Superconducting cavities made from niobium allow accelerating gradients of about $50ext{ }ext{ }mathrm{MV}/mathrm{m}$ close to the theoretical limit. Quite often, however, the rf losses increase with the gradient faster than quadratic. This observation is equivalent with a decrease of the quality factor $Q$ with the gradient, called ``$Q$ slope'' for intermediate gradients, and ``$Q$ drop'' for larger ones. The paper provides an explanation by an elementary model based on the two-fluid theory of rf superconductivity and applies it to experimental data for a large variety of cavity tests.
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机译:由铌制成的超导腔体可加速梯度达到约50美元 text {} text {} mathrm {MV} / mathrm {m} $,接近理论极限。但是,射频损耗随梯度的增加常常快于平方。该观察结果等同于质量因数$ Q $随梯度降低,中间梯度称为``$ Q $斜率'',较大梯度称为``$ Q $下降''。本文通过基于射频超导性双流体理论的基本模型提供了解释,并将其应用于各种空腔测试的实验数据。
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