The potential role of magnetic shear, rational safety factor surfaces and shearing rate on the confinement is investigated on the basis of a database analysis of JET internal transport barriers (ITBs). The ITB is quantified using the JET ITB criterion (Tresset G et al 2002 Nucl. Fusion42 520). The relation between the shearing rate and the magnetic shear, already established for positive magnetic shear barrier (Tala T J J et al 2001 Plasma Phys. Control. Fusion43 507), is investigated at low and negative magnetic shear, where the threshold in shearing rate is found to be lower than for positive magnetic shear barriers. Defining the ITB from the departure from profile stiffness is found to be consistent with the database results, and the critical gradient length is found to be minimum at low magnetic shear. Finally, ITBs are found to be localized in the vicinity of integer safety factor surfaces in positive magnetic shear plasmas, whereas no correlation is found with integer values when the barrier is localized in negative magnetic shear regions.
磁剪切、有理安全因子面和剪切率对约束的潜在作用，基于JET内部输运垒（ITB）的数据库分析进行了研究。ITB采用JET ITB判据（Tresset G等，2002年，核聚变42，520）进行量化。剪切率与磁剪切之间的关系，已在正磁剪切垒中确立（Tala T J等，2001年，等离子体物理与受控聚变43，507），现于低磁剪切和负磁剪切条件下进行研究，发现剪切率的阈值低于正磁剪切垒。将ITB定义为偏离剖面刚性的行为，与数据库结果一致，且临界梯度长度在低磁剪切时达到最小值。最后，在正磁剪切等离子体中，ITB定位于有理安全因子面附近，而在负磁剪切区域中，当垒定位于该处时，未发现与有理数值的相关性。