Theoretical Field Limits for Multi-Layer Superconductors
Theoretical Field Limits for Multi-Layer Superconductors
复制标题
多层超导体的理论场限制
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
M. Transtrum
中科院分区：
文献类型：
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作者：
S. Posen;G. Catelani;M. Liepe;J. Sethna;M. Transtrum
SIS结构--在大块超导体上用一层薄绝缘膜隔开的一层薄超导膜--通过提高第一临界场B_{c1}$来保护替代SRF材料免受磁通穿透。在这项工作中，我们表明，事实上，B_{c1}$ = 0的SIS结构。我们计算的过热场$B_{sh}$，我们表明，它可以稍微提高使用SIS结构，但只有在一个小范围的膜厚度，只有当膜和散装是不同的材料。我们还表明，使用多层而不是一个单一的厚层是有害的，因为这降低了B_{sh}$的膜。我们计算了薄膜$B_{sh}$以上的涡穿透耗散，发现它对SRF应用是不可控制的。然而，我们发现，如果在序参量的相位中引入梯度，SIS结构可能能够屏蔽大的DC和低频场。我们认为，SIS结构是不是有益的SRF腔，但由于最近的实验表明，低表面电阻性能以上的B_{c1}$的腔由超导体与小的相干长度，我们认为，增强的$B_{c1}$是没有必要的，和替代材料的体膜显示出很大的希望。
The SIS structure---a thin superconducting film on a bulk superconductor separated by a thin insulating film---was propsed as a method to protect alternative SRF materials from flux penetration by enhancing the first critical field $B_{c1}$. In this work, we show that in fact $B_{c1}$ = 0 for a SIS structure. We calculate the superheating field $B_{sh}$, and we show that it can be enhanced slightly using the SIS structure, but only for a small range of film thicknesses and only if the film and the bulk are different materials. We also show that using a multilayer instead of a single thick layer is detrimental, as this decreases $B_{sh}$ of the film. We calculate the dissipation due to vortex penetration above the $B_{sh}$ of the film, and find that it is unmanageable for SRF applications. However, we find that if a gradient in the phase of the order parameter is introduced, SIS structures may be able to shield large DC and low frequency fields. We argue that the SIS structure is not beneficial for SRF cavities, but due to recent experiments showing low-surface-resistance performance above $B_{c1}$ in cavities made of superconductors with small coherence lengths, we argue that enhancement of $B_{c1}$ is not necessary, and that bulk films of alternative materials show great promise.