Abstract A helicon wave was tested for coupling at low power in the KSTAR, and high-power coupling has also been tried. When RF is applied to the antenna system, the reflected power gradually increases on a sub-millisecond timescale. A slower process than usual arcing suggests that a multipactor discharge causes the reflection. It is essential to mitigate or eliminate the multipactor discharge to apply a high-power helicon wave to the tokamak plasmas. A new VFT is fabricated following a design that focuses on the reduced total RF electric field and zero axial electric field on TiN-coated alumina and conductor surfaces. The unmatched impedance caused by the 1-cm-thick alumina is compensated by the series matching element positioned in the pressurized section. Particle in cell codes are used to predict the effects of secondary electrons caused by electrons emitted in the high-power RF transmissions. Different coating conditions are compared, and it is calculated that the designed VFT is free from multipacting. Thermomechanical stress and deformation due to the RF loss is also analyzed. The RF characteristics of the fabricated VFT agrees well with the design. Currently, a megawatt-level high-power test with the KSTAR helicon antenna in a vacuum is being prepared.

中文翻译：

---

科士达螺旋电流驱动多路抑制大功率VFT设计

摘要 在KSTAR中测试了螺旋波的低功率耦合，也尝试了高功率耦合。当 RF 应用于天线系统时，反射功率以亚毫秒的时间尺度逐渐增加。比通常电弧放电更慢的过程表明多方放电导致了反射。必须减轻或消除多方放电以将高功率螺旋波应用于托卡马克等离子体。一种新的 VFT 是按照专注于减少 TiN 涂层氧化铝和导体表面上的总射频电场和零轴向电场的设计制造的。由 1 厘米厚氧化铝引起的不匹配阻抗由位于加压部分的串联匹配元件补偿。单元代码中的粒子用于预测由高功率 RF 传输中发射的电子引起的二次电子的影响。比较了不同的涂层条件，计算出设计的VFT没有多重涂层。还分析了由于射频损耗引起的热机械应力和变形。制造的 VFT 的射频特性与设计非常吻合。目前，KSTAR螺旋天线在真空中的兆瓦级大功率测试正在准备中。