Alcator C Mod. Integrated Scenarios ITER H-mode Baseline. Presented by: Stephen M. Wolfe

Transcription

1 Integrated Scenarios ITER H-mode Baseline Presented by: Stephen M Wolfe C-Mod PAC Meeting MIT Plasma Science & Fusion Center Cambridge, MA Jan 28, 2010

2 Definitions and Scope By Integrated Scenarios, we mean research aimed at reaching attractive operating points, generally cutting across multiple science topics and often involving interaction and compatibility issues between different plasma processes or regions The ITER Q = 10 DT H-mode baseline scenario (aka Scenario 2 ) features Positive shear, q 0 < 1 q 95 3, β N = 18, H H 1, f NI 025,n/n G 085 Edge transport barrier B T = 53T,I p = 15MA, n e m 3 Research effort also supports aspects of the ITER Pre-nuclear Commissioning Phase Operation in H and/or He majority Reduced parameters ( 1 2 B T, I p ) Alternate RF Scenarios Issues of H-mode access, character C-Mod PAC Meeting Jan 28, 2010 smw 1

3 Research Focus and Orientation Compared to the Topical Science areas, the H-mode Integrated Scenarios Research Program is more focussed on support of ITER construction and operations planning Respond to requirements identified by IO Strong IO participation in program planning IO staff involvement in design, execution, analysis of experiments Participate in identification, definition, and execution of Joint Experiments and High Priority research activities of ITPA Proactively identify and address issues relevant to ITER planning and operation Address C-Mod issues of integration and scenario development impacting our ability to carry out ITER-related research C-Mod PAC Meeting Jan 28, 2010 smw 2

4 Addressing ITER H-mode Scenario issues requires integration Issues, Challenges are similar for C-Mod and ITER Divertor and wall materials and conditioning High heat flux requirement Compatibility with low core radiation, Z eff Hydrogen retention and recovery ICRF Heating Challenging RF power density Compatibility with H-mode edge, high n e operation, ELMs Compatibility with wall conditioning requirements Control of pedestal parameters, Edge relaxation Variation of edge parameters (ν,β) Particle and impurity control ELM control C-Mod PAC Meeting Jan 28, 2010 smw 3

5 C-Mod H-mode Scenarios Research Topics Demonstration and validation of ITER reference scenarios Scenarios for ITER Pre-nuclear phase H-mode access and performance requirements Power handling, particle control, and impurity seeding Plasma Material Interactions (addressed in Boundary section presentations) ELM and Pedestal Physics (see presentations on Transport and Pedestal Physics) Development and validation of Plasma Control strategies C-Mod PAC Meeting Jan 28, 2010 smw 4

6 ITER has determined that early diverting and large bore plasmas will reference be its baseline startup scenario Validation of ITER startup ITER is planning to divert at ~ 15 s in a 100 s Ip rampup Experiments begun 2008 (Sips), continuing (Kessel) (ITPA SSO-5) In order to simulate ITER-like discharges in C-Mod, the divert time has been reduced to ms out of a ITER startup 500 ms Ip scenario rampup requires low 07 < li < 1 ITER has determined t bore plasmas will be it for vertical stability Cleaner early plasma Proposed to 15 to MA flattop in 80 sec conditionsramp compared scales to C-Mod previous year 135MA in 035 to 06 sec (depending on htei) 2008 Full bore plasma with x-point formation at 14 maximum current needed to avoid overheating ITER limiters Recent development improved early X-point formation (I 03MA) 00Divert at msec p ITER is planning to divert at ~ 15 s i rampup In order to simulate ITER-like discha divert time has been reduced to ms Ip rampup Cleaner early plasma conditions compared to previous year Time, s 2008 Cleaner early plasma compared to later XPF Facilitates application of ICRF during current ramp 00 C-Mod PAC Meeting Jan 28, 2010 Time, s 05 smw

