Research on higher-order-mode (HOM) damping of superconducting cavities for the next-generation synchrotron light sources.

超导直线加速器是新一代同步加速器光源的关键技术之一。本文研究了超导腔的高阶模（HOM）阻尼方法，这是SC-linacs防止束流破裂（BBU）不稳定的重要问题之一。采用径向传输线对9单元1.3 ghz空腔进行了homm阻尼。我们通过计算机模拟和模型铜腔的射频测量研究了主要HOMs的q值。HOMs的q值与径向线与腔端之间的距离密切相关。对于类tm011和类tm020等单极子模式，典型的外q值约为10000。对于偶极子模式，TE111-like和TM110-like模式的典型q值分别约为10,000和10,000-100,000。由于这种方法的HOM阻尼总体上是好的，但是，对于类似tm110的模式，需要进一步的改进。我们正试图通过将束管半径从目前的39毫米扩大到更大的方法来改善这一点。从2005财年开始，高能加速器研究组织（KEK）和日本原子能机构（JAEA）开始合作开发用于下一代同步加速器光源的能量回收直线加速器（ERL）。为此成立了一个开发SC空腔的小组，并开始了他们的研究。我们研究的基础研究成果充分用于此目的。

The superconducting (SC) linear accelerator (linac) is one of the key technologies for the next-generation synchrotron light sources. We investigated method of higher-order-mode (HOM) damping for superconducting cavities, that is, one of the important issues for the SC-linacs for preventing beam breakup (BBU) instabilities.We applied the HOM damping method using radial-transmission lines to the 9-cell 1.3-GHz cavities. We investigated the Q-values of the principal HOMs by computer simulations, as well as by rf measurements of model copper cavity. The Q-values of HOMs depended strongly on the distance between the radial line and the end of the cavity. For the monopole modes, such as TM011-like and TM020-like modes, typical external Q-values of about 10,000 were obtained. For the dipole modes, typical Q-values were about 10,000 and about 10,000-100,000 for the TE111-like and the TM110-like modes, respectively. The HOM damping due to this method was good on the whole, however, further improvements are desirable for the TM110-like modes. We are trying to improve this point by such method as enlarging the beam-pipe radius from 39 mm (present) to larger ones.From FY2005,the development of the energy recovery linac (ERL) for the next-generation synchrotron light sources started by collaboration between the High Energy Accelerator Research Organization (KEK) and the Japan Atomic Energy Agency (JAEA). A team for developing the SC cavities for this purpose was organized, and they started their research. The basic research results from our research are fully used for this purpose.