Summary:

The SuperKEKB e+e- collider is designed to provide a very high luminosity for the Belle-II experiment, using the recently proposed nano-beam scheme. In this context, the fast luminosity monitoring collaboration aims to develop a reliable instrumentation to measure the luminosity and provide fast input for luminosity feedback corrections as well as for beam size minimisation at the IP, as part of the overall luminosity optimization process. The measurements are based on the detection of the positrons and photons arising from the Bhabha process at vanishing scattering angle, which offers a significant amount of signal. The fast luminosity monitors are located ten and thirty meters downstream of the interaction point in the low and high energy rings, respectively, just immediately outside the beam-pipe. In the low energy ring, a special beam pipe shape was designed to maximise the range of signal strengths available for the different luminosity levels expected with SuperKEKB. Several kind of detectors have been developed, based on complementary technologies, namely scintillator and Cherenkov (ZDLM project) and diamond (LumiBelle2 project), all requiring fast readout electronics to enable measuring averaged luminosities, both integrated over all bunches and bunch-by-bunch. The luminosity monitoring was operated successfully during the entire Phase 2 commissioning of SuperKEKB, and is presently being improved in preparation for the higher luminosities expected during Phase 3.

French members:
C. Rimbault, Ph. Bambade, S. di Carlo, D. Jehanno, V. Kubytskyi, C.-G. Pang, Y. Peinaud

Japanese members:
S. Uehara, Y. Funakoshi, T. Kawamoto, M. Masuzawa, T. Oki

References:

[1] "Early Phase 2 Results of LumiBelle2 for the SuperKEKB Electron Ring", by S. Di Carlo et al.: THYGBE4, presented at the 9th International Particle Accelerator Conference (IPAC 2018), Vancouver, Canada, 29 April - 4 May 2018. Published in J.Phys.Conf.Ser. 1067 (2018) no.7, 072025. [2] "First Tests of SuperKEKB Fast Luminosity Monitors During 2018 Phase-2 Commissioning", by C. Pang et al.: WEPAL038, presented at the 9th International Particle Accelerator Conference (IPAC 2018), Vancouver, Canada, 29 April - 4 May 2018. [3] "Simulation Study on Luminosity Feedback for Horizontal Beam Stabilization at SuperKEKB", by C. Pang et al.: WEPAL037, presented at the 9th International Particle Accelerator Conference (IPAC 2018), Vancouver, Canada, 29 April - 4 May 2018. Published in J.Phys.Conf.Ser. 1067 (2018) no.7, 072023.

Website:
http://www-superkekb.kek.jp/
https://www.belle2.org/

Summary:
KEK and CEA/Irfu are pursuing their effort to improve technology related to ILC cavity production/surface treatment. Presently, main steps studied are :
- Cavity Fabrication at Cavity Fabrication Facility at KEK
- Vertical Electro-polishing of cavities (VEP set-up at CEA Saclay and at Marui Galavanizing Company ltd.)
Alternative environmental-friendly surface treatments are also investigated (Electro-chemical Buffing).
The proposal mainly consists in the continuous process of cavity from fabrication at KEK through surface treatment and test at Saclay.
The aim is to optimize the process with the view of an industrial fabrication of cavities.

French members:
T. Proslier, C. Antoine, S. Berry, F. Eozenou, A. Four, C. Madec, C. Servouin,

Japanese members:
T. Kubo, H. Hayano, S. Kato, H. Monjushiro, T. Saeki, M. Sawabe

References:
[1] K. Nii et al., “Vertical Electro-polishing of Nb single-cell cavity using cathode with variable-geometry wings and its results of vertical test”, LINAC 2014, MOPP108.
[2] C. Antoine et al., "Study of nanometric superconducting multilayers for magnetic field screening applications", Applied Physics Letters, 2013; 102(10):102603
[3] T. Kubo, "Multilayer coating for higher accelerating fields in superconducting radio-frequency cavities: a review of theoretical aspects", Superconductor Science and Technology, 30, 023001 (2017)

Summary:
As a demonstrator for Future Linear Colliders (FLC) with nanometer (nm) size e+-e- beams, ATF2 (Accelerator Test Facility) has achieved 44nm vertical beam size, very near to its 37nm goal. It is realized under low intensity beam and the studies on beam intensity dependence will continue. Next major step for our French and Japanese Teams is maintaining the beam position stability of 2nm at IP. To achieve this, numerous studies on Beam Position Monitors in a vacuum chamber with internal moving mechanisms were done. Two diamond strip sensor based scanners were installed for horizontal and vertical beam halo studies together with a vertical dedicated collimator. Clear cuts in the halo from upstream apertures were identified. Ground Motion sensors are being used for vibration source identification and for the development of a new Ground Motion feedforward acting on the beam stability. In addition, improvement of the QF1FF Final Focus magnet support has to be done. These studies will be of paramount importance for the preparation of the ILC, in this context the French team was invited to join a new KEK-based study group charged with re-optimizing ILC IP/BDS/DR parameters for a staged ILC project starting with a 250 GeV centre-of-mass energy. This program is the ideal framework for the training of students in the Accelerators Physics field.

