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This work focuses on the investigation of K+, K- and ϕ-meson production in Ag(1.58 A GeV)+Ag collisions. The energetically cheapest channel for direct K+ production in binary NN-collisions NN→NΛK+ lies at exactly this energy. For the remaining K- and ϕ-mesons, an excess energy of 0.31 GeV and 0.34 GeV in the centre of mass system has to be provided by the system. This makes these particles an excellent probe for effects inside the medium.
K+ and K- mesons can be reconstructed directly as they possess a cτ of approximately 3.7 m. Using the approximately 3 billion recorded Ag(1.58 A GeV)+Ag 0-30% most central collision events, all reconstructed K+ and K- within the detector acceptance are investigated for their kinematic properties and their particle production rates compared to a selection of existing models.
The Compressed Baryonic Matter (CBM) is one of the core experiments at the future Facility for Anti-proton and Ion Research (FAIR), Darmstadt, Germany. Its goal is to investigate nuclear matter characteristics at high net-baryon densities and moderate temperatures. The Silicon Tracking System (STS) is a central detector system of CBM.
It is placed inside a 1Tm magnet and operated at a temperature of about −10 °C to keep radiation-induced bulk current in the 300μm double-sided microstrip silicon sensors low. The design of the STS aims to minimize the material budget in the detector acceptance (2.5° < θ < 25°). In order to do so, the readout electronics is placed outside the active area, and the analog signals are transported via ultra-thin micro-cables. The STS comprises eight tracking stations with 876 modules. Each module is assembled on a carbon fiber ladder, which is subsequently mounted in the C-shaped aluminum frame.
The scope of the thesis focused on developing a modular control system framework that can be implemented for different sizes of experimental setups. The developed framework was used for setups that required a remote operation, like the irradiation of the powering modules for the front-end electronics (FEE), but also in laboratory-based setups where the automation and archiving were needed (thermal cycling of the STS electronics).
The low voltage powering modules will be placed in the vicinity of the experiment, therefore they will experience a total dose of up to 40mGy over the 10 years of STS lifetime.
To estimate the effects of the radiation on the low-voltage module performance, a dedicated irradiation campaign took place. It aimed at estimating the rate of radiation induced soft errors, that lead to the switch off of the FEE.
Regular power cycles of multiple front-end boards (FEBs) pose a risk to the experiment operation. Firstly, such behavior could negatively influence the physics performance but also have deteriorating effects on the hardware. It was further assessed what are the limitations of the FEBs with respect to the thermal cycling and the mechanical stress. The results served as an indication of possible failure modes of the FEB at the end of STS lifetime. Failure modes after repeated cycles and potential reasons were determined (e.g., Coefficient of Thermal Expansion (CTE) difference between the materials).
Due to the conditions inside the STS efficient temperature and humidity monitoring and control are required to avoid icing or water condensation on the electronics or silicon sensors. The most important properties of a suitable sensor candidate are resilience to the magnetic field, ionizing radiation tolerance, and fairly small size.
A general strategy for ambient parameters monitoring inside the STS was developed, and potential sensor candidates were chosen. To characterize the chosen relative humidity sensors the developed control framework was introduced. A sampling system with a ceramic sensor and Fiber Optic Sensors (FOS) were identified as reliable solutions for the distributed sensing system. Additionally, the industrial capacitive sensors will be used as a reference during the commissioning.
Two different designs of FOS were tested: a hygrometer and 5 sensors multiplexed in an array. The FOS hygrometer turned out to be a more reliable solution. One of the possible reasons for a worse performance is a relatively low distance between the subsequent sensors (15 cm) and a thicker coating. The results obtained from the time response study pointed out that the thinner coating of about 15μm should be a good compromise between the humidity sensitivity and the time response.
The implementation of the containerized-based control system framework for the mSTS is described in detail. The deployed EPICS-based framework proved to be a reliable solution and ensured the safety of the detector for almost 1.5 years. Moreover, the data related to the performance of the detector modules were analyzed and significant progress in the quality of modules was noted. Obtained data was also used to estimate the total fluence, which was based on the leakage current changes.
The developed framework provided a unique opportunity to automate and control different experimental setups which provided crucial data for the STS. Furthermore, the work underlines the importance of such a system and outlines the next steps toward the realization of a reliable Detector Control System for STS.
