Compensated Phase Jump at Transition Crossing in the CERN PS

The transition energy must be crossed in the CERN PS to accelerate proton and ion beams to flat-top energy. A phase jump of the accelerating RF voltage with respect to the phase of the bunches by about 180 degrees minus twice the synchronous phase is required at the instant of transition. This phase offset is injected into the beam phase loop which locks the phase of the vector sum of the RF voltage in the cavities to the beam. The polarities of the cavity return signal and of the stable phase programme are usually flipped at transition. However, both actions are difficult to perfectly synchronize in time, causing the beam phase loop to partially lock out and relock at the new stable phase. The resulting glitch can be avoided by well-controlled phase jumps applied to both, cavity drive and return signals simultaneously. This improved implementation of transition crossing makes it virtually transparent to the beam phase loop. The new scheme has been successfully tested with proton and ion beams, and it will become fully operational in the CERN PS after the long shutdown.Comment: Poster presented at LLRF Workshop 2019 (LLRF2019, arXiv:1909.06754

High-precision RF voltage measurements using longitudinal phase-space tomography in CERN PSB and SPS

Precisely determining the gap voltage and phase in an RF cavity is essential for the calibration of the LLRF feedbacks. Following the conventional approach, measured RF power is converted into gap voltage, assuming a given shunt impedance. However, power and impedance evaluations can both have large uncertainties. Alternatively, the voltage can be obtained precisely with a technique based on longitudinal phase-space tomography. From a set of bunch profiles, tomography reconstructs the bunch distribution in the longitudinal phase-space. The quality of the reconstruction strongly depends on the RF voltage and therefore allows to derive its absolute value. In this paper we describe the tomography-based voltage measurements performed in the CERN PSB and SPS, where this method allowed to detect significant voltage errors for the main RF systems. After applying the correction factors in the LLRF, 1\% accuracies were reached. We report here also the remarkable results achieved by using this technique to calibrate the voltage of the SPS higher-harmonic cavities at 800 MHz, as well as their relative phases with respect to the 200 MHz cavities.Comment: Talk presented at LLRF Workshop 2023 (LLRF2023, arXiv: 2310.03199

Towards a muon collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work

Towards a Muon Collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.Comment: 118 pages, 103 figure

Erratum: Towards a muon collider

The original online version of this article was revised: The additional reference [139] has been added. Tao Han’s ORICD ID has been incorrectly assigned to Chengcheng Han and Chengcheng Han’s ORCID ID to Tao Han. Yang Ma’s ORCID ID has been incorrectly assigned to Lianliang Ma, and Lianliang Ma’s ORCID ID to Yang Ma. The original article has been corrected

Towards a muon collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work

CAS course on "RF for Accelerators", 18 June - 01 July 2023, Berlin Germany

Beyond increasing the energy of charged particles, RF frequency systems in accelerators allow to control longitudinal beam properties like distance between the bunches, their length, position in time, as well as the orbit length in a synchrotron. This is essential to adapt the beam parameters to the requirements of experiments or downstream accelerators. Already with a single-harmonic RF system a variety of manipulations to bunch or de-bunch a beam and to control the bunch length can be performed. More flexibility is reached with multiple RF systems, often at different harmonic numbers of the revolution frequency. For example, a change of harmonic number to merge or split bunches, respectively doubles, or halves the intensity per bunch. A sequential increase of the RF harmonic can also be applied to reduce bunch spacing. Even more evolved RF manipulations become possible with non-sinusoidal RF systems driving wide-band RF cavities, gaining almost full control of the longitudinal beam structure. Special attention is moreover paid to the technical implementation of RF manipulations, complemented by examples of applications in major accelerator facilities

CAS course on "RF for Accelerators", 18 June - 01 July 2023, Berlin Germany

Radio-frequency (RF) systems in particle accelerators are usually designed to transfer energy to the beam or to define its longitudinal structure. However, charged particles passing through an RF cavity induce a voltage which acts back on themselves and on subsequent particles. The additional contribution of the beam to the cavity voltage moreover changes the effective properties of the RF system and is generally referred to as beam loading. The fundamental theorem of beam loading is introduced to derive the effect of a single bunch passage through an RF cavity. The choice of the cavity parameters, notably shunt impedance divided by quality factor, plays an important role to reduce the beam induced voltage. Extending the single bunch case to the periodic passage of bunches allows to calculate the steady state cavity detuning due to beam loading for a continuous bunch pattern. Special emphasis is given to the partially filled ring, with gaps in the filling pattern, which is the most common case of transient beam loading in electron and hadron synchrotrons