LORENTZ FORCE DETUNING ANALYSIS OF THE SPALLATION NEUTRON SOURCE (SNS) ACCELERATING CAVITIES
LORENTZ FORCE DETUNING ANALYSIS OF THE SPALLATION NEUTRON SOURCE (SNS) ACCELERATING CAVITIES
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发表时间：
2001-09
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通讯作者：
R. Mitchell;K. Matsumoto;G. Ciovati;K. Davis;K. Macha;R. Sundelin
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作者：
R. Mitchell;K. Matsumoto;G. Ciovati;K. Davis;K. Macha;R. Sundelin
散裂中子源（SNS）项目在脉冲模式直线加速器的最后部分采用了超导射频（SRF）加速器。在SRF部分使用了几何β值为β = 0.61和β = 0.81的腔，它们由薄壁铌制成，在靠近光阑的单元之间焊接有加强环。焊接的钛制氦气容器和调谐器组件对腔的束管进行约束。β值小于1的腔具有相对陡峭和平坦的侧壁，这使得腔容易受到射频的影响。射频诱导的循环洛伦兹压力会对腔产生机械激励，产生与连续射频系统不同的动态洛伦兹力失谐。对于给定的腔设计，动态失谐的幅度是机械阻尼、调谐器/氦气容器组件的刚度、射频脉冲轮廓以及射频脉冲频率的函数。本文介绍了迄今为止的分析和测试结果，并指出了需要进一步研究的领域。中等β = 0.61的腔是一种薄壁（3.8毫米）铌结构，在光阑和赤道处采用电子束焊接（见图2）。在半径为80毫米的光阑附近焊接有一个加强环。腔被焊接到一个纯钛制氦气容器中。腔的一端直接焊接到氦气容器上，而另一端则通过不锈钢调谐器连接到氦气容器上。中等β腔容易受到洛伦兹力失谐的影响，因为与非常高β的腔相比，它们具有相对较大、平坦且有弹性的侧面。
The Spallation Neutron Source (SNS) project incorporates a superconducting radio-frequency (SRF) accelerator for the final section of the pulsed mode linac Cavities with geometrical β values of β =0.61 and β=0.81 are utilized in the SRF section, and are constructed out of thin-walled niobium with stiffener rings welded between the cells near the iris. The welded titanium helium vessel and tuner assembly restrains the cavity beam tubes Cavities with β values less than one have relatively steep and flat side-walls making the cavities susceptible to lsed RF induces cyclic Lorentz pressures that mechanically excite the cavities, producing a dynamic Lorentz force detuning different from a continuous RF system. The amplitude of the dynamic detuning for a given cavity design is a function of the mechanical damping, stiffness of the tuner/helium vessel assembly, RF pulse profile, and the RF pulse rate. This paper presents analysis and testing results to date, and indicates areas where more investigation is required. The medium β =.61 cavity is a thin wall (3.8mm) niobium structure that utilizes electron beam welding at the iris and equator (see Fig. 2). A stiffening ring is welded near the iris at an 80mm radius. The cavity is welded into a pure titanium helium vessel. One end of the cavity is welded directly to the helium vessel while the opposing end is attached to the helium vessel by the stainless steel tuner. The medium β cavities are susceptible to Lorentz force detuning because they have relatively large, flat sides that are flexible compared to very high β cavities.