Alcator C Mod. ITER Support and Burning Plasma Research at Alcator C-Mod. Presented by: Stephen M. Wolfe

Transcription

1 ITER Support and Burning Plasma Research at C-Mod Presented by: Stephen M Wolfe C-Mod PAC Meeting MIT Plasma Science & Fusion Center Cambridge, MA Feb 2, 2005

2 C-Mod ITER Research is carried out in all Topical Science Areas, Thrusts Transport Pedestal Dynamics, Edge Relaxation H-mode threshold physics Rotation with no/low external torque Edge/Divertor High Z-metallic PFC s Plasma, neutral transport in SOL, divertor Impurity lifecycle - co-deposition MHD Disruption Mitigation Nonaxisymmetric field effects NTM Physics Alfvén Eigenmode stability RF ICRF Antenna Development Weak single-pass absorption heating scenarios Mode conversion Current and Flow Drive Energetic particle driven modes AT Physics - Lower Hybrid ITB Physics LHCD for off-axis current drive, NTM stabilization Hybrid Scenario studies Advanced Scenario development Burning Plasma Demonstration Discharges in relevant parameter regimes Operational Scenario Development C-Mod PAC Meeting Feb 2, 2005 smw 1

3 C-Mod offers Unique Capabilities for Research in Support of Burning Plasma experiments Reactor relevant B (5-8 tesla) and n e (to m 3 ) High power density and SOL power ( < 1 GW/m2 ) Reactor-level absolute pressure (P 0 1 MPa) High-Z metallic first wall and PFC s Long pulse length compared to τ CR RF heating and current drive No central particle or momentum source T e T i, τ e/i τ E typical C-Mod PAC Meeting Feb 2, 2005 smw 2

4 ITPA High Priority Research Tasks Steady State Operation Investigate hybrid scenarios for prolonged plasma operation and develop full current drive plasmas with significant bootstrap current: assess beta limits Develop real time current profile control using heating and CD actuators: assess predictability, in particular for off-axis CD Transport Physics Improve experimental characterization and understanding of critical issues for reactor relevant regimes with enhanced confinement, by: Obtaining physics documentation for transport modeling of ITER hybrid and steady-state demonstration discharges Addressing reactor relevant conditions, eg, electron heating, Te Ti, impurities, density, edge-core interaction, low momentum input Contribute to and utilize international experimental ITPA database for tests of the commonality of hybrid and steady state scenario transport physics across devices Encourage tests of simulation predictions via comparisons to measurements of turbulence characteristics, code-to-code comparisons and comparisons to transport scalings Major or Unique C-Mod capability or emphasis Strong C-Mod contribution

5 ITPA High Priority Research Tasks Confinement Database and Modeling Assemble and manage multi-machine databases, analysis tools, and physics models Evaluate global and local models for plasma confinement by testing against the databases Predict the performance of Burning Plasma Experiments using the models, and include an estimate of the uncertainty of the predictions Pedestal and Edge Construct a Profile DB based on Inter machine experiment and perform tests of modeling using the profile DB as TG work Improve predictive capability of pedestal structure through profile modelling Construct physics-based and empirical scaling of pedestal parameters Improve predictive capability for ELM size and frequency and assess accessibility to regimes with small or no ELMs Major or Unique C-Mod capability or emphasis Strong C-Mod contribution

6 ITPA High Priority Research Tasks MHD Perform MHD stability analysis of H-mode edge transport barrier under Type I and tolerable ELM conditions Investigate/Determine island onset threshold of NTMs, stabilisation of (3,2) and (2,1) NTM islands at high and recovery, and possible operation with benign NTMs (FIR, seed island control); identify requirements for reactor plasmas Enhance understanding and mitigation of the effects of RWMs by analysis, experimental verification of control, determination of role of plasma rotation and error fields Determination of control system requirements for diagnostics Construct new disruption DB including conventional and advanced scenarios and heat loads on wall/targets Develop disruption mitigation techniques, particularly by noble gas injection Study fast particles collective modes in low and reversed magnetic shear configurations: Identify key parameters Perform theory-data comparison on damping and stability, including non-linear mode dynamics and fast particle transport Major or Unique C-Mod capability or emphasis Strong C-Mod contribution