7 Benchmarking of ITER simulations in ohmic, ICRH heated current rise C Kessel ITER needs to conserve Volt-sec and achieve low l i in ramp-up ITER (and C-Mod) TSC Simulations predict that ICRH during (L-mode) ramp-up reduces resistive V-s consumption and broadens J profile Reduction in resistive volt-seconds with ICRH during L-mode current rise verified in C-Mod experiments Reduction in l i in I p ramp not observed on C-Mod li(1) P(ICRF), MW rampup flattop rampdown rampup flattop rampdown C-Mod PAC Meeting Jan 28, 2010 time, s time, s smw 6 Ip, MA 10 I(OH1), ka

8 Transport models used for ITER predictions require adjustment to match C-Mod current rise Coppi-Tang model used for ITER L-mode predictions Based on profile consistency and analytic drift wave theory Adjustable parameters control magnitude and shape of χ(ρ), with corresponding variation in T e (ρ) profile Broader T e (ρ) profile observed in C-Mod experimental data than predicted using model normally used for ITER simulations Adjusting χ parameters to match experimental profile provides better match for evolution of l i (t) Alternate models including Bohm/gyroBohm (used on JET) and CDBM (used on JT60-U) will be examined Te(R), ev li(1) TSC simulation ECE Thomson R, cm time, s C-Mod PAC Meeting Jan 28, 2010 smw 7

9 C-Mod rampdown experiments address issues, constraints on ITER rampdown C Kessel Maintain diverted plasma to low current ( 10% flattop) Reduce elongation (κ 14) to avoid vertical instability as l i rises (minimize l i by adjusting ramp-down rate, heating) Avoid flux consumption, CS (OH1) over-current during H to L transition Confirmed CS-coil (OH1) over-current predicted at H-L transition Pedestal density and temperature decrease with I p during rampdown H-mode effective in delaying rise in l i early in rampdown Faster ramps avoid OH1 overcurrent but increase l i I(OH1), ka Wth, kj H to L-mode transition Ip, MA li(1) time, s H L 115sec (EOF) H L 145sec H L 165sec H L 13sec, with faster Ip rampdown C-Mod PAC Meeting Jan 28, 2010 smw 8

10 Scenario demonstrations: Full discharge sequence C Mod Demonstration of Scenario 2 - like equilibrium, p, T e /T i, power density (IOS-11) Control of operating point Benchmark transport, stability modeling Evaluate impurity, particle control Evaluate disruptivity, stability issues Exploration of variations about reference scenario Continue Validation of robust ramp-down, shut-down sequence (IOS-22) Compatibility of core and boundary Interaction with plasma-facing materials, particle control, impurity seeding IOS-12) including heat-flux and Demonstration of reliable, benign fault-handling and mitigation techniques C-Mod PAC Meeting Jan 28, 2010 smw 9

11 ITER Scenario Demonstration: IOS-11 IOS 11 ITER baseline at q=3, β N = 18,n e = 085n G (D, H, He) Some flexibility allowed in parameters Initial full-field C-Mod experiments at more modest n/n G ( ) Issues include ICRF at high density, stationary H-mode at q < 35, acheivable β N Target condition for seeding experiment IOS-12, Ramp-down validation IOS-22 May not be compatible with strikepoint restrictions (W tile) Defer to summer campaign? Lower field option relieves some constraints Relevant to pre-nuclear phase studies (next section) Initial experiments carried out Jan, 2010, at half-field (27 T) Extension of demo experiments at higher and lower density in next campaigns C-Mod PAC Meeting Jan 28, 2010 smw 10