In the last twenty years, a variety of unexpected resonances had been observed within the charmonium mass region. Although the existence of unconventional states has been predicted by the quantum chromodynamics (QCD), a quantum field theory describing the strong force, a clear evidence was missing. The Y(4260) is such an unexpected and supernummerary state, first observed at BaBar in 2005, and aroused great interest, because it couples much stronger to hidden charm decays (charm-anticharm states like J/Psi or h_c) instead of open charm decays (D meson pairs). This is unusual for states with masses above the D anti-D threshold. Furthermore, it decays into a charged exotic state Y(4260)->Z_c(3900)^+- pi^-+. The charge of the Z_c(3900)^+- is an indication that it comprises of two more quarks than the charm-anticharm pair, and could therefore be assumed to be a four-quark state. Due to these still not understood properties of these QCD-allowed states, they are referred to as exotic XYZ states to emphasize their particularity.
In 2017, the collaboration of the Beijing Spectrometer III (BESIII) investigated the production reaction of the Y(4260) resonance based on a high-luminosity data set. This significantly improved precision of the measurement of the cross-section sigma(e+e- -> J/Psi pi^+ pi^-) permitted a resolution into two resonances, the Y(4230) and the Y(4360). The Z_c(3900)^+- had been discovered by the BESIII collaboration in 2013, thus this experiment at the Beijing Electron-Positron Collider II (BEPCII) is a top-performing facililty to study exotic charmonium-like states.
In this work, an inclusive reconstruction of the strange hyperon Lambda in the charmonium mass region is performed to study possible decays of Y states in order to provide further insight into their nature. Finding more states or new decay channels may provide crucial hints to understand the strong interaction beyond nonperturbative approaches.
Three resonances are observed in the energy dependent cross-section: the first with a mass of (4222.01 +- 5.68) MeV and a width of (154.26 +- 28.16) MeV, the second with a mass of (4358.88 +- 4.97) MeV and a width of (49.58 +- 13.54) MeV and the third with a mass of (4416.41 +- 2.37) MeV and a width of (23.88 +- 7.18) MeV. These resonances, with a statistical significance Z > 5sigma, can be interpreted as the states Y(4230), Y(4360) and psi(4415).
Additionally, a proton momentum-dependent analysis strategy has been used in terms of the inclusiveness of the reconstruction and to address the momentum discrepancies between generic MC and measured data.
This Ph. D. thesis with the title "Characterisation of laser-driven radiation beams: Gamma-ray dosimetry and Monte Carlo simulations of optimised target geometry for record-breaking efficiency of MeV gamma-sources" is dedicated to the study of the acceleration of electrons by intense sub-picosecond laser pulses propagating in a sub-millimeter plasma with near-critical electron density (NCD) and resulting generation of the gamma bremsstrahlung and positrons in the targets of different materials and thickness.
Laser-driven particle acceleration is an area of increasing scientific interest since the recent development of short pulse, high-intensity laser systems. The interaction of intense high-energy, short-pulse lasers with solid targets leads to the production of high-energy electrons in the relativistic laser intensity regime of more than 1018 W /cm2. These electrons play the leading role in the first stage of the interaction of laser with matter, which leads to the creation of laser sources of particles and radiation. Therefore, the optimisation of the electron beam parameters in the direction of increasing the effective temperature and beam charge, together with a slight divergence, plays a decisive role, especially for further detection and characterisation of laser-driven photon and positron beams.
In the context of this work, experiments were carried out at the PHELIX laser system (Petawatt High-Energy Laser for Heavy Ion eXperiments) at GSI Helmholtz Center for Heavy-Ion Research GmbH in Darmstadt, Germany. This thesis presents a thermoluminescence dosimetry (TLD) based method for the measurement of bremsstrahlung spectra in the energy range from 30 keV to 100 MeV. The results of the TLD measurements reinforced the observed tendency towards the strong increase of the mean electron energy and number of super-ponderomotive electrons. In the case of laser interaction with long-scale NCD-plasmas, the dose caused by the gamma-radiation measured in the direction of the laser pulse propagation showed a 1000-fold increase compared to the high contrast shots onto plane foils and doses measured perpendicular to the laser propagation direction for all used combinations of targets and laser parameters.
