Progress on NSTX towards steady state at low aspect ratio A. Gates, Princeton Plasma Physics Laboratory ehalf of the NSTX Research Team NOVA P HOTON P HOTON Supported by * Work supported by US DOE Contract No. DE-AC02-76CH03073 ST Requires high bootstrap fraction, f bs , simultaneous with high t • High f bs and high t competing requirements (at fixed shape and N ) • Progress for ST and advanced tokamak given by sus f bs t ~ SN 2 [S = q 95 (I p /(aB t ))] – If Nmax = C Troyon , then only shape improves sus – sus increases linearly with increasing S [S = q 95 (I p /(aB t ))] – Component Test Facility requires t ~ 20% and f bs ~ 50%, sus = 10% – ARIES-ST requires t ~ 40% and f bs ~ 90% • Optimized shaping with new PF coils for high triangularity and elongation • NSTX has achieved record values of elongation and shape factor – Leads directly to record values of the sus for the ST • For NSTX 100% non-inductive operation with N ~ 7 only with strong shaping New inboard divertor coils increase accessibility of high- triangularity, high-elongation shapes • Highest now obtained at highest ≈0.8 S q 95 I P /aB T = 41 MA/m·T • Small (Type V) ELM regime recovered at high > 2.5 with new coils – Previously observed onset of large ELM-like events when > 2.2 D. Gates , J. Menard Highest elongation =3.0 (transient) Sustained elongation =2.7 (0.1s) Record pulse-lengths achieved at high current by operating with sustained H-mode • H-mode with small ELMs lower flux consumption, slow density rise 0 1 0.998 0 1 0.998 0 1 0.996 0.5 1.0 1.5 0 100 Radius (m 0.996 n e (10 20 m -3 ) T e (keV T i (keV v i (km/s 0 I p (MA) 0 1 0 1 0.0 0.5 1.0 0 1 Time (s V loop (V) p n e /n e <G> 121152 P NBI (MW)/10 T = 20% N = 5.2%m•T/MA E = 52ms H 89L = 2.0 1.4, = 2.3, L = 0.75, l i = 0.49 Long duration discharges reach ~70% non-inductive current • TRANSP model agrees with measured neutron rate during high-phase – Model includes anomalous fast ion diffusion during later phase when low- m MHD activity is present • 85% of non-inductive current is p-driven – Bootstrap + Diamagnetic + Pfirsch-Schlüter • 1/1 mode onset causes drop, fast ion diffusion (Menard, PRL) 0.0 0.5 1.0 1.5 0.0 0.5 1.0 Time (s 2 1 0 116318A13 Bootstrap (NCLASS) ∇p NB-riven Curren fraci Measure Moelle DD neuron rae (10 14 /s) 1 0 2 1 0 I p (MA) p P NBI (MW)/10 Ohmic Expected performance improvements observed as shaping has increased Reduction in control system latency increases elongation (2004) Plasma shaping enhancements Upgrade of PF1A coil enables simultaneous achievement of high and Overlay of EFIT boundaries from shots 117707 and 117814 between 0.3 and 0.9s ~3cm includes MHD perturbat ions Control points Boundary overlay time window Implementation of rtEFIT improves shape control reproducibility Modified PF1A Coil Old PF1A Coil Shot 121241 (record ) All shots 2001-2003 All shots 2004-2006 2001 2005 2004 2002-3 = 2.75, = 0.8, S ~ 37 = 1.8, = 0.6, S ~ 22 = 2.0, = 0.8, S ~ 23 = 2.3, = 0.6, S ~ 27 = 3, = 0.8, S ~ 41 2006 Pulse averaged approximate sus versus S (S is averaged over the same time window as sus ) N H89 vs. pulse /E Pulse averaged t versus pulse length Data are sorted by year and by S 2001-2004 2005-2006 External kink mode ultimate limit on t - long pulse discharges above no-wall limit Troyon diagram showing tmax vs. I p /aB t PEST eigenfunction Shot 117707 Time history of t and n=1 (no-wall) kink mode growth rate, , for Shot 117707, calculated by PEST using LRDFIT equilibrium including MSE Alfven % Each point in the above plots represents an EFIT equilibrium reconstruction Data span entire NSTX database and are filtered against rapid plasma motion Effect of modifications provide clear increase in NSTX operating space
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Progress on NSTX towards steady state at low aspect ratio D. A. Gates, Princeton Plasma Physics Laboratory on behalf of the NSTX Research Team Supported.
