jet pwi work plan for 2008+ w. fundamenski eu pwi tf, madrid, 29/10/07 jet plasma-wall interaction...

JET PWI work plan for 2008+ W. Fundamenski EU PWI TF, Madrid, 29/10/07

JET plasma-wall interaction work plan for 2008+

as part of the EFDA-JET Task Force

for Exhaust Physics (TF-E)

W. Fundamenski, UKAEA, Culham (TF-E leader)

S. Brezinsek, FZJ, Julich; T. Eich, IPP, Garching (TF-E deputy leaders)


• Further enhancements to the JET Facilities carried out during the 2007 Shutdown:– A new ITER-like ICRH antenna

– External conjugate-T matching installed on the A2 ICRH antenna modules for ELM resilience

– Refurbished fast protection electronics on the LHCD system for improved LHCD coupling

– A High Frequency Pellet Injection system

– A few new or improved diagnostics

• NBI and ICRF heating power available on JET is foreseen as follows:– NBI: 13MW on Octant 8 and 12MW on Octant 4, adding up to ~ 25MW max

– The power delivered by the A2 antennas of the ICRH system expected to routinely provide 3-4 MW in H-mode and 10MW in L-mode

– The new ITER-like ICRH antenna is expected, ultimately, to provide a maximum power of 7.2MW for 10s.

Present and foreseen machine statusPresent and foreseen machine status


• HEADLINE 1: High level commissioning and full exploitation of new systems and issues that could impact on the design of ITER components– H 1.1: Commission the ITER-like ICRH antenna to full performance/reliable operation and begin exploitation

• Matching, various frequencies, long pulse, high power• Assess power density limits, including arc detection and protection strategy, and impact on antenna structure• Assess the fraction of power absorbed by the plasma (with and without ELMs), parasitic losses, RF sheets• Study the influence of differences in k|| spectra on various heating scenarios• Start assessment of dominant electron heating in ITER relevant scenarios

– H 1.2: Commission the externally matched conjugate T ICRH antenna – H 1.3: Prepare for the ITER-like wall project

• Fuel (D/H/T) retention study in H-mode, including effects of disruptions• Exploit improved disruption mitigation valve and characterise heat loads on plasma facing components following disruptions

Headlines for 2008+ JET programmeHeadlines for 2008+ JET programme


– H 1.3: Prepare for the ITER-like wall project, continued• Characterise divertor physics and the importance of intrinsic carbon radiation towards controlled detachment

• Establish compatibility of the ITER-like wall with fast particle losses, including those from NBI, ICRH and LHCD

– H 1.4: Commission the new high frequency JET pellet injector and validate it for use for ELM mitigation by pellet pacing

– H 1.5: Bring new diagnostics to full performance

– H 1.6: Address issues impacting on ITER H&CD systems design• Establish the level of off-axis NBCD in view of its application to ITER [subject to confirmation of Asdex-Upgrade anomaly on JET during

2007]

• Measure the absorption of LH waves by fast ions

• Extend measurements of Alfvén Eigenmode stability and fast ion losses toward low energies and map radial eigenfunctions of the most relevant fast ion driven instabilities



Headlines for 2008+ JET programmeHeadlines for 2008+ JET programme• HEADLINE 2: Qualification of integrated operating scenarios for ITER

– H 2.1: Develop edge conditions suited to the baseline, hybrid and advanced steady-state scenarios that are compatible with the ITER-like wall on JET, including intrinsically benign ELM scenarios (type II, mixed, convective, grassy and type III) and active ELM control

• Exploit active techniques for producing tolerable ELMs for integration into the scenarios (pellets, fuel and impurity seeding, error fields, etc.)