7 ITPA High Priority Research Tasks Divertor and SOL Understand the effect of ELMs/disruptions on divertor and first wall structures Improve understanding of Tritium retention & processes that determine it Improve understanding of SOL plasma interaction with the main chamber Develop improved prescription of SOL perpendicular transport coefficients and boundary conditions for input to BPX modelling Diagnostics Develop methods of measuring the energy and density distribution of confined and escaping alphas Review requirements for measurements of neutron/a source profile and assessment of possible methods of measurement Determine life-time of plasma facing mirrors used in optical systems Develop new methods to measure steady state magnetic fields accurately in a nuclear environment and assessment of thermal EMF on irradiated coils used for steady state magnetic field measurements Develop requirements for measurements of dust, and assessment of techniques for measurement of dust and erosion Major or Unique C-Mod capability or emphasis Strong C-Mod contribution

8 ITER/Burning Plasma Support Research was a major component of the FY2004 C-Mod Experimental Campaign 19 Research Days ( 25%) devoted to ITPA experiments under the Topical Science areas L-H Threshold studies SOL Transport Rotation and momentum transport Joint Experiments on Pedestal Physics and Edge Relaxation Locked mode threshold Alfvén mode damping experiments Sawtooth control using ICRF 65 Research Days ( 9%) devoted to Burning Plasma Thrust Configuration optimization, including SN vs DN performance comparison and equilibrium development for ITER-like κ, I N Extension of C-Mod operation to 2MA, 8 tesla in preparation for high performance experiments, ρ scaling studies, etc C-Mod PAC Meeting Feb 2, 2005 smw 7

9 C-Mod operated with the ITER shape and B T 8 PF1 PF2 6 4 CS2U CS3U g5 g4 PF3 2 Z, m 0 CS1U g6 g3-2 CS1L -4 CS2L g1 g2 PF4-6 CS3L PF6 PF R, m I p = 15MA,B T = 53T I p = 16MA,B T = 53T C-Mod PAC Meeting Feb 2, 2005 smw 8

10 2 MA, 8 tesla Operation provides target plasma for high-performance scenarios, scaling studies q 95 = 31,I N = 11 Ohmic L-mode with T i T e 3keV n e m 3 01n G Error field compensation required for locked mode suppression C-Mod PAC Meeting Feb 2, 2005 smw 9

11 Lyman opacity key issue for ITER, being addressed with C-Mod data Radiation trapping may strongly affect the divertor modelling of ITER when implemented Makes it harder to achieve detachment and thus may limit operation Need high divertor N 0 L (C-Mod has N 0, JET has L) to have data close to that of ITER Factor of 6-10 lower Brightness (x10 18 ph/s/m 2 /sr) Ly β A D α x 3-1 A brightness 3-2 Ly γ x t (s) At low density Ly tracks D At high density Ly no longer tracks D, clear evidence of opacity of Ly & Ly While Ly still tracks D Experiment IEA/ITPA DSOL-5 relies on C-Mod data Modelling (started) Plasma background/grid being prepared (Lisgo, UT) Reiter will utilize EIRENNE Monte Carlo code to study radiation transport C-Mod PAC Meeting Feb 2-4, 2005 smw 10

12 Time-averaged transport analysis of far SOL transport shows similarities across tokamaks Status Far SOL transport (transport coeff) Magnitudes similar across C-Mod, DIII-D and JET Increasing across the SOL Little/no dependence on *, * and Plans Expand operational space of inferred transport coefficients on C-Mod Mini-proposal submitted & accepted at C-Mod for wide range of I p, n e, B t Expand experimental collaborations across tokamaks DIII-D H-mode data taken, travel planned for initial analysis effort ASDEX-Upgrade shots allocated MAST run proposal being written veff (m/s) Deff (m 2 /s) r/a D eff / n, v eff /n } C-Mod C-Mod{ } JET DIII-D{ r/a C-Mod PAC Meeting Feb 2-4, 2005 smw 11

