• I. Montero, L.S. Aguilera
  CSIC, Madrid
• F. Caspers, E. Montesinos
  CERN, Geneva
• L. Galan
  UAM, Madrid
• D. Raboso
  ESA-ESTEC, NOORDWIJK

We are presenting first results of direct measurements of the secondary electron emission yield (SEY) for several magnetic materials like ferrites at energies of primary electrons from 5 to 10⁰⁰ eV. In order to minimize the impact of surface charging, the primary electron beam had a short pulse modulation of 400ns with a very low repetition rate. This paper discusses a method of developing a secondary-electron-suppressing highly textured ferrite surface with low SEY by depositing a layer of very fine ferrite particles onto a substrate. The experimental results indicate that the SEY of the particulate ferrite surfaces is much lower than that of flat ferrites. In comparison we have confirmed that ordinary carbon coating with rather large grain size returns SEY value close to unity. However, a surface with very finely powdered carbon has a much smaller secondary emission yield of about 0.5, but the adhesion of these carbon powders to the surface is often not reliable enough for many applications. As a remarkable fact it has been found that gold- and also carbon-coated ferrites have SEY peak values lower than unity up to 1000eV.

• Y. Morita, K. Akai, T. Furuya, A. Kabe, S. Mitsunobu, M. Nishiwaki, S. Takano
  KEK, Ibaraki

Eight superconducting accelerating cavities have been stably operated in the KEKB with sufficiently low trip rates. Two superconducting crab cavities were installed in 2007 and soon the crab crossing operation started. Recently the KEKB luminosity reached the world record of 2.1 x 10³⁴ cm^-1s^-1. Stable operations of the accelerating cavities contributed for the luminosity increase. For the future Super-KEKB, we are developing a high power coupler for an input power of 600 kW and a HOM damper for RF power absorption more than 30 kW. The Super-KEKB requires RF operations with the high beam loading and the low RF voltage than the present KEKB operation. To suppress klystron output powers the external Q value has to be reduced. A new operation was proposed for superconducting cavities. In order to keep high RF voltages in each cavity, some cavities reverse its synchronous beam phase while the total RF voltage is kept as low as the required one. Beam studies were successfully carried out with one cavity reversed its synchronous beam phase.

• N. Nakamura
  ISSP/SRL, Chiba
• K. Harada
  KEK, Ibaraki

Orbit correction in an ERL is more complicated than those of an ordinary linac and a transport line, because the ERL beam passes a straight section containing main superconducting cavities at least two times with different energies. A corrector in this section gives a different kick angle to the beam in a different turn. Therefore a sophisticated orbit correction method is required for ERLs and ERL-based light sources. The eigenvector method with constraints (EVC)* can perform global orbit correction under constraint conditions and has been proposed and used for uniting global and exact local orbit corrections mainly in storage-ring based SR sources**. We applied this EVC method to orbit correction in an ERL. In this paper, we present how to use the EVC method for an ERL and simulation results of orbit correction for the compact ERL.

* N. Nakamura et al., Nucl. Instr. Meth. A 556 (2006) 421-432.
** K. Harada et al., Nucl. Instr. Meth. A 604 (2009) 481-488.

• M. Sawamura
  JAEA/ERL, Ibaraki
• T. Furuya, H. Sakai, K. Umemori
  KEK, Ibaraki
• K. Shinoe
  ISSP/SRL, Chiba

HOM absorbers are one of the key components to determine the ERL cavity performance to reduce the HOM problem for the high current operation. When a beam line HOM damper is installed inside the cryomodule, the HOM absorber is cooled down to liquid nitrogen temperature. The RF absorber used for the HOM absorber is required to have good frequency and temperature properties at low temperature. The RF absorber was selected by permittivity and permeability measurement of some ferrites and ceramics from room temperature to 40 K. The HOM absorber is designed by optimizing the parameters such as length, thickness and position with microwave simulation codes. The HOM absorber test model was designed and fabricated to test the RF, mechanical, cooling and temperature properties.

• H. Yu
  SSRF, Shanghai
• M. Chen, Z.Q. Feng, H.T. Hou, J.F. Liu, Z.Y. Ma, D.Q. Mao, B. Yin
  SINAP, Shanghai

To investigate the higher order mode(HOM) damping in the higher harmonic cavity for Shanghai Synchrotron Radiation Facility(SSRF) when using HOM absorbers,simulations have been done for changing the position and the length as well as the thickness of ferrite of HOM damper. The best values under which the Q value of HOMs can be greatly lowered and the impedance of harmonic cavity will be trapped in the impedance threshold have been found.

