Accélérateur linéaire

Résumé

thumb|upright=1.8|Diagramme animé montrant le fonctionnement d'un accélérateur linéaire thumb|Partie d'un accélérateur linéaire situé à Clayton, Victoria, Australie. Un accélérateur linéaire est un dispositif permettant d'accélérer des particules chargées afin de leur fournir une énergie cinétique importante dans le but de produire des réactions avec la matière. Les particules accélérées peuvent être des électrons, des protons, ou bien des ions lourds. La particularité de ce type d'accélérateur de particules est la méthode d'accélération des particules chargée, via un champ électrique local ou non et en ligne droite. Lors de son passage dans l'accélérateur, la particule subit une force proportionnelle au champ électrique, la force d'interaction Coulombienne . Accélérateurs d'électrons Accélérateurs utilisés en médecine La médecine utilise des accélérateurs pour le radiodiagnostic et la radiothérapie. Dans les deux cas, ce sont des rayons X qui sont utilisés s

Source officielle

https://fr.wikipedia.org/wiki/Acc%C3%A9l%C3%A9rateur_lin%C3%A9aire

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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

Chargement

Radiation protection studies for CERN Linac4/SPL accelerator complex

Egidio Mauro

CERN is presently designing a new chain of accelerators to replace the present Proton Synchrotron (PS) complex: a 160 MeV room-temperature H- linac (Linac4) to replace the present 50 MeV proton linac injector, a 3.5 GeV Superconducting Proton Linac (SPL) to replace the 1.4 GeV PS booster (PSB) and a 50 GeV synchrotron (named PS2) to replace the 26 GeV PS. Linac4 has been funded and the civil engineering work started in October 2008, whilst the SPL is in an advanced stage of design. Beyond injecting into the future 50 GeV PS, the ultimate goal of the SPL is to generate a 4 MW beam for the production of intense neutrino beams. The radiation protection design is driven by the latter requirement. This thesis summarizes the radiation protection studies conducted for Linac4. FLUKA Monte Carlo simulations, complemented by analytical estimates, were performed 1) to evaluate the propagation of neutrons through the waveguide, ventilation and cable ducts placed along the accelerator, 2) to estimate the radiological impact of the accelerator in its low energy section, where the access area is located, and 3) to calculate the induced radioactivity in the air and in the components of the accelerator. The latter study is particularly important for maintenance interventions and final disposal of radioactive waste. Two possible layouts for the CCDTL section of the machine were considered in order to evaluate the feasibility, from the radiological standpoint, of replacing electromagnetic quadrupoles with permanent magnet quadrupoles with high content of cobalt. The present work provides complete information on beam loss assumptions, accelerator structure and duct and maze design, in order to make the present results of sufficiently general interest and provide guidelines for similar studies for intermediate energy proton accelerators. In addition to the Linac4-specific studies, this thesis also discusses FLUKA simulations performed to test the capability of the code, in a proton therapy application, in predicting induced radioactivity from intermediate energy protons. The thesis also reviews the analytical models mostly used for the calculation of neutron streaming through penetration traversing shielding barriers, discusses the FLUKA simulations performed to test the reliability of these models and, on the basis of the simulations, derives a universal expression that can be used to estimate the neutron transmission through a straight duct in direct view of the source, model missing so far in the literature.

EPFL2009

Chargement

With preparation of Hi-Lumi LHC fully underway, and the FCC machines under study, accelerators will reach unprecedented energies and along with it very large amount of synchrotron radiation (SR). This will desorb photoelectrons and molecules from accelerator walls, which contribute to electron cloud buildup and increase the residual pressure - both effects reducing the beam lifetime. In current accelerators these two effects are among the principal limiting factors, therefore precise calculation of synchrotron radiation and pressure properties are very important, desirably in the early design phase. This PhD project shows the modernization and a major upgrade of two codes, Molflow and Synrad, originally written by R. Kersevan in the 1990s, which are based on the test-particle Monte Carlo method and allow ultra-high vacuum and synchrotron radiation calculations. The new versions contain new physics, and are built as an all-in-one package - available to the public. Existing vacuum calculation methods are overviewed, then the steady-state and time-dependent algorithms behind the ultra-high vacuum simulator Molflow are presented. Some practices to tackle the most common problems that arise when simulating large systems are also discussed. Results are compared to theory, and validated through two experiments. Next the the main steps of synchrotron radiation simulations are presented. Properties of SR are summarized, along with optimizations that allow simulating the rather complex underlying physics at a higher speed. The resulting software's photon generation algorithm is benchmarked against published data. The phenomenon of photon stimulated desorption and its literature is overviewed, then two dedicated photodesorption experiments carried out in KEK (Tsukuba, Japan) are presented: one with six room-temperature samples and an other at liquid nitrogen temperature. A simple synchrotron radiation calculation is performed for the LHeC interaction region, allowing to compare Synrad+ results with published analytic calculations. Then the calculations are repeated for a more precise geometry description. The pressure profile of a crotch absorber of the recently started Max IV light source is calculated using Molflow+ and Synrad+ together. Finally the pressure analysis of the SuperKEKB interaction region is presented, consisting of modeling the vacuum chamber and the optics, calculating synchrotron radiation, then performing vacuum simulations. It is confirmed that pressure is expected to meet the design requirements during operation of the machine.

EPFL2016

Chargement

Radiation protection studies for CERN Linac4/SPL accelerator complex

Egidio Mauro

EPFL2009

EPFL2018

EPFL2016