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Volume 16
Issue 12
10.3390/app16125733
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This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Article

S-Band Klystron Intra-Pulse Phase Feedback Upgrade at SPARC_LAB Facility

by
Xianghe Fang
1,2,*,
Marco Bellaveglia
1,
Alessandro Gallo
1,
Riccardo Magnanimi
1,
Andrea Michelotti
1,
Sergio Quaglia
1,
Michele Scampati
1,
Giorgio Scarselletta
1,
Beatrice Serenellini
1,
Simone Tocci
1 and
Luca Piersanti
1,*
1
Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare, Via Enrico Fermi 54, 00044 Frascati, Italy
2
Dipartimento di Fisica, Sapienza Università di Roma, 00185 Roma, Italy
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2026, 16(12), 5733; https://doi.org/10.3390/app16125733
Submission received: 31 March 2026 / Revised: 27 May 2026 / Accepted: 29 May 2026 / Published: 6 June 2026
(This article belongs to the Special Issue New Challenges in Plasma Accelerators)
Versions Notes

Abstract

One of the main technological challenges in plasma wakefield acceleration (PWFA) research and development is achieving stable and reproducible acceleration. In particular, for PWFA schemes based on particle-driven plasma wave excitation, beam stability and timing jitter are increasingly critical. In these configurations, magnetic or radio-frequency (RF) compression schemes are often used, and the beam time-of-arrival jitter at the end of the linear accelerator can be strongly correlated with the phase noise of RF accelerating structures operated off-crest. For this reason, since 2008, an RF phase fast-feedback system acting within each RF pulse has been successfully implemented at Laboratori Nazionali di Frascati, Istituto Nazionale di Fisica Nucleare (LNF-INFN) at the Sources for Plasma Accelerators and Radiation Compton with Laser And Beam (SPARC_LAB) facility, operating on both S-band ( 2.856 GHz) and C-band ( 5.712 GHz) klystrons. This paper presents the upgrade and optimization of the fast-feedback system for an S-band klystron powered by a pulse-forming network modulator. This technology introduces significantly higher intrinsic phase noise than, for instance, solid state-based modulators. It is therefore essential to minimize such phase fluctuations to keep the machine stability under control. Both the feedback hardware (electronic boards and RF circuitry) and the software (controller and user interface) have been upgraded. Tests performed at SPARC_LAB achieved a reduction in klystron-induced jitter of a factor of 30, reaching values below 15 fs rms on both power plants. Moreover, adding a remote control of the feedback loop enabled a straightforward optimization of the operating point, allowing the phase stability performance to be pushed close to its practical limits. A detailed analysis of RF phase noise measurements with the fast-feedback loop in operation is also presented.
Keywords: plasma wakefield acceleration; radio frequency; synchronization; timing jitter; phase noise; feedbacks; controls plasma wakefield acceleration; radio frequency; synchronization; timing jitter; phase noise; feedbacks; controls

Share and Cite

MDPI and ACS Style

Fang, X.; Bellaveglia, M.; Gallo, A.; Magnanimi, R.; Michelotti, A.; Quaglia, S.; Scampati, M.; Scarselletta, G.; Serenellini, B.; Tocci, S.; et al. S-Band Klystron Intra-Pulse Phase Feedback Upgrade at SPARC_LAB Facility. Appl. Sci. 2026, 16, 5733. https://doi.org/10.3390/app16125733

AMA Style

Fang X, Bellaveglia M, Gallo A, Magnanimi R, Michelotti A, Quaglia S, Scampati M, Scarselletta G, Serenellini B, Tocci S, et al. S-Band Klystron Intra-Pulse Phase Feedback Upgrade at SPARC_LAB Facility. Applied Sciences. 2026; 16(12):5733. https://doi.org/10.3390/app16125733

Chicago/Turabian Style

Fang, Xianghe, Marco Bellaveglia, Alessandro Gallo, Riccardo Magnanimi, Andrea Michelotti, Sergio Quaglia, Michele Scampati, Giorgio Scarselletta, Beatrice Serenellini, Simone Tocci, and et al. 2026. "S-Band Klystron Intra-Pulse Phase Feedback Upgrade at SPARC_LAB Facility" Applied Sciences 16, no. 12: 5733. https://doi.org/10.3390/app16125733

APA Style

Fang, X., Bellaveglia, M., Gallo, A., Magnanimi, R., Michelotti, A., Quaglia, S., Scampati, M., Scarselletta, G., Serenellini, B., Tocci, S., & Piersanti, L. (2026). S-Band Klystron Intra-Pulse Phase Feedback Upgrade at SPARC_LAB Facility. Applied Sciences, 16(12), 5733. https://doi.org/10.3390/app16125733

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