13 Pedestal Relaxation - Comparison of C-Mod EDA to JFT-2M HRS C-Mod and JFT-2M successfully ran H-mode parameter scans in matched shape, except for aspect ratio Operational space of regimes (q 95,ν ) in two machines is very similar, suggesting EDA and HRS regimes are same instability Aspect ratio does not play a dominant role Details of fluctuations look similar but not identical, more study needed At low ν, obtained a regime of large (Type 1?) ELMs, without QC mode Matches JFT-2M large ELM regime Unusual for C-Mod Experiments to be completed in 2005 Inspired new proposals Expand aspect ratio range (w NSTX) Revisit large ELM regime C-Mod PAC Meeting Feb 2, 2005 smw 12

14 C-Mod Operating space in q 95 vs ν* looks very similar to JFT-2M C-Mod JFT-2M 6 q 95 vs ν* e,95, Steady EDA 6 ELMy (large ELMs) Mix (grassy ELMs) HRS (small ELMs) 5 ELMs (Type 1?) EDA+ELMs (Type 2?) 5 Transient H/weak EDA q 95 4 ELM-free q ν* e 2 01 ν 1 10 e * Suggests C-Mod EDA corresponds to JFT-2M HRS, C-Mod EDA + ELMs corresponds to JFT-2M mixed regime At lowest ν*, got pure large ELMy regime, no QC mode Type I?? C-Mod PAC Meeting Feb 2, 2005 smw 13

15 Modify Sawtooth Period Via Antenna Phasing Sawtooth period for central minority absorption in L-mode discharges: varies with antenna phasing for 08 MA discharges but is phase independent for 1 MA discharges Inversion radius remains unchanged in all cases The sawtooth period is similar for all phases when the minority resonance is placed near the q=1 surface on the high field side of the magnetic axis Future plans include: Identify operational space under which monster and small sawteeth are obtained Identify physics that sets sawtooth period Compare experimental sawtooth data with sawtooth models T e0 (kev) T e0 (kev) T e0 (kev) Heating Time [sec] C-Mod PAC Meeting Feb 2, 2005 smw 14

16 Non-dimensional Locked mode identity experiment carried out with JET, DIII-D ITER may be susceptible, particularly the low-density ohmic target plasma, due to low rotation Uncertain size and field scaling Match non-dimensional plasma parameters na 2, Ba 5/4, T a 1/2 constant Geometry matched (LSN), q = 32 C-Mod parameters B = 63T, I p = 13MA 1 < n e < m Match poloidal mode spectrum of JET EFCC coil - ne (10 20 m -3 ) Locked Not Locked app (mt) /1 Orientation (Identity Expt) B app (mt) -04 B m1 (mt) B 21 Mode Spectrum (Identity Experiment) m C-Mod PAC Meeting Feb 2, 2005 smw 15

17 Comparison with JET/DIII-D tests non-dimensional identity Identity experiments (same ρ,ν,q ψ,β) should have identical B 21 /B T, validating extrapolation in size to ITER by α R =2α n +125α B 5 JET Total C-Mod B 21 including intrinsic field from source model consistent with bounds from raw data JET points (scaled to C-Mod units) agree within error bars DIII-D data disagree by factor 2 Reasons under investigation - ne (10 20 m -3 ) C-Mod (locked) C-Mod (no lock) JET (thresh) DIII-D (thresh) B tot 21 [model] (mt) C-Mod PAC Meeting Feb 2, 2005 smw 16

18 C-Mod data spans the ITER field Locking threshold B 21 /B T 10 4 similar to larger (and smaller!) lower field experiments 1 C-Mod field scaling (α B 06 ± 06) uncertain, maybe weaker than JET/DIII-D, definitely not as strong as old Compass results Projection to ITER indicates proposed error field compensation system (correction to ) should be adequate B ~ /BT q 95 =32 ITER field B T (T) (C-Mod data B 21 B T others B pen B T at constant nr/b, at constant n) 1 R J Buttery, et al, Nucl Fusion C-Mod PAC Meeting Feb 2, 2005 smw 17

19 For 2005 Experimental Campaign ITER, BP Thrust remain high priority, 1/3 of projected runtime ITPA Research Activities and Joint Experiments about 30% of High Priority proposals in the Topical Areas and AT Thrust Initial allocation for Burning Plasma Thrust 10% First Wall, Materials studies Integrated Scenario Development, Performance enhancement Pedestal and Edge Relaxation Studies Non-dimensional Scaling Joint Experiments Level-1 OFES Target addresses first wall issues which impact ITER and Reactor C-Mod PAC Meeting Feb 2, 2005 smw 18

