Study of High-gradient Structures for the Linear Collider

直线对撞机高梯度结构研究

基本信息

批准号：
03044141
负责人：
TAKATA Koji
金额：
$ 5.76万
依托单位：
National Laboratory for High Energy Physics (KEK)
依托单位国家：
日本
项目类别：
Grant-in-Aid for international Scientific Research
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-03044141/
关键词：
linear collider linac klystron high gradient acceleration high electric field dark current oxygen free copper precision machining リニアコライダ-加速管高電界加速無酸素銅ろう付電界放出電子

项目摘要

Experimental and theoretical studies have been carried out for accelerating structures of the main linac of linear colliders. The structure is of a traveling wave type driven with 11.4GHz X-band RF power. The accelerating gradient is desired to be as high as 100MV/m. In this fiscal year, we fabricated a proto-type structure of oxygen free copper with a very accurate and fine surface finish. It was then high power tested at KEK by using a 30MW klystron which had been developed at KEK. We were able to reach the high gradient after a 500 hour conditioning. We also made detailed measurements of dark currents due to surface emission under the very high RF electric field.In order to achieve a high gradient, a high power klystron is absolutely necessary. However, the fabrication technology of klystrons becomes extremely difficult as the operation frequency raises. Therefore high gradient experiments were carried out at the S-band(2.86GHz), at which frequency the high power klystrons are easil … More y available. In fact at this frequency we achieved over 80MV/m average gradients successfully and also tested beam acceleration too. For the TeV energy linear collider, however, the RF frequency should be an X-band(11.4GHz) one at the lowest, since otherwise the total ac power becomes impractically high. KEK has been developing X-band high power klystron for a long time, and recently we succeeded to get a first tube which can deliver 30MW RF power. This experiment is carried out by using this tube.CERN has a different idea for the TeV linear collider. Particularly they are considering a K-band(30GHz) frequency generated by a FEL. Its realization is still far in the future. They are, on the other hand, developing technologies to fabricate accelerating structure which is capable of such high gradients. They are therefore wanting to test the structure as soon as possible even at lower frequencies. Hence a joint experiment started at KEK.In this experiment CERN and KEK made structures of the same dimensions. The main specification is : number of cell 20, coupler cell 2, cell length 2.9mm, phase shift per cell 2pi/3, constant impedance structure, beam aperture 6mm, cell diameter 10.4mm, disk thickness 1mm. The Q value is 6500, attenuation is 1.54/m, impedance is 104MOMEGA/m. The maximum surface field over the beam aperture is 3.9 times the average gradient. The most critical point in the fabrication was to achieve a sufficient smoothness on the beam aperture. It is accomplished by carefully choosing diamond bits. We also paid attention to avoid metallic and organic dusts falling inside the structure. They are usually a serious cause to limit the maximum attainable gradient by inducing heavy discharges.The test was carried out at the klystron repetition rate 50Hz. The RF pulse length was typically 100ns. The KEK structure reached 70MV/m after 60million pulses, While the CERN one did 100MV/m after 9 million pulses. In the CERN case, we also used a SLED system to boost the RF power.Observed dark currents were analized by use of a modified Fowler-Nordheim formula. The important measure therein is the field enhancement factor beta. For ther both structures, we obtained similar values around 50 for beta.The absolute value of the dark current was found to be rather high for the KEK structure and further studies are necessitated to resolve this. Less

实验性和理论研究是针对线性碰撞者主利纳克的加速结构进行的。该结构是由11.4GHz X波段RF功率驱动的波动波型。加速梯度希望高达100mV/m。在这个财政年度，我们制造了一种不含氧气的原型型铜结构，并具有非常准确且表面效果非常精细。然后，通过使用Kek开发的30MW Klystron在KEK进行了高功率测试。经过500小时的调理后，我们能够达到高梯度。我们还对非常高的RF电场下的表面发射引起的深色电流进行了详细的测量。为了达到高梯度，绝对需要高功率klystron。但是，随着操作频率提高，克莱斯特龙的制造技术变得极为困难。因此，在S波段（2.86GHz）进行了高梯度实验，在该实验频率高功率klystrons很容易……更可用。实际上，在此频率下，我们成功地达到了超过80mV/m的平均梯度，并且也测试了梁加速度。但是，对于TEV Energy线性对撞机，RF频率应为最低的X波段（11.4GHz），因为否则，总交流功率不切实际。 Kek很长一段时间以来一直在开发X波段的高力量Klystron，最近我们成功获得了可以提供30MW RF功率的第一管。该实验是通过使用此管进行的。CERN对TEV线性对撞机的想法不同。特别是他们正在考虑由FEL产生的K波段（30GHz）频率。它的意识在将来还很遥远。另一方面，它们是开发技术加速结构的技术，该结构能够具有如此高的梯度。因此，他们希望即使在较低的频率下也要尽快测试结构。因此，在kek开始进行联合实验。在该实验中，库克和凯克制造了相同维度的结构。主要规范是：单元格20，耦合器电池2，单元长2.9mm，每个单元2PI/3的相移，恒定阻抗结构，束光圈6mm，单元格直径10.4mm，磁盘厚度为1mm。 Q值为6500，衰减为1.54/m，阻抗为104momega/m。梁孔径上的最大表面场是平均梯度的3.9倍。制造中最关键的点是在梁孔径上实现足够的平滑度。它是通过仔细选择钻石碎片来完成的。我们还关注避免金属和有机紫外线插入结构内。它们通常是通过诱导的重量排放来限制最大可达到的梯度的严重原因。测试以50Hz的Klystron重复率进行。 RF脉冲长度通常为100N。 6000万脉冲后，KEK结构达到70mV/m，而CERN ONE在900万脉冲后进行了100mV/m。在CERN情况下，我们还使用雪橇系统来增强RF功率。使用改良的Fowler-Nordheim公式对观察到的深色电流进行了分析。其中的重要措施是现场增强因子β。对于这两种结构，我们在Beta的50左右获得了相似的值。发现黑暗电流的绝对值对于Kek结构非常高，并且需要进一步的研究来解决此问题。较少的