Long Pulse High Performance Plasma Scenario Development for NSTX C. Kessel and S. Kaye - providing TRANSP runs of specific discharges S. Sabbagh - provided EFIT work to recover discharge G. Taylor - Update/expand picture on EBW E. Fredrickson - plots of MHD in ?? Or other, and TRANSP NB loss HHFW issues and plans to examine MHD stability??

Goals of NSTX Advanced ST Program Long Pulse with 100% Non-inductive Current –B T ≈ 0.45 T Scenario Simulations –t flattop ≥  CR Experimental Progress –  N ≥  N no wall Scenario of Recent Discharge Long Pulse High  with 100% Non-inductive Current –B T ≈ 0.35 T Scenario Simulations –t flattop >>  CR Experimental Progress –  N >  N no wall Scenario of Recent Discharge Non-Solenoidal Startup and I P Rampup –CHI, PF breakdown and early startup –HHFW non-inductive I P rampup Scenario Simulations –NBI non-inductive I P rampup Experimental Progress

Integrated Scenario Modeling is Identifying Critical Features for Advanced ST Plasmas Reproduction simulations of discharges Extrapolate to near-term modifications of discharges Extrapolate to long-term modifications of discharges Stronger plasma shaping Density control Early heating/H-mode Electron Bernstein Waves for off-axis CD Broader J NB profile HHFW for flexibility in NBI discharges and heating/CD in non- solenoidal rampup

Transport Evolution and Source Analysis Tokamak Simulation Code (TSC) Predictive, free-boundary eq.(PF coils, structures, feedback control systems 1D surface averaged transport 2D MHD-Maxwell’s equations Peripheral models (bootstrap, sawtooth, ballooning stability, etc.) TRANSP Interpretive, fixed boundary eq. description 1D surface averaged flux-conservation eqns Monte Carlo neutral beam calculation CURRAY, SPRUCE/FPPRF,LSC Fast particles Neutral particle effects Peripheral models (bootstrap, sawtooth, etc.) CURRAY (for HHFW) Ray-tracing Hot electrons/cold ions for propagation Energetic ions treated as equivalent Maxwellian GENRAY/CQL3D Ray-tracing JSOLVER/BALMSC/PEST2/DCON/VALEN Ideal MHD analysis

Discharge (2002) is Used for a Benchmark to Project to High Performance TSC simulation to reproduce the discharge End of discharge Time-slice for H-mode flattop characteristics

Long Pulse, High f NI Requires n Control, Early Heating/H-mode and Higher ,  E discharge Higher , and n control Higher , n control, and early heat/H-mode Higher , n control, early heat/H-mode, and higher  E   f BS  n  j NB  Early heat q(0)   E, n  I BS , I NB /I BS  f NI > 50% f NI > 90%

More details on comparison of and purple case on previous page

Scenario Shows High Non-Inductive Current Fraction, But Also Dropping q(0) Ip = 800 kA B T = 0.5 T  = 2.5 P NB = 5.5 MW I BS = 355 kA I NB = 355 kA n 20 (0) = 0.31 T e (0) = 1.4 keV T i (0) = 3.0 keV H 98(y,2) = 1.23  N = 4.7  = 13.2%  p = 1.15 f NI = 92 % li(1) = 0.78 q(0) = 1.4s Ip = 800 kA B T = 0.5 T  = 2.0 P NB = 5.5 MW I BS = 250 kA I NB = 150 kA n 20 (0) = 0.5 T e (0) = 1.1 keV T i (0) = 1.7 keV H 98(y,2) = 1.25  N = 5.8  = 15.2%  p = 0.85 f NI = 50 % li(1) = 0.67 q(0) = 0.55s (2002)Scenario

Higher elongation is now routine on NSTX  ≥ 2.25 are typical Experimental Progress Toward Long Pulse 100% Non-Inductive Scenario (2002) (2004) (2005) Early heating/H-mode produces longer discharges li sustained for 3  CR, lasts to TF coil limit Sustaining broader current profiles li(1) ≈ 0.6 at  N up to 6.0  CR

Plasma Elongation and Triangularity are Increased to Enhance Performance (2002)  = 2.0,  = (2004)  = 2.3,  = (2005)  = 2.4,  =

Recent Discharges are Achieving Higher f NI for Longer Times Density is higher in recent discharges > NB driven current is suppressed Density profile peaking is much stronger in recent discharges > Bootstrap current is enhanced Avoiding high T e early avoids discharge ending MHD > Weak or no shear reversal? t = 0.20 s 0.45 s 0.60 s 0.85 s t = 0.20 s 0.30 s 0.40 s 0.50 s

