Qingxi Yang

First results of the use of a continuously flowing lithium limiter in high performance discharges in the EAST device

As an alternative choice of solid plasma facing components (PFCs), flowing liquid lithium can serve as a limiter or divertor PFC and offers a self-healing surface with acceptable heat removal and good impurity control. Such a system could improve plasma performance, and therefore be attractive for future fusion devices. Recently, a continuously flowing liquid lithium (FLiLi) limiter has been successfully designed and tested in the EAST superconducting tokamak. A circulating lithium layer with a thickness of <0.1 mm and a flow rate ~2 cm3 s−1 was achieved. A novel in-vessel electro-magnetic pump, working with the toroidal magnetic field of the EAST device, was reliable to control the lithium flow speed. The flowing liquid limiter was found to be fully compatible with various plasma scenarios, including high confinement mode plasmas heated by lower hybrid waves or by neutral beam injection. It was also found that the controllable lithium emission from the limiter was beneficial for the reduction of recycling and impurities, for the reduction of divertor heat flux, and in certain cases, for the improvement of plasma stored energy, which bodes well application for the use of flowing liquid lithium PFCs in future fusion devices.

Progress of the Keda Torus eXperiment Project in China: design and mission

The Keda Torus eXperiment (KTX) is a medium-sized reversed field pinch (RFP) device under construction at the University of Science and Technology of China. The KTX has a major radius of 1.4 m and a minor radius of 0.4 m with an Ohmic discharge current up to 1 MA. The expected electron density and temperature are, respectively, 2 × 1019 m−3 and 800 eV. A combination of a stainless steel vacuum chamber and a thin copper shell (with a penetration time of 20 ms) surrounding the plasma provides an opportunity for studying resistive wall mode instabilities. The unique double-C design of the KTX vacuum vessel allows access to the interior of the KTX for easy first-wall modifications and investigations of power and particle handling, a largely unexplored territory in RFP research leading to demonstration of the fusion potential of the RFP concept. An active feedback mode control system is designed and will be implemented in the second phase of the KTX program. The recent progress of this program will be presented, including the design of the vacuum vessel, magnet systems and power supplies.

Making ICRF power compatible with a high-Z wall in ASDEX Upgrade

A comparison of the ASDEX Upgrade 3-strap ICRF antenna data with the linear electro-magnetic TOPICA calculations is presented. The comparison substantiates a reduction of the local electric field at the radially protruding plasma-facing elements of the antenna as a relevant approach for minimizing tungsten (W) sputtering in conditions when the slow wave is strongly evanescent. The measured reaction of the time-averaged RF current at the antenna limiters to the antenna feeding variations is less sensitive than predicted by the calculations. This is likely to have been caused by temporal and spatial fluctuations in the 3D plasma density distribution affected by local non-linear interactions. The 3-strap antenna with the W-coated limiters produces drastically less W sputtering compared to the W-coated 2-strap antennas. This is consistent with the non-linear asymptotic SSWICH-SW calculations for RF sheaths.

First results with 3-strap ICRF antennas in ASDEX Upgrade

The 3-strap antennas in ASDEX Upgrade allow ICRF operation with low tungsten (W) content in the confined plasma with W-coated antenna limiters. With the 3-strap antenna configuration, the local W impurity source at the antenna is drastically reduced and the core W concentration is similar to that of the boron coated 2-strap antenna at a given ICRF power. Operation of the 3-strap antennas with the power ratio between the central and the outer straps of and is adopted to minimize the ICRF-specific W release.

RF, disruption and thermal analyses of EAST antennas

CAS IPP and MIT PSFC are collaborating on Experimental Advanced Superconducting Tokamak (EAST), the first tokamak with superconducting toroidal and poloidal magnets and a testbed for technologies proposed for the ITER project. Presented in this paper are RF, disruption and thermal analyses of EAST antennas. All were performed by COMSOL commercial software package Version 5. Analyzed are the I port 4 strap and B port 2 × 2 strap antennas, which are currently installed on EAST. RF analysis over the Ion Cyclotron Range of Frequencies (ICRF) gets insight into the coupling mechanism to optimize antenna plasma coupling. A lossy dielectric model was created which loads the antenna. The Scattering parameters (Sparameter) were extracted. Peak electric field parallel to the magnetic field of the straps, coaxes and other components were determined. Parametric analysis of the operation frequencies on the electric field are also performed. Disruption analysis addresses the impact of the magnetic field and plasma. Temporal currents of poloidal field and plasma as well as the spatial toroidal field were imported into the electromagnetic (EM) model. The structural analysis afterwards determined the stress due to antenna loads generated during the disruption. The loads resulted from the reaction of circulating eddy currents in the antennas with the toroidal and poloidal magnetic fields. Thermal analysis, a fluid - heat transfer - structural multiphysics analysis, performed for the strap and Faraday rod by applying heat loads from the plasma, ripple trapped particles and RF heating for steady state, are also presented. Finally, benefits of a future field-aligned 4 strap antenna were discussed.