• L. Hagge, J.A. Dammann, J. Iversen, J. Kreutzkamp, W. Singer
  DESY, Hamburg

For the series production of s.c. cavities for European XFEL, thorough quality assurance procedures are under preparation to ensure that all cavities satisfy their performance requirements. Each cavity needs to pass a number of quality gates at different levels of completion. At each quality gate, the so-far available manufacturing data and documentation is reviewed and approved by the XFEL cavity production team. To ensure reliable and repeatable procedures with timely responses, the QA efforts are supported by the DESY Product Lifecycle Management (PLM) System, aka DESY EDMS. The EDMS manages fabrication data, coordinates acceptance tests, manages signoffs and provides fabrication progress monitoring. In particular, the EDMS tracks the entire history of all individual cavities, their parts and their semi-finished products. The setup benefits from experience which has been gained at DESY in the cavity production for FLASH. The poster explains the planned QA procedures and customization of the EDMS, and reports inital experience.

• A.S. Dhavale
  BARC, Mumbai
• K.C. Mittal
  BARC-EBC, Mumbai

The performance of superconducting cavity, couplers and ceramic windows is greatly affected due to multipacting. The present paper describes the multipacting simulations carried out on the co-axial coupler. The equation of motion of electron in RF field is calculated numerically. The enhanced counter function (ECF) is calculated to find out whether a particular electron will give rise to the multipacting. The simulation was carried out for a co-axial coupler having the inner conductor diameter of 34.78 mm and outer conductor diameter of 80 mm at a RF frequency of 350MHz, 700MHz and 1050MHz.

• K. Nakanishi, K. Hara, K. Hosoyama, A. Kabe, Y. Kojima
  KEK, Ibaraki

Hydrogen absorbed in niobium was measured using effect of hydrogen Q-degradation. A niobium cavity was designed and manufactured for this experiment. Hydrogen was introduced from outside of the cavity by electrolysis of diluted sulfuric acid on the outer surface of the cavity with an anode made by stainless steel. The Q-factor is one of the most unstable property of superconducting cavities. Especially, the reproducibility of Q-factor cannot be so expected after disassembled and reassembled it. In this experiment, the Q-factor was measured without disassembling, because hydrogen was introduced from outside of the cavity. The Q-degradation was observed successfully. And the Q-factor becomes worse and worse, when hydrogen was introduced more and more. To estimate the amount of hydrogen which is absorbed in niobium, small and thin niobium samples were prepared. They were warmed by the energizing heating in vacuum after having introduced hydrogen. The out-gas was analyzed by QMS, and the amount of hydrogen was estimated. This method can be applied to measure the absorbed hydrogen during electro or chemical polishing of cavities without some influence of changing the surface morphology.

• K. Umemori, T. Furuya, H. Sakai, T. Takahashi
  KEK, Ibaraki
• M. Sawamura
  JAEA/ERL, Ibaraki
• K. Shinoe
  ISSP/SRL, Chiba

In order to verify the technology needed for ERL main linac cavities, we fabricated a prototype of L-band 9-cell KEK-ERL superconducting cavity. For the ERL, along with high gradient and high Q-value, strong HOM damping is required. Its cell shape is optimized for the HOM damping. The cavity has large irises of 80 mm diameter, large beampipes of 120 mm and 100 mm diameter and the eccentric fluted beampipe. After a series of surface treatment, such as annealing, electro-polishing, high-pressure-rinsing and baking, several vertical tests have been performed. As for cavity diagnostics, a rotating X-ray and temperature mapping system was constructed. The cavity performance was limited to less than 20 MV/m by the field emissions. The X-ray distributions caused by field emission were clearly observed by X-ray mapping system. In this report, we summarize the recent results of the vertical tests.

• K. Watanabe, H. Hayano, E. Kako, S. Noguchi, T. Shishido, Y. Yamamoto
  KEK, Ibaraki
• Y. Iwashita
  Kyoto ICR, Uji, Kyoto
• Y. Kikuchi
  Tohoku Gakuin University, Miyagi

Nine 1.3 GHz 9-cell superconducting cavities (MHI-01 ~ 09) for International Linear Collider (ILC) project were fabricated from 2005 to 2009 at KEK-STF. The vertical test (with temperature and X-ray mapping) and optical inspection using by high resolution camera system for nine cavities were carried out from 2006 to 2009 for STF Phase-I project and S1-Global project at KEK. The cavities were separated to three series. The first series is MHI-01 ~ 04 (fabricated at 2005). They were made the Centrifugal barrel polishing (CBP) at initial surface treatment. The second series is MHI-05 and 06 (fabricated 2008). The third series is MHI-07 ~ 09 (fabricated at 2009). The surface treatments of second and third series cavity were made only Electro Polishing (EP) process (without CBP), because of the EBW seams of equator and iris were improved by the feedback of optical inspection method. A good correlation has been so far observed between the hot spots localized by thermometry measurements in the vertical test and the positions of surface defects found by this system. The result of optical inspection will be reported in this paper.

