arXiv subjects

M. Walter

Publications and source records attributed to M. Walter.

15 recordsLinked to original sources

arXiv2025

Fast Adaptive Neural Control of Resonant Extraction at Fermilab

We present progress on the development of a machine learning (ML) regulation system for third-order resonant extraction of the beam delivered to the Mu2e experiment at Fermilab. We consider classical and ML-based controllers optimized on semi-analytic simulations and provide performance comparisons for several models. Additionally, we discuss the efficiency of each model in training, which has implications for future work on adaptive control. We also discuss progress on developing optimized implementations of ML models for edge-based inference.

physics.acc-ph↗

arXiv2025

Project 8 Apparatus for Cyclotron Radiation Emission Spectroscopy with $^\mathrm{83m}$Kr and Tritium

Cyclotron Radiation Emission Spectroscopy (CRES) is a novel technique for the precise measurement of relativistic electron energy. This technique is being employed by the Project~8 collaboration for measuring a high-precision tritium beta decay spectrum to perform a frequency-based measurement of the neutrino mass. In this work, we describe the Project 8 Phase II apparatus, used for the detection of the CRES signal from the conversion electrons of $\mathrm{^{83m}Kr}$ and the first CRES measurement of the beta-decay spectrum of molecular tritium.

physics.ins-det↗

arXiv2022

Forbush decrease observed by SEVAN particle detector network on November 4, 2021

On November 3-4 2021, an interplanetary coronal mass injection (ICME) hits the magnetosphere, sparking a strong G3-class geomagnetic storm and auroras as far south as California and New Mexico. All detectors of the SEVAN network registered a Forbush decrease (FD) of 5-10 percentdeep in 1 minute time series of count rates. We present the results of a comparison of Fd registered on mountain altitudes on Aragats (Armenia), Lomnicky Stit (Slovakia), Musala (Bulgaria), and at sea level DESY (Hamburg, Germany), and in Mileshovka, Czechia. We present as well purity and barometric coefficients of different coincidences of SEVAN detector layers on Aragats. We demonstrate disturbances of the near-surface electric (NSEF) and geomagnetic fields at the arrival of the ICME on Earth.

physics.space-ph↗

arXiv2019

Locust: C++ software for simulation of RF detection

The Locust simulation package is a new C++ software tool developed to simulate the measurement of time-varying electromagnetic fields using RF detection techniques. Modularity and flexibility allow for arbitrary input signals, while concurrently supporting tight integration with physics-based simulations as input. External signals driven by the Kassiopeia particle tracking package are discussed, demonstrating conditional feedback between Locust and Kassiopeia during software execution. An application of the simulation to the Project 8 experiment is described. Locust is publicly available at https://github.com/project8/locust_mc.

physics.comp-ph↗

arXiv2019

Electron Radiated Power in Cyclotron Radiation Emission Spectroscopy Experiments

The recently developed technique of Cyclotron Radiation Emission Spectroscopy (CRES) uses frequency information from the cyclotron motion of an electron in a magnetic bottle to infer its kinetic energy. Here we derive the expected radio frequency signal from an electron in a waveguide CRES apparatus from first principles. We demonstrate that the frequency-domain signal is rich in information about the electron's kinematic parameters, and extract a set of measurables that in a suitably designed system are sufficient for disentangling the electron's kinetic energy from the rest of its kinematic features. This lays the groundwork for high-resolution energy measurements in future CRES experiments, such as the Project 8 neutrino mass measurement.

physics.ins-det↗

arXiv2018

Impact of effective polarisability models on the predicted release dynamics of CH$_4$ and CO$_2$ from premelted ice