• Establish regimes with a highly radiative edge and assess effect on wall and divertor power loading

• Raise the edge density of the steady state scenario using gas fuelling and pellets for compatibility with ITER-like wall materials

• Extend viable intrinsically benign ELM regimes to high performance and current, and address issues of extrapolability of these regimes to ITER-like wall and ITER

– H 2.2: Qualify hybrid scenario as a viable option for ITER• Extend performance of hybrid scenarios (increased current and magnetic field with lower q) to approach ITER relevant parameters (Te/Ti,

collisionality, rotation) and assess ELMs, density peaking and impurity accumulation. Vary q95 for comparison with steady state scenarios


• Extend performance limit scaling and its understanding (b limit vs r*, role of q0, density limits), exploiting increases in heating power

• Sustain and (real time) control the current profile on a resistive time scale, understanding the role of core MHD and current drive requirements to maintain the scenario

– H 2.3: Qualify a robust steady-state non-inductive scenario for application to ITER • Exploit increased ICRH power with the ITER-like ICRH antenna:

– to extend high bN parameter space to higher current and magnetic field– to operate closer to ITER relevant critical conditions (Te/Ti approaching unity, lower toroidal rotation (Mach number), lower r*, low n*) and

investigate fuel and impurity transport and density peaking

• Assess control tools for sustaining performance and plasma profiles in steady-state highly non-inductive regimes with a high bootstrap current fraction close to the stability limit (bN~3 and Iboot/Ip50%) and at high density (nl>31019m-3)

• Exploit the n=2 error field correction coil capability to extend understanding of resistive wall mode beta limits in ITER



– H 2.4: Develop highly shaped ELMy H-mode operation to 4MA or higher• Integrate techniques for sawtooth and NTM control, understanding triggering, marginal stability, and the role of core MHD and fast particles• Integrate techniques for sawtooth and NTM control, understanding triggering, marginal stability, and the role of core MHD and fast particles• Extend confinement scalings ( and *), documenting ELMs, power loading, density and impurity peaking, and pedestal. Test extrapolation to ITER,

addressing proximity to L/H threshold• Identify consequences of high Greenwald fraction with pellet fuelling

• HEADLINE 3: Physics issues essential to efficient exploitation of ITER– Determine heat, particle and momentum transport properties in plasmas with low external momentum input and ITER-relevant Te/Ti and

collisionality

– Exploit the High Frequency Pellet Injector for particle deposition and transport studies including radial drift and fuelling efficiency

– Explore ‘burning plasma’ physics in all ITER-relevant regimes, with the ability to generate significant populations of fast particles (bfast~0.5%; fast 4He nuclei with similar population strengths to ITER), etc.



Heat load and ELM control TFS1 TFS2 TFD TFE TFH TFM TFT

develop reference scenarios for operation with the ITER-like Wall on JET

X X X X X ILW

control the heat load on plasma facing components by impurity seeding in preparation for the ITER-like Wall on JET and the detached divertor conditions predicted for ITER;

X X X X ILW, ITER

determine the effect of pellet pace-making (size, frequency, location), external magnetic perturbation fields (amplitude, toroidal phase, mode number), vertical kicks (frequency, influence on control system), impurity seeding (species, fluxes) and TF Ripple (amplitude) on ELM characteristics (energy losses, frequency);

X X X X X ILW, ITER

determine the compatibility of heat load reduction and ELM mitigation techniques;

X X X X ILW, Phys.

quantify changes in disruption heat loads, halo currents and runaway electron generation, particularly when using the Disruption Mitigation Valve, and test real-time disruption prediction algorithms

X X ILW

monitor localised heat loads and material erosion, especially due to fast particles, sheath effects and LH-accelerated electrons.

X X X X ILW

Topics for 2008+ programmeTopics for 2008+ programme


Pedestal and L-H transition TFS1 TFS2 TFD TFE TFH TFM TFT

obtain a scaling of the pedestal (width, ne and Te

gradients) with r*, including pedestal characteristics close to those expected in ITER (Te~2-3keV,

ne~5x1019m-3), and 1MJ ELMs for ablation studies;

X X X X X ITER, ILW

quantify the impact of ELM mitigation on confinement, including the effect on the pedestal and core

X X X X X X ITER, Phys

quantify the threshold conditions for the L-H transition and access to high confinement, particularly at low density, momentum input and r*.

