RESEARCH ON BEAM FLATTENING BY USING THE HIGHER HARMONIC CAVITY IN THE HIGH INTENSITY PROTON ACCELERATOR.

从减缓空间电荷效应的角度看，在高强度质子加速器中形成扁平束状是必不可少的。二次谐波腔用于此目的，其中需要精确控制腔相位到基频相位。本项目拟在英国卢瑟福阿普尔顿实验室（RAL）世界上最高的质子同步加速器设施ISIS进行束流实验，利用低输出阻抗（LOI）二次谐波腔研究空间电荷效应。由于LOI腔体不受光束载荷的影响，因此可以实现对腔体相位的精确控制。2005年8月，我们成功地为LOI系统产生了所需的RF电压，每个间隙12.6kV：频率在2.6至6.2MHz范围内以50Hz扫频，输出阻抗小于30欧姆。虽然驱动阶段的波形失真问题仍有待解决，但LOI系统几乎已经准备好安装到ISIS同步加速器中进行波束测试。然而，在2006年，一个关于介子电离冷却实验的新项目（MICE项目）在RAL提出。我们目前使用的实验区是为这个项目分配的，我们别无选择，只能搬到其他地方。ISIS设施的2号厅进行了翻新，以适应我们的LOI系统。LOI的移动和所有电源线和控制线的重新布线始于2006年10月。截至2007年3月底，这些工程已完成。因此，拟议的实验研究无法进行，束流实验预计在2007财年或以后进行。

It is essential to form a flattened bunch shape in a high intensity proton accelerator from view point of mitigation of the space charge effect. The second harmonic cavity is used for this end, where precise control of the cavity phase to the fundamental one is required. This project is intended for the beam experiments at the world highest proton synchrotron facility, ISIS, Rutherford Appleton Laboratory (RAL), UK in order to investigate the space charge effects by using the low-output impedance (LOI) second harmonic cavity. Since the LOI cavity is free from beam loading, precise control of the cavity phase can be achieved.In August, 2005, we succeeded in producing a required RF voltage, 12.6kV per gap, for the LOI system : the frequency was swept at 50Hz from 2.6 to 6.2MHz, and the output impedance less than 30ohms. Although a problem on waveform distortions in the driver stage remained to be solved, the LOI system became almost ready for installation into the ISIS synchrotron for beam test.In 2006, however, a new project on the muon ionization cooling experiment (MICE project) came up at the RAL. The experimental area we have used so far was allocated for this project, and we had no choice but to move elsewhere. The Hall 2 of the ISIS facility was refurbished to accommodate our LOI system. The movement of the LOI and re-cabling of all the power lines and control lines began in October, 2006. By the end of March, 2007, these works have been completed. Therefore, the proposed experimental research could not be performed : the beam experiments are foreseen in Fy2007 or later.