The trajectory simulation and optimization of ion source chimney for SC200 cyclotron

SC200 is an isochronous cyclotron which generate 200 MeV, 500 nA proton for particle therapy. As an important component of the cyclotron, the ion source chimney needs to be tested and optimized. Th...

Upgraded flowing liquid lithium limiter for improving Li coverage uniformity and erosion resistance in EAST device

We report on design and technology improvements for a flowing liquid lithium (FLiLi) limiter inserted into auxiliary heated discharges in the experimental advanced superconducting tokamak device. In order to enhance Li coverage uniformity and erosion resistance, a new liquid Li distributor with homogenous channels was implemented. In addition, two independent electromagnetic pumps and a new horizontal capillary structure contributed to an improvement in the observed Li flow uniformity (from 30% in the previous FLiLi design to >80% in this FLiLi design). To improve limiter surface erosion resistance, hot isostatic press technology was applied, which improved the thermal contact between thin stainless steel protective layers covering the Cu heat sink. The thickness of the stainless steel layer was increased from 0.1 mm to 0.5 mm, which also helped macroscopic erosion resilience. Despite the high auxiliary heating power up to 4.5 MW, no Li bursts were recorded from FLiLi, underscoring the improved performance of this new design.

RF, Disruption, and Thermal Stress Analyses of EAST I and B Port Antennas

Chinese Academy of Sciences Institute of Plasma Physics and Massachusetts Institute of Technology Plasma Science and Fusion Center have been collaborating on experimental advanced superconducting tokamak (EAST). Presented in this paper are RF, disruption, and thermal stress analyses of EAST antennas. Analyzed are I port four-strap and B port 2 × 2 strap antennas, which are currently installed on EAST. As for RF analysis, scattering parameters are checked to make sure that the antennas are loaded, and then electric field parallel to magnetic field are checked to find out if they are below the permissible level. As for disruption analysis, mechanical stresses for both straps with the support box and Faraday screen are obtained. As for thermal stress analysis, temperature and thermal stress for a typical strap and a Faraday tube were presented. All analyses were performed by COMSOL commercial finite-element analysis software package version 5 or 5.2.

Engineering design and fabrication of the new-type antenna for EAST

One new-type of the antenna named Radiation stripline antenna (RSA) is designed to verify the design principles of that proposed for EAST, in relevant plasma conditions. It is expected to launch 1.5 MW of RF power to the plasma of the EAST machine during operation. RSA antenna is a new type of EAST antenna with heating frequency ranging from 27MHz~75MHz, one insulation layer with high-voltage resistance (30Kv) is designed to make current strap totally insulate from ground. The antenna mainly consists of faraday shield, four toroidal current straps, antenna frame, vacuum transmission line and vacuum feedthrough. Faraday shield subdivided four sections of screen, antenna frame is connected by six rods supporting the antenna weight, the rods can be moved along the radial direction by the rear driver system. During design of antenna, some analysis using finite element method (FEM) and high frequency structure simulation (HFSS) have been carried out for the RSA components, results promise that RSA antenna satisfies what are expected during antenna system operation. some In addition, a prototype RSA antenna have been fabricated and will be put into test for the long pulse, high power of EAST incoming operation.

Ion cyclotron resonance heating systems upgrade toward high power and CW operations in WEST

The design of the WEST (Tungsten-W Environment in Steady-state Tokamak) Ion cyclotron resonance heating antennas is based on a previously tested conjugate-T Resonant Double Loops prototype equipped with internal vacuum matching capacitors. The design and construction of three new WEST ICRH antennas are being carried out in close collaboration with ASIPP, within the framework of the Associated Laboratory in the fusion field between IRFM and ASIPP. The coupling performance to the plasma and the load-tolerance have been improved, while adding Continuous Wave operation capability by introducing water cooling in the entire antenna. On the generator side, the operation class of the high power tetrodes is changed from AB to B in order to allow high power operation (up to 3 MW per antenna) under higher VSWR (up to 2:1). Reliability of the generators is also improved by increasing the cavity breakdown voltage. The control and data acquisition system is also upgraded in order to resolve and react on fast events, such as ELMs. A new optical arc detection system comes in reinforcement of the Vr/Vf and SHAD systems.