X X X X ITER, Phys


RF power optimisation TFS1 TFS2 TFD TFE TFH TFM TFT

establish efficient power coupling for different ELM-tolerant ICRH systems;

X X X X ILW

establish gas injection requirements for optimal ICRF and LH coupling, while maintaining good plasma confinement, also with ITER-relevant antenna-separatrix distances (~0.15m).

X X X X ILW, ITER


Fuelling and particle control TFS1 TFS2 TFD TFE TFH TFM TFT

quantify fuel retention and material migration (beryllium erosion and 13C tracers) for ITER-like Wall reference scenarios;

X X ILW

compare gas and pellet fuelling efficiencies and to control the density and impurity profiles using pellet injection and ICRH for ITER-like Wall reference scenarios and under ITER-like pedestal/SOL conditions;

X X X X X ILW, ITER

compensate density pump-out (on application of error field correction coils and TF Ripple) using gas fuelling and pellet injection, determine their dependence on n*, and clarify electron and ion loss mechanisms.

X X X X X Phys



Core confinement TFS1 TFS2 TFD TFE TFH TFM TFT

consolidate the dependence of global confinement on b, concentrating on different plasma shapes (d~0.2 and ~0.45);

X X ITER, Phys

establish improved confinement (H98>1) by maintaining an

optimised q profile;

X X X X X ITER

determine the effect of rotation on confinement, particularly with high power ICRH (~10MW) and with magnetic braking;

X X X X X X ITER

provide a basis for estimating the toroidal rotation profile in ITER, focussing on intrinsic and extrinsic sources and momentum transport pinches;

X X X X X ITER, Phys

determine the dependence of critical gradients on s, q, Te/Ti

and rotation, to quantify impact on global confinement, extrapolate to ITER, and discriminate theoretical models.

X X Phys

Stability and control at high beta TFS1 TFS2 TFD TFE TFH TFM TFT

establish reference scenarios with target profile control in the current ramp-up phase (including the testing of an ITER-relevant controller for vertical stability) and with the necessary off-axis non-inductive current drive and plasma pressure control in high bn (~3) operation;

X X X X ITER

establish the dependence of the b-limit on q profile, shape and rotation, and exercise b-control close to the b-limit;

X X ITER, Phys

achieve high current (~4MA) and high bn (~3) plasmas using

core MHD control and NTM avoidance strategies, including optimisation through improved understanding of the NTM seeds and triggers at low r*, n* and rotation;

X X X X ITER, Phys

measure fast ion losses due to Alfvénic modes for different q profiles, and benchmark models.

X X X X ITER, Phys



Monday 19th Tuesday 20th Wednesday 21st Thursday 22nd Friday 23rd

9 Parallel sessions Parallel sessions Combined sessions Report by WG1 (30’)Report by WG2 (30’)

10 Introduction(F, Romanelli) 45’

WG1, WG2, WG3,Coffee break


between WGsCoffee break

Report by WG3 (30’)Coffee break

11 Machine status and new hardware 30’

WG4, WG5, WG6. WG4, WG5, WG6. Report by WG4 (30’)Report by WG5 (30’)

12 Meal Meal Meal Meal Report by WG6 (30’)

13 Break Break Break Break

14 Review topic 1 (30’)Review topic 2 (30’)

Parallel sessions Parallel sessions Combined sessions Summary (?)

15 Review topic 3 (30’)Coffee break



between WGsCoffee break

16 Review topic 4 (30’)Review topic 5 (30’)

WG4, WG5, WG6. WG4, WG5, WG6. Meeting between Chair

17 Review topic 6 (30’)Planning, objectives for working groups (WGs) and chairs

Meeting between Chair persons and TFLs

Meeting between Chair persons and TFLs

persons and TFLs

18

19 Diner ??

Tentative agenda of inter-TF meetingTentative agenda of inter-TF meeting


TF-E strategy for 2008+ (C20-25) TF-E strategy for 2008+ (C20-25)

We envision three types of TF-E experimental activities in 2008+

– The first type, in which TF-E plays a leading role• Preparation for ITER-like wall (ILW) operation