In this thesis I present novel characterisation method using a combination of TLD measurements and Monte Carlo FLUKA simulations applicable to laser-driven beams. The thermoluminescence detector-based spectrometry method for simultaneous detection of electrons and photons from relativistic laser-induced plasmas initially developed by Behrens et al. (Behrens et al., 2003) and further applied in experiments at PHELIX laser (Horst et al., 2015) delivered good spectral information from keV energies up to some MeV, but as it was presented in (Horst et al., 2015) this method was not really suitable to resolve the content of photon spectra above 10 MeV because of the dominant presence of electrons. Therefore, I created new evaluation method of the incident electron spectra from the readings of TLDs. For this purpose, by means of MatLab programming language an unfolding algorithm was written. It was based on a sequential enumeration of matching data series of the dose values measured by the dosimeters and calculated with of FLUKA-simulations. The significant advantage of this method is the ability to obtain the spectrum of incident electrons in the low energy range from 1 keV, which is very difficult to measure reliably using traditional electron spectrometers.
The results of the evaluation of the effective temperature of super-ponderomotive electrons retrieved from the measured TLD-doses by means of the Monte-Carlo simulations demonstrated, that application of low density polymer foam layers irradiated by the relativistic sub-ps laser pulse provided a strong increase of the electron effective temperature from 1.5 - 2 MeV in the case of the relativistic laser interaction with a metallic foil up to 13 MeV for the laser shots onto the pre-ionized foam and more than 10 times higher charge carried by relativistic electrons.
The progressive simulation method of whole electron spectra described with two -temperatures Maxwellian distribution function has been developed and the results of dose simulations were compared with the acquired experimental data. The advanced feature of this method, which distinguishes it from the results of the simulation of the photon spectrum using the interaction with the target of mono-energetic electron beams (Nilgün Demir, 2013; Nilgün Demir, 2019) or the initial electron spectrum expressed as a function of one electron temperature (Fiorini, 2012), is the ability to simulate the initial electron spectrum described by the Maxwellian distribution function with two temperatures.
The important objective of this thesis was dedicated to the study and characterisation of laser-driven photon beams. In addition to this, the positron beams were evaluated. The investigation of bremsstrahlung photons and positrons spectra from high Z targets by varying the target thickness from 10 µm to 4 mm in simulated models of the interactions of electron spectra with Maxwellian distribution functions allowed to define an optimal thickness when the fluences of photons and positrons are maximal. Furthermore based on the results of FLUKA simulations the gold material was found to be the most suitable for the future experiments as e − γ target because of its highest bremsstrahlung yield.
Additionally Monte Carlo simulations were performed applying the obtained electron beam parameters from the electron acceleration process in laser-plasma interactions simulated with particle-in-cell (PIC) code for two laser energies of 20 J and 200 J. The corresponding electron spectra were imported into a Monte Carlo code FLUKA to simulate the production process of bremsstrahlung photons and positrons in Au converter. FLUKA simulations showed the record conversion of efficiency in MeV gammas can reach 10%, which reinforces the generation of positrons. The obtained results demonstrate the advantages of long-scale plasmas of near critical density (NCD) to increase the parameters of MeV particles and photon beams generated in relativistic laser-plasma interaction. The efficiency of the laser-driven generation of MeV electrons and photons by application of low-density polymer foams is essentially enhanced.
