84 research outputs found
Detector characterization for LEGEND-200 experiment
No full textThe LEGEND Collaboration is developing an experimental search for the neutrinoless double-beta (0νββ) decay of the 76Ge isotope. Its first phase, LEGEND-200, uses 200 kg of 76Ge-enriched high-purity germanium detectors in an active liquid argon shield and is currently under construction at the Laboratori Nazionali del Gran Sasso (LNGS) of the INFN in Italy. Inverted coaxial pointcontact detectors are deployed in the experiment. Their unique geometry provides
an excellent energy resolution in a broad energy range and impressive discrimination of signal against background events. LEGEND’s search for 0νββ requires a precise
understanding of the behavior of germanium detectors, necessitating extensive detector characterization. The acceptance tests aim to verify whether the performance of the delivered detectors meets specifications and to determine their optimal operational parameters. We discuss the first results in the characterization program
The GERDA Experiment in the Search for Neutrinoless Double-Beta Decay
No full textAn open question still involves the nature of neutrinos: are they equal to their anti-matter counterpart? The most promising way to test this Majorana nature of neutrinos is searching for the neutrinoless double beta decay (0 nu beta beta), a hypothetical lepton number violating nuclear process. Furthermore, its observation would give an extraordinary insight into why our universe is predominantly composed of matter, which is another unsolved puzzle of cosmology and particle physics. Since 2011, the Gerda collaboration has searched for 0 nu beta beta of Ge-76 by operating bare germanium detectors, enriched in the double-beta decaying isotope Ge-76, in liquid argon. Exploiting the combination of excellent energy resolution of germanium detectors and scintillating properties of argon, the Gerda experiment succeeded to achieve an unprecedented background-free regime. In December 2019, after fulfilling and exceeding the design goals of the experiment, data taking was stopped. No signal has been observed, hence a lower limit on the half-life of 0 nu beta beta in Ge-76 has been set at T-1/2(0 nu) > 1.8 x 10(26) years at 90% C.L. The final results of the 12 Gerda experiment are discussed
Space charge impedance and electromagnetic fields in elliptical vacuum chambers
No full textStarting from the electric fields produced by a point charge and a dipole traveling inside a circular vacuum chamber, in this paper we derive a formalism for a complete set of equations that describe the electromagnetic fields and the longitudinal and transverse coupling impedances arising by the interaction of a beam with a perfectly conducting pipe in the case of elliptic geometry. The expressions, which are valid for any frequency and beam energy, are written in terms of expansions of Mathieu functions, allow to range from a circular geometry to the parallel plates, and show an interesting parallelism with the well-known expressions for a circular pipe. We also obtain that, under the approximation of low frequency, the formalism allows us to derive the Laslett coefficients for parallel plates, circular and elliptic beam pipe
The mode matching method applied to beam coupling impedance calculations of finite length devices
No full textThe infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be less accurate approximation for segmented devices. In this contribution we present the study of the beam coupling impedance of a finite length device: a cylindrical cavity loaded with a toroidal slab of lossy dielectric. In order to take into account the finite length, we will decompose the fields in the cavity and in the beam pipe into a set of orthonormal modes and apply the mode matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations as well as applications to the evaluation of the impedance of short beam pipe inserts, where the longitudinal and transverse dimensions are difficult to model in numerical simulations
Resistive wall impedance in elliptical multilayer vacuum chambers
No full textThe resistive wall impedance of a vacuum chamber with elliptic cross section is of particular interest for circular particle accelerators as well as for undulators in free electron lasers. By using the electric field of a point charge and of a small dipole moving at arbitrary speed in an elliptical vacuum chamber, expressed in terms of Mathieu functions, in this paper we take into account the finite conductivity of the beam pipe walls by means of the surface impedance, and evaluate the longitudinal and transverse driving and detuning impedances for any beam velocity. We also extend the definition of the Yokoya form factors, valid in the thick wall regime, at any beam energy, and show that, in the ultra-relativistic limit, they coincide with the ones that are found in literature. The method is also extended to the multilayer vacuum chamber case. Under conditions generally satisfied with particle accelerator beam pipes, the classical transmission line theory can be used to modelling the impedance seen by a bunch in a vacuum chamber with several layers as an equivalent circuit with the same number of load impedances, giving, as result, a surface impedance that can be used in combination with the fields of the elliptic geometry to obtain the resistive wall impedance in an elliptical multilayer vacuum chamber. The results are also compared with a more time consuming 3D electromagnetic code and with solutions for known cases of circular and flat beam pipe
