Integrated Scenarios: Advanced Regimes

Transcription

1 Integrated Scenarios: Advanced Regimes Program Advisory Committee Meeting February 6-8, 2008 MIT PSFC Presented by A. Hubbard, for the Advanced Scenarios thrust group

2 Outline Scope and niche of Advanced Integrated Scenarios program. Progress since last PAC meeting. Proposed five-year research plan.

3 Scope and niche of Integrated Scenarios research Overarching Goal: Support development of ITER Advanced Scenarios by demonstrating operating regimes with relevant plasma parameters and control tools. Includes improving and testing predictive capability through integrated scenario modeling. Research is also relevant to DEMO and to proposed interim devices which may be needed to fill gaps before DEMO. We recognize that research will add to an extensive body of advanced scenario research elsewhere (including DIII-D, AUG, JT60-U, JET), which has demonstrated attractive operating regimes (eg high β N, high bootstrap and noninductive fraction, hybrid scenario). We see the role not so much as setting new parameter records, as extending the parameter space of these regimes in important ways, using different tools (all RF) and extending pulse lengths to many current relaxation times.

4 Progress in 2007: Current profile control In 2006 we had demonstrated near-full LHCD into ohmic target plasmas. At 2007 PAC, top priority of advanced integrated scenarios thrust was to start using LHCD in integrated scenarios with higher heating power and confinement. Key LH challenges, all also critical for ITER: Combining LH and ICRF Coupling LH into H-mode Good LHCD at higher n e (L and H-modes).

5 Progress in 2007: Current profile control In 2006 we had demonstrated near-full LHCD into ohmic target plasmas. At 2007 PAC, top priority of advanced integrated scenarios thrust was to start using LHCD in integrated scenarios with higher heating power and confinement. Key LH challenges, all also critical for ITER: Combining LH and ICRF Coupling LH into H-mode Good LHCD at higher n e? (L and H-modes). two out of three ain t bad Another major advance was getting q profiles from MSE Γ Shot Net LH Power [kw] LH Reflection Coefficient ICRF Power [MW] time [s]

6 HXR Count Rate (10 3 /s kev) Combining LHCD with ICRF raises T e, broadens LH deposition. Good success combining LH and ICRF, except for adjacent antenna (D-port) 4 2 P ICRF (MW) 0.8 MA, 5.4 T, USN L-Mode Unfavorable magnetic configuration (USN) was used to stay in improved L- mode (á la ASDEX), increasing T e and giving H 89 > 1. Higher T e is expected to move LH deposition further off axis. Broadening is observed in the nonthermal electron emission measured by hard x-ray camera, in qualitative agreement with modeling P LH (MW) T e0 (kev) ne (10 20 m -3 ) LH+ ICRF LH only time (s) HXR Raw profile 40 to 60 kev LH only (T e0 2.2 kev) LH+ICRF(T e0 4 kev) Chord Number (vertical pos'n)

7 LHCD in current ramp delays q 0 =1 by much more than ICRH alone. ohmic ICRF only, 2.25 MW LH only, 0.4 MW ICRF 2.25 MW and LH 0.4 MW sawtooth onset time LHCD and ICRH applied in slow (500 ms) current ramp discharges. Te(0), kev Marked effect of LHCD on j(r) evolution, good benchmark of TSC simulations. (C. Kessel) time, s

8 LHCD has been coupled into, and even triggered, H-modes. Reflection coefficients into ICRF H-modes are even lower than L-modes, though with higher fluctuations. Boronization seems to make this easier. In some discharges with ohmic targets, the additional LH heating power triggered an H-mode. Γ 2 LH Reflection Coeff n 18 probe [x 10 m -3 ] However, the launched power available (typically kw in these experiments) was insufficient for significant current drive at H- mode densities. Consistent with expectations, and with high-n e L-mode results. null result on possible issues with LH & H-mode pedestal. Need to both reduce H-mode density and raise LH power ICRF and H-Mode Coupling LSN H Mode USN L Mode o o

9 Progress in 2007: Density control A key new tool, the cryopump in upper vacuum vessel, and used routinely. Meets expected pumping speed, 9600 liters/sec (D 2 ). Excellent density control in L-mode. USN, Rev B H-modes, 600 ka, with cryopump. (two shots with low, stronger initial fuelling) Unpumped n e cryopumped Control of H-mode densities is more complex due to strong role of edge particle transport barrier. For high I p, LSN configurations, effect on n ped is weak (though T ped increases). Some promising conditions for pumping H-modes, reducing n ped have been found. More study and optimization needed, a priority for Then apply LHCD to lowest n cases

10 Research Plans for Current profile control Hybrid scenario LHCD in H-modes, double barriers Increase LH coupled power Combine LHCD, minority ICRH, FWCD Benchmark RF CD models for ITER Assess feasibility of hybrid scenario with LHCD Increase beta, study MHD tions instabilities to co Document pedestal and core contrib. to confinement Real-time j(r) control Compare with MHD, turbulence models to elucidate mechanisms Non-inductive Scenarios Core Transport Control Assess non-inductive scenarios - f BS ~ 30 % Higher n, H: f BS -60%, ITBs, f BS >60 % Lower B, High β N scenarios Assess effect of shear on ITBs with off-axis heating. ITBs with LHCD only Barrier formationwith reversed shear. Explore real-time transport control with LH and ICRF. Core-edge Integration H-mode density control Document heat loads in non-inductive scenarios Divertor upgrades Extend pulses to 4-5 seconds Integrated Scenario Modeling TSC+LSC+TRANSP + TGLF Transport simulations Integrated Plasma Simulator (w CQL3D-GENRAY, AORSA, TORIC) Participate in developing and benchmarking time-dependent ITER simulations Comparison with experimental scenarios (hybrid, non-inductive, double-barrier.)