– Fuel retention

– Power exhaust– Material migration

– Divertor heat load mitigation & detachment

– The second type, in which TF-E plays a co-leading role• Disruption mitigation studies (with M)• SOL characterisation in ICRH heated plasma (with H)• Scenario development for ILW operation with (with S1 and S2)

– The third type, in which TF-E plays a supporting role• Development of active ELM mitigation techniques (with S1 and M)• Edge plasma transport studies (with T)• Hydrogen plasmas (with all TFs)



Preparation for ITER-like wall (ILW) operationEstablishing a database of results with present (C) wall, in order to provide a reference for comparison with the future (Be/W) wall (ILW). This includes SOL characterisation, recycling and impurity fluxes, short and long term material migration, fuel retention, etc. Breakdown below:

– Fuel retention studies with higher accuracy of AGHS system• Effect of start up scenario (X-point vs. limiter start-up)• Effect of ELM size• Effect of magnetic configuration• Effect of deuterium fuelling rate

– Power exhaust studies in order to establish operational limits for the ILW• Continue to characterise ELM-wall interaction using IR and visible cameras, bolometry, QMB and probes. Scans in wall clearance, ELM size, plasma

shape, etc.• Continue the study of impurity influx due to large ELMs on the plasma discharge (material ablation/melting limits)

Headline 1.3



– Material migration studies with refurbished deposition monitors – QMBs• Dependence of erosion/deposition on strike point position in inner divertor

• Dependence of erosion/deposition on neutrals in private flux region (QMB below tile 5)

• Dependence of erosion/deposition on ELM energy load on inner and outer divertors

• Dependence of erosion/deposition on substrate temperature

– Material migration studies with fresh Be evaporation• L-mode vs. H-mode plasma: effect of ELMs on Be erosion

• Impact of limiter phase – early strike point formation

– Material migration studies with C13 tracer injection • 13CH4 injection with post-mortem analysis to monitor material migration

• Possible mid-term (eg. end of C23) tracer experiment (e.g. TMB) as marker to study material migration, complete in C25 (test for experimental approach with ILW)

• Combination with fuel retention experiment (gas balance) for one configuration

• Different plasma configuration, injection location or species than in the previous 3 experiments. Possible scheme: injection in SOL from GIM9 with OSP fixed on tile 5

– Observation of dust (parasitic)• Examination of Thomson Scattering spikes due to dust particles (cf. P.West at DIIID)

• Combined with QMB, bolometry, IR cameras, VIS cameras, VIS spectroscopy etc.


– Divertor heat load mitigation: impurity seeded, highly radiative plasmas• Progress in highly radiative (frad ~70-80%) type-III ELMy H-mode plasmas

– Continue development from 3 to 3.5 MA, at q95 ~ 2.6– Complete N-seeded plasmas; repeat with Neon and/or mixture of the two

• Continuation of work on Type-III ELMs in the hybrid-scenario (with S1)

– Investigation of divertor plasma detachment at both divertor targets• Degree of detachment and volumetric recombination in L-mode and H-mode• Impact of detachment on chemical/physical sputtering• Effect of strike point position, divertor closure, X-point proximity to inner baffle and fuelling location/method (gas, pellets) on inner and outer target detachment• X-point MARFE formation and possibility of real time control• Plasma fuelling (similarity experiments ITPA: AUG/JET/DIIID)

– Participation in the development of ILW compatible scenarios for TF S1 (standard scenarios) and S2 (AT scenarios):• Replacement of carbon as radiating species (by N, Ne, Ar or mixture of these)• Achievement of tolerable particle and heat fluxes in the inner and outer divertor target plates (partial detachment)




• Investigation of active disruption mitigation techniques (with M)DMV valve should be commissioned by 2008 with He pre-fill to increase valve response, and fixed D/Ar mixture to increase gas response– DMV valve commissioning

• Explore pressure range, timescales for TQ and CQ, recovery...• Mixing efficiency