Transverse impedance studies of 2D azimuthally symmetric devices of finite length
No full textThe accurate calculation of the beam coupling impedance for particle accelerators is necessary to carefully assess the machine stability against impedance-driven collective effects. A first order evaluation of the beam coupling impedance is often done by means of analytical formulas and/or 2D numerical codes. The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be a less accurate approximation for segmented devices. In this work, we present the application of the mode matching method to the calculation of the transverse dipolar impedance of a cylindrical cavity loaded with a toroidal insert. By choosing different insert electromagnetic properties (permittivity, permeability, and conductivity) and dimensions, the model can represent a beam pipe, a thin insert, a lossy cavity, or a collimator for which the effect of the finite length is investigated. The method is successfully benchmarked against available analytical formulas, field-matching codes, and 3D commercial solvers. The proposed model allows for performing wide parametric scans and reaching accurate results, therefore becoming an essential tool for the impedance evaluation of accelerator devices
Electromagnetic fields and Green’s functions in elliptical vacuum chambers
No full textIn this paper, we discuss the electromagnetic interaction between a point charge travelling inside a waveguide of elliptical cross section, and the waveguide itself. By using a convenient expansion of the Mathieu functions, useful in particular for treating a variety of problems in applied mathematics and physics with elliptic geometry, we first obtain the longitudinal electromagnetic field of a point charge (Green’s function) in free space in terms of elliptical coordinates. This expression allows, then, to calculate the scattered field due to the boundary conditions in our geometry. By summing the contribution of the direct or primary field and the indirect field scattered by the boundary, after a careful choice of some expansion expressions, we derive a novel formula of the longitudinal electric field, in any transverse position of the elliptical cross section, generated by the charge moving along the longitudinal axis of the waveguide. The obtained expression is represented in a closed form, it can be differentiated and integrated, it can be used to fully describe the radiation process of a particle beam travelling inside a waveguide of elliptical cross section, and it is valid for any elliptic geometry. The equations are used to evaluate the coupling impedance due to indirect space charge in case of elliptical geometry. In addition, they are useful as preliminary studies for the determination of the coupling impedance in different cases involving elliptic vacuum chambers, as, for example, the effect of the finite conductivity of the beam pipe wall or the geometrical variation of the vacuum chamber due to elliptic step transitions existing in some accelerators
The mode matching technique applied to the transverse beam coupling impedance calculation of azimuthally symmetric devices of finite length
No full textThe infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be a less accurate approximation for segmented devices. In this contribution we present the extension of the study of the beam coupling impedance of a finite length device to the transverse plane. In order to take into account the finite length, we decompose the fields in the cavity and in the beam pipe into a set of orthonormal modes and apply the Mode Matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations
Impedance studies of 2D azimuthally symmetric devices of finite length
No full textIn particle accelerators, the beam quality can be strongly affected by the interaction with self-induced electromagnetic fields excited by the beam in the passage through the elements of the accelerator. The beam coupling impedance quantifies this interaction and allows predicting the stability of the dynamics of high intensity, high brilliance beams. The coupling impedance can be evaluated with finite element methods or using analytical approaches, such as field matching or mode matching. In this paper we present an application of the mode matching technique for an azimuthally uniform structure of finite length: a cylindrical cavity loaded with a toroidal slab of lossy dielectric, connected with cylindrical beam pipes. In order to take into account the finite length of the structure, with respect to the infinite length approximation, we decompose the fields in the cavity into a set of orthonormal modes. We obtain a complete set of equations using the magnetic field matching and the nonuniform convergence of the electric field on the cavity boundaries. We present benchmarks done with CST Particle Studio simulations and existing analytical formulas and codes, pointing out the effect of different material conductivities, finite length, and nonultrarelativistic particle beam velocity
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