11 Key facility upgrades for Integrated Scenarios program The program and schedule outlined will require timely implementation and upgrade of several key tools, including: LHCD upgrades: Improved, lower-loss launcher (FY09), plus second launcher. (FY11) Upgrade to 4 MW source. (FY09) Provides ~2.6 MW launched, possibility of compound spectra. j(r) measurements: MSE upgrade + new polarimeter. (FY09) Goal is routine measurements, eventually real-time inputs. ICRF upgrades: Modify 4-strap launcher to reduce sheath effect on boron, wall interactions. (FY09) 2 nd 4-strap launcher to preserve 8 MW source. (FY10/11) FMIT 1&2 upgrade to variable frequency MHz. (FY12) Divertor upgrades: DEMO-like divertor upgrade for 4+ sec, 8 MW input. (FY11) As can be seen, this research integrates hardware tools, as well as physics understanding, across the whole program!

12 Current profile control Active external current profile control is essential for advanced scenarios, since we already run pulse lengths >> τ CR. Key tool is LHCD. As discussed, this has already demonstrated some far off-axis j(r) control in plasmas with n e0 ~0.5-1.x10 20 m -3 (near ITER range). Next steps are Extending LHCD to H-modes, double barriers. Increasing power, for greater shear modification over a wider density range. Exploring multiple N // spectra (with 2 launchers) for greater localization. We will also use FWCD for on-axis seed current. First demonstrate alone, then use in non-inductive scenarios~2011. Real time control with DPCS ~ <j.b>/<b 2 >, MA/T-m sqrt( φ/φb) total LHCD bootstrap Itotal = 600 ka IBS = 205 ka ILH = 456 ka (n = 2.15) TSC simulation of scenario with <n e > ~10 20 m -3, adding 3 MW LH at N // = MW ICRH 5.4 T, 600 ka. T e0 6.1 kev, T i0 4.1 kev

13 Hybrid Scenario Hybrid Scenario is one of 3 main scenarios planned for ITER operation. While there is not yet a universally accepted definition, features include low central shear, with q 0 ~ 1, and improved confinement and stability over standard H-mode. On other experiments, flat q is typically produced using heating and/or current drive in I p ramp, with strong NBI, and aided by NTMs. Several open issues for extrapolation to ITER (see ITPA priorities) can be addressed on : Can it be produced with coupled e-i, no particle or momentum input? Can it be produced with j(r) control by RF (without relying on MHD)? If so, how do confinement, and MHD, compare? First experiments planned 2008 (with SSO-ITPA, Sips et al). Needs LHCD in H-modes. How low will shear be? May require higher LH power (2009).

14 Non-inductive Scenarios As higher power becomes available, the integrated scenarios program will focus on non-inductive, quasi-steady, regimes. Progression from majority external CD (as on ITER) to majority bootstrap (as on ARIES RS) regimes. Both dictated by available LH and ICRF powers, and useful in understanding advantages and difficulties of these regimes for future machines. Ip, ka time, s total total Non-ind Bootstrap LHCD <j.b>/<b 2 >, MA/m 2 -T sqrt(norm tor flx) total BS LH FW TSC simulation of scenario with H-mode n e profiles, <n e > ~1.5 x10 20 m -3, adding 2.5 MW LH, 4 MW ICRH. 5.4 T, 600 ka, assumed H 98y =1.44. f BS 60%.

15 Non-inductive Scenarios (cont) Scenarios will also progress from higher q, lower β N regimes to lower q and higher β N. This will likely need lower B T (4-4.5 T); there are tradeoffs with LH accessibility and efficiency. For full input power, and high beta, at reduced fields we need ICRF FMIT upgrade to tunable freq (f=50-80 MHz; FY12 incremental). Stability calculations indicate no-wall limit β N ~3. Approaching this regime would allow studies of MHD behaviour, boundaries vs. shaping, profiles, and control methods to avoid limit. ACCOME If we succeed in producing regimes limited by β N, would begin design studies for stabilization methods (in collaboration with other labs.) Implementation would be deferred to next five-year period.

16 Control of core transport Above scenarios assumed only modest increase in global confinement above standard H-modes (H H ~1.4, vs H H ~1.2 typical of our low n H-modes) If core transport barriers can be maintained and controlled, higher bootstrap fractions (70-80%?) should be possible. ITB research will focus on effect of j(r) on barrier formation, location. Based on results elsewhere, we expect flat or reversed shear to lead to easier ITB formation. (evidence of this in recent LHCD expts!) This often affects just ion or electron channel. will be able to study in conditions of coupled e-i. We will explore active control of core particle & energy transport, by varying both ICRH profile and j(r), in these new regimes. If impurity buildup, and MHD instabilities, can be avoided, ITB regimes become very attractive! Would then use real-time control of T e, n e profile peaking, via DPCS, with ICRH and LH powers, phases as actuators.

