Design and characterization of magnetic systems in race-track microtrons

During last four or five decades there has been a growing demand in particle accelerators which can provide electron beams in the energy ranging from 2 MeV to 100 MeV with high energy resolution and good dose control. Other important requirements are that the machines must be compact, of low power consumption, low price and relatively low maintenance cost. There is a variety of sectors interested in such particle accelerators ranging from industry (industrial radiography) to nuclear physics experiments. One type of machines that meet all these requirements are the electron accelerators with beam recirculation. Fair representatives of this class of accelerators are race-track microtrons (RTM). These sources of electron beam are the most efficient equipment for applications with a relatively low beam current and medium energies ranging from 2 MeV to 100 MeV. The aim of the present thesis is to perform studies of some aspects of the RTMs. One part of the thesis is devoted to the design and development of magnetic elements with permanent magnets of two RTMs for different applications. The first one, which is currently under construction at the UPC (Universidad Politécnica de Cataluña), is a novel accelerator with the beam energy variable between 6 MeV and 12 MeV for medical applications (Intraoperative Radiation Therapy treatments). The other machine is a 55 MeV RTM for the detection of explosives by means of photonuclear reactions, which is at the stage of tests at the Skobeltsyn Institute of Nuclear Physics (SINP). The magnetic field in the designed magnets is generated by rare earth permanent magnet (REPM) materials. This allows to get quite compact magnetic systems compatible with high vacuum environment. In the thesis the design and magnetic properties characterization of the magnetic system of these RTMs are carried out. The calculations were performed by means of 2D and 3D simulations using the POISSON, FEMM and ANSYS codes. In the case of the UPC RTM the design of the 180º dipoles, extraction magnets and quadrupole magnet are carried out. For the SINP 55 MeV RTM the optimization of the magnetic field shielding with the aim to reduce the stray magnetic field generated by the extraction magnet is presented. The results of the simulations were confirmed by experimental measurements of the magnetic field of the magnet with the optimized magnetic field shielding. In the other part of the thesis some aspects of the beam dynamics in RTM magnetic systems are studied. A detailed analysis of the fringe - field focusing in RTM dipole magnets is carried out. Equations for calculation of the fringe - field effect on electron beam trajectories are derived and are applied for a study of the end magnets of the UPC 12 MeV RTM. A general formalism for describing the longitudinal beam dynamics in RTMs for electron beams with arbitrary energy and end magnets with arbitrary magnetic field profile is also developed. This formalism is used for the calculation of the phase-slip effect in RTMs with low energy injection

Performance of the magnetic system of a 12 MeV UPC race-track microtron

The per­for­mance of the mag­netic sys­tem of a 12 MeV elec­tron race-track mi­cro­tron (RTM) which is under con­struc­tion at the Uni­ver­si­tat Politècnica de Catalunya (UPC) is de­scribed. The RTM mag­netic sys­tem con­sists of two four-pole end mag­nets with the main field level about 0.8 T, one quadru­pole and four beam ex­trac­tion dipoles. As a source of the mag­netic field in these mag­nets a Sa-Co rare earth per­ma­nent mag­net ma­te­r­ial is used. This helps to get a quite com­pact de­sign of the RTM and al­lows to place the mag­netic sys­tems in a high vac­uum en­vi­ron­ment of the ac­cel­er­a­tor vac­uum cham­ber. We dis­cuss re­sults of nu­mer­i­cal sim­u­la­tions of the tun­ing of the end mag­nets by mean of spe­cial tuners and de­scribe their en­gi­neer­ing de­sign which per­mits to as­sem­ble the mag­nets and fix the Sa-Co blocks with­out glu­ing. Also a method and re­sults of mag­netic field dis­tri­b­u­tion mea­sure­ments and mag­net tun­ing are re­ported.Postprint (published version

Assessment Of Intra-coronary Stent Location And Extension In Intravascular Ultrasound Sequences.