We present a theory for Casimir--Polder forces acting on greenhouse gas molecules dissolved in a thin water film. Such a nanosized film has recently been predicted to arise on th surface of melting ice as stabilized by repulsive Lifshitz forces. We show that different models for the effective polarizability of greenhouse gas molecules in water lead to different predictions for how Casimir--Polder forces influence the extraction of CH$_4$ and CO$_2$ molecules from the melting ice surface. In the most intricate model of a finite-sized molecule inside a cavity, dispersion potentials push the methane molecules towards the ice surface whereas the carbon dioxide typically will be attracted towards the closest interface (ice or air). Previous models for effective polarizability had suggested that CO$_2$ would also be pushed towards the ice surface. Release of greenhouse gas molecules from the surface of melting ice can potentially influence climate greenhouse effects.

physics.ao-ph↗

arXiv2017

Mitigation of $^{42}$Ar/$^{42}$K background for the GERDA Phase II experiment

Background coming from the $^{42}$Ar decay chain is considered to be one of the most relevant for the GERDA experiment, which aims to search of the neutrinoless double beta decay of $^{76}$Ge. The sensitivity strongly relies on the absence of background around the Q-value of the decay. Background coming from $^{42}$K, a progeny of $^{42}$Ar, can contribute to that background via electrons from the continuous spectrum with an endpoint of 3.5 MeV. Research and development on the suppression methods targeting this source of background were performed at the low-background test facility LArGe. It was demonstrated that by reducing $^{42}$K ion collection on the surfaces of the broad energy germanium detectors in combination with pulse shape discrimination techniques and an argon scintillation veto, it is possible to suppress the $^{42}$K background by three orders of magnitude. This is sufficient for Phase II of the GERDA experiment.

physics.ins-det↗

arXiv2016

Modeling contrary size effects of tensile- and torsion-loaded oligocrystalline gold microwires

When Chen et al. (2015, Acta Mater. 87, 78-85) investigated the deformation behavior of oligocrystalline gold microwires with varying diameters in both uniaxial tension and torsion, contrary size effects were observed for the different load cases. In accompanying microstructural studies it was found, that the microwires of different thickness reveal distinctive differences in grain size and texture, respectively. As a consequence, a significant influence of these microstructural variations on the determined size effects was assumed. However, within the frame of their work, a direct confirmation could only be presented for the effect of the grain size. In the present work, the size-dependent mechanical response of the microwires is modeled with a gradient plasticity theory. By finite element simulations of simplified grain aggregates, the influence of the texture on the size effects is investigated under both loading conditions. It is shown that the experimentally observed contrary size effects can only be reproduced when taking into account the individual textures of the microwires of different thickness within the modeling.

cond-mat.mtrl-sci↗

arXiv2015

Scintillation efficiency of liquid argon in low energy neutron-argon scattering

Experiments searching for weak interacting massive particles with noble gases such as liquid argon require very low detection thresholds for nuclear recoils. A determination of the scintillation efficiency is crucial to quantify the response of the detector at low energy. We report the results obtained with a small liquid argon cell using a monoenergetic neutron beam produced by a deuterium-deuterium fusion source. The light yield relative to electrons was measured for six argon recoil energies between 11 and 120 keV at zero electric drift field.

physics.ins-det↗

arXiv2013

CosMO - A Cosmic Muon Observer Experiment for Students

What are cosmic particles and where do they come from? These are questions which are not only fascinating for scientists in astrophysics. With the CosMO experiment (Cosmic Muon Observer) students can autonomously study these particles. They can perform their own hands-on experiments to become familiar with modern scientific working methods and to obtain a direct insight into astroparticle physics. In this contribution we present the experimental setup and possible measurements. The detector consists of three scintillator boxes. Events are triggered and read out by a data acquisition board developed for the QuarkNet Project. With a Python program running on a netbook under Linux, the trigger and data taking conditions can be defined. The program displays the particle rates in real-time and stores the data for offline analysis. Possible student experiments are the measurement of cosmic particle rates dependent on the zenith angle, the distribution of geometrical size of particle showers, and the lifetime of muons. Twenty CosMO detectors have been built at DESY. They are used within the German outreach network Netzwerk Teilchenwelt at 15 astroparticle-research institutes and universities for project work with students.

