eeFACT2018 - List of Authors (Ohmi, K.)

Paper	Title	Page
TUOAB04	Optics Corrections including IP Local Coupling at SuperKEKB	63
	A. Morita, H. Koiso, K. Ohmi, Y. Ohnishi, H. Sugimoto, D. Zhou KEK, Ibaraki, Japan
	The phase-2 commissioning of the SuperKEKB accelerator with the interaction point(IP) has been performed from March 19 to July 17. In the collision operation during this commissioning, the vertical beta function at the IP was squeezed down to 3mm. In order to achieve such low beta collision operation, many optics corrections were performed. We present the result of those optics measurement and correction.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUOAB04
About •	paper received ※ 12 October 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019
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TUOBB01	Optics Aberration at IP and Beam-beam Effects	66
	K. Ohmi, Y. Funakoshi, H. Koiso, A. Morita, Y. Ohnishi, D. Zhou KEK, Ibaraki, Japan K. Hirosawa Sokendai, Ibaraki, Japan
	Collision in SuperKEKB phase II commissioning has started in April 2018. Luminosity was lower than the geomterical value even in very low bunch current. Linear x-y coupling at IP caused by skew of QCS was conjectured as error source. x-y coupling correction using skew corrector of QCS resulted in luminosity recover of 2 times. After the QCS skew correction, luminosity is still limited at relatively low bunch current. Nonlinear x-y coupling at IP is conjectured as a source of the luminosity limitation. We discuss effects of linear and nonlinear x-y coupling at IP on the beam-beam performance.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUOBB01
About •	paper received ※ 25 September 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019
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TUOBB02	Off-momentum Optics at SuperKEKB	71
	Y. Ohnishi, H. Koiso, A. Morita, K. Ohmi, H. Sugimoto KEK, Ibaraki, Japan K. Oide CERN, Meyrin, Switzerland
	The nano-beam scheme can squeeze the vertical beta function at the IP much smaller than the bunch length. It implies that the large chromaticity is generated in the vicinity of the final focus quadrupole magnets and the strong sextupoles are adopted to correct the chromaticity, for instance the local chromaticity corrections. While understanding of the off-momentum optics is important to optimize the dynamic aperture to make Touschek lifetime long and to reduce the luminosity degradation due to chromatic behaviors. In general, there is a discrepancy between measurements and those obtained from the optics model. The chromatic phase-advance is introduced to measure the off-momentum optics and correct by using sextupole magnets.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUOBB02
About •	paper received ※ 12 October 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUYAA04	Study to Mitigate Electron Cloud Effect in SuperKEKB	95
	Y. Suetsugu, H. Fukuma, K. Ohmi, K. Shibata, M. Tobiyama KEK, Ibaraki, Japan
	During Phase-1 commissioning of the SuperKEKB from February to June 2016, electron cloud effects (ECE) were observed in the positron ring. The electron clouds were considered to exist in the beam pipes in the drift spaces of the ring, where the beam pipes have antechambers and titanium nitride (TiN) coating as countermeasures against ECE. Following this, permanent magnets and solenoids were attached to the beam pipes as additional countermeasures. Consequently, during Phase-2 commissioning from March to July 2018, experiments showed that the threshold beam current for exciting ECE increased by a factor of at least two relative to that during Phase-1 commissioning. While the countermeasures were strengthened, the effectiveness of the antechambers and TiN film coating was re-evaluated. From various simulations and experiments during Phase-2 commissioning, the antechamber was found to be less effective than expected with regard to reducing the number of photoelectrons in the beam channel. The TiN film coating, on the other hand, was considered to have a low secondary electron yield as expected.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUYAA04
About •	paper received ※ 27 September 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUYBA01	Benchmarking of Simulations of Coherent Beam-beam Instability	103
	K. Ohmi, H. Koiso, Y. Ohnishi KEK, Ibaraki, Japan D. El Khechen CERN, Geneva, Switzerland K. Hirosawa Sokendai, Ibaraki, Japan
	Coherent beam-beam nstability in head-tail mode has been predicted in collision with a large crossing angle. The instability is serious for design of future e⁺e⁻ colliders based on the large crossing angle collision. It is possible to observe the instability in SuperKEKB commissioning. Horizontal beam size blow-up of both beams has been seen depending on the tune operating point. We report the measurement results of the instability in SuperKEKB phaseII commissioning.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUYBA01
About •	paper received ※ 25 September 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Optics Corrections including IP Local Coupling at SuperKEKB