12 ITER Pre-Nuclear Phase (first 2-3 years) ITER_D_2FB8AC v 20 IC/STAC-6/4-1 No deuterium operation majority H (or He), minority He 3 Heating, CD sources under commissioning P tot < 73MW (NBI, EC, IC) 40 < f ICRF < 55MHz, P ICRF 20MW B T between half and full field CFC divertor (decision on transition to W tbd) Issues: Access to H-mode Alternate RF scenarios Plasma control at q 95 5, L-mode (l i > 1?) Operation with strikepoints on W baffle section Fig 321 Available operation space in hydrogen and helium plasmas for various heating systems on ITER in terms of plasma current, toroidal field, and plasma density The figure shows the plasma current (left axis) and density (right axis) against toroidal field The three diagonal lines correspond to 85% of the Greenwald limit for q 95 = 3, 4 and 5 The area delimited by the dotted lines correspond to fundamental He 3 minority ion cyclotron resonance heating (ICRH) for the available frequency range This band also corresponds to 2 nd harmonic T The area delimited by the dashed lines corresponds to H minority ICRH (see text) The blue bands correspond to the accessible domain for the main Electron Cyclotron Resonance Heating (ECRH) system at the fundamental and 2 nd harmonic, making use of both O-mode and X-mode heating and constraining the ECRH resonance so that full absorption occurs within ρ=09 (the source calculation is performed for scenario 2, with Te(0)~25 kev and n=10 20 m -3 ) The bands are vertically displaced relative to one another to show the overlap between ECRH and ICRH The horizontal green lines at m -3 and at m -3 correspond to the estimated neutral beam injection (NBI) shine-through limits for 087MeV hydrogen for hydrogen and helium plasmas respectively, assuming the NB shine-through armour is installed The significance of the black and green arrows is discussed later in Section 3246 C-Mod PAC Meeting Jan 28, 2010 It is anticipated that considerable operational time will be saved by parallel smw 11 commissioning of the heating systems and by pulse sharing Operation at 5MA/25T, q 95 = 4 (in hydrogen plasmas) would allow commissioning of all systems simultaneously if operating with densities above 80% of the

13 Comparison of L-H threshold in D and He plasmas Experiment carried out over a single (long) day Target density varied across discharges ICRH ramp, staircases determine L-H threshold Began day in He, low density Changeover to D midday, decrease density toward initial value Principal result: Deuterium data P th,he /P th,d 12 : have 18, atypically difference most pronounced high threshold at lowest power (helium density, threshold power However: Multi-machine experiments give inconsistent comparisons of He and D threshold Implications for ITER Helium operation inconclusive Further investigations warranted J Snipes (IO) Observed P thresh much higher in He than D Density varied across discharges and ICRF ramp, staircases used to determine H-mode threshold Began day in He, changed over to D midday P th,he /P th,d ~12 18 above 18x10 20 m -3 contamination?) JW Hughes, 17 th ITPA Pedestal TG meeting, Princeton, NJ, 5 Oct Approximate trajectory Of experiment C-Mod PAC Meeting Jan 28, 2010 smw 12

14 Near-term C-Mod Activities in support of pre-nuclear phase Investigate L-H threshold (TC-4) Species dependence of transition and confinement He (and H?) majority Evaluate dependence on X-point height, equilibrium details Characterize He majority H-modes Limited experience in C-Mod indicates differences in pedestal relaxation, divertor characteristics, impurity transport Evaluate ELM characteristics Extend systematic studies to ITER-relevant regimes, benchmark simulation models Assess relevant ICRF scenarios He 3 minority Consider H majority scenarios Assess ITER ramp-up, flattop, ramp-down scenarios in L-mode, q 95 5 C-Mod PAC Meeting Jan 28, 2010 smw 13

15 H-mode access: Power Requirements for high confinement H-modes The run was a full day Experimental goals: Examine pedestal and confinement characteristics as function of margin above threshold power (P L H ) Margin above P L H required to reach H 1 in stationary conditions Role of core/edge radiation on power requirement devoted to create Ne and Ar seeded EDA ( ) and ELMy H-modes ( ) to compare to unseeded plasmas with the same net power (P TOT -P RAD ) from Run Summary for Seeding Experiments Approach: obtained seeded EDA s for both Ne and Ar Access stationary (EDA and ELMy) H-modes with varying ratios of P in /P L H reproduce discharges with impurity seeding, matching P net remade the ELMy targets obtained seeded ELMy s for Ar A Loarte(IO),JHughes, MReinke Mo XXXII Br [AU] Edge SXR Br [kw/m 2 ] ZAVE p [psi] 14, 20 25, Time [sec] C-Mod PAC Meeting Jan 28, 2010 smw 14