– Electron penetration / critical field for secondary RE generation (RE suppression in ITER requires several 1e22 e/m3)

– Runaway electron generation/suppression studies• Critical gas amount (species) for RE generation/suppression

– Wall loads• Asymmetries (peaking factors), power deposition / balance (divertor/wall), particle release, preparation for ILW

– Basic mechanism of gas mitigated disruption• Gas / cold front penetration to q=2

– Forces / halo currents during current quench (with M)

Headline 1.3


• SOL characterisation in ICRH heated plasmas (with H)Tentative antenna schedule (M-L Mayoral): Commissioning of new antenna in C20-23; coupling to ELMy H-mode plasmas in C24; full power only in C25 – SOL characterisation with and without ICRH heating

• This should be part of the commissioning process, but requires dedicated time !

– Effect of separatrix, near-SOL and far-SOL density perturbations, both driven (gas puffing in various locations) and inherent (e.g. ELM filaments), on ICRH power coupling

• Variation of gas puff location, types of gas, q_95

• Measurement of far SOL density during ELMs use of RCP in double probe mode, to counter act ICRH shift of potential

– Production of fast ion populations in the far-SOL• Sheath rectification effects

• Outer/inner divertor baffle erosion

• Impurity source and SOL screening

• Heat load pattern on PFCs (divertor, limiter, upper dump plate)


Headline 1.1


• Participation in ITER-relevant integrated scenario development (with S1 and S2) TF-E must play an active role in ITER-relevant scenario development, in respect to particle and power exhaust at highest

possible current– SOL characterisation in high current scenarios, in excess of 3 MA

• This is particularly important for the scaling of ELM losses for which data is very scare for currents greater than 3 MA

– SOL characterisation in AT scenarios (with TF-S2)• Continuation of the work begun in 2006

• Proceed with whatever AT scenario is deemed most relevant by TF-S2 for its future programme, with modifications for edge diagnostics – Basic idea is characterise the SOL in main AT scenarios, and combine with high density edge / high radiation, to ensure compatibily with ILW. – Optimise shape (inner strike point, X-point to tile 1 distance) to allow partial detachment of the inner, as well as the outer, divertor leg

Headline 2.1-4


TF-E strategy for 2008+ (C20-25) TF-E strategy for 2008+ (C20-25) • Development of active ELM mitigation techniques (with S1 & M)

Ideally should form an inter-TF working group, which would characterise the ELMs (MHD, pedestal drop, wall loads) with each type of technique. The three active mitigation techniques most likely to be investigated in 2008 are:

– Pellet pacing: experiments well overdue on JET• provided pellet launcher online

• Characterise pellet generated ELM filaments and heat loads with regular small ELMs (type I, II or III)

– EFCC coils (n = 1 , 2)• Can the magnetic pump-out be counter-acted with additional fuelling by pellets or gas, without significant confinement degradation? Short term wall pumping?

• Is this technique compatible with partially detachmed divertors?

• Is it compatible with highly radiative, impurity seeded plasmas?

• Effect on impurity transport and content

– Vertical kicks• Technique appears to work in increasing the ELM frequency

Headline 2.1


• Edge plasma transport studies (with T)– Hot-ion H-mode pedestal with Te ~ 3-4 keV

• possible only before the installation of the ILW • pedestal with the same resistivity as the ITER pedestal. • high edge current densities.• modify the balance of MHD instabilities that can trigger an ELM, more current driven

modes

– Edge/SOL momentum transport • influence of SOL flows on rotation using reversed B and transition from single to

double null configuration • ELMs as momentum perturbation

– L-H transition in low momentum plasmas• LH transition at low momentum input; investigate with enhanced edge diagnostics• Extended parameter range with new antenna

– Impurity control and influx under ICRH • Study of the ICRH effects on both impurity and bulk ion transport • Impurity production and pollution due to ICRH ?• ICRH effects in highly radiative, impurity seeded plasmas


Headline 3.3


• Hydrogen plasmas before 2008 shutdown (with all TFs)Information for ITER Hydrogen phase, and the subsequent extrapolation to ITER

Deuterium phase, e.g. L-H transition, divertor detachment, SOL widths, etc.– Characterisation of Hydrogen discharges: SOL and power deposition profiles, L-

H transition in ITER-like shapes, ICRH efficiency in H– Isotopic effect (D vs. H) on combined plasma performance in matched

discharges – Timing:

• if neutron activation of vessel becomes an issue for the ILW shutdown, then H campaign (or mini-campaign) would fit naturally at end of C25; however, ITER-like antenna full power only available in C25, so may face competition from other studies?

