER with a full W Divertor’

based on a summary report by G. Federici et al for the F4E W divertor TF

presented by R. Neu

EU PWI TF meeting, Nov. 4-6, 2009, Warsaw R. Neu 2

Outline

• Background information

• ITER updated schedule and possible consequences

• Task force motivation / charge and members

• Key findings

• Recommendations

• Summary

EU PWI TF meeting, Nov. 4-6, 2009, Warsaw R. Neu 3

Background

• Selection of PFMs for the ITER divertor has been one of the most contentious issues over the last few years.

• All the options being considered have some pros and cons.

• This contentiousness has its origin in the shortage of decisive information about the operational characteristics of tungsten in divertor tokamaks.

• current ITER baseline:

– CFC strike-point divertor for the initial non-active phase of operation with H and He plasmas

– full W divertor for the nuclear phase with deuterium and deuterium-tritium (D-T) (use of CFC not precluded)

Procurement sharing

EU PWI TF meeting, Nov. 4-6, 2009, Warsaw R. Neu 4

Issues using C as PFM

– necessity to conduct a full exchange of the divertor prior to DT,– need to remove residual C deposits formed during H/He phases (e.g.,

time consuming & difficult C scrubbing/cleaning),– delay of the physics programme – necessity to commission W-divertor,

possibly including time for H operation,– additional cost of building two divertor sets during construction phase

to achieve important and urgent scientific milestones (e.g., Q=10), (CFC div. designed with load specifications including heating power)

• Provides easier learning process in the early phases of operation

- development of start-up/ramp-down scenarios

- expansion of the operational space

- commissioning of techniques to reliably mitigate transient loads due to ELMs and disruptions.

• Broad consensus in the fusion community as the most reasonable based on presently existing experimental evidence.

• Potential shortcomings:

EU PWI TF meeting, Nov. 4-6, 2009, Warsaw R. Neu 5

Updated ITER Operation Schedule(Scenario 1)

Installation of divertor 3 years later as foreseen in original schedule

EU PWI TF meeting, Nov. 4-6, 2009, Warsaw R. Neu 6

TF Motivation and Charge

• to evaluate the option to start operation in ITER with a full W divertor:

– assess existing knowledge and research in the area of W characteristics and usage.

– asses all the risks and benefits

– define a meaningful workplan for R&D necessary to qualify a full-W divertor for use in ITER.

• experts were selected on the basis of either their experience on tokamak operation with high-Z metal machines or their technical expertise on design, manufacturing and procurement of PFCs.

• work was undertaken without prejudicing the ongoing (CFC) divertor R&D and procurement activities

F4E established TF in January 2009

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F4E Task Force composition Name Institution Areas of Expertise

Asakura Nobuyuki JA/ JT-60U Tokamak physics and operation – JT60-U

Federici Gianfranco F4E Chair

Grosman Andre CEA Div. manufacturing, tokamak operation, project management

Horton Lorne JET Tokamak physics and operation – JET/ ASDEX-U

Lackner Karl IPP Garching Tokamak physics and operation – ASDEX-U

Lipschultz Bruce US/ MIT Tokamak physics and operation – C-MOD

Lorenzetto Patrick F4E Divertor target design and manufacturing

Nakano Tomohide JA/ JT-60U Spectoscopy, tokamak edge physics

Neu Rudolf IPP Garching Tokamak physics and operation – ASDEX-U

Philipps Volker IPP Juelich PWIs and tokamak edge physics

Riccardi Bruno F4E Target technology

Thomas Paul F4E Physics integration/ tokamak operation

Tsitrone Emmanuelle CEA PWIs and edge physics

Numerous valuable contributions from members of the ITER team: David Campbell, Alberto Loarte, Richard Pitts and Mario Merola

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Key findings/1

• operational experience with high-Z divertor target, mainly from Alcator C-Mod (Mo) and ASDEX-Upgrade (W),

has been greatly increased

• further W experimental research concerning W issues, including material mixing issues, has been and is being

performed in other tokamaks (TEXTOR, FTU), divertor plasma simulators and ion beam facilities (PISCES-A/B,

NAGDIS, Pilot-PSI, PSI-2, etc.)

• behaviour of W under transient loads has been and is being studied in plasma-gun and electron beam facilities

(MK-200UG, QSPA-T, QSPA-Kh, JUDITH, etc.).

• significant research programmes are in place (ITER IO, ITPA, EU-PWI TF) to investigate PSI with W and its

effect on the core plasma operation

• a number of key issues required to assess the scientific viability of ITER with a W divertor from the start of

plasma operation remain to be studied in detail

EU PWI TF meeting, Nov. 4-6, 2009, Warsaw R. Neu 9

Key findings/2

• JET's ILW project envisages the installation of a metal wall with Be

armour on main chamber components and an all W divertor

(shutdown to be completed at the end of 2010)

• updated ITER construction schedule (Scenario 1) offers the opportunity

to implement the necessary R&D

– (i) to qualify the technology of a high heat flux W target

– (ii) to expand the physics basis in tokamaks with W, eventually in time to

make a decision on the armour material, without affecting the present

machine construction schedule.

