Trembach Dallas, Xiao Chijin, Dreval Mykola, Hirose Akira
Plasma Physics Laboratory, University of Saskatchewan, 116 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada.
Rev Sci Instrum. 2009 May;80(5):053502. doi: 10.1063/1.3126526.
Diamagnetic measurements of poloidal beta have been performed in the STOR-M tokamak by a flux loop placed exterior to the vacuum chamber with compensation for the vacuum toroidal field using a nonenclosing coplanar coil, and vibrational compensation from auxiliary coils. It was found that in STOR-M conditions (20% toroidal magnetic field decay over discharge) there is significant influence on the diamagnetic flux measurements from strong residual signals, presumably from image currents being induced by the toroidal field coils, requiring further compensation. A blank (nonplasma) shot is used specifically to eliminate the residual component which is not proportional to the toroidal magnetic field. Data from normal Ohmic discharge operation is presented and calculations of poloidal beta from coil data (beta(theta) approximately 0.5) is found to be in reasonable agreement with the values of poloidal beta obtained from measurements of electron density and Spitzer temperature with neoclassical corrections for trapped electrons. Contributions present in the blank shot (residual) signal and the limitations of this method are discussed.
在STOR - M托卡马克装置中，通过放置在真空室外部的磁通环进行极向β值的抗磁测量。该磁通环使用非封闭共面线圈对真空环形磁场进行补偿，并通过辅助线圈进行振动补偿。研究发现，在STOR - M装置的条件下（放电过程中环形磁场衰减20%），强残余信号对抗磁通量测量有显著影响，这些残余信号可能是由环形场线圈感应出的镜像电流产生的，因此需要进一步补偿。专门使用一次空白（无等离子体）放电来消除与环形磁场不成比例的残余分量。给出了正常欧姆放电运行的数据，并且根据线圈数据计算得到的极向β值（β(θ)约为0.5）与通过测量电子密度和斯皮策温度并对捕获电子进行新经典修正后得到的极向β值合理吻合。文中讨论了空白放电（残余）信号中存在的贡献以及该方法的局限性。
