Abstract Since the 2021 IAEA FEC, EAST experiments have been carried out in support of high-performance steady-state operation and physics understanding for ITER and CFETR. The first demonstration of ...reproducible 403 s long-pulse steady-state H-mode plasma with H98y2>1.3, βP~2.5, βN~1.6, ne/nGW~0.7 and a good control of impurity and heat exhaust have been achieved on EAST using the pure radio frequency (RF) power heating and current drive. In support of ITER and CFETR long pulse operation, a thousand-second time scale (~1056 s) fully non-inductive plasma has been achieved. The EAST operational regime of high βP has been significantly extended (H98y2>1.3, βP~4.0, βN~2.4 and ne/nGW~1.0) using RF and neutral beam (NB). The full edge localized mode suppression using the n = 4 resonant magnetic perturbations (RMP) has been achieved in ITER-like standard type-I ELMy H-mode plasmas with q95 ≈ 3.1 on EAST, extrapolating favorably to the ITER baseline scenario. The sustained large ELM control and stable partial detachment have been achieved with Ne seeding. The plasma-beta effect for error field penetration is investigated with n = 1 RMP. Breakdown and plasma initiation at low toroidal electric fields (<0.3 V/m) with EC pre-ionization is developed. The transport and control of high-Z impurity of tungsten is investigated.
Fusion energy is a promising source of clean energy, which could solve energy shortages and environmental pollution. Research into controlled fusion energy has been ongoing for over half a century. ...China has created a clear roadmap for magnetic confinement fusion development, where superconducting tokamaks will be used in commercial fusion reactors. The Experimental Advanced Superconducting Tokamak (EAST) is the world’s first fully superconducting tokamak with upper and lower divertors, which aims at long-pulse, steady-state, H-mode operation, and 101-s H-mode discharge had been achieved. In 2007, China joined the International Thermonuclear Experimental Reactor (ITER) and became one of its seven members. Thirteen procurement packages are undertaken by China, covering superconducting magnets, power supplies, plasma-facing components (PFCs), diagnostics, etc. To bridge the gap between the ITER and fusion demonstration power plants (DEMOs), China is planning to build the Chinese Fusion Engineering Testing Reactor (CFETR) to demonstrate related technologies and physics models. The engineering design of the CFETR was completed in 2020, and Comprehensive Research Facilities for Fusion Technology (CRAFT) are being constructed to explore the key technologies used in the CFETR.
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•Fusion energy is a promising source of clean energy•Tokamak is the most widely studied magnetic confinement fusion device•China built the world’s first fully superconducting tokamak -EAST•China is one of the seven members of the ITER project•CFETR engineering design has been completed, and its R&D is ongoing
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.
•Hydrogen recycling properties have been investigated by evaluating the density decay time after the fueling termination.•A repeat of discharges diminishes the wall conditioning effect and enhances ...hydrogen recycling.•Approach of the strike point position to the pumping slot enhances the particle exhaust capability.•The hydrogen recycling coefficient of the LHCD discharge is increased during stop of fueling, although such increase appears not to be seen in the ohmic discharges.
Deuterium recycling properties have been investigated in the EAST superconducting tokamak by evaluating the density decay time after the fueling termination. The density decay time of the latter discharge of the experiment of a day is ∼2.9 s, which is more than three times longer than that of the beginning discharge (∼0.88 s), indicating that a repeat of discharges diminishes the wall conditioning effect by lithium coating. However, the difference in deuterium recycling among three magnetic configurations (lower single null, double null, and upper single null) is unclear. The density decay times are 3.3 s and 4.1 s when the strike point (SP) positions are located on the horizontal and vertical plates of the lower outer divertor, showing that the particle exhaust capability becomes stronger as the SP position approaches the pumping slot. Furthermore, the lower hybrid current drive (LHCD) power enhances deuterium recycling since the density decay times of high (∼2.7 MW) and low (∼0.8 MW) power LHCD discharges are 4.3 s and 1.2 s, respectively. The density decay time in the LHCD discharge linearly increases with an increase in a period of exponential fitting, implying that the recycling coefficient increases during the stop of fueling. However, the density decay time in the ohmic discharge is independent of the fitting time.
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 (
T
e >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.
All superconducting tokamak: EAST Hu, Jiansheng; Xi, Weibin; Zhang, Jian ...
AAPPS bulletin,
12/2023, Volume:
33, Issue:
1
Journal Article
Peer reviewed
Open access
Experimental Advanced Superconducting Tokamak (EAST) was built to demonstrate high-power, long-pulse operations under fusion-relevant conditions, with major radius
R
= 1.9 m, minor radius
a
= 0.5 m, ...and design pulse length up to 1000s. It has an ITER-like D-shaped cross-section with two symmetric divertors at the top and bottom, accommodating both single null and double null divertor configurations. EAST construction was started in 2000, and its first plasma was successfully obtained in 2006. In the past 15 years, plasma-facing components, plasma heating, diagnostics, and other systems have been upgraded step by step to meet its mission on exploring of the scientific and technological bases for fusion reactors and studying the physics and engineering technology issues with long pulse steady-state operation. An advanced steady-state plasma operation scenario has been developed, and plasma parameters were greatly improved. Meanwhile, front physics on the magnetic confinement plasmas have been systemically investigated and lots of fruitful results were realized, covering transport and confinement, MHD stabilities, pedestal physics, divertor and scrap-off layer (SOL) physics, and energetic particle physics. This brief review of EAST on engineering upgrading, stand-steady operation scenario development, and plasma physics investigation would be useful for the reference on construction and operation of a superconducting tokamak, such as ITER and future fusion reactor.