• In the latest EU procurement schedule, the contract for the purchase of

the CFC required for the series production must be signed by the end

of 2012, thus providing a period of approximately 3 years that should

be used to carry out the necessary R&D on W

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Physics issues initial phase of operation

• Issues for discharge development

- disruptions and ELMs control

- melt layer dynamics

- cracking

- high Te/ Self sputtering

- detachment achievement and control

- low density start-up and ramp-down

• Issues for routine operation

- level of allowable W concentration consistent with good core confinement

- ICRH and W

- power load control with radiation

- Be/W alloying

- behaviour of W under He irradiation

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• development and qualification of W technology for strike point conditions

• adaptation of divertor design to W strike point, perform analyses, tile

shadowing, optimization of alignment, shaping and castellation

• ELMs tests plus thermal fatigue testing to assess crack initiation and

propagation

• mock-ups and prototype fabrication and testing

• acceptance criteria on W mock-ups

• neutron irradiation test programme, integration into qualification program

• assess consequences of possible W recrystallization on W performance

which may occur under ELM like heat loads and slow transients

Technology issues

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Preliminary risk analysis

Areas of highest risks are:

1. divertor damage by unmitigated ELMs, and unmitigated

disruptions.

2. major difficulty in developing low density plasma ramp-up and

ramp-down scenarios

3. avoidance of divertor conditions leading to enhanced W-erosion

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Main recommendations/1

• A vigorous W physics and technology R&D programme of about 3 years duration should be pursued in

order to be able to potentially affect the procurement decision for the material at the strike point by the

end of 2012, without causing any delay to the fabrication schedule envisaged by the EU.

• The key elements of this R&D programme can be summarized as follows:

– assess the possible occurrence, conditions and consequences of melting during plasma operation,

– investigate ELM control with W divertor and assess consequences for H-mode discharges,

– investigate the implications of a change to a full-W divertor on disruption avoidance and mitigation,

– identify and avoid divertor conditions leading to enhanced W-erosion and the resulting potential for

enhanced W levels in the core plasma, limiting performance and access to H-mode,

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Main recommendations/2

– demonstrate the capability to run low density ramp-up/down as well as low density steady state discharge

phases with additional heating,

– determine allowable level of W in the core plasma,

– study crack formation and propagation on W targets especially for many sub-threshold ELM loads (< 0.3

MJ/m2),

– develop and qualify W technology for strike point conditions and of acceptance criteria, including thermal testing

under combined loads (e.g., short pulse loads to represent ELMs plus thermal fatigue testing),

– confirm performance of n-irradiated W samples/mock-ups.

• Improve design by avoiding plasma leading edges from manufacturing tolerances (e.g., by tile shadowing,

optimization of shaping and castellation).

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Conclusions

• a vigorous tungsten physics and technology R&D programme is recommended

• some leverage on the program of tokamaks is needed to make sure that work is carried out on time

• further exploitation of non-EU plasma simulation facility is needed

• the task force notes that there is a general confidence in the ability to develop/ qualify W technology that meets power handling requirements

• strong commitment and leverage from all involved bodies would be needed to ensure, accelerate and to monitor the implementation of the recommended R&D, together with the required prequalification programme and to speed-up progress in order to still enable a decision by end of 2012

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Preliminary results ofhigh heat flux tests

• promising experimental results have been obtained in high heat flux thermal fatigue testing performed on W monoblock and flat tile components but with a cooling diameter of 10 mm.

• medium scale prototype has sustained 15 MW/m2 for 1000 cycles on the W part and another medium scale mock up has sustained 15 MW/m2 for 2000 cycles on the W part.

• full W flat tile armoured prototype has sustained 20 MW/m2 of absorbed heat flux.

• Similar positive results were also obtained on irradiated W mock-ups, which sustained 18 MW/m2 (to 0.1 and 0.5 dpa 200o C)

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ITER Scenario 1Installation divertor end of 2020 (3 years later)

Install blanket/FW & divertor

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2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

EU Fabrication Schedule Divertor

Scenario 1

Manufacture CFC Prototypical BatchManufacture CFC Batch 1 (8 Units)

Manufacture CFC Batch 2 (24 Units)Manufacture CFC Batch 3 (28 Units)

Evaluation of experimental results and decision about final staging

Pre-engineering and Prototyping of IVT

Manufacture IVT Stage 1 (6 Units)

Manufacture IVT Stage 2 (24 Units)Manufacture IVTStage 3 (30 Units)

Manufacture and Testing of Prototype Cassette Bodies

Establish Production Facilities for Divertor Cassette

Manufacturing and Assembly of Divertor Cassette Batch 1 (6 Units)

Manufacturing and Assembly of Divertor Cassette Batch 2 (24 Units)Manufacturing and Assembly of

Divertor Cassette Batch 3 (30 Units)Full W Qualification

Full W prototyping of IVT