IPAC2018 - List of Authors (Baudrenghien, P.)

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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MOPMF039	First Xenon-Xenon Collisions in the LHC	180
	M. Schaumann, R. Alemany-Fernández, P. Baudrenghien, T. Bohl, C. Bracco, R. Bruce, N. Fuster-Martínez, M.A. Jebramcik, J.M. Jowett, T. Mertens, D. Mirarchi, S. Redaelli, B. Salvachua, M. Solfaroli, H. Timko, J. Wenninger CERN, Geneva, Switzerland
	In 2017, the CERN accelerator complex once again demonstrated its flexibility by producing beams of a new ion species, xenon, that were successfully injected into LHC. On 12 October, collisions of fully stripped xenon nuclei were recorded for the first time in the LHC at a centre-of-mass energy per colliding nucleon pair of 5.44 TeV. Physics data taking started 9.5 h after the first injection of xenon beams and lasted a total of 6 h. The integrated luminosity delivered to the four LHC experiments was sufficient that new physics results can be expected soon. We provide a general overview of this Xe-Xe pilot run before focussing on beam data at injection energy and at flat-top.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF039
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THPML121	Compensation of Transient Beam Loading in Ramping Synchrotrons Using a Fixed Frequency Processing Clock	4957
SUSPL061	use link to see paper's listing under its alternate paper code
	F.J. Galindo Guarch, J.M.M.A. Moreno Arostegui Universitat Politécnica de Catalunya, Barcelona, Spain P. Baudrenghien, F.J. Galindo Guarch CERN, Geneva, Switzerland
	Transient beam loading compensation schemes, such as One-Turn-FeedBack (OTFB), require beam synchronous processing (BSP). Swept clocks derived from the RF, and therefore harmonic to the revolution frequency, are widely used in CERN synchrotrons; this simplifies implementation with energy ramping, where the revolution frequency changes. It is however not optimal for state-of-the-art digital hardware that prefers fixed frequency clocks. An alternative to the swept clocking is the use of a deterministic protocol, for example, White Rabbit (WR): a fixed reference clock can be extracted from its data stream, while enabling digital distribution of the RF frequency among other data. New algorithms must be developed for BSP using this fixed clock and the digital data transmitted on the WR link. This is the strategy adopted for the SPS Low Level RF (LLRF) upgrade. The paper gives an overview of the technical, technological and historical motivations for such a paradigm evolution. It lists the problems of fixed clock BSP, and presents an innovative solution based on a real-time variable ratio re-sampler for implementing an OTFB with the new fixed clock scheme.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML121
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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)

MOPMF039

First Xenon-Xenon Collisions in the LHC

180

M. Schaumann, R. Alemany-Fernández, P. Baudrenghien, T. Bohl, C. Bracco, R. Bruce, N. Fuster-Martínez, M.A. Jebramcik, J.M. Jowett, T. Mertens, D. Mirarchi, S. Redaelli, B. Salvachua, M. Solfaroli, H. Timko, J. Wenninger
CERN, Geneva, Switzerland

In 2017, the CERN accelerator complex once again demonstrated its flexibility by producing beams of a new ion species, xenon, that were successfully injected into LHC. On 12 October, collisions of fully stripped xenon nuclei were recorded for the first time in the LHC at a centre-of-mass energy per colliding nucleon pair of 5.44 TeV. Physics data taking started 9.5 h after the first injection of xenon beams and lasted a total of 6 h. The integrated luminosity delivered to the four LHC experiments was sufficient that new physics results can be expected soon. We provide a general overview of this Xe-Xe pilot run before focussing on beam data at injection energy and at flat-top.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF039

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

THPML121

Compensation of Transient Beam Loading in Ramping Synchrotrons Using a Fixed Frequency Processing Clock

4957

SUSPL061

use link to see paper's listing under its alternate paper code

F.J. Galindo Guarch, J.M.M.A. Moreno Arostegui
Universitat Politécnica de Catalunya, Barcelona, Spain
P. Baudrenghien, F.J. Galindo Guarch
CERN, Geneva, Switzerland

Transient beam loading compensation schemes, such as One-Turn-FeedBack (OTFB), require beam synchronous processing (BSP). Swept clocks derived from the RF, and therefore harmonic to the revolution frequency, are widely used in CERN synchrotrons; this simplifies implementation with energy ramping, where the revolution frequency changes. It is however not optimal for state-of-the-art digital hardware that prefers fixed frequency clocks. An alternative to the swept clocking is the use of a deterministic protocol, for example, White Rabbit (WR): a fixed reference clock can be extracted from its data stream, while enabling digital distribution of the RF frequency among other data. New algorithms must be developed for BSP using this fixed clock and the digital data transmitted on the WR link. This is the strategy adopted for the SPS Low Level RF (LLRF) upgrade. The paper gives an overview of the technical, technological and historical motivations for such a paradigm evolution. It lists the problems of fixed clock BSP, and presents an innovative solution based on a real-time variable ratio re-sampler for implementing an OTFB with the new fixed clock scheme.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML121

Export •

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