Enhanced Energy Confinement Discharges with L-mode-like Edge Particle Transport*

Transcription

1 Enhanced Energy Confinement Discharges with L-mode-like Edge Particle Transport* E. Marmar, B. Lipschultz, A. Dominguez, M. Greenwald, N. Howard, A. Hubbard, J. Hughes, B. LaBombard, R. McDermott, M. Reinke, J. Rice, D. Whyte, MIT-PSFC, C. Kessel, PPPL Phenomenology of I-mode Access conditions Energy and particle confinement properties Parametric dependences of I- to H-mode threshold Pedestal properties Kinetic profiles Edge fluctuations Radial electric field Core rotation Stationary conditions *Supported by DoE awards DE-FC2-99ER54512 and DE-AC2-76CH373 51st APS-DPP November 29 GO4.2

2 I-mode: H-mode Energy Confinement, L-mode Particle Confinement Obtained with unfavorable drift (high L-H thresholds)* Globally, the regime is characterized by high energy confinement, often matching H- mode scaling (H 98y2 ~1.) But, no particle barrier or impurity accumulation With cryopumping, density can be controlled at the level of the ohmic target P rad stays very low. Does not require recent boronization Compatible with low Z impurity seeding *See Ryter, et al., PPCF 4(1998) B=5.6 T, I p =1.2 MA, q 95 =3.3 τ 1 E / τ ITER-98-Y2.5 Te (kev) n e (1 2 m -3 ) L T e Pedestal (kev) <P> (atmosphere) ICRF Input Power (MW) D-D Fusion Rate (1 14 /s) 6 4 Radiated Power (MW) Time (s) I H (ELM-free)

3 Parameter scans revealing operational space for I-mode Confinement quality improves at highest pressures (power, current) But need to stay out of H- mode (density barrier) With unfavorable drift, H- mode threshold appears highest with a combination of Low q 95 (<3.5) Strong shaping Role of density less clear Cryopumping key to density control Exploration of lower density targets will be subject of upcoming studies <P> (bar) MA H 98 =1 1. MA.8 MA <P> [H 98 =1] (bar) H 98 =.8

4 Parameter scans revealing operational space for I-mode Confinement quality improves at highest pressures (power, current) But need to stay out of H-mode (density barrier) With unfavorable drift, H-mode threshold appears highest with a combination of Low q 95 (<3.5) Strong shaping As high as 3x the ITER scaling for threshold with normal drift Role of density less clear Cryopumping key to density control Exploration of lower density targets will be subject of upcoming studies H threshold vs q 95

5 Edge/Pedestal Density and Magnetics Fluctuations in L-, I- and H-mode L I H Ohmic L Frequency (khz) Reflectometer f = 88 GHz Time (s) L-mode: broadband fluctuations (5 2 khz) drive energy and particle transport I-mode: broad band reduced, ~2 khz appears; particle transport similar to L, energy transport suppressed ELM-free H-mode: ~2 khz also gone, impurity accumulation

6 Edge/Pedestal Density and Magnetics Fluctuations in L-, I- and H-mode L I H Ohmic L Frequency (khz) Reflectometer f = 88 GHz Time (s) L-mode: broadband fluctuations (5 2 khz) drive energy and particle transport I-mode: broad band reduced, ~2 khz appears; particle transport similar to L, energy transport suppressed ELM-free H-mode: ~2 khz also gone, impurity accumulation

7 Edge/Pedestal Density and Magnetics Fluctuations in L-, I- and H-mode L I H Ohmic L Frequency (khz) Reflectometer f = 88 GHz Time (s) L-mode: broadband fluctuations (5 2 khz) drive energy and particle transport I-mode: broad band reduced, ~2 khz appears; particle transport similar to L, energy transport suppressed ELM-free H-mode: ~2 khz also gone, impurity accumulation A. Dominguez, G4.12

8 Direct Impurity Measurements Confirm I-mode Particle Confinement Laser blow-off system used to inject CaF 2 Calcium evolution followed with X- ray crystal spectroscopy I-mode has impurity confinement of L- mode, energy confinement of H- mode L-mode EDA H-mode I-mode N. Howard, PP8.11

9 Strong Temperature Pedestal Develops with Significant E r Shear Temperature at the top of the pedestal approaches that seen in our best H-modes Density remains flat n* ped ~.1 SOL density significantly higher than in H-modes Good news for divertor power handling E r well develops About ½ the strength of H-mode ne (12 m-3) Te (kev) H-mode (ELM-free) I-mode L-mode H-mode (ELM-free) I-mode L-mode Distance from Last Closed Flux Surface (mm) J.W. Hughes BI3.4

10 Strong Temperature Pedestal Develops with Significant E r Shear Temperature at the top of the pedestal approaches that seen in our best H-modes Density remains flat n* ped ~.1 SOL density significantly higher than in H-modes Good news for divertor power handling E r well develops About ½ the strength of H-mode Er (kv/m) I-mode H-mode (EDA) L-mode Distance from LCFS (cm) * R.M. McDermott, et al., Phys. Plasmas 16(29)5613 Separatrix

11 Core intrinsic rotation in I-mode similar to that in L- and H-mode Intrinsic core toroidal rotation proportional to Pressure/I p * Dimensionless parameters: Mach number, β N For I-mode, rotation follows the same scaling ΔM i L- & H-mode I-mode *J. Rice, et al., PPCF 5(28) Δβ N

12 I-mode can be sustained in stationary state Power level kept just below the H-mode threshold I-mode maintained for length of ICRF pulse Up to 2 τ E, multiple resistive skin times B=5. T, I p =.8 MA, q 95 =4.38, H 98 =.9 4 T () (kev) e 2 1 n (1 2 m -3 ) e Radiated Power (MW) ICRF Power (MW) Time (s)

13 Summary I-mode combines many desirable confinement properties Edge energy barrier, H-mode τ E, L-mode τ P Compatible with (even prefers) low collisionality edge No need for ELMs Divertor power handling Broad scrape-off layer density profile Compatible with low-z seeding Further study of the regime should shed light on barrier physics, including the H-mode What keeps the I-mode plasma from forming a particle barrier? Application to future devices (including ITER) Significant advantages warrant investigation into the possibilities