Artificial intelligence in heavy-ion collisions : bridging the gap between theory and experiments
(2023)
Artificial Intelligence (AI) methods are employed to study heavy-ion collisions at intermediate collision energies, where high baryon density and moderate temperature QCD matter is produced. The experimental measurements of various conventional observables such as collective flow, particle number fluctuations, etc. are usually compared with expensive model calculations to infer the physics governing the evolution of the matter produced in the collisions. Various experimental effects and processing algorithms can greatly affect the sensitivity of these observables. AI methods are used to bridge this gap between theory and experiments of heavy-ion collisions. The problems with conventional methods of analyzing experimental data are illustrated in a comparative study of the Glauber MC model and the UrQMD transport model. It is found that the centrality determination and the estimated fluctuations of the number of participant nucleons suffer from strong model dependencies for Au-Au collisions at 1.23 AGeV. This can bias the results of the experimental analysis if the number of participant nucleons used is not consistent throughout the analysis and in the final model-to-data comparison. The measurable consequences of this model dependence of the number of participant nucleons are also discussed. In this context, PointNet-based AI models are developed to accurately reconstruct the impact parameter or the number of participant nucleons in a collision event from the hits and/or reconstructed track of particles in 10 AGeV Au-Au collisions at the CBM experiment. In the last part of the thesis, different AI methods to study the equation of state (EoS) at high baryon densities are discussed. First, a Bayesian inference is performed to constrain the density dependence of the EoS from the available experimental measurements of elliptical flow and mean transverse kinetic energy of mid rapidity protons in intermediate energy collisions. The UrQMD model was augmented to include arbitrary potentials (or equivalently the EoSs) in the QMD part to provide a consistent treatment of the EoS throughout the evolution of the system. The experimental data constrain the posterior constructed for the EoS for densities up to four times saturation density. However, beyond three times saturation density, the shape of the posterior depends on the choice of observables used. There is a tension in the measurements at a collision energy of about 4 GeV. This could indicate large uncertainties in the measurements, or alternatively the inability of the underlying model to describe the observables with a given input EoS. Tighter constraints and fully conclusive statements on the EoS require accurate, high statistics data in the whole beam energy range of 2-10 GeV, which will hopefully be provided by the beam energy scan programme of STAR-FXT at RHIC, the upcoming CBM experiment at FAIR, and future experiments at HIAF and NICA. Finally, it is shown that the PointNet-based models can also be used to identify the equation of state in the CBM experiment. Despite the uncertainties due to limited detector acceptance and biases in the reconstruction algorithms, the PointNet-based models are able to learn the features that can accurately identify the underlying physics of the collision. The PointNet-based models are an ideal AI tool to study heavy-ion collisions, not only to identify the geometric event features, such as the impact parameter or the number of participant nucleons, but also to extract abstract physical features, such as the EoS, directly from the detector outputs.
A synchrotron is a particular type of cyclic particle accelerator and the first accelerator concept to enable the construction of large-scale facilities [10], such as the largest particle accelerator in the world, the 27-kilometre-circumference Large Hadron Collider (LHC) by CERN near Geneva, Switzerland, the European Synchrotron Radiation Facility (ESRF) in Grenoble, France for the synchrotron radiation, the superconducting, heavy ion synchrotron SIS100 under construction for the FAIR facility at GSI, Darmstadt, Germany and so on. Unlike a cyclotron, which can accelerate particles starting at low kinetic energy, a synchrotron needs a pre-acceleration facility to accelerate particles to an appropriate initial value before synchrotron injection. A pre-acceleration can be realized by a chain of other accelerator structures like a linac, a microtron in case of electrons, for example, Proton and ion injectors Linac 4 and Linac 3 for the LHC, UNLAC as the injector for the SIS18 in GSI and in future the SIS18 as injector for the SIS100. The linac is a commonly used injector for the ion synchrotron and consists of some key components. The three main parts of a linac are: An ion source creating the particles, a buncher system or an RFQ followed by the main drift tube accelerator DTL. In order to meet the energy and the beam current requirement of a synchrotron injector linac, its cost is a remarkable percentage of the total facility costs.
However, the normal conducting linac operation at cryogenic temperatures can be a promising solution in improving the efficiency and reducing the costs of a linac. Synchrotron injectors operate at very low duty factor with beam pulse lengths in 1 micros to 100 micros range, as most of the time is needed to perform the synchrotron cycle. Superconducting linacs are not convenient, as they cannot efficiently operate at low duty factor and high beam currents.
The cryogenic operation of ion linacs is discussed and investigated at IAP in Frankfurt since around 2012 [1, 37]. The motivation was to develop very compact synchrotron injectors at reduced overall linac costs per MV of acceleration voltage. As the needed beam currents for new facilities are increasing as well, the new technology will also allow an efficient realization of higher injector linac energies, which is needed in that case. Operating normal conducting structures at cryogenic temperature exploits the significantly higher conductivity of copper at temperatures of liquid nitrogen and below. On the other hand, the anomalous skin effect reduces the gain in shunt impedance quite a bit[25, 31, 9]. Some intense studies and experiments were performed recently, which are encouraging with respect to increased field levels at linac operation temperatures between 30 K and 70 K [17, 24, 4, 23, 5, 8]. While these studies are motivated by applications in electron acceleration at GHz-frequencies, the aim of this paper is to find applications in the 100 to 700 MHz range, typical for proton and ion acceleration. At these frequencies, a higher impact in saving RF power is expected due to the larger skin depth, which is proportional to the frequency to the power of negative half with respect to the normal skin effect. On the other hand, it is assumed that the improvement in maximum surface field levels will be similar to what was demonstrated already for electron accelerator cavities. This should allow to find a good compromise between reduced RF power needs for achieving a given accelerator voltage and a reduced total linac length to save building costs.