16 Core profiles relatively stiff: confinement drop appears linked to pedestal Power requirements for high confinement H-modes EDA dataset compiled with Ar, Ne, and N 2 seeding Quantitative analysis pending accurate calibration of bolometer arrays (May, 2010) Good confinement (H 98y2 1) obtained with P rad sufficient to reduce divertor heat load Degradation of confinement observed at low P core net corrlates with decrease in pedestal temperature Pedestal cooling more pronounced with Ar than Ne or N 2, as expected from radiation profiles Impurity seeding reduces incidence of high Z impurity injections also reduces ICRF trips Neon seeding actually leads to higher performance H-modes T e [kev] Thomson Scattering R [m] LEGEND JW Hughes, 17 th ITPA Pedestal TG meeting, Princeton, NJ, 5 Oct Ne Ar puff pressure Ne Ar [psi] C-Mod PAC Meeting Jan 28, 2010 smw 15

17 Full power accounting requires inclusion of divertor radiation Foil and AXUV divertor bolometer arrays provide excellent coverage Spatial profiles vary with Z N 2 higher divertor radiation than Ar/Ne X-point radiation > 05M W observed with Ne seeding C-Mod PAC Meeting Jan 28, 2010 smw 16 MReinke

18 Operational control of divertor power balance using radiation seeding (IOS-12) Seeding reduced divertor tile heatin and impurity injections Goal is to reduce divertor heat load by increasing radiative loss without compromising pedestal, core confinement (ITER scenario) C-Mod experiments feature ITER-like divertor power density, geometry, neutral opacity, Extensive pedestal and divertor diagnostics Feedack controlled impurity puffing using recycling and non-recycling impurities Cryopump provides sink for better regulation, control of impurity level Begin experiments Impurity seeding (midplane) portion of H-mode access experiment Continue with divertor seeding (2010) Apply to ITER demo-like conditions Continue with high heat-flux, symmetric W divertor ( ) With either Argon or Neon, seeding greatly reduces peak dive temperatures Also eliminates i 12 high h Z impurity it injections, which h can be a prob extremely high power density on C-Mod This reduces ICRF 10 Net result can be higher performance H-modes with Neon see starting to 08 use in other high power experiments Confinement Factor H 98 A Hubbard, 3rd ITPA IOS 06TG meeting, Frascati, Oct N 2 Ne Ar D Brunner Power to Divertor [AU] C-Mod PAC Meeting Jan 28, 2010 smw 17

19 Development of plasma operational control methods C-Mod & ITER PF sets have similar arrangement and (multi-parameter) functionality Large vessel and structure currents, especially during startup, ramp-down MIMO shape control with few actuators, minimal null space, operation near current, voltage, stress limits RF-based actuators for heating, non-inductive current drive Negligible central particle, momentum sources C-Mod PAC Meeting Jan 28, 2010 smw 18

20 Development and testing of plasma control algorithms Testing of plasma control strategies in relevant scenarios Effects of sensor noise, transient events Effects of currents in passive structures on control and reconstructions Benchmarking of simulation codes Development and testing of machine protection algorithms Identification of and response to sensor, actuator faults Response to proximity to actuator limits adaptive transfer to safe shutdown sequence or real-time pulse rescheduling Real-time identification of proximity to plasma instability boundaries Implementation of disruption mitigation algorithms in routine tokamak operation for evaluation of robustness and reliability C-Mod PAC Meeting Jan 28, 2010 smw 19

