Overview of recent physics results from the National Spherical Torus Experiment (NSTX)

Ménard, J.; Bell, M.G.; Bell, R. E.; Bernabei, S.; Bialek, J.; Biewer, T. M.; Blanchard, W.; Boedo, J.A.; Bush, C. E.; Carter, M. D.; Choe, Wonho; Crocker, N. A.; Darrow, D. S.; Davis, W. M.; Delgado‐Aparicio, L.; Diem, S. J.; Domier, Calvin; D’Ippolito, D. A.; Ferron, J. R.; Field, A. R.; Foley, J.; Fredrickson, E. D.; Gates, D.; Gibney, T.; Harvey, R. W.; Hatcher, R.; Heidbrink, W. W.; Hill, K. W.; Hosea, J.; Jarboe, T. R.; Johnson, D. W.; Kaita, R.; Kaye, S. M.; Kessel, C.E.; Kubota, S.; Kugel, H.; Lawson, J.; LeBlanc, B.P.; Lee, K. C.; Levinton, F. M.; Luhmann, N. C.; Maingi, R.; Majeski, R.; Manickam, J.; Mansfield, D. K.; Maqueda, R. J.; Marsala, R.; Mastrovito, D.; Mau, T. K.; Mazzucato, E.; Medley, S. S.; Meyer, H.; Mikkelsen, D. R.; Mueller, D.; Munsat, T.; Myra, J. R.; Nelson, B.A.; Neumeyer, C.; Nishino, Norikazu; Ono, M.; Park, H. K.; Park, W.; Paul, S. F.; Peebles, T.; Peng, M.; Phillips, C. K.; Pigarov, A. Yu.; Pinsker, R. I.; Ram, A. K.; Ramakrishnan, S.; Raman, R.; Rasmussen, D. A.; Redi, M. H.; Rensink, M.E.; Rewoldt, G.; Robinson, John A. T.; Roney, P.; Roquemore, A. L.; Ruskov, E.; Ryan, P. M.; Sabbagh, S. A.; Schneider, H.; Skinner, C.H.; Smith, D. R.; Sontag, A. C.; Soukhanovskii, V.; Stevenson, T. N.; Stotler, D.P.; Stratton, B.; Stutman, D.; Swain, D. W.; Synakowski, E. J.; Takase, Y.; Taylor, G.; Tritz, K.; Halle, A. von; Wade, M. R.; White, R. B.; Wilgen, J. B.; Williams, M. D.; Wilson, J. R.; Yuh, H.; Zakharov, L.; Zhu, W.; Zweben, S. J.; Akers, R.; Beiersdörfer, P.; Betti, R.; Bigelow, T.; Bitter, M.; Bonoli, P. T.; Bourdelle, C.; Chang, C. S.; Chrzanowski, J.; Dudek, L.; Efthimion, P. C.; Finkenthal, M.; Fredd, E.; Fu, G. Y.; Glasser, A. H.; Goldston, Robert James; Greenough, N.; Grisham, L.; Gorelenkov, N. N.; Guazzotto, L.; Hawryluk, R. J.; Hogan, J.; Houlberg, W. A.; Humphreys, D.A.; Jaeger, F.; Kalish, M.; Krasheninnikov, S. I.; Lao, L. L.; Lawrence, Jason; Leuer, J.A.; Liu, D.; Oliaro, G.; Pacella, D.; Parsells, R.; Schaffer, M. J.; Semenov, I.; Shaing, K. C.; Shapiro, Michael A.; Shinohara, K.; Sichta, P.; Tang, Xian-Zhu; Vero, R.; Walker, M.L.; Wampler, W.R.

doi:10.1088/0029-5515/47/10/s13

Cited by 47 publications

(40 citation statements)

References 44 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In particular, precise rtEFIT/isoflux [14,15] control of the plasma boundary during the current ramp-up phase at high elongation required the real-time acquisition of additional magnetic field sensors in the divertor region and a more accurate vessel current model [16] with additional measurements. Although not the subject of this paper, the control system data acquisition was also expanded to include capabilities for resistive wall mode feedback experiments [17] and error field control experiments [18] as described in [11]. Whereas the expanded technical capabilities were in place at the end of 2005, the first NSTX run that took full advantage of these capabilities was in 2006.…”

Section: Improvements In Plasma Shaping Capability On Nstxmentioning

confidence: 99%

See 1 more Smart Citation

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Gates¹,

Ménard²,

Maingi³

et al. 2007

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

Modifications to the plasma control capabilities and poloidal field coils of the National Spherical Torus Experiment (NSTX) have enabled a significant enhancement in shaping capability which has led to the transient achievement of a record shape factor (S ≡ q 95 (I p /aB t )) of ∼41 (MA m −1 T −1 ) simultaneous with a record plasma elongation of κ ≡ b/a ∼ 3. This result was obtained using isoflux control and real-time equilibrium reconstruction. Achieving high shape factor together with tolerable divertor loading is an important result for future ST burning plasma experiments as exemplified by studies for future ST reactor concepts, as well as neutron producing devices, which rely on achieving high shape factors in order to achieve steady state operation while maintaining MHD stability. Statistical evidence is presented which demonstrates the expected correlation between increased shaping and improved plasma performance. Plasmas with high shape factor have been sustained for pulse lengths which correspond to τ pulse = 1.6s ∼ 50τ E ∼ 5τ CR , where τ CR is the current relaxation time and τ E is the energy confinement time. Plasmas with higher β t ∼ 20% have been sustained for τ pulse = 1.2s ∼ 25τ E ∼ 3τ CR with noninductive current fractions f NI ∼ 50%, with ∼40% pressure driven current and ∼10% neutral beam driven current. An interesting feature of these discharges is the observation that the central value of the safety factor q(0) remains elevated and constant for several current diffusion times without sawteeth, similar to the 'hybrid mode'. Calculations of the profiles of inductive and non-inductive current are compared with measurements of the total current profile and are shown to be in quantitative agreement. Results are shown from experiments which investigate the applicability of high harmonic fast waves (HHFWs) and electron Bernstein waves (EBWs) as current drive and heating sources, and the possibility of LHCD for future ST devices is raised. A calculated scenario which provides 100% non-inductive current drive is described. NSTX operates with peak divertor heat fluxes which are in the same range as those expected for the ITER device, i.e. with P heat max ∼ 10 MW m −2 . High triangularity, high elongation plasmas on NSTX have been demonstrated to have reduced peak heat flux to the divertor plates to <3 MW m −2 .