Purpose An intraluminal coronary stent is a metal scaffold deployed in a stenotic artery during percutaneous coronary intervention (PCI). In order to have an effective deployment, a stent should be optimally placed with regard to anatomical structures such as bifurcations and stenoses. Intravascular ultrasound (IVUS) is a catheter-based imaging technique generally used for PCI guiding and assessing the correct placement of the stent. A novel approach that automatically detects the boundaries and the position of the stent along the IVUS pullback is presented. Such a technique aims at optimizing the stent deployment. Methods The method requires the identification of the stable frames of the sequence and the reliable detection of stent struts. Using these data, a measure of likelihood for a frame to contain a stent is computed. Then, a robust binary representation of the presence of the stent in the pullback is obtained applying an iterative and multiscale quantization of the signal to symbols using the Symbolic Aggregate approXimation algorithm. Results The technique was extensively validated on a set of 103 IVUS of sequences of in vivo coronary arteries containing metallic and bioabsorbable stents acquired through an international multicentric collaboration across five clinical centers. The method was able to detect the stent position with an overall F-measure of 86.4%, a Jaccard index score of 75% and a mean distance of 2.5 mm from manually annotated stent boundaries, and in bioabsorbable stents with an overall F-measure of 88.6%, a Jaccard score of 77.7 and a mean distance of 1.5 mm from manually annotated stent boundaries. Additionally, a map indicating the distance between the lumen and the stent along the pullback is created in order to show the angular sectors of the sequence in which the malapposition is present. Conclusions Results obtained comparing the automatic results vs the manual annotation of two observers shows that the method approaches the interobserver variability. Similar performances are obtained on both metallic and bioabsorbable stents, showing the flexibility and robustness of the method

Acute thrombosis induced by drug-coated balloons dilation in neoatherosclerosis plaque, successfully treated with a MicroNet-covered stent: A Case Report and Literature Review

Preprint enviat per a la seva publicació en una revista científica: Journal of Endovascular Therapy Case Report (ISSN: 1526-6028, 1545-1550)Background The operator's ability in performing carotid stenting (CAS) has improved clinical outcomes. However, more than 3% of patients need to be treated again after CAS. Most of the cases requiring further intervention are affected by hyperplasia. The recommended procedure is the DEBalloon. On the other hand, the literature reports a small number of carotid neoatherosclerosis cases and is recommended to be treated using elective Micronet-covered stent. Discriminating between the two types of in-stent-restenosis ISR (hyperplasia or neoatherosclerosis) is critical for a positive outcome. Case summary We describe a case in which a patient treated with carotid stenting 8 years before, was diagnosed with ISR. Due to the development of neurological symptoms and progressive increases in Peak Systolic Velocity (PSV) eight years following carotid stenting, a DEBalloon was used in a carotid in-stent-restenosis (ISR) standard procedure. About ten minutes after the procedure, the patient developed hemiplegia consistent with the treated carotid territory. The implantation of a MicroNet-covered stent excluded the thrombus and reverted symptoms with a normal MR control at 24 h. Conclusion This case illustrates that when in-stent stenosis evolves years after the stent implantation, neoatherosclerosis should be assessed, and a MicroNet-covered stent should be considered

Rare-earth end magnets of a miniature race-track microtron and their tuning

We report basic results on the tuning of permanent end magnets of a compact 12 MeV race-track microtron (RTM) which is under construction at the Technical University of Catalonia. They are magnetic systems composed of four dipoles with the rare-earth permanent magnet (REPM) material used as a source of the magnetic field. The steel poles of the magnets are equipped with tuning plungers which allow to adjust the magnetic field level. In the article we shortly describe the tuning procedure and different techniques that were used in order to fulfill strict requirements of the field characteristics of the end magnets. It is shown that the obtained magnetic systems provide correct beam trajectories in the 12 MeV RTM. More detailed information about tuning procedure and results of tuning will be published elsewhere.Postprint (published version

Quadrupole lens and extraction magnets of a miniature race-track microtron

A compact 12 MeV race-track microtron (RTM) which is under construction at the Technical University of Catalonia includes a quadrupole magnet for horizontal beam focusing and four dipole magnets for beam extraction. As the source of the magnetic field in these magnets a rare-earth permanent magnet (REPM) material is used. In the article the main design characteristics of the quadrupole lens and extraction dipoles are described and a procedure of tuning of their magnetic fields is described. We report on the manufacturing of these magnetic systems and results of the tuning of their magnetic fields.Postprint (published version

