论文标题
低温条件下的异常皮肤效应和铜腔操作
The anomalous skin effect and copper cavity operation at cryogenic conditions
论文作者
论文摘要
基于球形费米表面和使用等效的皮肤层模型的几何模型允许计算表面电阻，这与腔壁中的RF功率损耗相关。得出了这种传导电子模型在皮肤层中的精确解决方案。将其与Reuter，Sondheimer和Chambers制定的传统扩散模型的测量和预测进行了比较。将重点放在与ION LINAC加速度相关的频率上。在到GHz的频率下 - 几何模型允许的电阻值高达15％ - 当电子自由路径长度的长度约为经典皮肤深度五倍时。尽管两个模型假设都有很大不同，但结果彼此接近。由散装铜建造了一个340 MHz测试腔。质量 - 因子测量在腔体阶段的液体氦低温恒温器中进行。腔体首先是在抛光大块铜面后测量的。在下一步中，该表面被镀铜。在400摄氏度的400摄氏度退火一小时后，达到了相应的RRR值约120。在40摄氏度左右的低温温度下运行的具有铜腔的离子Linac预计将允许有吸引力的，紧凑的未来Linac设计。脉冲操作中热传导的模拟可带来令人鼓舞的结果。
A geometric model based on a spherical Fermi - surface and using the equivalent skin-layer model allows to calculate the surface resistance, which is relevant for the RF power losses in the cavity walls. An exact solution for this conduction electron model in skin layers was derived. It is compared with measurements and with predictions from the traditional diffusion model as formulated by Reuter, Sondheimer and Chambers. A focus is put on frequencies with relevance in ion linac acceleration. At frequencies up to the GHz - range the geometric model gives up to 15% higher resistance values - when the electron free path length is about five times longer then the classical skin depth. Though both model assumptions differ a lot, the results are close to each other. A 340 MHz test cavity was built from bulk copper. The quality - factor measurements were performed in a liquid helium cryostat during the warming up phase of the cavity.The cavity was at first measured after just polishing the bulk copper surface. In the next step this surface was copper-plated. After annealing for one hour at 400 deg Celsius, a corresponding RRR - value around 120 was reached. An ion linac with copper cavities operated at cryogenic temperatures around 40 deg Celsius is expected to allow attractive, compact future linac designs. Simulations on heat conduction in pulsed operation give promising results.
