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Disruptions and run-aways

This report discusses the impact of disruptions and run-aways in high energy plasmas, specifically focusing on the JET facility and its implications for ITER. It includes proposed experiments and tasks for the 2015-16 campaign, as well as a summary and discussion of key findings.

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Disruptions and run-aways

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  1. Disruptions and run-aways E. Joffrin With thanks to P. Lomas

  2. Outline Key deliverable for 2015-16 Some pictures … of disruptions/run-aways with the ILW Key issues on disruptions/run-aways from C33 campaigns Proposed experiments and tasks for 2015-16 Summary & discussion E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 2

  3. JET key deliverable & context “Quantify disruption mitigation efficiency in high energy plasmas and extrapolate to ITER” • For JET, disruption is an integrated part of development to high Ip and Wth (see next slides) • For ITER, disruption is the top identified risk for its future operation (mitigation essential above 8MA) A memorandum (by E. Joffrin & P. Martin) on a commonstrategy for the study of disruptions and run-away in EUROfusion has been circulated last october http://users.jet.efda.org/pages/tfe1e2/Proposals_2015_16/20141029_disruption_report.pdf E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 3

  4. Place where large disruptions (red) & run-away (yellow) damages have been observed Upper dump plates Innerguard limiter E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 4

  5. JET –ILW has already undergone severe damage to the Be component by disruptions and run-aways spray of droplets stuck on wall Bubble-like damage to the upper dump and IGWL place from run-aways toroidally asymmetric Outer ends beryllium UDP protection tiles all damaged in a similar way toroidally See also Reux IAEA 2014 E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 5

  6. Run-away impact seen on the upper dump plates by the wide angle IR camera during the experiments • Footprint on upper dump-plate: • Localized hots spots on dump plate ribs • Toroidally and poloidallylocalized • Consistent withupwardsmovement of plasma centroid E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 6

  7. Run-away and heat load impact: 2012 vs 2014 IWGL 7X 2014 IWGL 7X 2012 New runaway damage Unchanged except run has disappeared Name of presenter | Conference | Venue | Date | Page 7

  8. Run-aways produces bubble-like damage to the Be limiters 2012 Be Upper dump plates 2014 Be Upper dump plates New, runaway! E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 8

  9. JET hardware for 2015 – 2016 campaigns (2008) Octant 1 (2013) Octant 3 (2015) Octant 5 • DMV1 installed 4.6m away from the plasma separatrix. Not DT compatible. • DMV2/DMV3 installed 3.0 and 2.4m respectively away from separatrix. DT compatible • Diagnostic: •  Bolometry camera (KB5V (octant 3) and KB5H (octant 6)) close to DMV2 and DMV3. • Old bolometry camera (KB1) diagnostics in Octant 2/3/6/7: radiation asymmetries. • Fast camera installed in oct 8 has a direct line of sight to the DMV1 gas entry tube. E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 9

  10. H1.3: Quantify disruption mitigation efficiency in high energy plasmas and extrapolate to ITER • Disruption mitigation at high energy content. • use of the 3 DMVs) • Modellingincluded • (4) <2.5MA Higher current included in the baseline and hybrids to high current (for Ip>2.5MA) + task: disruption prediction and avoidance schemes. Radiation asymmetry of mitigated and unmitigated disruptions (2) + task: modelling of halo current TOTAL: 9 sessions Mitigation of run-awaywith high Z-material(3) + task: modelling runaway electrons stability Initially: 19 proposals and 29 sessions requested.

  11. Can the TQ mitigation efficiency of 90% be confirmed at high thermal energy (high current)? JET observes a decreasing radiation efficiency with increasing thermal enrgy • EM loaddepends on the Currentquench CQ rate: • Long CQ  high halo current • Short CQ  high eddycurrents • How should we tailor the current quench time to get the smallest forces with acceptable heat load mitigation? • What is the best DMV arrangements for recovering 90% TQ mitigation efficiency? • Modelling and extrapolation for ITER of mitigation efficiency Also: decrease of radiation efficiency, is not changed by increasing the argon fraction >10% in the DMV. (Reux, IAEA 2014). E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 11

