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, A. Pastushenko, V. Cilento, L. Brunetti, A. Jeremie, G. Balik, M. Serluca

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

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:
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, V. Kubytskyi, Y. Han, B. Bai

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

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:

French members:
L. Brunetti, G. Balik, M. Serluca, E. Muza, P. Bambade, S. Wallon, S. Di Carlo

Japanese members:
M. Mazusawa, H. Yamaoka

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:
D. Nutarelli, A. Martens, L. Amoudry, K. Cassou, 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.

Summary:

French members:
J. Plouin, E. Cenni, C. Marchand, T. Proslier

Japanese members:
M. Masuzawa, K. Umemori, K. Tsuchiya, R. Ueki, T. Okada

Summary:
Large-scale production of superconducting radio-frequency (SRF) cavities is an industrial challenge, not only because of the increasing number of unit for future projects but also because of requirements in term of reliability, reproducibility and performances very close to the physical limit of polycrystalline bulk Niobium. Challenging SRF accelerator projects like ILC (International Linear Collider) and FCC (Future Circular Collider) are being studied. For such large-scale facilities, higher performances, reduction in fabrication and operation costs are required and essential to proceed with industrialization. An alternative pathway to reduce these costs and improve performances has been proposed by C. Antoine (CEA).

Firstly, it consists in applying directly on Niobium sheets an optimized metallographic polishing procedure aiming at removing the damaged layer generated during Niobium sheet manufacturing. This process has been studied in the framework of H2020 European program, European Nuclear Science and Applications Research - 2 (ENSAR2) project (grant agreement N°654002) in collaboration with CEA/IRFU.

Secondly, polished Niobium sheets have to be formed and welded to build an elliptical cavity. However, conventional forming techniques might not be applicable as this process would damage too significantly the pre-polished surfaces. All the benefits of the high-quality metallographic polishing would then be lost as a conventional chemical treatment would need to be performed.

The aim of this collaborative proposal is to address this second step of the alternative pathway for cavity fabrication. KEK has the experience, ability and facilities to build elliptical cavities. IJCLab/IRFU have the ability and equipment to perform the optimized metallographic polishing procedure for SRF applications and proceed with surface characterization. Sharing and combining our experience and effort will allow us to address, in a very efficient manner, the second step of this alternative pathway.

French members:
D. Longuevergne, C. Antoine, O. Hryhorenko

Japanese members:
T. Dohmae, W. Yuichi, M. Yamanaka, K. Umemori

References:
[1] “Metallographic Polishing Pathway to the Future of Large Scale SRF Facilities”, O Hryhorenko, CZ Antoine, M Chabot, D Longuevergne, 19th Int. Conf. on RF Superconductivity (SRF'19), Dresden, Germany, 2019.
[2] Oleksandr Hryhorenko. "Development and optimization of mechanical polishing process for superconducting accelerating cavities". Accelerator Physics [physics.acc-ph]. Université Paris-Saclay, 2019. English. ffNNT : 2019SACLS566ff. fftel-02455975.

Summary:
Field emission is one of the main reasons for the degradation of superconducting cavity quality factor. Its presence can limit the ultimate performances of superconducting RF (SRF) cavities and hence the cryomodule in which they are assembled. In general, the field emitted current tends to become more severe during the beam operation. Hence, it can affect the entire machine final performance. Dust particles on the cavity surface is one of the most common source of contamination leading to field emission during the cavity operation. For these reasons, it is essential to better understand how this phenomenon is generated and evolve from the SRF cavity preparation, in the clean room, through their assembly in the cryomodule until their final test and operation on the machine.

French members:
E. Cenni, S. Berry, M. Baudrier, L. Maurice, J. Plouin

Japanese members:
H. Sakai, K. Umemori

Summary:

French members:
M. Fouaidy, D. Longuevergne, G. Martinet, E. Cenni

Japanese members:
K. Umemori, E. Kako, H. Sakai, T. Konomi, M. Omet, R. Katayama, H. Itoh, T. Okada, K. Takahashi

Summary:

French members:
F. Eozenou, T. Proslier, C. Madec, C. Antoine, S. Berry, E. Cenni, C. Servouin

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

Summary:
The goal of our project is to investigate and demonstrate of the use of Machine Learning (ML) techniques for advanced control and performance optimization of the accelerators and in particular the KEK injector. We search for very precise control and stability of the beams, better understanding of multi-parameter non-linear system with profound feature importance analysis. There are tree major steps in this project. One is the collection, processing, alignment, understanding and labelling of the raw data (machine parameters, diagnostics, BPMs etc, temperatures) to form the dataset for further deep learning. The next step is the development of the ML models, training, test and validation of several architectures of deep neural networks (DNNs) and convolutional neural networks (CNNs). Understanding of the models robustness with respect to the noise of different origins is crucial. The final step is tests of the models on the live data from the machine and analysis of the improvements of the Linac performance. The predicted parameters then could be inserted to the EPICS data channel for the monitoring purposes.

French members:
V. Kubytskyi, H. Guler, I. Chaikovska

Japanese members:
M. Satoh, I. Satake, F. Miyahara, K. Furukawa