New spiral beam screen design for the FCC-hh injection kicker magnet

Agnieszka Chmielinska
IOP PUBLISHING LTD, 2019
Article de conférence

Résumé

The injection kicker system for the Future Circular Collider (FCC-hh) must satisfy demanding requirements. To achieve low pulse ripple and fast field rise and fall times, the injection system will use ferrite loaded transmission line type magnets. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, interaction of the high intensity beam with the real part of the longitudinal beam coupling impedance can result in high power deposition in the ferrite yoke. This gives a significant risk that the ferrite yoke will exceed its Curie temperature: hence, a suitable beam screen will be a critical feature. In this paper, we present a novel concept a spiral beam screen. The fundamental advantage of the new design is a significant reduction of the maximum voltage induced on the screen conductors, thus decreased probability of electrical breakdown. In addition, the longitudinal beam coupling impedance is optimized to minimize power deposition in the magnet.

Official source

https://infoscience.epfl.ch/record/277265?ln=fr

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The Future Circular Collider for hadrons (FCC-hh) is a proposed high-energy frontier particle accelerator, which would be built in a new ~100 km circumference tunnel and would enable proton-proton collisions at a centre-of-mass energy of 100 TeV. The baseline injection energy is 3.3 TeV. The FCC-hh will require a fast injection kicker system that is highly reliable and does not limit accelerator performance. To achieve low ripple and fast rise and fall time field pulses, the injection system will use ferrite loaded transmission line type magnets. The FCC-hh will operate at high beam intensity: hence, the beam coupling impedance will be an issue. The problems are twofold: longitudinal and transverse impedance may drive beam instabilities, while the real part of the longitudinal impedance gives rise to beam induced heating. The power deposition in the kicker magnet can cause a temperature increase of the ferrite yoke above its Curie point: this would affect the ability to inject beam. For a high beam current and a short bunch length, a high power deposition would occur in unshielded FCC-hh injection kicker magnets: hence, a beam screen is a critical feature. Amongst the most challenging requirements for the beam screen are: low broadband beam coupling impedance, fast field rise and fall time, low field ripple during the flat-top field and good high voltage behaviour. In this thesis, we propose and develop a novel concept of a spiral beam screen. The fundamental advantage of the new design, in comparison to the conventional straight screen conductors used for example in the LHC injection kickers, is a significant reduction of the maximum voltage induced on the conductors, thus a greatly reduced probability of an electrical breakdown of the beam screen. Also, the spiral screen design allows a reduction of the maximum transverse beam coupling impedance of the kicker system. Both the conventional and spiral designs are studied from a theoretical, a numerical, and an experimental point of view. Important new contributions brought to the field of kicker magnets include: real-time data analysis of the output waveform of the LHC kicker magnet to ensure the ferrite yoke is below its Curie point; a new CST and PSpice model of the FCC-hh injection kicker magnets; proposal and development of new calculation and measurement methods for determining power loss distribution in the ferrite of a kicker magnet; and novel measurements of the electromagnetic properties of ferrites as a function of frequency and temperature.

EPFL2019

Chargement

Helical beam screen for the Future Circular Collider for hadrons injection kicker magnets

Agnieszka Chmielinska

The Future Circular Collider for hadrons (FCC-hh) is the proposed high-energy frontier particle collider, which is expected to enable proton-proton collisions at a center-of-mass energy of 100 TeV. The specifications for the FCC-hh injection kicker system are very challenging. To provide fast magnetic field rise and fall times, and low ripple during the flat-top, ferrite loaded transmission line type magnets will be used. To limit the beam coupling impedance, a suitable beam screen will be placed in the aperture of each kicker magnet. Due to issues associated with the "conventional" beam screen design, used in the injection kickers magnets of the Large Hadron Collider (LHC), such as high voltage (HV) breakdowns and yoke heating problems, we have developed a novel concept of a helical beam screen. The fundamental advantage of the new design, in comparison to the conventional beam screen, is a significant reduction of the maximum voltage induced on the screen conductors, thus a greatly reduced probability of an electrical breakdown of the beam screen. In addition, the longitudinal beam coupling impedance of the helical beam screen is optimized to reduce power deposition in the kicker magnet. Furthermore, the helical beam screen allows a reduction of the maximum transverse beam coupling impedance of the kicker system. Detailed numerical simulations, theoretical studies and experimental results demonstrate that a new design is a promising solution not only for the FCC-hh, but also for existing machines.

2020

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EPFL2019