Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena

The I-mode is a natural edge localized mode (ELM)-free regime with H-mode-like improved energy confinement and L-mode-like particle confinement, making it an attractive scenario for future tokamak-based fusion reactors. A kind of low-frequency oscillation has been widely observed, with a frequency between stationary zonal flow and geodesic-acoustic mode (GAM) zonal flow. In EAST, most stationary I-mode shots have such a mode, called edge temperature ring oscillation (ETRO). This mode probably plays an important role in development and maintenance of the I-mode , while investigations are needed to clarify the differences between ETRO and similar mode low-frequency oscillation in other devices, such as limit cycle oscillation (LCO). In this paper, the properties of ETRO are described in detail, including the structure of its magnetic components, its radial propagation characteristics, statistics of its central frequency, a linear analysis of the alternating transition turbulences and a comparison with GAM and LCO. Although some similarities can be found between ETRO and both GAM and LCO, the main features are not identical. ETRO is probably a novel type of finite frequency zonal flow or pressure gradient-induced drift that is unique to the I-mode. It is found that modest fueling can reduce ETRO intensity while maintaining I-mode confinement, suggesting that supersonic molecular beam injection could be used as an effective tool to control ETRO.

Section: Discussionmentioning

confidence: 92%

“…The question now remains whether ETRO can be considered a form of LCO, a symmetric structure that arises during L-H transition [14,24,[48][49][50][51][52]. LCO also possesses harmonics and magnetic components featuring an m/n = 1/0 configuration.…”

Section: Discussionmentioning

confidence: 99%

Characteristics of edge temperature ring oscillation during the stationary improved confinement mode in EAST

Liu,

Zou,

Zhong

et al. 2023

“…Consequently, the L-H transition time, t LH , was determined as the time point at which the density started to rise and simultaneously the Balmer alpha line radiation, H α , (or T α in the T pulses) in the divertor dropped. At the same time the slopes of the edge temperature as well as the energy content of the plasma, W MHD rose, too, and in most of the cases an M-mode [27] (also called I-phase [28]) appeared in the very same moment. The latter makes it difficult to identify the drop of the H α signal, since the M-mode bursts can blur the signal in the time range, where the L-H transition happens.…”

Section: Experimental Strategy and Dynamics Of L-h Transition Pulsesmentioning

confidence: 92%

The power threshold of H-mode access in mixed hydrogen–tritium and pure tritium plasmas at JET with ITER-like wall

Birkenmeier

Solano²,

Lerche

et al. 2022

Self Cite

The heating power to access the high confinement mode (H-mode), PLH, scales approximately inversely with the isotope mass of the main ion plasma species as found in (protonic) hydrogen, deuterium and tritium plasmas in many fusion facilities over the last decades. In first dedicated L-H transition experiments at the Joint European Torus (JET) tokamak facility with the ITER-like wall (ILW), the power threshold, PLH , was studied systematically in plasmas of pure tritium and hydrogen- tritium mixtures at a magnetic field of 1.8 T and a plasma current of 1.7 MA in order to assess whether this scaling still holds in a metallic wall device. The measured power thresholds, PLH, in Ohmically heated tritium plasmas agree well with the expected isotope scaling for metallic walls and the lowest power threshold was found in Ohmic phases at low density. The measured power thresholds in ion cyclotron heated plasmas of pure tritium or hydrogen-tritium mixtures are significantly higher than the expected isotope mass scaling due to higher radiation levels. However, when the radiated power is taken into account, the ion cyclotron heated plasmas exhibit similar power thresholds as a neutral beam heated plasma, and are close to the scaling. The tritium plasmas in this study tended to higher electron heating fractions and, when heated with ion cyclotron waves, to relatively higher radiation fractions compared to other isotopes potentially impeding access to sustained H-modes.

“…Further comparison to other models and scalings will be discussed in section 5. Motivated by the success of (8), the frequency of HFOs observed in JET, AUG [26], COMPASS [10] was also assembled into a database for comparison with (9). Furthermore, guided by ( 9) more detailed analysis found the HFO feature also in Globus-M. As can be seen in figure 4, the measured HFO frequency band ranges agree within order of magnitude and follow the machine size scaling ∝ 1/R predicted by the high-frequency solution (9)).…”

Section: Comparison Of the Model Predictions With Experimental Observ...mentioning

confidence: 99%

“…Particularly the phasing between the pressure profile relaxation and the magnetic signature is very similar. Another common feature is the observation of accompanying high-frequency oscillations (HFOs) in the range of a few ∼100 kHz observed by magnetic sensors [10,26].…”

Section: Introductionmentioning

confidence: 99%

Experimentally corroborated model of pressure relaxation limit cycle oscillations in the vicinity of the transition to high confinement in tokamaks

Grover,

Manz,

Yashin

et al. 2023

Self Cite

An analytical formula systematically predicts the observed frequency of pressure relaxation limit cycle oscillations in the vicinity of the transition to high confinement in four tokamaks (JET, ASDEX Upgrade, COMPASS, Globus-M). The experimental dataset spans the widest available range of frequencies, machine sizes and plasma ion species. The machine size dependence is explained by the connection length scale of plasma flows parallel to the magnetic field. The model also explains the observed up-down poloidal current asymmetry and the impact of the plasma ion species mass and charge.