New Tokamak Plasma Regime with Stationary Temperature Oscillations

Giruzzi, G.; Imbeaux, F.; Ségui, J. L.; Garbet, X.; Huysmans, G.; Artaud, J.F.; Bécoulet, A.; Hoang, G. T.; Litaudon, X.; Maget, P.; Saoutic, B.

doi:10.1103/physrevlett.91.135001

Cited by 60 publications

(55 citation statements)

References 24 publications

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“…Although these oscillations have very low frequency (∼10 Hz) and are azimuthally and poloidally symmetric (m = n = 0) and thus are not of an MHD nature themselves, they are seen to coexist with underlying MHD modes [23,24]. A similar phenomenon has been documented on the Tore Supra tokamak, where it has been dubbed the O-regime and occurs in fully or nearly noninductive discharges with lower hybrid current drive and negative central magnetic shear [25].…”

Section: Mhd Activity In Eitbsmentioning

confidence: 77%

The physics of electron internal transport barriers in the TCV tokamak

et al. 2007

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Electron internal transport barriers (eITBs) are generated in the TCV tokamak with strong electron cyclotron resonance heating in a variety of conditions, ranging from steady-state fully noninductive scenarios to stationary discharges with a finite inductive component and finally to transient current ramps without current drive. The confinement improvement over L-mode ranges from 3 to 6; the bootstrap current fraction is invariably large and is above 70% in the highest confinement cases, with good current profile alignment permitting the attainment of steady state. Barriers are observed both in the electron temperature and density profiles, with a strong correlation both in location and in steepness. The dominant role of the current profile in the formation and properties of eITBs has been conclusively proven in a TCV experiment exploiting the large current drive efficiency of the Ohmic transformer: small current perturbations accompanied by negligible energy transfer dramatically alter the confinement. The crucial element in the formation of the barrier is the appearance of a central region of negative magnetic shear, with the barrier strength improving with increasingly steep shear. This connection has also been corroborated by transport modelling assisted by gyrofluid simulations. Rational safety-factor (q) values do not appear to play a role in the barrier formation, at least in the q range 1.3-2.3, as evidenced by the smooth dependence of the confinement enhancement on the loop voltage over a broad eITB database. MHD mode activity is however influenced by rational q values and results in a complex, sometimes cyclic, dynamic evolution.

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Section: Mhd Activity In Eitbsmentioning

confidence: 77%

The physics of electron internal transport barriers in the TCV tokamak

et al. 2007

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“…In Tore Supra, where smooth cyclical evolutions of the equilibrium conditions are observed in the so-called oscillation-regime [11], frequency jumps between modes with different mode numbers are commonly observed, but the mode position evolves continuously even during the frequency jumps. Moreover, in the regime with frequency jumps among several modes, the reanalysis of the mode numbers shows that the continuous evolution of the mode position corresponds to a decreasing sequence (an inverse cascade) in mode numbers starting by an m/n = 4/4 mode and finishing in a 1/1 mode.…”

Section: Discussionmentioning

confidence: 99%

“…As a consequence of the continuous evolution of E • g λ during the frequency jumps, the experimental correlation between the frequency jumps and the radial profile of the suprathermal electron distribution cannot be attributed to different resonant conditions on the E • g λ product, as claimed in [7,8]. In fact, there is an indirect relationship between these two quantities, once the evolutions of the stability condition of the modes (which are likely determined by the equilibrium profiles) and of the position of the LH absorption (which affects the radial distribution of the supra-thermal electron population) are both related to the phase of the central temperature oscillation [11,15].…”

Section: Continuous Evolution Of the Resonant Conditions During Frequmentioning

confidence: 92%

Electron fishbones in FTU and Tore Supra tokamaks

et al. 2012

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This work presents a comparative study of the experimental observation of MHD instabilities identified as electron fishbone-like modes that appear in plasmas with lower hybrid current drive in FTU and Tore Supra tokamaks. Initially, the mode-induced electronic temperature oscillations measured by electron cyclotron emission were used to study the evolutions of the frequency and position of these modes. In FTU, where fishbones with and without bursting behaviour are observed, it was found that the evolutions of the mode position and frequency follow opposite trend in the two regimes. In Tore Supra, where abrupt changes between modes with different mode structures are often observed, it was found that the mode position evolves continuously and the wavenumbers follow an inverse cascade starting from an m/n = 4/4 mode and finishing in an 1/1 mode. In a second step, the energy of resonant electrons was estimated from the resonant condition of the precession drift frequency. It was found that in Tore Supra the resonant condition does not change during the frequency jumps. The relevance of the correction due to the pitch angle of the resonant electrons and the possible role of the energetic passing particles in the drive of these modes are discussed from the results obtained in both machines.

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“…As it can be seen, the desired targets have been achieved without any problem, showing that the LH power is a very good actuator for the feedback control of the maximum of the ρ * T e profile. Considered the link of ρ * T e with the electron temperature, this kind of application could also be effectively used to detect the triggering of LHEP modes [14] and to perform the control of a regime characterized by reduced electron transport.…”

Section: Search Optimisation Controllermentioning

confidence: 99%