Plasma Scenarios and Control

Transcription

1 Plasma Scenarios and Control R. J. Hawryluk Presented at the SECOND IAEA DEMO PROGRAMME WORKSHOP December 19, 2013

2 What is the Difference in the Scenario and Control Requirements Between ITER and DEMO? How do differences in scenarios affect the control requirements? Y. Kamada F. Poli Discussion How are the actuators different in DEMO compared with ITER? P. Thomas A. Garofalo Discussion F. Orsitto W. Biel Discussion P. Lang Discussion In a stellarator DEMO what are the additional issues? What issues go away? R. Wolf ---- Discussion Thanks to the speakers for their slides. Errors and misunderstandings are mine.

3 Operating Space For DEMO Overlaps and Extends the ITER Operating Space JT-60SA Target DEMO reactors b N Existing Tokamaks FB ideal MHD limit JT-60U ITER Inductive Sustainment Time (s) ITER Steady-state EU DEMO studies are an extension of ITER Inductive to longer pulse. Most other DEMO studies strive for fully non-inductive. Does DEMO need to demonstrate economic attractiveness or is the emphasis on producing electricity?

4 Integrated Control Scenario Development Understanding & Control of the highly self-regulating combined plasma system for DEMO High-beta, high-bootstrap fraction plasma => a highly self regulating non-linear system governed by strong linkages among j(r), p(r) and Vt(r) in core & pedestal. Strong spatial linkage : Core Pedestal SOL Divertor plasmas Study controllability & Plasma response Determine the minimum suitable set of actuators & logic. + control margin against operation boundaries Measure, Predict, Control, Decide 4

5 ITER Studies Show that High Performance Steady-State Operation Entails Complex Interaction Between Physics and Actuators With LHCD broad current profiles q min > 1.5 r(q min ) > 0.4 Without LHCD peaked current profiles q min < 1.5 r(q min ) < 0.4 Baseline + 20MW LH Baseline + 40MW LH Stability depends on pressure profile Baseline + 20MW EC Unstable even with wall if r EC <0.3 Stable with EL/UL power sharing and r EL >0.45 Δ Baseline Stable without wall, but low performance Fully non-inductive, MHD stable plasmas with b N >2.5 can be achieved only with LH waves Francesca Poli 2 nd IAEA-DEMO workshop, Vienna Dec 17-20, /16

6 More Sophisticated Control Systems Will Be Required Due to Restricted No. of Diagnostics Dynamic observer for tokamak plasma state actuator commands [Real-timecontrol] Tokamak state measurements (F. Felici, see poster) Plasma controller next time Tokamak Simulation state + updated state predicted state state update predicted measurements - measurement residual Observer gain Fault detection & classification Exception handling Controler Model-based, dynamicstateestimator ("observer") Supervision Run tokamak simulation in parallel with plasma evolution Correct simulated state estimate based on difference between predicted and true measurements Detection & classification of excessive discrepancies The plasma controller may initiate fast rampdown or disruption mitigation if a discrepancy cannot be resolved otherwise

7 Can We Simplify the Control Problem By Relying on Self-Regulating (Hybrid) Operational Modes? How does the current redistribution mechanism extrapolate to ITER and DEMO?

8 Comparison of Surface Occupation ( TBR 1.1) Areas (m 2 ) Machine Diagnostics Heating and Current Drive JET ICH antennae (internal) ITER (includes HNB3 and LH) DEMO P Thomas

9 System H&CD Current-drive efficiency DEMO required current drive efficiency η wp. CD = Physics current drive efficiency CD Wall-plug efficiency η wp as per ITER design ECCD (upper value) ICCD (matching?) Product η wp. CD Product η wp. CD with technical improvement (gyrotron at 70% - K Sakamoto) HH FWCD??? NBCD (photon neutraliser) EC is OK on η wp but is struggling with CD until T e >50keV Conventional IC not applicable and FWCD an unknown NB OK on physics but needs photon neutraliser

10 Helicons Are Predicted to Drive Times More Off-axis Current than ECCD in FNSF-AT Higher CD efficiency is why helicons were chosen for ARIES-AT PoP tests on DIII-D in 2016 FNSF-AT Equilibrium Helicons may reduce the tension between high density for ameliorating the power exhaust issue and low density for improving current drive efficiency 20 AM Garofalo/2 nd IAEA DEMO Workshop/Vienna/Dec. 19, 2013

11 H&CD Conclusions DEMO technical requirements for H&CD are different to those of ITER Impact of T breeding requirements Neutron fluence Current drive efficiency Availability ITER will benefit DEMO in respect of technical progress, the physics of H&CD with a burning plasma, safety and generic maintenance issues. An aggressive R&D programme should be mounted, to develop high-power (4MW), efficient ( 70%) gyrotrons and photon neutralisers for NBI, Helicon and FWCD with a folded waveguide.