French members:
A. Faus-Golfe, P. Bambade, F. Bogard, L. Brunetti, P. Cornebise, A. Jeremie, S. Wallon, R. Yang

Japanese members:
K. Kubo, S. Araki, S. Kuroda, Y. Morikawa, T. Naito, T. Okugi, T. Tauchi, N. Terunuma

References:
[1] G.White et al., Experimental Validation of a Novel Compact Focusing Scheme for Future Energy-Frontier Linear Lepton Colliders, Phys. Rev. Lett. 112 (2014) 034802
[2] T. Okugi et al., Linear and second order optics corrections for the KEK Accelerator Test Facility final focus beam line, Physical Review Special Topics - Accelerators and Beams 17, 023501 (2014)
[3] S. Liu et al., Design and high order optimization of the Accelerator Test Facility lattices, Physical Review Special Topics - Accelerators and Beams 17, 021002 (2014)
[4] D. Wang et al., In vacuum diamond sensor scanner for beam halo measurements in the beam line at the KEK Accelerator Test Facility, Nucl.Instrum.Meth. A832 (2016) 231-242
[5] Y. Renier et al., Trajectory measurements and correlations in the final focus beam line at the KEK Accelerator Test Facility, Physical Review Special Topics - Accelerators and Beams 16, 062803 (2013)
[6] P. Bambade et al., Present status and first results of the final focus beam line at the KEK Accelerator Test Facility, Phys. Rev. ST Accel. Beams 13, (2010) 042801
[7] D. Bett et al., GROUND MOTION COMPENSATION USING FEED-FORWARD CONTROL AT ATF2, WEPOR005, 7th International Particle Accelerator Conference (IPAC 2016), Busan, Korea, 8-13 May, 2016
[8] N. Fuster-Martinez et al., ATF2 Beam Halo Collimation Background and Wakefield Measurements in 2016 Runs, IPAC 2017
[9] R. Yang et al., Experimental Study of Halo Formation at ATF2, IPAC 2017
[10] R. Yang et al., Numerical Investigation of Beam Halo From Beam Gas Scattering in KEK-ATF, IPAC2017, published in J.Phys.Conf.Ser. 874 (2017) no.1, 012063

Website:
http://lcdev.kek.jp/ATF2/
http://atf.kek.jp/twiki/bin/view/Public/TopPageE?redirectedfrom=Public.WebHome

Summary:
In F.Y. 2017, KEK and CEA started the R&D for power coupler in SRF accelerator. First of all, the effect of the ultrasonic rinsing on copper plating was investigated. Consequently, in some cases, it turned out that the copper plating was peeled out, and in the other cases, there were white marks on the copper plating samples. This result was presented in LCWS2017. As next step, the residual resistivity ratio (RRR) is being investigated between KEK and CEA, because RRR is essential for the quality control of copper plating. Some types of copper plating samples were already fabricated, and tested. This preliminary result will be presented in LINAC2018. From F.Y. 2018, LAL newly joined this collaboration. In future, the effect of the ultrasonic rinsing will be investigated for the STF-type power couplers by collaboration between KEK and LAL. And also, impurity of copper plating will be investigated. Recently, KEK obtained some successful results in the measurement of secondary electron emission coefficient for some ceramic samples. For these ceramic samples, the rinsing effect will be investigated by collaboration of Japan-France.

French members:
W. Kaabi, H. Guler, C. Arcambal, E. Cenni

Japanese members:
Y .Yamamoto, E. Kako, A. Yamamoto, S. Michizono, T. Matsumoto, H. Sakai

References:
[1] Y. Yamamoto, et al., LCWS2017, Strasbourg, France (2017).
[2] Y. Yamamoto, et al., US-Japan ILC Cost Reduction Workshop, KEK, Japan (2017).
[3] Y. Yamamoto, et al., THPO097, LINAC2018, Beijing, China (2018).