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Progress on NSTX towards steady state at low aspect ratio
D. A. Gates, Princeton Plasma Physics Laboratoryon behalf of the NSTX Research Team
NOVA PHOTONICS, INC.PHOTONICS, INC.Supported by
* Work supported by US DOE Contract No. DE-AC02-76CH03073
ST Requires high bootstrap fraction, fbs, simultaneous with high t
• High fbs and high t competing requirements (at fixed shape and N)
• Progress for ST and advanced tokamak given by sus fbst ~ SN2 [S
= q95(Ip/(aBt))]
– If Nmax = CTroyon, then only shape improves sus
– sus increases linearly with increasing S [S = q95(Ip/(aBt))]
– Component Test Facility requires t ~ 20% and fbs ~ 50%, sus = 10%
– ARIES-ST requires t ~ 40% and fbs ~ 90%
• Optimized shaping with new PF coils for high triangularity and elongation
• NSTX has achieved record values of elongation and shape factor
– Leads directly to record values of the sus for the ST
• For NSTX 100% non-inductive operation with N ~ 7 only with strong
shaping
New inboard divertor coils increase accessibility of high-triangularity, high-elongation shapes
• Highest now obtained at highest ≈0.8 S q95 IP/aBT = 41 MA/m·T
• Small (Type V) ELM regime recovered at high > 2.5 with new coils– Previously observed onset of large ELM-like events when > 2.2
= 2.75, = 0.8, S ~ 37 = 1.8, = 0.6, S ~ 22 = 2.0, = 0.8, S ~ 23 = 2.3, = 0.6, S ~ 27 = 3, = 0.8, S ~ 41
2006
Pulse averaged approximate sus versus S (S is averaged over the same time window as sus)
NH89 vs. pulse/E
Pulse averaged t versus pulse length Data are sorted by year and by S
2001-20042005-2006
External kink mode ultimate limit on t -long pulse discharges above no-wall limit
Troyon diagram showing tmax vs. Ip/aBt
PEST eigenfunction Shot 117707
Time history of t and n=1 (no-wall) kink mode growth rate, , for Shot 117707, calculated by PEST using
LRDFIT equilibrium including MSE
Alfven
%
Each point in the above plots represents an EFIT equilibrium reconstructionData span entire NSTX database and are filtered against rapid plasma motion
Effect of modifications provide clear increase in NSTX operating space
117407 LSN117432 DN117424 high- DN
0
2
4
6
8
10
12
0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1Radius [m]
Tile Gap
6 MW DN ( L~0.40)
6 ( MW DNL~0.75)
( )outer strike region
#117407: 0.373LSN@ s#117432: 0.316DN@ s#117424: 0.316DN@ s
6 ( MW LSNL~0.40) 117407 LSN
117432 DN
117424 high- DN
Increased triangularity actually reduces peak heat flux to divertor target
• Flux expansion decreases peak heat flux despite reduced major radius• Compare single-null & double-null configurations with triangularity
≈ 0.4 at X-point and high triangularity = 0.8 double-null plasmas– Measure heat flux with IR thermography of carbon divertor tiles
• Peak heat flux decreases as 1 : 0.5 : 0.2• ELM character changes: Type I Mixed Type V
R. Maingi
Changes in X-point balance affect ELM characteristics
• Very small changes in the plasma boundary reproducibly lead to large differences in ELM behavior
• ELMs have a major impact on plasma performance, controlling them is crucial• Precise plasma control provides an important tool for controlling ELMs - highly ITER relevant
rsep (mm) for 117424 (black)and 117425 (red)
Shot 117424 Shot 117425
Shot 117424
Shot 117425
rsep is the radial separation of the flux surfaces which pass through the x-points
measured at the outboard midplane
1.0 0.0
Encouraging results from both EBW emission and HHFW current drive experiments
Long pulse discharges have elevated q(0) without low frequency MHD modes
Experiment(116313)
Target
The time history of shot 120001 showing:
1) the components of non-inductive current as indicated in the
plot legend,
2) The plasma current (black) and the surface voltage (red),
3) the reconstructed q(0) (black) and qmin (red) and q(0) as
determined by a TRANSP magnetic diffusion calculation
(blue)
4) t (black) and the neutral beam power (red). The profiles in
preceding figure are calculated over the time interval indicated
in green.
• A spectrogram of magnetic fluctuations as
measured by a Mirnov coil for shot 120001.
• The colors represent toroidal mode numbers
as indicated in the legend.
• Notice the period of time after 0.6s where
there are only small amplitude high-n MHD
modes present.
Measured
• EBW uses efficient Ohkhawa current drive
• Data on efficiency of EBW emission from identical
plasmas for which the EBW antenna pointing angle
is varied.
• The colors represent measured efficiencies of - 81-90% (red)
- 71-80% (orange),
- 61-70% (green)
- 51-60% (blue)
- 41-50% (purple),
- 31-40% (black).
• The ellipses are contours of theoretically predicted