Philip Burrows

Abstract:

We study experimentally the effect of linear plasma density gradients on the self-modulation of a 400 GeV proton bunch. Results show that a positive or negative gradient increases or decreases the number of microbunches and the relative charge per microbunch observed after 10 m of plasma. The measured modulation frequency also increases or decreases. With the largest positive gradient we observe two frequencies in the modulation power spectrum. Results are consistent with changes in wakefields’ phase velocity due to plasma density gradients adding to the slow wakefields’ phase velocity during self-modulation growth predicted by linear theory.

Abstract:

The design of a primary electron beam facility at CERN is described. The study has been carried out within the framework of the wider Physics Beyond Colliders study. It re-enables the Super Proton Synchrotron (SPS) as an electron accelerator, and leverages the development invested in Compact Linear Collider (CLIC) technology for its injector and as an accelerator research and development infrastructure. The facility would be relevant for several of the key priorities in the 2020 update of the European Strategy for Particle Physics, such as an electron-positron Higgs factory, accelerator R&D, dark sector physics, and neutrino physics. In addition, it could serve experiments in nuclear physics. The electron beam delivered by this facility would provide access to light dark matter production significantly beyond the targets predicted by a thermal dark matter origin, and for natures of dark matter particles that are not accessible by direct detection experiments. It would also enable electro-nuclear measurements crucial for precise modelling the energy dependence of neutrino-nucleus interactions, which is needed to precisely measure neutrino oscillations as a function of energy. The implementation of the facility is the natural next step in the development of X-band high-gradient acceleration technology, a key technology for compact and cost-effective electron/positron linacs. It would also become the only facility with multi-GeV drive bunches and truly independent electron witness bunches for plasma wakefield acceleration. A second phase capable to deliver positron witness bunches would make it a complete facility for plasma wakefield collider studies.
The facility would be used for the development and studies of a large number of components and phenomena for a future electron-positron Higgs and electroweak factory as the first stage of a next circular collider at CERN, and its cavities in the SPS would be the same type as foreseen for such a future collider. The operation of the SPS with electrons would train a new generation of CERN staff on circular electron accelerators. The facility could start operation in about five years, and would operate in parallel and without interference with Run 4 of the LHC.

Abstract:

The luminosity of a particle collider is an extremely crucial performance parameter describing its capability of producing interactions in the collision point. However, imperfections in a collider can lead to luminosity loss. Among different imperfections, an important one is stray magnetic fields. For the Compact Linear Collider (CLIC), a collider being considered as one of the main options in Europe after the Large Hadron Collider, simulations showed an unprecedented sensitivity of the machine to fields on the order of 0.1 nT. Hence, such tight constraints require special design considerations to prevent performance loss. Different shielding techniques are available in the literature, typically relying on an active shielding strategy and capable of reducing the magnetic field amplitudes down to the nano-Tesla level. However, measuring fields with such amplitudes is challenging by using state-of-the-art commercially available sensors and therefore, a passive shielding strategy, consisting in enveloping sections of the beamline with a magnetic shield, is a more attractive option. For CLIC, Mumetal®, a Ni–Fe alloy with advertised relative permeability above 100,000, was chosen. In this paper, the DC and AC magnetic characterization of two samples of Mumetal®, one annealed in its final form and the other one non-annealed is presented, showcasing how the annealing results in a boost of the magnetic permeability of more than order of magnitude. As a case study, the shielding performance of a 1-mm thin layer of Mumetal® enveloping CLIC’s beamline is estimated.

Abstract:

Plasma Physics and Controlled Fusion PAPER Proton beam defocusing in AWAKE: comparison of simulations and measurements A A Gorn1,2, M Turner3, E Adli4, R Agnello5, M Aladi6, Y Andrebe5, O Apsimon7,8, R Apsimon7,8, A-M Bachmann3,9,10, M A Baistrukov1,2Show full author list Published 6 November 2020 • © 2020 IOP Publishing Ltd Plasma Physics and Controlled Fusion, Volume 62, Number 12 Citation A A Gorn et al 2020 Plasma Phys. Control. Fusion 62 125023 80 Total downloads Turn on MathJax Get permission to re-use this article Share this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on Mendeley Article information Abstract In 2017, AWAKE demonstrated the seeded self-modulation (SSM) of a 400 GeV proton beam from the Super Proton Synchrotron at CERN. The angular distribution of the protons deflected due to SSM is a quantitative measure of the process, which agrees with simulations by the two-dimensional (axisymmetric) particle-in-cell code LCODE to about 5%. The agreement is achieved in beam population scans at two selected plasma densities and in the scan of longitudinal plasma density gradient. The agreement is reached only in the case of a wide enough simulation box (several plasma wavelengths) that is closer to experimental conditions, but requires more computational power. Therefore, particle-in-cell codes can be used to interpret the SSM physics underlying the experimental data.