High-beta operation and magnetohydrodynamic activity on the TFTR tokamak

McGuire, K.; Arunasalam, V.; Barnes, Cris W.; Bell, M.G.; Bitter, M.; Boivin, R. L.; Bretz, N.; Budny, R.; Bush, C. E.; Cavallo, A.; Chu, T. K.; Cohen, Samuel A.; Colestock, P.; Davis, S.; Dimock, D.; Dylla, H. F.; Efthimion, P. C.; Ehrhrardt, A. B.; Fonck, R. J.; Fredrickson, E. D.; Furth, H. P.; Gammel, G.; Goldston, Robert James; Greene, G. J.; Grek, B.; Grisham, L. R.; Hammett, G. W.; Hawryluk, R. J.; Hendel, H. W.; Hill, K. W.; Hinnov, E.; Hoffman, D. J.; Hosea, J. C.; Howell, Robert B.; Hsuan, H.; Hülse, R.; Janos, A.; Jassby, D.L.; Jobes, F. C.; Johnson, D. W.; Johnson, L. C.; Kaita, R.; Kieras‐Phillips, C.; Kilpatrick, S. J.; LaMarche, P. H.; LeBlanc, B.; Manos, D. M.; Mansfield, D. K.; Mazzucato, E.; McCarthy, Michael; McCune, Matt; Mcneill, D. H.; Meade, D. M.; Medley, S. S.; Mikkelsen, D. R.; Monticello, D.; Motley, R. W.; Mueller, D.; Murphy, John A.; Nagayama, Y.; Nazakian, D. R.; Neischmidt, E. B.; Owens, D. K.; Park, H.; Park, W.; Pitcher, S.; Ramsey, A. T.; Redi, M. H.; Roquemore, A. L.; Rutherford, P. H.; Schilling, G.; Schivell, J.; Schmidt, G. L.; Scott, Steve; Sinnis, J.; Stevens, J.; Stratton, B.; Stodiek, W.; Synakowski, E. J.; Tang, W. M.; Taylor, G.; Timberlake, J.; Towner, H. H.; Ulrickson, M.; Goeler, S. von; Wieland, R.; Williams, M. D.; Wilson, J. R.; Wong, K. L.; Yamada, Masakazu; Yoshikawa, S.; Young, K. M.; Zarnstorff, M. C.; Zweben, S. J.

doi:10.1063/1.859544

Cited by 39 publications

(22 citation statements)

References 5 publications

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“…Our results confirm the findings of Kaye et al 3 and McGuire et al 4 that one or more short bursts of high frequency fluctuations precede the ELM by a fraction of a millisecond. Our findings give a more precise characterization of the TFTR ELM precursors: the precursor bursts occur in the 500 kHz range propagating in the ion drift direction, and therefore have a spectral density which is distinctly different from both the stationary spectrum between ELMs and the ELM spectrum itself.…”

Section: Introductionsupporting

confidence: 93%

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Spectral estimation of plasma fluctuations. II. Nonstationary analysis of edge localized mode spectra

et al. 1994

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Several analysis methods for nonstationary fluctuations are described and applied to the edge localized mode (ELM) instabilities of limiter H-mode plasmas. The microwave scattering diagnostic observes poloidal k θ values of 3.3 cm −1 , averaged over a 20 cm region at the plasma edge. A short autoregressive filter enhances the nonstationary component of the plasma fluctuations by removing much of the background level of stationary fluctuations. Between ELMs, the spectrum predominantly consists of broad-banded 300-700 kHz fluctuations propagating in the electron diamagnetic drift direction, indicating the presence of a negative electric field near the plasma edge. The time-frequency spectrogram is computed with the multiple taper technique. By using the singular value decomposition of the spectrogram, it is shown that the spectrum during the ELM is broader and more symmetric than that of the stationary spectrum. The ELM period and the evolution of the spectrum between ELMs varies from discharge to discharge. For the discharge under consideration which has distinct ELMs with a 1 msec period, the spectrum has a maximum in the electron drift direction which relaxes to a near constant value in the first half millisecond after the end of the ELM and then grows slowly. In contrast, the level of the fluctuations in the ion drift direction increases exponentially by a factor of eight in the five milliseconds after the ELM. High frequency precursors are found which occur one millisecond before the ELMs and propagate in the ion drift direction. These precursors are very short (∼ 10µsecs), coherent bursts, and they predict the occurrence of an ELM with a high success rate. A second detector, measuring fluctuations 20 cm from the plasma edge with k θ values of 8.5 cm −1 , shows no precursor activity. The spectra in the ion drift direction are very similar on both detectors, while the "electron" spectrum level is significantly larger on this second detector.