– Duration: • To save NBI changeover time, could try with RF heating only?

New item; not a headline


• There is a double motivation for (edge) modelling work on JET: – interpretation of particular JET experiments either in the upcoming (C20-25) or previous

(C1-19) campaigns, and – validation and verification of codes (models) against JET experimental data. Although

such validation is an on-going process, involving many tokamaks, JET, being the closest to ITER in size, is in most respects the most important tokamak for model validation allowing meaningful ITER prediction.

– On JET, edge modelling has made significant gains over the past years, largely as a consequence of an annual ‘modelling month’ hosted by TF-E.

– Hence, irrespective of the details of the experimental programme, TF-E plans to host such a ‘modelling month’ near the beginning of the 2008 campaigns

Edge plasma modelling issues for JETEdge plasma modelling issues for JET

JET

ITER

Other

tokamaks

Model

Experiment

Repeat until

converged

Experiment

predictionITPA,

IEA,

EU-ITM validated


Power exhaust: Time-averaged heat loads on plasma facing components (PFCs)

Transients (ELMs): Transient (peak) electron, ion and heat loads on plasma facing components

Edge plasma modelling issues for ITEREdge plasma modelling issues for ITER

Particle exhaust: neutral (hydrogenic and impurity) pressure at pumping duct; SOL screening of impurity influx into the core

Material migration and fuel retention: PFC material erosion, transport and co-depostion with tritium

Edge-SOL turbulence,

Parallel heat flux (kinetic limits),

Impurity radiatiation and CX,

Divertor detachment

2-3D G-S (equilibrium)

2-3D multi-fluid (plasma),

3D MC (neutrals),

2-3D QL/NL (turbulence)

Practical issue Key Physics Numerical codes

Edge transport barrier (collapse),

ELM filaments (dynamics),

Parallel plasma response,

Magnetic reconnection at X-pt?

Plasma recycling and fuelling,

Neutral compression,

Impurity enrichment,

Anomalous parallel SOL flows

Edge-SOL turbulence,

divertor detachment,

radiative impurities,

Mixed material layers

2-3D non-ideal MHD (field),


1-3D MC (neutrals),

1D3V kinetic (filament)


3D MC (neutrals),

2-3D MC (impurities),

2-3D QL/NL (turbulence)


3D MC (neutrals),

2-3D MC (impurities),

1-3D FE (mass/heat diff.)


Back-up slide on C13 experiment Back-up slide on C13 experiment

• C13 tracer experiment (as the last session of C25 campaign)C13 tracer injection combined with post-mortem analysis is an established technique (at JET and elsewhere) for monitoring

material migration– Mid-term (end of C23 or C24) tracer experiment (e.g. TMB) to study material migration in complete C25 (test for experimental

approach with ILW)– Choose different plasma configuration, injection location or species than in the previous 3 attempts– Possible combination with fuel retention experiment with gas balance analysis for one particular configuration

• Possible scheme: methane injection from GIM9 and OSP on tile 5 with injection into SOL. The 2004 experiment required that a multi-step erosion process took place to migrate 13C into the PFR. This process occurred due to the geometry of the field lines wrt the target surface. Injecting from GIM9 will change that geometry and should move 13C away from the separatrix. Such a geometry might be useful for minimizing and removing ITER tritium retention.

Headline 1.3

jet pwi work plan for 2008+ w. fundamenski eu pwi tf, madrid, 29/10/07 jet plasma-wall interaction...

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