Summary:
Field emission is one of the main issues for quality factor degradation at high gradient operation. We propose to develop a detection system equipped with scintillating fiber in order to precisely detect field emission sources on the cavity surface. Currently, this is achieved by PIN diodes that require long installation time and cannot be mounted on cavities in their final configuration (with helium tank).
The photon energy, produced by electrons impact on the cavity surface, can be estimated once the scintillating fibers are connected to a multi-channel analyzer. This will allow not only to detect the electron impact locations but also their energy, hence determine their origin more precisely respect to other detection systems.
A detection system prototype will be designed and manufactured with different fibers (geometry and composition) and equipped with photomultiplier and multi-channel analyzer

French members:
E. Cenni, J. Plouin

Japanese members :
Y. Yamamoto, H. Sakai, K. Umemori

References:
[1] H. Sakai, T. Furuya, T. Takahashi, S. Sakanaka, and K. Umemori, IPAC 10.
[2] Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, M. Sato, T. Shishido, K. Umemori, and K. Watanabe, in Proceeding PAC (2009).
[3] Y. Yamamoto, H. Hayano, E. Kako, S. Noguchi, T. Shishido, K. Umemori, K. Watanabe, H. Sakai, K. Shinoe, and S. I. Moon, SRF2007 Peking Univ Beijing China (2007).

Summary:
Positron sources are critical components of the future linear or circular collider projects. This is essentially due to the very high beam intensity required to achieve a high luminosity. Moreover, positron sources are complex devices, where each stage (production, capture, acceleration, injection strategy) has an impact on the final efficiency of the system. Therefore, the technology and design optimization has to be performed for the whole chain. The French (LAL/IPNL) and Japanese (KEK) groups have a long-standing collaboration on the positron source R&D since several years. Currently, two teams are working to improve the performance of the world’s highest intensity positron source in operation of SuperKEKB which is under commissioning now and design of the positron injector for the e+/e- Future Circular Collider FCC-ee. Final performance of the FCC-ee positron source will definitely benefit from the lessons learned during the SuperKEKB commissioning and operation.

French members:
I. Chaikovska, R. Chehab, H. Guler

Japanese members:
Y. Enomoto, K. Furukawa, T. Kamitani, F. Miyahara, M. Satoh, Y. Seimiya, T. Suwada, H. Sugimura

References:
[1] Y. Uesugi, T, Akagi, R. Chehab, O. Dadoun, K. Furukawa, T. Kamitani, S. Kawada, T. Omori (KEK), T. Takahashi, K. Umemori, J. Urakawa, M. Satoh, V. Strakhovenko, T. Suwada, A. Variola, Development of an intense positron source using crystal-amorphous hybrid target for linear colliders., NIM B, Volume 319, 2014, Pages17-23
[2] X. Artru, I. Chaikovska, R. Chehab, M. Chevallier, O. Dadoun, K. Furukawa, H. Guler, T. Kamitani, F. Miyahara, M. Satoh, P. Sievers, T. Suwada, K. Umemori, A. Variola, Investigations on a hybrid positron source with a granular target, NIM B, Volume 355, 2015, Pages 60-64
[3] I. Chaikovska, R. Chehab, H. Guler, P. Sievers, X. Artru, M. Chevallier, T. Suwada, M. Satoh, T. Kamitani, K. Furukawa, F. Miyahara, K. Umemori, S. Jin, Optimization of an hybrid positron source using channeling, NIM B, Volume 402, 2017, Pages 58-62

Summary:
High intensity photon beams have various applications in advanced accelerators, from medical imagery (X-rays) to high energy physics (polarized positron beams, photon colliders) passing by nuclear physics (fundamental and applied). They can be obtained by laser-Compton backscattering off electrons, the main advantage being the possibility to produce high flux monochromatic photon beams. In this context, an optical cavity is a unique system to reach the requested laser beam power at high repetition rates. LAL and KEK are developing such light sources and are trying to push forward the technical limits to increase the maximal power stored in these optical cavities. Alternative operations modes as self-resonating and burst are also studied.

French members:
A. Martens, L. Amoudry, K. Cassou, D. Nutarelli, R. Chiche, V. Soskov, F. Zomer

Japanese members:
A. Aryshev, Y. Honda, M. Fukuda, T. Omori, K. Sakaue, T. Takahashi

References :
[1] J Bonis et al 2012 JINST 7 P01017, http://dx.doi.org/10.1088/1748-0221/7/01/P01017
[2] T Akagi et al 2012 JINST 7 P01021, http://dx.doi.org/10.1088/1748-0221/7/01/P01021
[3] ThomX Technical Design Report, http://hal.in2p3.fr/in2p3-00971281
[4]Chaikovska et al, High flux circularly polarized gamma beam factory: coupling a Fabry-Perot optical cavity with an electron storage ring, Scientific Reports 6, Article number: 36569 (2016)
[5]Liu et al, Laser frequency stabilization using folded cavity and mirror reflectivity tuning, Optics Communications 369 (2016) 84–88.