  12. Dependence of disruption radiation asymetries still not fully understood Toroidal pre-TQ asymetries can be controlled by multiple toroidal injection location Radiation peaking during the TQ is determined by the phase shift between the n=1 mode and the injection point both in JET and DIII-D. • Are there any other parameters that could explain radiation asymetries: • gas species? • q profiles (q>1 or <1) ? • Degraded plasma conditions (MHD, HL, …) • Magnetic asymetries (halo/eddy current) modelling E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 12

  13. Disruption mitigation at high energy content • Objectives • Establish the optimal parameter and configuration of the set of toroidally spaced MGIs for minimizing the current quench time to get the smallest EM forces and heat loads in JET scenarios up to 2.5MA (note only 2 MGIs can be used for DT phase). • Produce a scaling of the forces for mitigated disruptions with Ip and total energy content. • Validate the JOREK and simplified model prediction on the current scan and extrapolate to JET-DT scenarios and ITER. • In the condition of the experiment, monitor systematically if run-away are generated. • Relation with other experiment • This experiment has the objective to provide the optimised settings and DMV arrangements for minimising EM forces in the baseline scenario for Ip<2.5MA. • It will also bring information on radiation asymmetry • Monitor/detect systematically the presence of run-away and document the “run-away domain” Number of sessions: 4 Collaboration with MST1: close collaboration in particular on modelling of the MGI E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 13

  14. Disruption prevention and avoidance schemes for JET (task). • Objectives • Develop and compare off-line automated disruption identification and causes with real time capabilities. • Identify real time requirements and test on both JET and AUG database of disruptions. • Produce physics based (for instance locked mode) predictors using adequate signals and integrate into predictors. • Propose and test off-line a set of machine-independent quantities suitable as disruption identifiers and test on JET/AUG. • Establish a relation matrix between the alarms and the plasma response (scenario dependent) in coordination with the operation (SLs) group. Relation with other experiment/task  This task is the continuation of a task in C33-C34 with different objectives.  In 2015-16, this task must be closely connected with the scenarios operation and focus on the plasma response to give for a given alarm. Collaboration with MST1: (very!) close collaboration. The efforts on disruption prevention and avoidance schemes have to be coordinated on EUROfusion devices by JET1 and MST1 TFLs. E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 14

  15. Radiation asymmetry of mitigated and unmitigated disruptions • Objectives • Characterize the poloidal and toroidal radiation and heat load asymmetries in mitigated and unmitigated disruption. • Examine the asymmetry dependence with q profiles and/or different gas species • Determine mitigation efficiency and timescales in 'realistic' mitigation scenarios with unhealthy target plasmas (such as plasma with radiation pealing or MHD activity) Number of sessions: 2 Collaboration with MST1: Different measurements are present in JET and AUG would benefit from each other for the understanding of radiation asymmetries. E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 15

  16. Modelling of halo current (task) • Objectives • Model the role of hiro and halo current and current asymmetry in unmitigated disruption for JET with M3D. • Validate/apply modelling to cases with EFCCs (JET 2009) and determine if halo can be controlled or by applying vertical fields • Relation with other experiment/task • This task is a modelling task using existing codes and past data • The modelling may motivate and justify an experiment in JET, TCV or AUG. Collaboration with MST1: close collaboration on the modelling effort and validation of the models with data from different devices. E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 16

  17. Run-away domain has been identified in JET. Runawaydomain entry points in JET-C and JET-ILW: (fAr = 40%, Bt=3T) • Test the impact of the plasma magnetic topology on the run-away generation (modelling) • Compute the orbits of runaway electrons in the 3D electromagnetic field. • Test the importance of the de-confinement of runaway electrons by MHD turbulence E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 17

  18. ITER require to dissipate most of the runaway energy within a timescale of ~100ms  This is unlikely to be achieved by “deconfinement” using a magnetic perturbation Present strategy to ensure dissipation: aim for a sufficient high density of high-Z from the beginning of the CQ or after a fixed delay (thus increasing Ec)  Late injection into an existing runaway beam has shown negligible effects on runaway current, the HXR emission. • There are evidence in JET that with pre-CQ no RAs are generated (Reux IAEA 2014) • Increase in gas density is predicted to increase dissipation • Optimum flow rate in early CQ injection • Develop magnetic in advance modelling for RA control and kinetic modelling DMV2 DMV1 E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 18