21 Burn Control simulation experiments with ICRH 1 Study evolution and stationary states of plasma with power dependent on plasma parameters (IOS-63: Control of experimentally simulated burning state) Use ICRF minority heating to mimic centrally peaked fast ion heating Control (part of) P ICRF n 2 f(t ) or R DD to simulate burn Apply feedback to try to maintain constant burn power against perturbations such as ELMs, sawteeth, MHD, density excursions, etc 1 suggested by P Politzer (GA) C-Mod PAC Meeting Jan 28, 2010 smw 20

22 C-Mod H-mode Scenarios Research Program Program elements paced by ITER priorities C-Mod facility capabilities Actuators, Diagnostics, Control system, Internals : Approximately 85 run days so far Scenario demonstrations: Ramp-up, ramp-down; half-field scenarios H-mode access: Power requirements for high confinement Pre-nuclear phase: Comparison of L-H threshold in He and D Priority experiments for remainder of FY10 Pre-nuclear: Characterize ELM behavior in He Impurity seeding in ITER-like discharges (IOS-12) ITER demos (IOS-11) at full field (?) ELM pacing experiments (?) : LH launcher & klystrons, W tile repair, new ICRF antenna Extend ITER demo (IOS-11) studies to higher and lower collisionality (as feasible) Current rampup scenarios with LHCD Extend impurity seeding (IOS-12) studies, feedback control of divertor radiation Routine use of disruption mitigation techniques : New 4-strap ICRF antenna, LH launcher, outer divertor upgrade, DPCS enhancements Burn control studies Continue impurity seeding and power handling studies with high heat flux symmetric divertor Development and testing of advanced plasma control/fault sensing algorithms C-Mod PAC Meeting Jan 28, 2010 smw 21

23 H-mode Integrated Scenario research supports ReNEW goals Primary contribution to Thrust 4:Qualify operational scenarios and the supporting physics basis for ITER Transport during transient phases Ramp-up and ramp-down profiles, MHD effects H-mode access and dependence on Ion Species Prospects for ITER pre-nuclear phase H-mode sustainment Heating and fueling ICRH-specific effects on Integrated Scenario, including edge interaction and impurity generation (also see RF Topical area) H-mode pedestals Control of pedestal parameters, relaxation mechanisms (see Pedestal presentation) Thrust 5: Expand the limits for controlling and fusion plasmas Thurst 6: Develop predictive models for fusion plasmas, supported by theory and challenged with experimental measurement C-Mod PAC Meeting Jan 28, 2010 smw 22

24 H-mode Integrated Scenario research supports ITER/ITPA Joint Experiments Description Joint Notes on C-Mod Contributions Experiment Power ratio - hysteresis and access to H-mode with H 1 TC-2 Assess existing database; propose additional expt if warranted L-H threshold power at low density TC-3 Initial C-Mod expt completed X-point scaling H-mode transition and confinement dependence on ionic species TC-4 for ITER pre-nuclear phase begun 2009 He profiles and transport coefficients TC-11 Evaluating diagnostic capability 2010 H-mode access with different X-point height PEP-28 New (related to TC-3) ITER demo at q 95 = 3,β N = 18,n e 085n G IOS-11 Now includes He & H studies 2010 Study seeding effects on ITER demo IOS-12 Initial studies 2009 discharges Ramp-down from q 95 = 3 IOS-22 Continue experiments begun under SSO-5 Control of experimentally simulated burning state IOS-63 New DPCS enhancements, 2011 C-Mod PAC Meeting Jan 28, 2010 smw 23

25 C-Mod Research on Integrated Scenarios for ITER H-mode Baseline H-mode baseline research program addresses cross-cutting physics and technology issues Exploits ITER-relevant C-Mod parameters and tools Addresses High-priority ITER Research Needs Strongly coupled to ITPA tasks, Joint Experiments Many additional ITER-related experiments in Topical Science Groups Integrated Research in support of ITER Advanced Scenarios described in Next Presentation C-Mod PAC Meeting Jan 28, 2010 smw 24