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Section: Introductionsupporting

confidence: 93%

“…The precursor bursts, which we identify, have much shorter lifetime than previously reported measurements 2,4 , and are intermittent. Their high frequency, ion drift nature further suggests than the ELM onset is related to increased ion turbulence.…”

Section: Discussionsupporting

confidence: 47%

Spectral estimation of plasma fluctuations. II. Nonstationary analysis of edge localized mode spectra

et al. 1994

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“…Let us outline the theory first, which is now well developed and summarized in [426]. In general, MHD events evolve slowly except for fast reconnections which occur for m = 1/n = 1 sawtooth crash on very short time scales τ cr ≈ 10 −5 -10 −4 s (crash time) [427]. This time is so fast that it is comparable with the characteristic drift frequencies of EPs namely with their precession frequencies.…”

Section: Effects Of Kink Modes and Sawteeth On Ep Transportmentioning

confidence: 99%

Energetic particle physics in fusion research in preparation for burning plasma experiments

2014

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The area of energetic particle (EP) physics in fusion research has been actively and extensively researched in recent decades. The progress achieved in advancing and understanding EP physics has been substantial since the last comprehensive review on this topic by Heidbrink and Sadler (1994 Nucl. Fusion 34 535). That review coincided with the start of deuterium-tritium (DT) experiments on the Tokamak Fusion Test Reactor (TFTR) and full scale fusion alphas physics studies. Fusion research in recent years has been influenced by EP physics in many ways including the limitations imposed by the 'sea' of Alfvén eigenmodes (AEs), in particular by the toroidicity-induced AE (TAE) modes and reversed shear AEs (RSAEs). In the present paper we attempt a broad review of the progress that has been made in EP physics in tokamaks and spherical tori since the first DT experiments on TFTR and JET (Joint European Torus), including stellarator/helical devices. Introductory discussions on the basic ingredients of EP physics, i.e., particle orbits in STs, fundamental diagnostic techniques of EPs and instabilities, wave particle resonances and others, are given to help understanding of the advanced topics of EP physics. At the end we cover important and interesting physics issues related to the burning plasma experiments such as ITER (International Thermonuclear Experimental Reactor).

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“…Using a Sweet-Parker type analysis [24,25], the sawtooth crash time has been found by Kadomtsev to be about (τ A τ R ) 1/2 , where τ A is the Alfvén time, and τ R is the resistive time [2]. While the sawtooth crash times observed in small tokamaks with quite resistive plasmas can be explained by the Kadomtsev model [2], experimental measurements in high-temperature tokamak plasmas resulted in crash times of the order of 100 µs [3][4][5], being much shorter than that predicted by Kadomtsev. Therefore, several extensions of the theoretical model beyond resistive MHD have been considered, including the electron inertia effect [6], anomalous current diffusion [7][8][9][10], finite ion Larmor radius [12,[14][15][16] and the parallel electron viscosity [17], to understand the fast growth of the m/n = 1/1 island.…”

Section: Introductionmentioning

confidence: 99%

Formation of plasmoids during sawtooth crashes

Yu¹,

Günter²,

Lackner³

2014

Nucl. Fusion

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The nonlinear growth of the internal kink mode is studied numerically using reduced magnetohydrodynamic equations in cylinder geometry. For low Lundquist numbers, S < 107, the already well-known results have been reproduced: a m/n = 1/1 magnetic island (m: poloidal, n: toroidal mode number) grows while the original core shrinks until full reconnection is achieved. For higher S values, however, the dynamics is found to be qualitatively different from the well-known Kadomtsev's model (Kadomtsev 1975 Sov. J. Plasma Phys. 1 389). The growth of the 1/1 island causes the development of a very thin current sheet which becomes tearing unstable. The current sheet is thus broken up and secondary islands (plasmoids) form. These plasmoids strongly speed up the reconnection and eventually coalesce into one secondary island. The formation of a large secondary island stops the fast reconnection process, leading even to a partial reversal of this process. The final state of sawtooth reconnection is thus no longer an axis-symmetric equilibrium as in the case of complete reconnection for low S values, but a helical equilibrium with two coexisting magnetic islands.

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High-beta operation and magnetohydrodynamic activity on the TFTR tokamak

Cited by 39 publications

References 5 publications

Spectral estimation of plasma fluctuations. II. Nonstationary analysis of edge localized mode spectra

Spectral estimation of plasma fluctuations. II. Nonstationary analysis of edge localized mode spectra

Energetic particle physics in fusion research in preparation for burning plasma experiments

Formation of plasmoids during sawtooth crashes

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