20 C-Mod FY05 Level 1 Targets C-Mod FY2005 Level 1 OFES Science Target Target: Measure plasma behavior with high-z antenna guards and input power greater than 35 MW This FY2005 science target addresses issues related to first wall choices, and the trade-offs between low-z and high-z materials This choice can affect many important aspects of tokamak operation, including: impurity content and radiation losses from the plasma; hydrogen isotope content in the plasma and retention in the walls; disruption hardiness of device components All of these issues are significant when considering choices for next step devices to study burning plasma physics, especially ITER Definitive experimental results will be compared to model predictions, and will be documented in a Target Completion Report in September, 2005 Quarterly Milestones for target: Q1: Install molybdenum protection tiles on all RF antennas and remove boron-nitride tiles from active MHD antennas (Dec 31, 2004) Status (21 December 2004): The quarterly milestone is complete The milestone completion report can be found at: Q2: Begin measurements of plasma behavior with all high-z antenna guards during tokamak operation (March 31, 2005) Q3: Assess operation with significant auxiliary input power for L-Mode and H-Mode plasma regimes (June 30, 2005) Q4: Operate with input power in excess of 35 MW, measure plasma behavior, compare with previous operation using boron-nitride protection tiles; document results in a Target Completion Report (September 30, 2005) Research supported by USDoE Office of Fusion Energy Sciences 1 of 1 01/26/ :16 AM C-Mod PAC Meeting Feb 2, 2005 smw 19

21 Burning Plasma Support Thrust includes integrated operational issues and scenario development First Wall, Materials studies W-brush tile testing Evaluation of metallic internal structures (with other topical groups, Operations) FY05 Target Integrated Scenario Development, Performance Enhancement High Current, High RF power H-mode performance study Burn Control Simulation with ICRH (proposal by Politzer, GA) Use of LHCD to achieve Hybrid Scenario Current Profiles (ITPA) (proposals by Sips,IPP-Garching, Wilson PPPL) [with AT] C-Mod PAC Meeting Feb 2, 2005 smw 20

22 Initial testing of Tungsten brush tiles at ITER-relevant heat flux Monitor heat load and W influx, compare to Mo Compare mechanical to brazed attachment methods Test to high power, multi-second pulses C-Mod PAC Meeting Feb 2, 2005 smw 21

23 Performance investigations with high-power RF at high plasma current Extend parameter space for databases Extrapolation of Present Performance Assume τ E =2τ Access higher pressure, lower collisionality Demonstrate control techniques D-T equivalent power (MW) I p =20MA P in =6MW I p =14MA P in =6MW Stored Energy (J) D-D Neutron Rate (n/s) C-Mod PAC Meeting Feb 2, 2005 smw 22

24 Burn Control Simulation with ICRH Politzer (GA) Study evolution and stationary states of plasma with power dependent on plasma parameters Likely operating point of a reactor is unstable to temperature excursions, requiring active burn control 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 ELM s, sawteeth, MHD, density excursions, etc Power (arb) power vs temperature (fixed density) 1000 ignited operating point unstable equilibrium (ignition) 1 sub-ignited operating point Temperature (arb) source = alphas + auxiliary loss = conduction + radiation (m T 5/2 ; G-B) C-Mod Ideas Forum 2-3Dec04 C-Mod PAC Meeting Feb 2, 2005 smw 23

25 Burning Plasma Support Thrust also includes a range of ITER-targeted ITPA Joint Experiments Pedestal and Edge Relaxation Studies (see also Transport Topical Area) Non-dimensional identity study with JET, ASDEX-U, DIII-D (ITPA Joint Experiment PEP-7) Document Type I ELM characteristics on C-Mod C-Mod/NSTX/MAST Small ELM regime comparison (ITPA Joint Experiment PEP-16) Complete Comparison of EDA with JFT2-M Small HRS regime (ITPA Joint Experiment PEP-12) Effect of Error Fields on Pedestal and ELMs Non-dimensional Scaling Joint Experiments ρ scan with JET (DIII-D,ASDEX) (ITPA Joint Experiment CDB-8) Complete Locked mode threshold non-dimensional identity experiment with JET, DIII-D (ITPA Joint Experiment MDC-6) ν, n G scaling experiment with JET (ITPA Joint Experiment CDB-4) C-Mod PAC Meeting Feb 2, 2005 smw 24