Scenario Shows High Non-Inductive Current Fraction, But Also Dropping q(0) Ip = 800 kA B T = 0.5 T  = 2.5 t pulse = 1.4 s P NB = 5.5 MW I BS = 355 kA I NB = 355 kA n 20 (0) = 0.31 T e (0) = 1.4 keV T i (0) = 3.0 keV H 98(y,2) = 1.23  N = 4.7  = 13.2% n(0)/ = 1.10 f NI = 92 % li(1) = 0.78 q(0) = 1.4s Ip = 800 kA B T = 0.5 T  = 2.0 t pulse = 0.55 s P NB = 5.5 MW I BS = 250 kA I NB = 150 kA n 20 (0) = 0.5 T e (0) = 1.1 keV T i (0) = 1.7 keV H 98(y,2) = 1.25  N = 5.8  = 15.2% n(0)/ = 1.05 f NI = 50 % li(1) = 0.67 q(0) = 0.55s (2002)Scenario Ip = 750 kA B T = 0.45 T  = 2.3 t pulse = 1.5 s P NB = 5.0 MW I BS = 375 kA I NB = 80 kA n 20 (0) = 0.9 T e (0) = 0.8 keV T i (0) = 0.95 keV H 98(y,2) = 1.10  N = 6.0 (4.5)  = 20% n(0)/ = 1.75 f NI = 70 % li(1) = 0.60 q(0) = 1.1s (2005)

Scenario Analysis of Recent Discharges Shows n Control is Powerful Tool TSC calcs of , and with n modifications, possibly with EBW???

Long Pulse High , 100% Non- inductive Scenario Total NBCD BS EBW Higher  n control Early heat/H-mode and Higher P NB (E NB ) Higher  E EBWCD B T = 0.35 T H 98(y,2) = 1.37 H 98(y,2) = 1.55 H 98(y,2) = 1.55, broader j NB

Electron Bernstein Wave Off-axis CD Improves Ideal MHD and f NI Deposition similar for 14 GHz and lower  Large trapped particle fraction at low A on low field side enhances Ohkawa CD Conversion to EBWs allows EC techniques to be used in overdense (  pe 2 /  ce 2 >>1) plasmas typical of STs

High and Low Frequency MHD Could Lead to J NB Broadening or Reduction

High  Scenario Requires Better Energy Confinement, and EBW Off-axis CD Ip = kA B T = T  = t pulse = s P NB = MW I BS = kA I NB = kA I EBW = kA n 20 (0) = T e (0) = keV T i (0) = keV H 98(y,2) =  N =  = % f NI = % li(1) = q(0) = s Ip = 800 kA B T = 0.5 T  = 2.0 t pulse = 0.55 s P NB = 5.5 MW I BS = 250 kA I NB = 150 kA I EBW = 0.0 n 20 (0) = 0.5 T e (0) = 1.1 keV T i (0) = 1.7 keV H 98(y,2) = 1.25  N = 5.8  = 15.2% f NI = 50 % li(1) = 0.67 q(0) = 0.55s (2002)Scenarios Ip = 1000 kA B T = 0.45 T  = 2.2 t pulse = 1.0 s P NB = 6.3 MW I BS = ???kA I NB = ??? kA I EBW = 0.0 n 20 (0) = 0.85 T e (0) = ??? keV T i (0) = ??? keV H 98(y,2) =???  N =  = 23???% f NI = ??? % li(1) = 0.65 q(0) = (2005)

High Harmonic Fast Waves Can Provide Heating with NBI, But CD is Too Low In presence of NBI, significant HHFW power is absorbed on fast ions (seen on experiment) Theory also predicts thermal ion absorption for T i /T e > 1, which is typical of NBI heated discharges (not seen on experiment yet) CURRAY calculations indicate very low CD efficiency under these conditions

More on HHFW in Scenario Calcs and Statement of Challenges in Expt.

Non-Solenoidal Current Rampup Scenario HHFW is Critical for Low Ip - Low T e Regime CHI, PF Coil breakdown and startup (not modeled) HHFW Heating/CD into L/H-mode plasma HHFW & NBI into H- mode plasma I p rampup from HHFW heating/CD I p rampup from HHFW & NBI heating/CD

More on scenario calcs of non-solenoidal rampup

Expt. Data on HHFW Heating/CD at low Ip Ip Flattop Ip = 300 kA, k || = 7 m -1 co-CD Ip = 250 kA, k || = 14 m -1 heating OH Coil Current Clamped HHFW, 7 m -1 co-CD No HHFW

Conclusions Scenario simulations have shown paths to NSTX goals of producing advanced ST plasmas 100% Non-inductive,  N ≥  N no wall, for t flattop >  CR 100% Non-inductive,  N >  N no wall, for t flattop >>  CR Non-solenoidal startup and Ip rampup Experimental progress continues….. Scenario simulations now concentrate on recent discharges and near- term extrapolations….