Jianqiang Feng

Study and optimization of lower hybrid wave coupling in the experimental advanced superconducting (EAST) tokamak

The results presented in this paper are an extension of our recent (Kong et al 2012 Plasma Phys. Control. Fusion 54 105003) studies on lower hybrid wave (LHW) coupling. By optimizing the shape of the LH grill, the misalignment between the poloidal limiter (PL) and the LH grill is nearly eliminated and the coupling of LHW is improved, especially on the top row, although some discrepancies are still present in the case with low edge density. Density modifications both by LHW and ion cyclotron range of frequency (ICRF) power are studied in EAST. Experimental results show that the edge density modification in front of the LH grill during LHW power depends mainly on the competition between ponderomotive force (PMF) and the ionization of neutral gas, provided by gas puffing and edge recycling. However, the local edge density during ICRF power can be reduced rapidly. Furthermore, such a modification is more obvious with higher ICRF power and the relevant mechanism of density modification by ICRF power can be related to RF sheaths. In addition, another analogous effect of RF sheaths on the coupling of LHW is also investigated, i.e. the density convection induced by Er???B drift. The changes in LHW coupling associated with different ICRF antennas are discussed and it is shown that in some cases the coupling on the lower rows of the LH grill is improved possibly due to magnetic connection between ICRF antennas and the LH grill. The local coupling of LHW can be improved by gas puffing from gas introduction modules (GIM) on both sides of the launcher, but it is difficult to judge which one is more beneficial due to errors in measurements. Experimental results with gas (D2) injection during ICRF power clearly show that the coupling of LHW on the upper rows will be first improved by gas injection on the electron side and the coupling on the lower rows will be effectively improved by gas injection on the ion side. The results are consistent with the mapping of field lines.

Density modification in the scrape-off-layer during LHW coupling at EAST

The results presented in this paper are an extension of our recent studies (Kong et al 2013 Plasma Phys. Control. Fusion 55 065007, 065008) on lower hybrid wave (LHW) coupling. The effects of LHW power, edge recycling, edge-localized-mode (ELM) activity and gas puffing on the scrape-off-layer (SOL) density modifications will be further studied in this paper. The SOL density profile usually depends on the competition between an increment by ionization of neutrals and a depletion by the ponderomotive force (PMF) in L-mode plasma. Experimental results indicate that the SOL density with a lower edge recycling intensity could be reduced by a higher LHW power because ionization of a few neutrals cannot provide sufficient electrons to increase the SOL density and thus degrade the LHW coupling. In addition, in H-mode plasma, it is observed that the significant reduction of RC is associated with higher LHW power compared with the oscillation of RC during ELM activity, implying the priority of neutral gas ionization by LHW power. Studies also indicate that gas puffing in the GIM_e side could be more efficient in improving LHW coupling due to local ionization, inferred by the luminosities on the surface of the poloidal limiter (PL) and confirmed by SOL density measurement. The evolution of edge density with various puffing rates exhibits increments of far SOL density focused on the narrower layer several centimeters in front of the PL, possibly suggesting that the ionization of neutral gas mainly occurs in this region.

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.

Millimeter Wave Power Monitoring in EAST ECRH System

This paper presents a stable millimeter-wave power monitoring system for ECRH on EAST tokamak. The real-time power monitoring was realized based on power monitor miter bends. The “Exchange”method was proposed to monitor the reflection power for RF protection. A cRIO-based signal process unit was designed, it is robust and has the response time of 1 μs. The power monitoring system was tested and the experimental results were discussed.

Research on long pulse ECRH system of EAST in support of ITER

Experimental Advanced Superconducting Tokamak (EAST), as a fully superconducting tokamak in China, aims to achieve high performance plasma under steady-state operation. To fulfill the physical objectives of EAST, a program of 4-MW long pulse electron cyclotron resonance heating and current drive (EC H&CD) system, which would offer greater flexibility for plasma shape and plasma stabilization has been launched on EAST since 2011. The system, composed of 4 gyrotrons with nominal 1MW output power and 1000s pulse length each, is designed with the feature of steerable power handling capabilities at 140 GHz, using second harmonic of the extraordinary mode(X2). The missions of the ECRH system are to provide plasma heating, current drive, plasma profile tailoring and control of magneto-hydrodynamic (MHD) instabilities. Presently, the first two 140-GHz 1-MW gyrotrons, provided by GYCOM and CPI, respectively, have been tested at long pulse operation. The tubes, the associated power supplies, cooling system, cryogen...

The design of intelligent fault diagnosis system for high power microwave systems

Faults often cause serious damages on high power microwave system (HPMS). An intelligent diagnosis system is introduced in this paper. It helps operators in monitoring and diagnosing abnormal situations of HPMS. The HPMS architecture, the structure of the intelligent diagnosis system, the knowledge base, and the inference process are presented in detail. A diagnostic tree of HPMS is built by domain experts, and the diagnostic priorities of nodes in the tree are determined based on a fuzzy group multiple attribute decision making method. QNX operation system has been used in developing the proposed diagnosis system. Preliminary test has been carried out in actual engineering project, and satisfactory results were achieved.

A Fault Diagnosis Expert System for LHCD System on EAST

Lower hybrid current drive (LHCD) is an efficient method for noninductive current drive in fusion devices. The LHCD system has been constructed on the Experimental Advanced Superconduct Tokamak (EAST). It is a complex system due to lots of devices involved. Each device has possibility of faults, which causes great difficulties in fault diagnosis. Consequently, a fault diagnosis expert system is essential for a safe and steady operation of the LHCD system. This paper proposes an expert system called LFDES (lower hybrid current drive fault diagnosis expert system) to aid operators in diagnosing and analyzing abnormal situations of the LHCD system. After a brief description of the structure of LHCD system, the LFDES architecture, the knowledge base, the inference engine and the database are presented in detail. Based on an empirical knowledge, the diagnostic tree of LHCD system is built. A fuzzy group multiple attribute decision making method is used to determine the priorities of nodes in the diagnostic tree. KDevelop tool, QT Designer tool and Linux operation system have been used in developing the proposed system. In the study, satisfactory results were obtained. The analyses of the results indicated that LFDES can provide reliable, efficient and economical service.Copyright