Experimental Setup for Irradiation of Cell Cultures at L2A2

[EN] Laser-plasma proton sources and their applications to preclinical research has become a very active field of research in recent years. In addition to their small dimensions as compared to classical ion accelerators, they offer the possibility to study the biological effects of ultra-short particle bunches and the correspondingly high dose rates. We report on the design of an experimental setup for the irradiation of cell cultures at the L2A2 laboratory at the University of Santiago de Compostela, making use of a 1.2 J Ti: Sapphire laser with a 10 Hz repetition rate. Our setup comprises a proton energy separator consisting of two antiparallel magnetic fields realized by a set of permanent magnets. It allows for selecting a narrow energy window around an adaptable design value of 5 MeV out of the initially broad spectrum typical for Target Normal Sheath Acceleration (TNSA). At the same time, unwanted electrons and X-rays are segregated from the protons. This part of the setup is located inside the target vessel of the L2A2 laser. A subsequent vacuum flange sealed with a thin kapton window allows for particle passage to external sample irradiation. A combination of passive detector materials and real-time monitors is applied for measurement of the deposited radiation dose. A critical point of this interdisciplinary project is the manipulation of biological samples under well-controlled, sterile conditions. Cell cultures are prepared in sealed flasks with an ultra-thin entrance window and analysed at the nearby Fundacion Publica Galega Medicina Xenomica and IDIS. The first trials will be centred at the quantification of DNA double-strand breaks as a function of radiation dose.Projects RTI2018-101578-B-C21 and RTI2018-101578-B-C22 are funded by MCIN/AEI /10.13039/501100011033 and by FEDER "Una manera de hacer Europa". Project AICO/2020/207 is funded by Generalitat Valenciana. Supports PEJ2018-002035-A and PEJ2018-002037-A are financed by AEI and "El FSE invierte en tu futuro". Additional funding is by FPI predoctoral grant BES-2017-08917 and Unidad de Excelencia Maria de Maeztu, MdM-2016-0692-17-2. Action is co-financed by the European Union through the Programa Operativo del Fondo Europeo de Desarrollo Regional (FEDER) of the Comunitat Valenciana 2014-2020 (IDIFEDER/2018/022 and IDIFEDER/2021/004). FPGMX-IDIS research is partially supported by the Spanish Instituto de Salud Carlos III (ISCIII) funding, which is an initiative of the Spanish Ministry of Economy and Innovation partially supported by European Regional Development FEDER Funds (INT20/00071, PI19/01424, AC18/00117) and through the Autonomous Government of Galicia (Consolidation and structuring program: IN607B) given to A. Vega.Torralba, A.; Palenciano-Castro, L.; Reija, A.; Rigla, JP.; Peñas, J.; Llerena, JJ.; Contreras-Martinez, R.... (2022). Experimental Setup for Irradiation of Cell Cultures at L2A2. Quantum Beam Science. 6(1):1-11. https://doi.org/10.3390/qubs60100101116

A Fast 0.5 T Prepolarizer Module for Preclinical Magnetic Resonance Imaging

We present a magnet and high power electronics for Prepolarized Magnetic Resonance Imaging (PMRI) in a home-made, special-purpose preclinical system designed for simultaneous visualization of hard and soft biological tissues. The sensitivity of MRI systems grows with field strength, but so do their costs. PMRI can boost the signal-to-noise ratio (SNR) in affordable low-field scanners by means of a long and strong magnetic pulse. However, this must be rapidly switched off prior to the imaging pulse sequence, in timescales shorter than the spin relaxation (or T1) time of the sample. We have operated our prepolarizer at up to 0.5 T and demonstrated enhanced magnetization, image SNR and tissue contrast with PMRI of tap water, an ex vivo mouse brain and food samples. These have T1 times ranging from hundreds of milli-seconds to single seconds, while the preliminary high-power electronics setup employed in this work can switch off the prepolarization field in tens of milli-seconds. In order to make this system suitable for solid-state matter and hard tissues, which feature T1 times as short as 10 ms, we are developing new electronics which can cut switching times to ~ 300 μs. This does not require changes in the prepolarizer module, opening the door to the first experimental demonstration of PMRI on hard biological tissues