T. Saeki

Study on the 1.3 GHz low loss shape superconducting cavities at IHEP

As part of the international research program on the superconducting cavity for the International Linear Collider (ILC) R&D on the 1.3 GHz low loss superconducting cavities has been carried out at the Institute of High Energy Physics (IHEP) since 2005. A design of 1.3 GHz low loss cavity shape was proposed and six single-cell cavities of different niobium material were successfully fabricated with standard technology. In this study our priority was on large grain (LG) cavities. The two LG cavities were treated with complete procedures of surface treatments based on chemical polishing (CP) without electro polishing (EP) at IHEP. The two LG cavities and a fine grain cavity were sent to KEK for vertical testing. All the three cavities reached accelerating gradients higher than 35 MV/m and the maximum gradient of 40.27 MV/m was achieved in the LG cavity. This paper presents the process of the vertical RF tests and the comparison of the LG and fine grain cavitiess performance.

Test operation of ball-screw-type tuner for low-los high-gradient superconducting cavity at 77 K

Super-conducting Radio Frequency (SRF) 9-cell cavities have been developed in Low-Loss (LL) ICHIRO shape at KEK aiming at high-gradient operation for the International Linear Collider (ILC). One of the most important issues to realize high-gradient linac with SRF cavitiest in pulsed-mode operation is the compensation of the Lorentz detuning of cavities which amounts to 3 kHz at our goal of 45 MV/m acceleration field. None of tuners to date have achieved this specification. A coaxial ball- screw tuner was designed, fabricated and proven to reach this specification in room temperature. The performance was studied also at liquid-nitrogen temperature and the needed dynamic-range for 45 MV/m operation was proven at this temperature. The microphonic vibration was measured to be 100 Hz order in a test setup. In this paper, we describe these studies and evaluate the feasibility of ball-screw tuner operation at 2 K.

Experimental study on SC RF cavities by using China large grain niobium for ILC

Large grain niobium has the potential of simplifying the production sequence and consequently reducing the cost of the superconducting RF cavities for ILC. To investigate the feasibility of fabrication and the possibility to achieve high gradient by large grain cavities, two 1.3 GHz cavities were made of China large grain niobium and a series of vertical tests were carried out following several different surfaces treatment procedures. Two cavities have both reached the high gradient of more than 43 MV/m repeatedly and the maximum accelerating field of 47.9 MV/m has been achieved by China large grain niobium. This paper introduces the features of the fabrication and surface treatments on the large grain cavities and presents the preliminary results of the research.

Vertical Electropolishing Studies at Cornell with KEK and Marui

Cornells SRF group has been developing Vertical Electro-Polishing (VEP) which was applied on 1.3GHz Niobium SRF cavities as the primary surface treatment. The process was done in the vertical direction, the upper and the lower half cell had removal difference. Cavity need to be flipped over during the process to compensate this. Cornell has started collaboration with KEK and Marui Galvanizing Co. Ltd. (Marui) in 2014. The first step of collaboration focused on the demonstration of Marui’s original VEP cathode named “i-cathode Ninja®” at Cornell, which was developed to make more uniform VEP removal. The results of VEP using Ninja cathode at Cornell will be presented in this paper.

Revision of accelerating and damping structures for kek STF 45 MV/m accelerator modules

KEK is constructing its superconducting RF test facility and installing 1.3 GHz superconducting accelerator structures. Learning from experience with our first 45 MV/m 9-cell accelerating structures, we have redesigned the structures to improve the characteristics and the performances. Problems found in the earlier structures are resolved in the new structures.

Electro-polished cavities using china ningxia large grain niobium material

For the International Linear Collider (ILC), superconducting RF cavity technology was chosen. The superconducting cavity is made of polycrystalline niobium material so far. However, the material cost is high and the cavity performance has a rather scatter now. Large grain (LG) niobium cavity has the potential of simplifying the production and reducing the cost of the superconducting RF cavities for the ILC. To investigate the feasibility of fabrication and the possibility to achieve high gradient by LG cavities, three single-cell cavities were made of China Ningxia LG niobium. A series of vertical tests has been carried out on several different surfaces treatment procedures by electro polishing. One cavity has reached the high gradient of more than 43 MV/m repeatedly. The maximum accelerating field of 47.9 MV/m has been achieved. This paper describes the features of electro polishing on China Ningxia LG niobium and presents the preliminary results of the research.