Optimal choice of cell geometry for a multicell superconducting cavity
Optimal choice of cell geometry for a multicell superconducting cavity
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多单元超导腔单元几何形状的优化选择
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发表时间：
2009
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通讯作者：
V. Shemelin
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作者：
V. Shemelin
提出了一种多细胞腔细胞优化算法。当孔径、峰值电场与加速场之比${E}_{pk}/{E}_{mathm {acc}}$和壁坡角给定时，内腔优化为损耗最小或磁场最小。末端单元的优化是为了使损耗最小或加速最大。分析了末端细胞的两种形状——有和没有末端虹膜。这种方法有利于更高阶模式提取的进一步优化，因为它允许在改变细胞的某些维度时保持所获得的最优值几乎相同。将所提出的腔体几何形状与特斯拉腔体几何形状进行比较，说明了所提出方法的特点。结果还表明，较低的壁坡角值会导致内部细胞的重入形状，也有利于端细胞。对于康奈尔能量回收直线加速器来说，最危险的是导致束流破裂（BBU）的偶极子模式。利用电池参数相对于空腔电池几何参数的导数，实现了多电池腔中高阶模式（HOMs）功率的最小化。选取基模损失最小的形状作为优化的出发点。基模损耗参数$ gifmmodecdotelse experiodcenteredfi {}{R}_{maththrm {sh}}/Q$降低了1%以内，而电池参数降低了近3个数量级。BBU的阈值电流与该参数呈反比趋势。
An algorithm for optimization of the multicell cavity cells is proposed. Inner cells are optimized for minimal losses or minimal magnetic field, when the aperture diameter, ${E}_{pk}/{E}_{mathrm{acc}}$---the ratio of peak electric field to the accelerating field, and the wall slope angle are given. Optimization of the end cells is done for minimal losses or maximal acceleration in them. Two shapes of the end cells---with and without the end irises---are analyzed. This approach facilitates further optimization for higher order modes extraction because it permits keeping the achieved optimal values nearly the same while changing some dimensions of the cells. Comparison of the proposed cavity geometry with the TESLA cavity geometry illustrates the traits of the presented approach. It is also shown that lower values of the wall slope angle, which lead to the reentrant shape for the inner cells, are also beneficial for the end cells. For the Cornell Energy Recovery Linac most dangerous are dipole modes causing the beam breakup (BBU). Minimization of power of higher order modes (HOMs) in a multicell cavity was done using derivatives of the BBU parameter with respect to geometric parameters of the cavity cells. As a starting point of optimization, the shape with minimal losses at the fundamental mode was taken. Further changing the shape for better propagation of HOMs was done with degradation of the fundamental mode loss parameter $Gifmmodecdotelse extperiodcenteredfi{}{R}_{mathrm{sh}}/Q$ within 1% while decrease of the BBU parameter was nearly 3 orders of magnitude. The BBU threshold current tends to be inversely proportional to this parameter.