show abstract

Section: Improvements In Plasma Shaping Capability On Nstxmentioning

confidence: 99%

“…This is an important step towards using the HHFW as a tool for driving current during the startup phase of the NSTX plasma to aid plasma current ramp-up. The HHFW experiments are described in more detail in [18].…”

Section: Rf Heating and Current Drivementioning

confidence: 99%

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Gates¹,

Ménard²,

Maingi³

et al. 2007

Nucl. Fusion

Self Cite

View full text Add to dashboard Cite

show abstract

“…2 While the present fusion devices can tolerate the energy loss from these events, type I ELMs in future high-power machines can cause a transient heat load on the plasma facing components ͑PFCs͒ that exceeds the power handling capabilities of the materials and have a severe impact on the lifetime of the PFCs and divertor components. 3 On the National Spherical Torus Experiment ͑NSTX͒ device, 4 ELM behavior is similar to that of conventional, large aspect ratio machines, with a few exceptions. A small, type V ELM regime has been identified that combines the favorable edge density control and impurity particle handling properties of ELMs with a low transient peak heat flux.…”

Section: Introductionmentioning

confidence: 91%

Relationship between edge localized mode severity and electron transport in the National Spherical Torus Experiment

Tritz¹,

Kaye²,

Maingi³

et al. 2008

Physics of Plasmas

Self Cite

View full text Add to dashboard Cite

In the National Spherical Torus Experiment [J. Menard et al., Nucl. Fusion 47, S645 (2007)], “giant” edge localized modes (ELMs) can occur resulting in a loss of plasma stored energy of up to 30%. These events are distinct from type I ELMs, whose energy loss is typically 4–10%, and they are accompanied by a cold pulse that causes a global decrease in the electron temperature profile. Estimates of the electron thermal transport during the cold pulses show a large enhancement over the underlying cross-field thermal diffusivity, χe, of up to several tens of m2∕s. Following the ELM, short-wavelength fluctuations increase in the plasma edge and core, corresponding to an increase in the electron temperature gradient from the propagating cold pulse. Fast electron temperature measurements indicate that the normalized electron temperature scale length, R∕LTe, reaches the threshold value for instability predicted by a fit to linear stability calculations. This is observed on time scales that match the growth of the high-k fluctuations in the plasma core, indicating that the enhanced χe and energy loss from the “giant” ELM appears to be related to critical gradient physics and the destabilization of electron temperature gradient modes.

show abstract

“…The TRANSP analysis code [53,54] uses measured temperature and density (including impurity) profiles, rotation velocity and radiated power to compute the beam ion deposition and density using a Monte-Carlo approach to determine the sources and losses of energy AFID has been applied, for example, to MHD-induced energetic ion redistribution and/or loss effects in simulations of the E||B NPA spectra [13] including horizontal and vertical scanning measurements, in transport [55] and in beam-driven plasma current [3,56]. In the following analysis, the TRANSP option to follow the fast ion gyro-orbit is used (as opposed to the guiding center).…”

Section: Transp Code Analysismentioning

confidence: 99%

Investigation Of A Transient Energetic Charge Exchange Fux Enhancement ('spike-on-tail') Observed In Neutral-beam-heated H-mode Discharges In The National Spherical Torus Experiment

Medley¹

2011

View full text Add to dashboard Cite

In the National Spherical Torus Experiment (NSTX), a large increase in the charge exchange neutral flux localized at the Neutral Beam (NB) injection full energy is measured by the E||B (superimposed parallel electric and magnetic fields) Neutral Particle Analyzer (NPA). Termed the High-Energy Feature (HEF), it appears on the NB-injected energetic ion spectrum only in discharges where tearing or kink-type modes (f < 50 kHz) are absent, % in the measured neutron yield and total stored energy that are observed to coincide with the feature appear to be driven by concomitant broadening of measured Te(r), Ti(r) and n e (r) profiles and not the HEF itself. While the HEF has minimal impact on plasma performance, it nevertheless poses a challenging wave-particle interaction phenomenon to understand. Candidate mechanisms for HEF formation are developed based on quasilinear theory of wave-particle interaction. The only mechanism found to lead to the large NPA flux ratios, € H = F max /F min , observed in NSTX is the quasilinear evolution of the energetic ion distribution, , in phase space and the concomitant loss of some particles, which occurs due to the cyclotron interaction of the particles with destabilized modes having sufficiently high frequencies, kHz, in the plasma frame that are tentatively identified as Global Alfvén Eigenmodes.

show abstract

Overview of recent physics results from the National Spherical Torus Experiment (NSTX)

Cited by 47 publications

References 44 publications

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

Relationship between edge localized mode severity and electron transport in the National Spherical Torus Experiment

Investigation Of A Transient Energetic Charge Exchange Fux Enhancement ('spike-on-tail') Observed In Neutral-beam-heated H-mode Discharges In The National Spherical Torus Experiment

Contact Info

Product

Resources

About