63

A. Morita, H. Koiso, K. Ohmi, Y. Ohnishi, H. Sugimoto, D. Zhou
KEK, Ibaraki, Japan

The phase-2 commissioning of the SuperKEKB accelerator with the interaction point(IP) has been performed from March 19 to July 17. In the collision operation during this commissioning, the vertical beta function at the IP was squeezed down to 3mm. In order to achieve such low beta collision operation, many optics corrections were performed. We present the result of those optics measurement and correction.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUOAB04

About •

paper received ※ 12 October 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUOBB01

Optics Aberration at IP and Beam-beam Effects

66

K. Ohmi, Y. Funakoshi, H. Koiso, A. Morita, Y. Ohnishi, D. Zhou
KEK, Ibaraki, Japan
K. Hirosawa
Sokendai, Ibaraki, Japan

Collision in SuperKEKB phase II commissioning has started in April 2018. Luminosity was lower than the geomterical value even in very low bunch current. Linear x-y coupling at IP caused by skew of QCS was conjectured as error source. x-y coupling correction using skew corrector of QCS resulted in luminosity recover of 2 times. After the QCS skew correction, luminosity is still limited at relatively low bunch current. Nonlinear x-y coupling at IP is conjectured as a source of the luminosity limitation. We discuss effects of linear and nonlinear x-y coupling at IP on the beam-beam performance.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUOBB01

About •

paper received ※ 25 September 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUOBB02

Off-momentum Optics at SuperKEKB

71

Y. Ohnishi, H. Koiso, A. Morita, K. Ohmi, H. Sugimoto
KEK, Ibaraki, Japan
K. Oide
CERN, Meyrin, Switzerland

The nano-beam scheme can squeeze the vertical beta function at the IP much smaller than the bunch length. It implies that the large chromaticity is generated in the vicinity of the final focus quadrupole magnets and the strong sextupoles are adopted to correct the chromaticity, for instance the local chromaticity corrections. While understanding of the off-momentum optics is important to optimize the dynamic aperture to make Touschek lifetime long and to reduce the luminosity degradation due to chromatic behaviors. In general, there is a discrepancy between measurements and those obtained from the optics model. The chromatic phase-advance is introduced to measure the off-momentum optics and correct by using sextupole magnets.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUOBB02

About •

paper received ※ 12 October 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUYAA04

Study to Mitigate Electron Cloud Effect in SuperKEKB

95

Y. Suetsugu, H. Fukuma, K. Ohmi, K. Shibata, M. Tobiyama
KEK, Ibaraki, Japan

During Phase-1 commissioning of the SuperKEKB from February to June 2016, electron cloud effects (ECE) were observed in the positron ring. The electron clouds were considered to exist in the beam pipes in the drift spaces of the ring, where the beam pipes have antechambers and titanium nitride (TiN) coating as countermeasures against ECE. Following this, permanent magnets and solenoids were attached to the beam pipes as additional countermeasures. Consequently, during Phase-2 commissioning from March to July 2018, experiments showed that the threshold beam current for exciting ECE increased by a factor of at least two relative to that during Phase-1 commissioning. While the countermeasures were strengthened, the effectiveness of the antechambers and TiN film coating was re-evaluated. From various simulations and experiments during Phase-2 commissioning, the antechamber was found to be less effective than expected with regard to reducing the number of photoelectrons in the beam channel. The TiN film coating, on the other hand, was considered to have a low secondary electron yield as expected.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUYAA04

About •

paper received ※ 27 September 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUYBA01

Benchmarking of Simulations of Coherent Beam-beam Instability

103

K. Ohmi, H. Koiso, Y. Ohnishi
KEK, Ibaraki, Japan
D. El Khechen
CERN, Geneva, Switzerland
K. Hirosawa
Sokendai, Ibaraki, Japan

Coherent beam-beam nstability in head-tail mode has been predicted in collision with a large crossing angle. The instability is serious for design of future e⁺e⁻ colliders based on the large crossing angle collision. It is possible to observe the instability in SuperKEKB commissioning. Horizontal beam size blow-up of both beams has been seen depending on the tune operating point. We report the measurement results of the instability in SuperKEKB phaseII commissioning.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-eeFACT2018-TUYBA01

About •

paper received ※ 25 September 2018 paper accepted ※ 19 February 2019 issue date ※ 21 April 2019

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)