Design and test of voltage and current probes for EAST ICRF antenna impedance measurement

Abstract

On the experimental advanced superconducting tokamak (EAST), a pair of voltage and current probes (V/I probes) is installed on the ion cyclotron radio frequency transmission lines to measure the antenna input impedance, and supplement the conventional measurement technique based on voltage probe arrays. The coupling coefficients of V/I probes are sensitive to their sizes and installing locations, thus they should be determined properly to match the measurement range of data acquisition card. The V/I probes are tested in a testing platform at low power with various artificial loads. The testing results show that the deviation of coupling resistance is small for loads R L >2.5 Ω, while the resistance deviations appear large for loads R L <1.5 Ω, which implies that the power loss cannot be neglected at high VSWR. As the factors that give rise to the deviation of coupling resistance calculation, the phase measurement error is the more significant factor leads to deleterious results rather than the amplitude measurement error. To exclude the possible ingredients that may lead to phase measurement error, the phase detector can be calibrated in steady L-mode scenario and then use the calibrated data for calculation under H-mode cases in EAST experiments.

Design of improved compact decoupler based on adjustable capacitor for EAST-ICRF antenna

“…The Ion Cyclotron Radio Frequency (ICRF) heating antenna adopts the design of multi-radiation straps, which results in a strong power coupling between the straps [1][2][3][4][5][6][7]. To restrain such power coupling, variable decouplers have been developed in the world tokamak machines [8][9][10][11][12][13], and a decoupler based on the T-shape shorted stub was used on EAST [14][15][16][17]. However, during the experiment, it was discovered that the short-circuit type with piston had shortcomings such as long size, difficult to adjust electrical length, poor contact of the short-circuit finger which leads to easy burning out etc.…”

Design of a multi-voltage probe system for ICRF antenna coupling resistance measurement on EAST

“…The main methods for measuring coupling resistance in high reflection are a voltage/current probe pair and multivoltage probe arrays [6,7]. As the voltage/current probe pair has been applied and studied in many EAST-like systems recently, its performance has obviously been improved [8,9]. However, due to the interference of system noise and the limitation of the original minimization algorithm (Levenberg-Marquardt (L-M) algorithm), where the L-M algorithm strongly depends on the initial value and its convergence steps are also not stable, the performance of the original multi-voltage probe array system does not meet the measured requirement of low system noise and the more stable minimization algorithm of the coupling resistance of the ICRF antenna.…”

Advances in experimental research towards high confinement and steady state operation on the Experimental Advanced Superconducting Tokamak

“…天线 相位和功率反馈控制系统也完成调试, 成功应用于等离 子体加热实验. 此外, 每路天线馈线均布设电压电流探 针, 用于传输线阻抗监测 [22] , 还采用了传输线水冷技术 来实现系统长时间稳态运行. 通过优化波与等离子体耦 合, 以及开展ICRH, LHCD, ECRH协同加热, 在高约束 等离子实验研究方面取得了重大突破 [23,24] .…”