  19. Mitigation of run-away with high Z material • Objectives • Determine the efficiency of high Z impurity injection in a RA beam by changing the DMV flow rate, the DMV location and the time of injection wrt the CQ. • Modelling of results with kinetic modelling and fast equilibrium and produce an extrapolation to ITER. Number of sessions: 2 Collaboration with MST1: close collaboration on the mitigation methods with high Z impurity and modelling E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 19

  20. Modelling of run-away electrons as a test particle (Task) • Objectives • Test the importance of de-confinement of runaway electrons by magnetic perturbation and machine size effect in using the modelling of a test particle (JOREK). • Establish the basis for an experiment in a tokamak (JET or TCV) aiming at controlling the RA beam and testing the effect of applied vertical field or external magnetic perturbation. Relation with other experiment  This modelling Task should establish the experimental basis (or not) for the control of run-aways by magnetic perturbation for JET1 and/or MST1. Collaboration with MST1: Modelling that could apply to both JET and AUG E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 20

  21. Summary of the envisaged experiments/tasks in the main programme Initially: 19 proposals and 29 sessions requested. E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 21

  22. Proposals not considered in the Programme 1- Dependencies of run-away generation with the magnetic topology This proposed experiment is better suited in a tokamak like TCV. It is proposed to do it under MST1 (submitted to MST1) 2- ITPA joint experiment to study threshold conditions for runaway electron generation and suppression This proposal aims at using current plateau-born run-away and not disruptions run-away. These are not considered as relevant for run-away physics. Many devices have already contributed to the ITPA JE. 3- Disruption in Helium plasma No He campaign E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 22

  23. Part II: JET1 – MST1 collaboration/joint work E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 23

  24. Synergies between the JET proposed experiments and MST1 proposals (12 proposals) on H1.3 E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 24

  25. Specific proposals to the MST1 task Force Separateproposals in the MST1 list (8 proposals) Model based plasma supervision and disruption avaidance (D5) Disruption control in high bN and high density scenarios with ECCD/ECRH (D6) Control of the locking position of locked modes near disruptions (D7) Application of disruption avoidance techniques (ECCD/ECRH) in accessible scenarios (D8) Determination and correction of the staticintrinsicerrorfield (D9) 2/1 NTM walllockingavaoidance by forced rotation throughexternalmagnetic perturbations (D13) Effect of plasma shaping on run-awayelectrons (D15) (from JET!) Decorrelation of run-awayelectrons by magnetic perturbations and role of 3D plasma response (D17) Runawayelectron position control and currentramp-down (D19) En experimental investigation of the VDE dependence on plasma elongation and internal inductance in the TCV tokamak (D20) Detectionavoidance and mitigation of disruptions (D21)  Note that they are also 2 EnR projects launched on this topics in 2015: IPP05 (JOREK modelling) & CEA09 (run-away modelling) E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 25

  26. For discussion • A close collaboration activityisforeseen (and necessary!) with MST1 on the topic of disruption and run-aways. AUG isequippedwithsimilartoolsthan JET. • TLFs (MST1 & JET1) to seattogether and define the commondenominator and specificities in terms of experiments/tasks and deliverables. • In case of joint experiments, 2 scientificcoordinator JET1/MST1 willbeselected. • TFLs to contact PI of the 2 EnRprojects to coordinate the efforts on modelling • TFLs to organise joint TF-meeting and science meeting on thesesubjectswhennecessary. • Database • (…) • Anyotherideas? E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 26

  27. Headlines Key deliverable: quantify disruption mitigation efficiency in high energy plasmas and extrapolate to ITER • Headline 1.3: Avoidance and mitigation of disruption and runaways electrons • H1.3-D01: Develop robust operation of ITER scenarios and their safe termination • H1.3-D06: Document conditions for run-away electron generation and mitigation • H1.3-D07: Test control of runaway electrons by alternative methods (non-axisymmetric fields) • H1.3-D09: Develop disruption prediction methods that minimise the requirements for model training on ITER and real-time predictors methods optimised in term of model training, success rate, anticipation time, differentiation among different types of disruptions. • H1.3-D10: Develop full 3D codes (plasma + vessel) to describe halo current formation and asymmetries. • H1.3-D11: Qualification of Massive Gas Injection as a mitigation method for heat loads and forces (fuelling efficiency, local peaking of radiation load as function of MGI parameters and plasma conditions) • H1.3-D12: Develop Disruption workflow – including ELM module/RMP. E. Joffrin| GPM 2015| Lausanne | 19-23rd January| Page 27

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