IPAC2018 - List of Authors (Apsimon, R.)

Paper	Title	Page
MOPMF022	Luminosity Reduction Caused by the Full-Detuning LLRF Scheme on the HL-LHC Crab Cavities	129
	E. Yamakawa, R. Apsimon, A.C. Dexter Cockcroft Institute, Lancaster University, Lancaster, United Kingdom P. Baudrenghien, R. Calaga, F.J. Galindo Guarch CERN, Geneva, Switzerland
	The High-Luminosity LHC (HL-LHC) crab cavities (CCs) will be installed on both sides of IP1 (ATLAS) and IP5 (CMS) to compensate for the geometric luminosity reduction due to the crossing angle. To cope with the increased beam current (0.55 A DC for LHC, 1.1 A for HL-LHC), the operation of the LLRF system has been changed: rather than fully compensating the transient beam loading, we allow the phase to vary along the turn (100 ps peak-peak with 1.1 A DC). This has been implemented at LHC since July 2017. The CCs have high loaded Q (5e5) and the available RF power is insufficient to follow the bunch phase modulation. The crabbing voltage is not modulated, causing a phase error w.r.t. the individual bunch centroids, leading to transverse kicks of the centroids and an asymmetric crabbing of the bunch cores. We present an analytical model for the resulting luminosity reduction and validate with particle tracking simulations. Due to the symmetry of the bunch filling patterns for the counter-rotating beams, the peak luminosity is reduced by only 2% for nominal HL-LHC parameters at IPs 1 and 5, which is within tolerable limits.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF022
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THPAL084	An X-Band Lineariser for the CLARA FEL	3848
	L.S. Cowie, A.D. Brynes, J.K. Jones, A.E. Wheelhouse, P.H. Williams STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom R. Apsimon, G. Burt, W.L. Millar Cockcroft Institute, Lancaster University, Lancaster, United Kingdom Ö. Mete UMAN, Manchester, United Kingdom A.J. Moss STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	The CLARA FEL at Daresbury Laboratory will employ four S-band linacs to accelerate electron bunches to 250 MeV/c. In order to compress the bunch sufficiently to achieve peak currents suitable for FEL lasing, one must compensate for curvature imprinted on the longitudinal phase space of the bunch. For CLARA a harmonic RF linearization system has been designed to achieve this requirement. The linearization will be achieved by an X-band travelling wave cavity of the PSI/CERN design, which incorporates wake-field monitoring of the bunch position. A five-axis mover will align the cavity to the beam axis. Pulse compression of a 6 MW klystron pulse will provide the required power to achieve a 30 MV/m operational gradient.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL084
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Luminosity Reduction Caused by the Full-Detuning LLRF Scheme on the HL-LHC Crab Cavities

129

E. Yamakawa, R. Apsimon, A.C. Dexter
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
P. Baudrenghien, R. Calaga, F.J. Galindo Guarch
CERN, Geneva, Switzerland

The High-Luminosity LHC (HL-LHC) crab cavities (CCs) will be installed on both sides of IP1 (ATLAS) and IP5 (CMS) to compensate for the geometric luminosity reduction due to the crossing angle. To cope with the increased beam current (0.55 A DC for LHC, 1.1 A for HL-LHC), the operation of the LLRF system has been changed: rather than fully compensating the transient beam loading, we allow the phase to vary along the turn (100 ps peak-peak with 1.1 A DC). This has been implemented at LHC since July 2017. The CCs have high loaded Q (5e5) and the available RF power is insufficient to follow the bunch phase modulation. The crabbing voltage is not modulated, causing a phase error w.r.t. the individual bunch centroids, leading to transverse kicks of the centroids and an asymmetric crabbing of the bunch cores. We present an analytical model for the resulting luminosity reduction and validate with particle tracking simulations. Due to the symmetry of the bunch filling patterns for the counter-rotating beams, the peak luminosity is reduced by only 2% for nominal HL-LHC parameters at IPs 1 and 5, which is within tolerable limits.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF022

Export •

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

THPAL084

An X-Band Lineariser for the CLARA FEL

3848

L.S. Cowie, A.D. Brynes, J.K. Jones, A.E. Wheelhouse, P.H. Williams
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
R. Apsimon, G. Burt, W.L. Millar
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
Ö. Mete
UMAN, Manchester, United Kingdom
A.J. Moss
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

The CLARA FEL at Daresbury Laboratory will employ four S-band linacs to accelerate electron bunches to 250 MeV/c. In order to compress the bunch sufficiently to achieve peak currents suitable for FEL lasing, one must compensate for curvature imprinted on the longitudinal phase space of the bunch. For CLARA a harmonic RF linearization system has been designed to achieve this requirement. The linearization will be achieved by an X-band travelling wave cavity of the PSI/CERN design, which incorporates wake-field monitoring of the bunch position. A five-axis mover will align the cavity to the beam axis. Pulse compression of a 6 MW klystron pulse will provide the required power to achieve a 30 MV/m operational gradient.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAL084

Export •

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