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Person# Michael Schenk

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The Large Hadron Collider (LHC) is the world's largest and highest-energy particle collider. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008 in collaborat

The Future Circular Collider (FCC) is a proposed particle accelerator with an energy significantly above that of previous circular colliders, such as the Super Proton Synchrotron, the Tevatron, and

Physics is the natural science of matter, involving the study of matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. Phy

Related units (1)

Transverse collective instabilities induced by the beam-coupling impedance of the accelerator structure lead to beam quality degradation and pose a major limitation to the machine performance. Landau damping, a powerful stabilising mechanism that can be employed against various types of instabilities, is present in the transverse planes when there is a betatron frequency spread among the beam particles. Traditional approaches use octupole magnets to introduce betatron detuning with the transverse particle oscillation amplitudes. Their damping efficiency depends on the transverse geometric beam emittances which decrease with increasing beam energy and brightness. For the Future Circular Collider (FCC) they may hence no longer be the most suitable instability mitigation tool. Within the framework of this PhD thesis a novel approach to Landau damping is studied from the theoretical, numerical, and experimental points-of-view. The novelty of the method is to introduce the betatron frequency spread through detuning with the longitudinal instead of the transverse amplitudes. This is motivated by the fact that in typical high-energy proton machines the longitudinal emittance is several orders of magnitude larger compared to the transverse ones. Two equivalent detuning schemes are considered: a radio-frequency (rf) quadrupole cavity and nonlinear chromaticity.
The first achievement of the project is the development of the Vlasov theory for nonlinear chromaticity to provide the analytical foundation for the novel Landau damping technique. The formalism is validated successfully against the circulant matrix model and the PyHEADTAIL tracking code. Based on the new theory, two beam dynamics effects introduced by detuning with longitudinal amplitude are identified: Landau damping and a change of the effective impedance altering the head-tail instability formation mechanism. Second, the first numerical proof-of-concept of an rf quadrupole for Landau damping is realised in PyHEADTAIL. A two-family scheme for rf quadrupoles is also evaluated for FCC operational scenarios demonstrating an improved overall damping performance of the device. In particular, the required active magnetic length of the rf quadrupole is significantly shorter compared to octupole elements. Third, the numerical models and the theory are validated against measurements in the Large Hadron Collider (LHC) and the Super Proton Synchrotron (SPS) at CERN. In the two machines, the second-order chromaticity is successfully enhanced using a sextupole and an octupole scheme respectively and the measured nonlinear optics parameters are shown to be consistent with MAD-X calculations. The stabilisation of single bunches by means of a betatron frequency spread produced by nonlinear chromaticity is demonstrated in the LHC which marks the first experimental proof of the novel Landau damping method. The measurements are in good agreement with detailed PyHEADTAIL simulations. In particular, the two effects predicted by the theory are consistently observed in both experiments and simulations confirming a thorough understanding of the involved beam dynamics.

Loïc Thomas Davies Coyle, Ekaterina Krymova, Tatiana Pieloni, Michael Schenk

In the Large Hadron Collider, the beam losses are continuously measured for machine protection. By design, most of the particle losses occur in the collimation system, where the particles with high oscilla-tion amplitudes or large momentum error are scraped from the beams. The particle loss level is typically optimized manually by changing control parameters, among which are currents in the focusing and defocusing magnets. It is generally challenging to model and predict losses based only on the control parameters, due to the presence of various (non-linear) effects in the system, such as electron clouds, resonance effects, etc., and multiple sources of uncertainty. At the same time understanding the influence of control parameters on the losses is extremely important in order to improve the operation and performance, and future design of accelerators. Prior work [1] showed that modeling the losses as an instantaneous function of the control parameters does not generalize well to data from a different year, which is an indication that the leveraged statistical associations are not capturing the actual mechanisms which should be invariant from 1 year to the next. Given that this is most likely due to lagged effects, we propose to model the losses as a function of not only instantaneous but also previously observed control parameters as well as previous loss values. Using a standard reparameterization, we reformulate the model as a Kalman Filter (KF) which allows for a flexible and efficient estimation procedure. We consider two main variants: one with a scalar loss output, and a second one with a 4D output with loss, horizontal and vertical emittances, and aggregated heatload as components. The two models once learned can be run for a number of steps in the future, and the second model can forecast the evolution of quantities that are relevant to predicting the loss itself. Our results show that the proposed models trained on the beam loss data from 2017 are able to predict the losses on a time horizon of several minutes for the data of 2018 as well and successfully identify both local and global trends in the losses.

José Luis Abelleira Fernández, Bernhard Auchmann, Sandra Aumon, Fabio Avino, Javier Barranco Garcia, Manuel Bauer, Luca Bottura, Pierluigi Bruzzone, Xavier Buffat, Francesco Cerutti, Agnieszka Chmielinska, Roberto Contino, Marco Drewes, Sondre Vik Furuseth, Jie Gao, Massimo Giovannozzi, Patrik Gonçalves Jorge, Elena Graverini, Alexej Grudiev, Ruchi Gupta, Doohyun Kim, Mathias Oleg Knecht, Lotta Maria Mether, Giuseppe Montenero, Tatiana Pieloni, Leonid Rivkin, François Robert, Luca Rossi, Jean-Michel Sallese, Alexandra Sarabando de Carvalho, Michael Schenk, Rudiger Schmidt, Jan Steggemann, Alban Sublet, Claudia Tambasco, Sofia Vallecorsa, Martin Vogel, Rui Wang, Jorg Wenninger, Andrea Wulzer, Yi Zhang, Hua Zhang, Frank Zimmermann

We review the physics opportunities of the Future Circular Collider, covering its e(+)e(-), pp, ep and heavy ion programmes. We describe the measurement capabilities of each FCC component, addressing the study of electroweak, Higgs and strong interactions, the top quark and flavour, as well as phenomena beyond the Standard Model. We highlight the synergy and complementarity of the different colliders, which will contribute to a uniquely coherent and ambitious research programme, providing an unmatchable combination of precision and sensitivity to new physics.