26 Explore and Document Type I ELM regimes Large (Type I?) ELMs seen at on C-Mod low ν* in JFT2M shape (4/2004) Occurred for Tped 900 ev, nped 1020 m-3, ν* < 035 (Not Type III ELM regime) NO sign of QC mode; not EDA Discrete spikes on Dα, magnetics, Prad, edge x-rays, density, τ ~ ms Shot PCI channel e RF Power (MW) Nel CH 4 (m-2) W MHD (kj) D_alpha BP02_GH_OLD pi bolo (au) e magnetic probe BP01_ASP net RF power (MW) logarithmic scale 0799 time (s) min value: max value: 1000 C-Mod PAC Meeting Feb 2, 2005 smw 25

27 Multi-machine non-dimensional pedestal identity experiment (ITPA PEP-7 Maddison) Contradictory scaling trends observed for width vs height of density pedestal on BACKGROUND EDGE BARRIERS PEDESTAL WIDTH CMod different machines - balance of edge source effect and plasma physics? Proposed experiment matches non-dimensional plasma parameters at pedestal, with common Pedestal equilibrium width scaling/physics geometry, has onenormous C-Mod, leverage ASDEX-U, on ITER DIII-D, JET performance Distinguish atomic physics effects (not matched) from plasma Relative importance of plasma and atomic physics probed via Key aim isdimensionless to get common identity experiments dataset w/ DIII-D, for pedestal ASDEX-U profile database, comparisons Role of neutrals investigated with more sophisticated neutral modeling Also scan νped (kinetic, q effects 95 to look included) for fluctuations and pedestal scalings model C-Mod C-Mod PAC Meeting Feb 2, 2005 smw 26

28 C-Mod is actively participating in 2005 ITPA Joint Experiments CDB-4 Confinement scaling in ELMy H-modes: ν scans at fixed n/ng CDB-8 ρ scaling along an ITER relevant path at both high and low beta TP-1 Steady-state plasma development TP-32 Physics investigation of transport mechanisms with T e T i at high density TP-41 Similarity experiments with off-axis ICRF-generated density peaking TP-6 Obtain empirical scaling of spontaneous plasma rotation PEP-7 Pedestal width analysis by dimensionless edge identity experiments on JET, ASDEX Upgrade, C-Mod and DIII-D PEP-12 Comparison between C-Mod EDA and JFT-2M HRS regimes PEP-16 C-MOD/NSTX/MAST small ELM regime comparison C-Mod PAC Meeting Feb 2, 2005 smw 27

29 C-Mod 2005 ITPA Joint Experiments DSOL-3 Scaling of radial transport DSOL-5 Role of Lyman absorption in the divertor DSOL-7 Multi-machine modeling and database for edge density and temperature profiles DSOL-11 Disruption Mitigation experiments DSOL-13 Deuterium codeposition with carbon in gaps of plasma facing components DSOL-15 Inter-machine comparispn of blob characteristics MDC-1 Disruption mitigation by massive gas jet MDC-3 Joint experiments on NTMs(including error field effects) MDC-5 Comparison of sawtooth control methods for NTM suppression MDC-6 Low beta error field experiments MDC-9 Fast ion redistribution by beam driven Alfvén modes and excitation threshold for Alfvén cascades MDC-10 Measurement of damping rate of intermediate n Alfvén Eigenmodes C-Mod PAC Meeting Feb 2, 2005 smw 28

30 C-Mod Research addresses key issues for Next Step Burning Plasma Experiments Unique dimensional parameters Provide strong constraints on database scalings High leverage through dimensionless identity and similarity experiments Equilibrated electrons and ions High SOL power density, metallic Plasma Facing Components ITER/Reactor relevant Unique recycling properties, D/T retention Reactor-like normalized neutral mean free path Prototypical disruption forces Exclusively RF driven Heating/Current Drive decoupled from particle, momentum sources Efficient off-axis current drive (Lower Hybrid) Long pulse length relative to skin, L/R times C-Mod PAC Meeting Feb 2, 2005 smw 29