Electron | EPFL Graph Search

The electron (Electron or beta-) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron's mass is approximately 1/1836 that of the proton. Quantum mechanical properties of the electron include an intrinsic angular momentum (spin) of a half-integer value, expressed in units of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy the same quantum state, per the Pauli exclusion principle. Like all elementary particles, electrons exhibit properties of both particles and waves: They can collide with other particles and can be diffracted like light. The wave properties of electrons are easier to observe with experiments than those of other particles like neu

High-gradient and high-efficiency linear accelerators for hadron therapy

Stefano Benedetti

Hadron beams - approximately 200 MeV protons and 400 MeV/u fully stripped carbon ions - are better suited to treat deep-seated tumours than X ray beams - produced by electrons accelerated by linear accelerators (linacs) to 5-25 MeV - because they leave the maximum energy density at the end of their range in matter, in the so-called Bragg peak. This physical property allows dose depositions that are more conformal to the tumour target and spare much better the surrounding healthy tissues, so that hadron therapy treatment rooms could substitute X ray therapy rooms (about 20 000 worldwide) if the needed accelerators could be made of similar dimensions and costs. Cyclotrons and synchrotrons are at the heart of today proton and carbon ion therapy centres, respectively. At the end of 2015, more than 130 000 patients have been treated with proton beams and almost 20 000 with carbon ions [Particle Therapy Co-Operative Group data, \url{https://www.ptcog.ch/index.php/patient-statistics}]. High frequency hadron therapy linacs have been studied in the last 30 years. Their main advantage is represented by their active beam energy modulation, which permits quick treatments with superior beam quality and novel dose delivery techniques. This thesis is the last of many research works on the development of linear accelerators for hadron therapy. The preliminary design of two linear accelerator facilities, for proton therapy (TULIP) and carbon ion therapy (CABOTO), was completed. The introductory Chapter will review the rationale of hadron therapy as a treatment methodology, together with a discussion of the advantages of linacs in hadron therapy compared to state-of-art technologies. Finally, the most important past research activities based on which this thesis started will be presented. The second Chapter describes the RF design of accelerating structures performed for the proton and carbon ion therapy facilities later on presented. The third Chapter is dedicated to the proton linac design, called TULIP: TUrning LInac for Protontherapy. The forth Chapter describes the carbon ion linac design, called CABOTO: CArbon BOoster for Therapy in Oncology. The fifth Chapter presents the experimental activity performed on the backward travelling wave prototype built. Goal of the test is to study the high-gradient break-down limitation of S-Band cavities. The thesis is completed by an Appendix where the beam dynamics codes developed to design the linacs are discussed.

EPFL2018

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

The fabrication of defined and high-quality metal nanostructures is an ongoing topic of research. Direct-write deposition of copper nanostructures is of great value for many fields of research and industrial applications. Focused electron beam induced deposition (FEBID) is an additive fabrication technique with extremely high resolution and versatility. Physisorbed, gaseous precursor molecules are locally dissociated by a finely focused electron beam resulting in volatile fragments which desorb and non-volatile fragments forming the deposit. When applying suitable deposition parameters, these deposits can be as small as the beam diameter and have ideally little to no contamination. For electron beam induced metal deposition, metal-organic compounds are chosen as precursors. However, organic ligand material is often co-deposited, which is detrimental to the depositâs properties. This work addresses the study of the perfluorinated copper carboxylate [Cu2(ÎŒ-O2CC2F5)4] (Cu2(pfp)4) and its aminated derivatives Cu2(EtNH2)2(pfp)4 and Cu2(tBuNH2)2(pfp)4 as viable FEBID precursors. 25 at.% of copper was achieved with the amine free compound, and 15 at.% with each of the two aminated complexes. Based on the chemical analysis of the deposits, electron-induced dissociation paths were proposed for the adsorbed species, demonstrating the influence of the ligand chemistry and fragmentation on the deposit composition. In parallel, the perfluorinated silver carboxylate Ag2(pfp)2 was reported and compared directly to its copper equivalent. The silver complex yielded up to 74 at.% metal content and exhibited strong susceptibility to varying electron beam densities throughout the deposit. Cu2(pfp)4 did not manifest the same electron sensitivity. Theoretical models, combining analytical solutions with Monte Carlo simulations of primary and backscattered electrons were successfully fitted to the cross sections of deposits from both carboxylates, determining the growth regimes within a single spot deposit. Additionally, two previously reported Î²-diketonates, Cu(hfac)2 and Cu(tbaoac)2, were directly compared to the other Cu(II) precursors with the aim to determine any dependence of the ligand size, electron density or dwell time on the deposit purity. The investigations concluded that the metal content rather depends on the chemistry of the metal-ligand bond than on the ligand size. This applies to both, the variation of ligands and the variation of the metal center. vii Furthermore, two copper complexes, Cu(hfac)2 and Cu2(pfp)4, were investigated in situ with a dedicated, custom-made setup. The âeQCMâ combines a low energy electron source (10- 100 eV) with a quartz crystal microbalance and serves to study fundamental processes occurring during FEBI deposition. First results yielded the total dissociation cross section for each precursor at varying electron energies. Finally, alternative approaches for the electron induced copper deposition from Cu2(pfp)4 were investigated. A two-step post-purification recipe of as-deposited material was reported to yield pure copper crystals (> 97 at.%). Additionally, direct electron beam lithography in a layer of condensed precursor was explored. This room temperature deposition approach yielded in lower metal contents but could potentially produce high resolution deposition.

