Study of Striated Heat Flux on EAST Divertor Plates Induced by LHW Using Infrared Camera

An upgraded infrared (IR) imaging system which provides a wide field of view (FOV) has been installed on the Experimental Advanced Superconducting Tokamak (EAST) to monitor the surface temperatures on plasma facing components. Modified magnetic topology induced by lower hybrid wave (LHW) can lead to the formation of striated heat flux (SHF) on divertor plates which can be clearly observed by IR camera. In this paper, LHW power modulation is applied to analyze the appearance of SHF. It is also demonstrated that deuterium (D) pellet injection and supersonic molecular beam injection (SMBI) can to some extent reduce the heat flux on the outer strike point (OSP), but enhance the SHF on lower outer plates (LOP) of divertor. This may provide an optional approach to actively control the distribution of heat flux on diveror plates, which can protect materials from long duration high-heat flux

Advances in H-mode physics for long-pulse operation on EAST

Since the 2012 International Atomic Energy Agency Fusion Energy Conference (IAEA-FEC), significant advances in both physics and technology has been made on the Experimental Advanced Superconducting Tomakak (EAST) toward a long-pulse stable high-confinement (H-mode) plasma regime. The experimental capabilities of EAST have been technically upgraded with the power enhancement (source power up to 26 MW) of the continuous-wave heating and current drive system, replacement of the upper graphite divertor with an ITER-like W monoblock divertor, and installation of a new internal cryopump in the upper divertor and a set of 16 in-vessel resonant magnetic perturbation (RMP) coils. This new upgrade enables EAST to be a unique operating device capable of investigating ITER-relevant long-pulse high-performance operations with dominant electron heating and low torque input within the next 5 years. Remarkable physics progress in controlling transient and steady-state divertor heat fluxes has been achieved on EAST, e.g. (i) edge-localized mode (ELM) mitigation/suppression with a number of attractive methods including lower hybrid wave (LHW), supersonic molecular beam injection (SMBI), RMPs, and real-time Li aerosol injection; and (ii) active control of steady-state power distribution by the synergy of LHW and SMBI. In the 2014 experimental campaign, a long-pulse high-performance H-mode plasma with H98 ~ 1.2 has been obtained with a duration over 28 s (~200 times the energy confinement time). In addition, several new experimental advances have been achieved in the last EAST campaign, including: (i) high-performance H-mode with βN ~ 2 and stored plasma energy ~220 kJ; (ii) H-mode plasma sustained by neutral beam injection (NBI) alone or modulated NBI with lower hybrid current drive (LHCD), for the first time in EAST; (iii) high current drive efficiency and nearly full noninductive plasmas maintained by the new 4.6 GHz LHCD system; (iv) demonstration of a quasi-snowflake divertor configuration; and (v) observation of a new edge-coherent mode and its effects on edge transport in H-mode plasmas

Current status of ECE system on EAST tokamak

The electron cyclotron emission (ECE) diagnostic on the experimental advanced superconducting tokamak (EAST) has had a major upgrade since 2020, when EAST heating system also went through a significant upgrade, including one NBI system changed from counter-current to co-current (moving from port F to port D), and the antenna and the installation port of LHW and ICRF system have also been changed. The quasi-optical (QO) antenna of P port ECE system has been redesigned, the main purpose of which is to add one oblique ECE view. The angle with respect to perpendicular to the magnetic field is about 10°, which will facillitate measurement of the electron velocity distribution altered by LHW system. The ellipsoidal mirror has also been moved close to the plasma, about 70 cm away from the plasma center, and the poloidal beam waist radius in the plasma has been optimised to be less than 3 cm. The CECE system has also been moved from port G to port C. The frequency coverage of the CECE system has been upgraded to 104-132 GHz by adding one radio frequency (RF) module. Also in the intermediate frequency (IF) module, 8 narrow-band filters have been added to improve the spacial coverage of the system. On port F, a new superheterodyne radiometer with narrow-band filters in IF module has been installed. It consists of eight channels, the radial coverage is about 8 cm, the main purpose of this new system is to study the fine structure of magnetic island

Lower hybrid current drive experiments in support of high confinement long pulse operation in EAST

The lower hybrid current drive (LHCD) system plays a crucial role in the mission of the Experimental Advanced Superconducting Tokamak (EAST) and is a prerequisite for reaching long pulse, high confinement plasmas on EAST [1, 2]. LHCD experiments and modelling [3] have been carried out on EAST in 2015-2016, with the aim to optimising EAST long pulse scenarios, and at the same time gain experience for the exploitation of WEST [4]. Experiments have been carried out to study the LH current drive efficiency in different plasma configurations (Upper Single Null and Lower Single Null). The effect of the gas feed location on the LH wave coupling was investigated by comparing gas fuelling from high field side, low field side and upper divertor. In view of long pulse H-mode scenarios, a series of H-mode experiments were conducted where all the heating power was provided by RF heating methods only, i.e. LHCD, ECRH and ICRH. H-modes were sustained in both Upper Single Null (W divertor) and Lower Single Null (carbon divertor) configurations, with loop voltage maintained as low as 50 mV

Lower hybrid current drive experiments in support of high confinement long pulse operation in EAST

The lower hybrid current drive (LHCD) system plays a crucial role in the mission of the Experimental Advanced Superconducting Tokamak (EAST) and is a prerequisite for reaching long pulse, high confinement plasmas on EAST [1, 2]. LHCD experiments and modelling [3] have been carried out on EAST in 2015-2016, with the aim to optimising EAST long pulse scenarios, and at the same time gain experience for the exploitation of WEST [4]. Experiments have been carried out to study the LH current drive efficiency in different plasma configurations (Upper Single Null and Lower Single Null). The effect of the gas feed location on the LH wave coupling was investigated by comparing gas fuelling from high field side, low field side and upper divertor. In view of long pulse H-mode scenarios, a series of H-mode experiments were conducted where all the heating power was provided by RF heating methods only, i.e. LHCD, ECRH and ICRH. H-modes were sustained in both Upper Single Null (W divertor) and Lower Single Null (carbon divertor) configurations, with loop voltage maintained as low as 50 mV

Plasma heating and improvement of lower hybrid current drive efficiency by electron cyclotron waves on EAST

The electron cyclotron (EC) system on EAST consists of four gyrotrons with a frequency of 140 GHz (second harmonic of the extraordinary mode), each of which is expected to deliver a maximum power of 1.0 MW and be operated at 100-1000 s pulse length. Significant progress in long-pulse operation has been achieved recently, including the pulse duration up to 1056 s with EC power injected into plasma of 0.55 MW and the pulse duration of 310 s with EC power of 1.6 MW (output by 3 gyrotrons). High electron temperature (Te >12 keV) plasma measured by Thomson scattering was produced with the combination of EC and lower hybrid (LH) waves. It is found that the plasma heating effect depends on the EC power location greatly. By adjusting the EC power location, the plasma current profile can be modified. As a consequence of the increment of electron temperature by electron cyclotron resonance heating (ECRH), the lower hybrid current drive (LHCD) efficiency is improved, benefiting for the long-pulse operation. In addition, a synergy effect between EC and LH current drive was observed in steady-state operation on EAST