12 Diagnostic Issues Lifetime issues Ionizing radiation Neutron fluence and activation on DEMO behind the blanket is comparable to ITER first wall! High availability High tritium breeding ratio Important gaps and problems Monitoring of 1st wall + divertor integrity (no imaging diagnostics?) Control of the divertor plasma (detachment control) + heat fluxes Erosion, dust, tritium retention Plasma instabilities, modes etc. Additional issues for advanced scenarios (profile control if needed) Current density profile Indirect measurements with correlation reflectometry

13 MAIN MESSAGES DEMO diagnostics should focus on high priority parameters: diagnostics for machine protection and basic control to be useful for BURN control in long pulses. The space available for diagnostics is severely limited by the TBR : a minimum set of systems is used to protect and control the machine. The engineering of diagnostics must be inserted in the overall design of DEMO from the Beginning due to the optimization of the space dedicated, compatible with the TBR: likely the organization of diagnostics in PORT PLUGS of ITER will not be used. The high fluence of DEMO ( x ITER ) put the other important constraint on the diagnostics: in practice all the ITER diagnostics MUST BE REVISITED BECAUSE OF THE HIGH DPA IMPLIED IN DEMO OPERATIONS. Diagnostics feasible ( low extrapolation from ITER design and R&D needed ) Microwave ( and Far Infrared Light ) techniques Direct line-of-sight techniques (neutrons, x-rays)

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17 Implications for Pumping, Fuel Cycle and Disruption Summary Mitigation The three topics considered here have a quite different status/maturity with respect to their readiness for a fusion reactor Pumping and fuel cycle: System lay out ready for ITER, mock up tests in preparation Full concept for DEMO elaborated, sound full working plan at hand Fuelling system (pellets): System lay out ready for ITER, mock up tests in preparation DEMO could benefit from an improved concept R&D for elevated speed injection needs to be elaborated ( à la pumping ) Disruption mitigation: System lay out for ITER still pending, significant progress still required, Reliable and purposeful system will be a must DEMO faces the same class of problems at elevated magnitude Solutions coming along with the ITER R&D? P.T. Lang: Fuelling, pumping, disruption mitigation 27 2 nd IAEA DEMO WS, Vienna,

18 ELM mitigation? small / no ELM regime RMP : may be difficult to utilize in DEMO Pellet Pacing :needs requirements Small ELM regimes: grassy ELM, QH may be applicable How to control Pedestal SOL/Div in a integrated manner. grassy ELM

19 Control Functions from ITER control functions list, W Treutterer, private communication Measurement and reconstruction Tokamak (ITER)... Monitoring... Actuators Coils (incl. plasma break down and ELM mitigation) Gas, pellets, pumps Heating (NBI, ECRH, ICRH, LHCD) Glow discharge electrodes Stellarator (HELIAS, W7-X type) Coils (incl. ι - control and plasma position) Ditto Heating (ECRH, NBI, ICRH) Ditto Essential differences Fast equilibrium control Disruption mitigation Stability control Kinetic profile control Current profile control All stellarator control functions find their correspondence at the tokamak side, but different control parameters (resonant island divertor)... different physics (e.g. transport)... different operation conditions (e.g. density) R Wolf, 19 December nd IAEA DEMO PROGRAMME WORKSHOP 19

20 Issues with do not exist in a stellarator NTM stabilization No current driven instabilities up to Δι / ι ext < 15 % NTMs stable due to negative shear in regions of high BS current (e.g. NCSX) Soft beta-limit No current driven instabilities Confinement saturation at high power Equilibrium deteriorates at high beta Disruptions Toroidal plasma currents one to two orders of magnitude smaller than in tokamaks Thermal quench possible (but on slower time scale: no formation of large convective cells due to large scale instabilities) However, rotational transform remains intact during plasma quench R Wolf, 19 December nd IAEA DEMO PROGRAMME WORKSHOP 20

21 Summary Control functions point of view Tok Stell Essential differences Fast equilibrium control Disruption mitigation Stability control Kinetic profile control Current profile control Physics of control parameters point of view Tok Stell Additional (physics) items Plasma start-up Different control parameters (resonant island divertor) Different physics (e.g. transport) Different operation conditions (e.g. density)... R Wolf, 19 December nd IAEA DEMO PROGRAMME WORKSHOP 21