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.
Behaviors of impurity and hydrogen recycling are investigated based on passive spectroscopy measurement on HT-7. During LHCD long pulse discharges, impurity and hydrogen recycling shows complicated ...aspects in different phases depending on wall properties. An uncontrollable density increase is observed, correlated with impurity concentrations, injected energy and local heat flux on the limiter. Under certain conditions, high impurity radiation and uncontrollable density can reduce LHCD efficiency and thus lead to discharge termination. To reduce impurity levels, RF wall conditioning was applied. After boronization, high hydrogen emission led to uncontrollable density rise. When the H/(H+D) ratio was reduced to less than 25%, the electron density was easily controlled. The longest discharge up to 306s with central electron temperature Te(0)∼1.0keV and central electron density ne(0)∼0.8×1019m−3 was achieved. The evolution of recycling behavior has been investigated during long pulse discharges in terms of H/(H+D) ratio and the edge-recycling coefficient R.
In order to study the radial transport of tungsten ions in long-pulse H-mode discharges, a space-resolved spectrometer working at 30–520 Å has been newly developed to measure a radial profile of the ...tungsten line emission. The spectrometer is installed behind a long extension vacuum tube connected to a horizontal midplane diagnostic port of EAST tokamak. The long distance between the plasma and spectrometer, 8835.5 mm, enables observation of the radial profile of impurity line emissions in a wide vertical range of −8.5≤Z≤ 40 cm (−0.1≤ρ≤0.6). A good spectral resolution of Δλ0=4−5 pixels at the foot position of spectral line profiles and a high spatial resolution of ΔZ=2.5 cm are obtained in addition to a sufficient temporal resolution, e.g. 50 ms/frame. As a result, accurate radial profiles have been successfully obtained in EAST Ohmic and H-mode discharges for several impurity species such as carbon, oxygen, argon, iron and tungsten. The radial profiles of tungsten line emissions from W42+ – W45+ ions with 4p–4s transitions measured at two wavelength ranges of 45–70 Å and 120–140 Å are analyzed for the ion density evaluation based on the photon emissivity coefficient from ADAS database. The result shows that the density of W43+ – W45+ ions ranges at 2–6 × 108 cm−3 in steady H-mode discharges with Te(0)=3 keV and ne(0)=4 × 1013 cm−3.
Abstract
Recently, stationary plasma with a world-record pulse length of 1056 s was achieved on the Experimental Advanced Superconducting Tokamak (EAST). In this work, the core magnetohydrodynamics ...(MHD) events as well as mode coupling processes have been investigated in EAST long pulse operation with electron heating dominant and pure radio frequency wave heating low collisionality, by using several diagnostics and the nonlinear numerical code M3D together. A saturated
m
/
n
= 1/1 kink mode was observed in the core region, where a stable internal transport barrier was found in the electron temperature channel. The frequencies and 2D structures of these modes were studied by a combination of soft X-ray (SXR) imaging and electron cyclotron emission diagnostics. The frequency of the
m
/
n
= 1/1 mode exhibited a feature of chirping down with time, and this chirping rate corresponds to the rate of electron diamagnetic drift frequency change. A twisted pattern (‘Taichi structure in shape’) was reconstructed by SXR tomography of the
m
/
n
= 1/1 mode. The perturbations of electron temperature and density caused by
m
/
n
= 1/1 are different in size, the latter one being much smaller. The destabilization of
m
/
n
= 1/1 was due to the strong central heating combined with electron cyclotron resonance heating and lower hybrid current drive. In the presence of the
m
/
n
= 1/1 mode, a negative current was generated on the magnetic axis, which anomalously broadened the core current profile. A
m
/
n
= 3/2 tearing mode triggered by
m
/
n
= 1/1 mode was also observed. The
m
/
n
= 3/2 mode has a smaller frequency than the
m
/
n
= 1/1 mode, and carries an
m
/
n
= 3/2 island with detectable size. A novel 3D MHD model that separately evolves the plasma density and temperature is applied to the
m
/
n
= 3/2 triggered by
m
/
n
= 1/1. It is found that a toroidal current density at the
q
= 1.5 surface, caused by non-axisymmetric density perturbation during the
m
/
n
= 1/1 nonlinear growth phase, was generated and hence the destabilization of the
m
/
n
= 3/2 tearing mode. Both the modeled electron temperature and density perturbations agree well with experimental observations. In the last section of this paper, the interaction between the
m
/
n
= 1/1 mode and fast electrons as well as the active control of this mode are also presented.
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