astro-ph.IM↗

arXiv2012

Study of nuclear recoils in liquid argon with monoenergetic neutrons

For the development of liquid argon dark matter detectors we assembled a setup in the laboratory to scatter neutrons on a small liquid argon target. The neutrons are produced mono-energetically (E_kin=2.45 MeV) by nuclear fusion in a deuterium plasma and are collimated onto a 3" liquid argon cell operating in single-phase mode (zero electric field). Organic liquid scintillators are used to tag scattered neutrons and to provide a time-of-flight measurement. The setup is designed to study light pulse shapes and scintillation yields from nuclear and electronic recoils as well as from α-particles at working points relevant to dark matter searches. Liquid argon offers the possibility to scrutinise scintillation yields in noble liquids with respect to the populations of the two fundamental excimer states. Here we present experimental methods and first results from recent data towards such studies.

astro-ph.IM↗

arXiv2008

Quantum well states in two-dimensional gold clusters on MgO thin films

The electronic structure of ultra-small Au clusters on thin MgO/Ag(001) films has been analyzed by scanning tunneling spectroscopy and density functional theory. The clusters exhibit two-dimensional (2D) quantum well states, whose shapes resemble the eigen-states of a 2D electron gas confined in a parabolic potential. From the symmetries of the HOMO and LUMO of a particular cluster, its electron filling and charge state is determined. In accordance to a DFT Bader-charge analysis, aggregates containing up to twenty atoms accumulate one to four extra electrons due to a charge transfer from the MgO/Ag interface. The HOMO - LUMO gap is found to close for clusters containing between 70 and 100 atoms.

cond-mat.mtrl-sci↗

arXiv2005

The Presentation of the Algebra of Observables of the Closed Bosonic String in 1+3 Dimensions: Calculation up to Order \hbar^7

We proceed with the investigation of a method of quantization of the observable sector of closed bosonic strings. For the presentation of the quantum algebra of observables the construction cycle concerning elements of order \hbar^6 has been carried out. We have computed the quantum corrections to the only generating relation of order \hbar^6. This relation is of spin-parity J^P=0^+. We found that the quantum corrections to this relation break the semidirect splitting of the classical algebra into an abelian, infinitely generated subalgebra a and a non-abelian, finitely generated subalgebra U. We have established that there are no ("truly independent") generating relations of order \hbar^7.

math-ph↗

arXiv2001

Solutions of the Quantum-Yang-Baxter-Equation from Symmetric Spaces

We show that for each semi-Riemannian locally symmetric space the curvature tensor gives rise to a rational solution $r$ of the classical Yang-Baxter equation with spectral parameter. For several Riemannian globally symmetric spaces $M$ such as real, complex and quaternionic Grassmann manifolds we explicitly compute solutions $R$ of the quantum Yang Baxter equations (represented in the tangent spaces of $M$) which generalize the quantum $R$-matrix found by Zamolodchikov and Zamolodchikov in 1979.

math.QA↗

arXiv1999

Stopping of ion beam in a temperature anisotropic magnetized plasma

Using the dielectric theory for a weakly coupled plasma we investigate the stopping power of the ion in a temperature anisotropic magnetized electron plasma. The analysis is based on the assumption that the energy variation of the ion is much less than its kinetic energy. The obtained general expression for stopping power is analyzed for weak and strong magnetic fields (i.e., for the electron cyclotron frequency less than and greater than the plasma frequency), and for low and high ion velocities. It is found that the friction coefficient contains, in addition to the usual velocity independent friction coefficient, an anomulous term which diverges logarithmically as the projectile velocity approaches zero. The physical origin of this anomulous term is the coupling between the cyclotron motion of the electrons and the long-wave length, low-frequency fluctuations produced by the projectile ion.

physics.plasm-ph↗