• K. Watanabe, H. Hayano, E. Kako, S. Noguchi, T. Shishido, Y. Yamamoto
  KEK, Ibaraki
• Y. Iwashita
  Kyoto ICR, Uji, Kyoto

The repair techniques of superconducting cavity is important to obtain better yield of accelerating gradient of superconducting 1.3 GHz 9-cell cavities. The techniques for repair of the cavity are combination of the optical inspection, make a replica of defect, the local grinding and the result of temperature mapping in vertical test. The pit type defect (size: 0.7 mm x 0.5 mm, depth: about 115 um) was found at the quench location of MHI-08 cavity at 16 MV/m by optical inspection after 1st vertical test at June 2009. The location of defect is boundary between EBW seam and heat affected zone at 172 degree of 2-cell equator. If a cause of field limitation for MHI-08 is really this pit type defect, then the cavity can repair to remove the defect by mechanical grinding method. The defect was removed completely by the special grinding machine. After grinding, Electric polishing process and optical inspection were carried out to check the surface condition at grinding area. The 2nd vertical test of MHI-08 was carried out at October 2009. The accelerating field was improved from 16 MV/m to 27 MV/m. The result of repair of MHI-08 will be reported in this paper.

• H. Tongu, H. Fujisawa, Y. Iwashita
  Kyoto ICR, Uji, Kyoto
• H. Hayano, K. Watanabe, Y. Yamamoto
  KEK, Ibaraki

The vertical test is a performance trial done by cooling the superconducting cavity, and injecting the high-frequency electricity. The temperature mapping (T-map) system is developed for the vertical test. T-map system can find heat sources that may be caused by defects on inner surfaces of superconducting cavities. The purpose of our studies on T-map is to realize a high spacial resolution and easy installation of the sensors. CMOS analog multiplexers in the cryogenic temperature can manage about thousand sensors per 9 cells to send their signals with fewer lines. Inspection efficiencies to raise the production yield of the cavities would be improved by using such a high resolution T-map system. The preliminary test of the cryogenic temperature by the T-map system is reported.

• K. Sennyu, H. Hara, H. Hitomi, K. Kanaoka, M. Matsuoka, T. Yanagisawa
  MHI, Kobe

MHI has supplied superconducting cavity for the ILC R&D project to KEK in Japan for the last few years. We are improving the technology to design and fabricate the superconducting cavities. We can present some example of our work that have improved the productivity of the superconducting cavities.

• Q.Z. Xing, T.T. Liang, J. Lv, D.C. Tong
  TUB, Beijing

The application of the genetic algorithm in the diagnosis of the coupled cavity chain is investigated in this paper. One program named GANL2 has already been developed based on the genetic algorithm at Tsinghua University. The cell frequencies, quality factors, and coupling between the cells can be estimated by GANL2 if the pass-band reflection curve is known. This method has been applied in the diagnosis of the S-band and X-band standing-wave linac cavities. In this paper we present the preliminary investigation of the genetic algorithm in the diagnosis of the L-band 9-cell superconducting copper cavity model. The result of the calculation and measurement are compared. Not all the cells are diagnosed well. More precise measurement is needed for further study.

• H. Nakai, K. Hara, T. Honma, K. Hosoyama, A. Kabe, Y. Kojima, Y. Morita, K. Nakanishi
  KEK, Ibaraki
• T. Kanekiyo
  Hitachi Technologies and Services Co., Ltd., Kandatsu, Tsuchiura

Two superconducting crab cavities were successfully installed into the KEKB accelerator in January 2007. Since then the crab cavities have been in stable operation for 3 years up to now, thanks to reliable operation of the cryogenic system of the KEKB including a large-scale helium refrigerator. This means that the cryostat for the crab cavities was well designed and constructed properly, although there are some technical complexities in the cryostat, such as two helium vessels in a cryostat, a movable coaxial coupler which is cooled with liquid helium and so on. The KEKB cryogenic system was also appropriately modified to operate the two crab cavity cryostats stably. This cryogenic system is described in this presentation. A calorimetric method to measure the Q-factors of the crab cavities is suggested, which employs an electric compensation heater in the cryostat, instead of the conventional method, which measures the descending rate of liquid helium level. Measurement results of the Q-factors of crab cavities after being assembled in the cryostat and after being installed into the KEKB accelerator are compared with the vertical test results.