aichuan Hu

Experimental investigations of LHW?plasma coupling and current drive related to achieving H-mode plasmas in EAST

Aimed at high-confinement (H-mode) plasmas in the Experimental Advanced Superconducting Tokamak (EAST), the effect of local gas puffing from electron and ion sides of a lower hybrid wave (LHW) antenna on LHW?plasma coupling and high-density experiments with lower hybrid current drive (LHCD) are investigated in EAST. Experimental results show that gas puffing from the electron side is more favourable to improve coupling compared with gas puffing from the ion side. Investigations indicate that LHW?plasma coupling without gas puffing is affected by the density near the LHW grill (grill density), hence leading to multi-transition of low?high?low (L?H?L) confinement, with a correspondingly periodic characteristic behaviour in the plasma radiation. High-density experiments with LHCD suggest that strong lithiation gives a significant improvement on current drive efficiency in the higher density region than 2???1019?m?3. Studies indicate that the sharp decrease in current drive efficiency is mainly correlated with parametric decay instability.Using lithium coating and gas puffing from the electron side of the LHW antenna, an H-mode plasma is obtained by LHCD in a wide range of parameters, whether LHW is deposited inside the half-minor radius or not, implying that a central and large driven current is not a necessary condition for the H-mode plasma. H-mode is investigated with CRONOS.

Neutronics analysis for the test blanket modules proposed for EAST and ITER

The dual-functional lithium lead-test blanket module (DFLL-TBM) system, which is designated to demonstrate the integrated technologies of both the He single coolant (SLL) blanket and the He-LiPb dual coolant (DLL) blanket, is proposed for testing in ITER to check and validate the feasibility of the Chinese LiPb blankets. Considering the conflict between the limited ITER resources for TBM testing and the requirement of various blanket concepts proposed by the parties, EAST, the superconducting tokamak being operated in China, can serve as a valuable pre-testing platform with some comparable design parameters to ITER for DFLL-TBM. In the contribution, neutronics calculations and activation of the TBMs in EAST are carried out and compared with those in the D–D and D–T phase of ITER. The results from EAST can make an analogy to ITER (to some extent).

First results of LHCD experiments with 4.6 GHz system toward steady-state plasma in EAST

A 4.6 GHz lower-hybrid current drive (LHCD) system has been firstly commissioned in EAST in the 2014 campaign. The first LHCD results with 4.6 GHz show that LHW can be coupled to plasma with a low reflection coefficient, drive plasma current and plasma rotation, modify the plasma current profile, and heat plasma effectively. By means of configuration optimization and local gas puffing near the LHW antenna, good LHW–plasma coupling with a reflection coefficient less than 5% is obtained. The maximum LHW power coupled to plasma is up to 3.5 MW. The current drive (CD) efficiency is up to 1.1 × 1019 A m−2 W−1 and the central electron temperature is above 4 keV, suggesting that LH power could be mainly deposited in the core region, which is in agreement with code simulation. Experiments show that the current profile is effectively modified and toroidal rotation in the co-current direction is driven by the LHCD. Also, the CD efficiency and current profile depend on the launched wave spectrum, suggesting the possibility of controlling the current profile by changing the phase difference. Repeatable H-mode plasma is obtained by either the 4.6 GHz LHCD system alone, or together with a 2.45 GHz LHCD system, the NBI (neutral beam injection) system. The different ELM features of H-mode between the different heating methods are under investigation.

Status of ECRH project on EAST Tokamak

A 140GHz electron cyclotron resonance heating and current drive (EC H&CD) project for EAST Tokamak is launched in 2011 with a total power of 4MW and pulse length of 100 s. The main objectives of the system are to provide central H&CD, assist start-up and control of MHD activities. The system comprises four gyrotrons each with nominal output power of 1MW at 140GHz. The RF power, transmitted through four evacuated corrugated waveguides will be injected into plasma from the low field side (radial port). The front steering equatorial launcher directs the RF beam over ±25° toroidally and scans over 38° poloidally. At present, the construction of the first 1MW system is undergoing for the expected campaign in the end of 2013. In this paper, the current status of the development and the design of the 140-GHz ECRH system are presented.