EPFL2020

Electron Cloud and Synchrotron Radiation characterization of technical surfaces with the Large Hadron Collider Vacuum Pilot Sector

Elena Buratin

This PhD thesis presents the experimental study on electron cloud (EC) and synchrotron radiation (SR) phenomena affecting the LHC storage ring performance. These phenomena are one of the major issues of the LHC storage ring, generating beam instabilities, pressure rise and heat loads on the beam pipes. This experimental study is carried out with an innovative system installed in a room temperature and field free section of the Large Hadron Collider (LHC), the Vacuum Pilot Sector (VPS). ln this system, several surfaces are simultaneously tested, in particular standard copper, amorphous carbon coating, NEG. Thanks to a wide spectrum of detectors, the EC and SR signals were studied as a function of beam parameters and beam pipe properties. The EC behaviour increases linearly with the number of bunches and bunch population above the multipacting threshold. This phenomenon increases linearly also with the bunch length for the Long Straight Sections of LHC (LSS). As expected, the bunch spacing has a crucial importance on the formation of EC dynamic: the 50 ns filling scheme avoids the multipacting effect at 450 GeV. At 6.5 TeV the photoelectron contribution is visible, with no multipacting. This scheme is not sufficient for the LHC collision studies and cannot be used as standard filling scheme. Instead, the 25 ns bunch spacing scheme suffers of EC; in this case this phenomenon can be drastically reduced only by bombarding the surface with electrons during dedicated scrubbing runs, or thanks to the installation of beam pipe surface with a low SEY, such as the amorphous-carbon coating. The measurements performed with pick-ups show the evolution of the EC dynamics for the first time in the LHC. The energy spectrum detectors and the gas analysers were also installed for the first time in the LHC history: the electron cloud spectrum and the gas composition could be measured during the machine operation. The electron energy spectrum evidences a peak at around 100 eV, corresponding to the accelerated electrons responsible for multipacting. The gas analysers measured the main gasses present in the LHC ultra-high vacuum system, such as methane, carbon dioxide and monoxide, water, hydrogen and traces of 2-Propynenitrile 3-fluoro (C3FN), probably linked to the effect of radiation into the kapton cables. It has been possible to estimate the Electron Stimulated Desorption (ESD) parameter of a copper surface as a function of the accumulated electron dose. The heat loads due to impedance, EC and SR were measured and, finally, the operation of HL-LHC machine has been estimated in terms of electron current, pressure and power deposition thanks to the results of this study. Doubling of the bunch population will increase the electron current and the pressure of one order of magnitude, while the deposited power due to EC will be smaller than 1 W/mchamber for a beam pipe SEY lower than 1.8.

EPFL2020

Electron Cloud and Synchrotron Radiation characterization of technical surfaces with the Large Hadron Collider Vacuum Pilot Sector

Elena Buratin

EPFL2020

Electron Beam Induced Copper Deposition from Carboxylate Precursors and the Study of Underlying Growth Mechanisms

Luisa Berger

EPFL2020

High-gradient and high-efficiency linear accelerators for hadron therapy

Stefano Benedetti

EPFL2018