17 Core-edge integration With a strong Boundary program, and record SOL heat fluxes (upstream q // exceeding ITER, approaching DEMO), is very well placed to address the issues of integrating advanced scenarios with tolerable edge fluxes. For all scenarios explored, we will optimize and document H-mode pedestal and SOL/divertor parameters. (Note pedestal physics is already influencing our choice of plasma parameters). For high beta, we need both full ICRF power and clean, high confinement plasmas, so resolving RF-wall effects is critical. (Also true for ITER, could influence W vs C PFC decision.) Divertor heat fluxes will be a particular challenge for advanced scenarios due to lower density and longer pulses. Motivates DEMO-like divertor upgrade Local T rises may limit pulse duration to 3-4 s (still several τ CR ). Will test materials (W tiles), techniques such as sweeping, to their limits. Will assess integrating with radiative divertor. Is this compatible with LHCD (which needs reduced n e ) and high bootstrap fraction (which needs improved confinement)?

18 Heat loads, upgrades, and diagnostics Calendar Year Solutions 2nd row W-lamellae New DEMO-like outer divertor Manufacture Install Design B-coating limiters Manufacture Install Strike-point sweeping Impurity puffing New IR camera Diagnostics Standard divertor diagnostics (e.g. Langmuir probes) DEMO divertor calorimeter and Langmuir probes Upgraded Divertor Bolometry? Power loading ICRF LHCD 6 MW 4.0 MW ~ 1 MW MW 6 MW 2.5 MW Plasma period 1.5 sec 3 sec 5 sec

19 Integrated scenario modelling Integrated modeling is already being used to plan and interpret advanced scenario experiments. Currently we chiefly use TSC-TRANSP (with LSC for LHCD) for our time-dependent simulations several examples have been shown. Transport coefficients adjusted to match prior experimental profiles. Also using Fokker-Planck/ray tracing package CQL3D-GENRAY for more accurate analysis of LH deposition and current drive, for single time slices, with n, T profiles input. Synthetic diagnostics of x-rays, ECE have been added and compared to expt (examples in LH, theory talks). Looking ahead (~2009), plan to link these and other codes (eg TORIC) to exploit best features of each. Utilize Integrated Plasma Simulator, via strong MIT involvement in SciDac, SWIM projects. A key feature will be to also simulate transport, using TGLF or other codes, to model profile evolution with changing j(r). We anticipate this or similar packages will be used to simulate ITER advanced scenarios. team will help benchmark codes, develop operation scenarios.

20 Contributions to ITER/ITPA The integrated scenarios research programs are both primarily aimed at contributing to ITER scenarios we feel our parameters and tools are extremely relevant. This is reflected in a long list of anticipated contributions to several ITPA/ITER high priority research needs (see the proposal), especially to SSO and Transport Physics. Some of the most important and unique contributions expected are: To obtain and test understanding of improved core transport regimes with reactor relevant conditions, specifically electron heating, T e ~T i and low momentum input (ITPA) To test LHCD as for non-inductive CD (volt-s reduction) and j(r) control tool for I p ramp, and for both hybrid and steady state scenarios, at the ITER field and density. (Support development of a plan for Day 1 LHCD as per STAC recommendation; results so far are positive.) We plan increasing participation in ITPA joint experiments, starting with hybrid scenario (SSO ) in 2008/9.

21 Connection to US fusion (FESAC) priorities The integrated scenarios research aligns well with several of the recommended priority areas recommended by 2005 FESAC panel, especially: Carry out additional science and technology activities supporting ITER. Integrated understanding of plasma self-organization and external control, enabling high-pressure sustained plasmas. Extend understanding and capability to control and manipulate plasmas with external waves. Also will contribute to resolving some of the Issues in research for DEMO identified by 2007 FESAC panel, especially 2: Integration of high-performance, steady-state, burning plasmas. 3. Validated theory and predictive modeling. 4: Control. Should provide key information relevant to future steady state, high heat flux devices we feel may be needed to resolve Plasma Wall Interaction and Plasma Facing Component and issues ( Gaps G-9, G-10).

22 Summary research program has made good progress in past year on both current profile and density control needed for advanced scenarios. Over the next five years, we will be upgrading and exploiting these tools to demonstrate and assess integrated scenarios which are progressively more ambitious. Hybrid scenarios Non-inductive steady state High bootstrap fractions Reduced divertor heat flux. This research is motivated primarily by the needs of ITER and aims to extend results elsewhere by showing that such regimes can be obtained in high density, low momentum plasmas, using LHCD to tailor j(r). Ultimately we aim, in collaboration with the international fusion community, for a more complete understanding and predictive capability. This would be embodied in accurate integrated models which can be used to predict scenarios for ITER and devices beyond ITER.