Experimental investigation of density behaviors in front of the lower hybrid launcher in experimental advanced superconducting tokamak

A triple Langmuir probe is mounted on the top of the Lower Hybrid (LH) antenna to measure the electron density near the LH grills in Experimental Advanced Superconducting Tokamak. In this work, the LH power density ranges from 2.3 MWm−2 to 10.3 MWm−2 and the rate of puffing gas varies from 1.7 × 1020 el/s to 14 × 1020 el/s. The relation between the edge density (from 0.3 × ne_cutoff to 20 × ne_cutoff, where ne_cutoff is the cutoff density, ne_cutoff = 0.74 × 1017 m−3 for 2.45 GHz lower hybrid current drive) near the LH grill and the LH power reflection coefficients is investigated. The factors, including the gap between the LH grills and the last closed magnetic flux surface, line-averaged density, LH power, edge safety factor, and gas puffing, are analyzed. The experiments show that injection of LH power is beneficial for increasing edge density. Gas puffing is beneficial for increasing grill density but excess gas puffing is unfavorable for coupling and current drive.

Effort of lower hybrid current drive experiments toward to H-mode in EAST

Lower hybrid current drive (LHCD) is an effective tool to achieve high confinement (H-mode) plasma in EAST. To utilize LHCD for accessing H-mode plasma, efforts have been made to improve LHW (lower hybrid wave)-plasma coupling and current drive capability at high density. Improved LHW-plasma coupling by means of local gas puffing and gas puffing from the electron side is routinely used during EAST operation with LHCD. High density experiments suggest that low recycling and high LH frequency are preferred for LHCD experiments at high density, consistent with previous results in other machines. The effect of LHCD on the current profile in EAST demonstrates that it is possible to control the plasma profile by optimizing the LHW spectrum. Repeatable H-mode plasma was obtained by LHCD and the maximum density during H-mode with the combination of 2.45 GHz and 4.6 GHz LH waves was up to 4.5 × 1019 m−3.

Design of Control System for Suppression of Neoclassical Tearing Modes with Electron Cyclotron Heating and Current Drive on EAST

Abstract This paper discusses a control system for the Experimental Advanced Superconducting Tokamak (EAST) that suppresses neoclassical tearing modes (NTMs) (3/2 and 2/1) by applying electron cyclotron (EC) heating and current drive. It allows the magnetic island to be detected and localized in real time and the EC beam to be deposited exactly on the island position by stepwise tuning of the steerable launch mirror. The mode features are identified with temperature perturbation to develop the algorithm for real-time island location. The necessary parameters for the design of the control system are discussed and determined based on simulation of the nonlinear island growth of NTMs with application of EC current drive. Although similar work has been done on many other devices, this is the first attempt on EAST.

Overcurrent protection for gyrotrons on the experimental advanced superconducting tokamak

In this paper, an overcurrent protection system is designed to ensure the safety of the gyrotrons in the EAST ECRH system. Two overcurrent protection systems were established, a fast one and a slow one. The fast one uses the current transformers as the current sensors. The models of the current transformers and the superconducting magnet were built to analyze the effect of the environmental magnetic field on the current transformers using FI method. The analysis results show that the magnetic induction at the position near the current transformers must less than 0.002 T, i.e., the current transformers should be placed at a distance greater than 2.2 meters from the magnet center to ensure its normal work. The slow one uses the shunt to monitor the currents. An anti-fuse FPGA and a timer is used to realize the signal processing in the fast protection circuit and the slow protection circuit respectively. The response time of the fast protection circuit is less than 100 ns, and the response time of the slow protection circuit is less than 31 μs.

Design of the klystron filament power supply control system for EAST LHCD

A filament is a critical component of the klystron used to heat the cathode. There are totally 44 klystrons in experimental advanced superconducting tokamak (EAST) lower hybrid current drive (LHCD) systems. All klystron filaments are powered by AC power suppliers through isolated transformers. In order to achieve better klystron preheat, a klystron filament power supply control system is designed to obtain the automatic control of all filament power suppliers. Klystron filament current is measured by PLC and the interlock between filament current and klystron high voltage system is also implemented. This design has already been deployed in two LHCD systems and proves feasible completely.

Study of lower hybrid current drive towards long-pulse operation with high performance in EAST

High density experiments with 2.45 GHz lower hybrid current drive (LHCD) in EAST are analyzed by means of simulation and modeling, showing that parametric instabilities (PI), collisional absorption and density fluctuations in the edge region could be responsible for the low CD efficiency at high density. In addition, recent LHCD results with 4.6 GHz are presented, showing that lower hybrid wave can be coupled to plasma with low reflection coefficient, drive plasma current and modify the current profile, and heat plasma effectively. The related results between two systems (2.45 GHz and 4.6 GHz) are also compared, including CD efficiency and PI behavior.