A very important point is the temperature stability of the cavity surface during the RF pulse. This is of increasing importance the lower the operating temperature is chosen: the temperature dependence of the electric conductivity in copper gets rather strong below 80 K, as long as the RRR - value of the copper is adequate. It is very clear, that this technology is suited for low duty cycle operated cavities only - with RF pulse lengths below one millisecond. At longer pulses the cavity surface will be heated within the pulse to temperatures, where the conductivity advantage is reduced substantially. These conditions fit very well to synchrotron injectors or to pulsed beam power applications.
H – Mode structures of the IH – and of the CH – type are well-known to have rather small cavity diameters at a given operating frequency. Moreover, they can achieve effective acceleration voltage gains above 10 MV/m even at low beam energies, and already at room temperature operation[29]. With the new techniques of 3d – printing of stainless steel and copper components one can reduce cavity sizes even further – making the realization of complex cooling channels much easier.
Another topic are copper components in superconducting cavities – like power couplers. It is of great importance to know exactly the thermal losses at these surfaces, which can’t be cooled efficiently in an easy way.
Im Rahmen dieser Arbeit wurde ein verbessertes Buncher-System für Hochfrequenzbeschleuniger mit niedrigem und mittlerem Ionenstrom entwickelt. Die entwickelte Methodik hat ermöglicht, ein effektives, vereinfachtes Buncher-System für die Injektion in HF-Beschleuniger wie RFQs, Zyklotrons, DTLs usw. zu entwerfen, welches kleine Ausgangsemittanzen und beträchtliche Strahltransmissionen erzielt. Um einen mono-energetischen und kontinuierlichen Strahl aus einer Ionenquelle für den Einschuss in eine Hochfrequenz-Beschleunigerstruktur anzupassen, wird eine Energiemodulation benötigt, die im weiteren Verlauf (Driftstrecke) zur Längsfokussierung des Strahls führt. Durch eine Sägezahnwellenform wird die ideale Energiemodulation aufgrund der linearen Abhängigkeit zwischen der Energie der Teilchen und ihren relativen Phasen erreicht. Dies ist jedoch technologisch nicht möglich, da Teilchenbeschleuniger Spannungsniveaus im Bereich kV bis 100 kV benötigen. Dagegen ist für eine solche Zielsetzung eine räumliche Trennung der sinusförmigen Anregung mit der Grundfrequenz und höheren Harmonischen möglich.
Daher wurde in dieser Arbeit ein verbesserter harmonischer Buncher, der sogenannte „Double Drift Harmonic Buncher - DDHB“ entwickelt, welcher zahlreiche Vorteile hat. Eine geringe longitudinale Emittanz sowie finanzielle Aspekte sprechen für diesen Lösungsansatz. Die Hauptelemente eines DDHB Systems sind zwei Kavitäten, die durch eine Driftlänge L1 getrennt sind, wobei der erste Resonator mit der Grundfrequenz bei -90° synchroner Phase und angelegter Spannung V1 und der zweite Resonator bei der zweiten harmonischen Frequenz mit +90 synchroner Phase und angelegter Spannung V2 betrieben werden. Schließlich ist eine zweite Drift L2 am Ende des Arrays für eine longitudinale Strahlfokussierung am Hauptbeschleunigereingang erforderlich. Somit erfüllt ein solcher Aufbau das angestrebte Ziel einer hohen Einfangseffizienz und einer kleinen longitudinalen Emittanz durch Anpassen der vier Designparameter V1, L1, V2 und L2.
Das Verständnis der Fokussierung, ausgehend von einem Gleichstromstrahl, einschließlich der Raumladungskräfte, ist einer der wesentlichen Bestandteile der Strahlphysik. Viele kommerzielle Codes bieten Simulationsmöglichkeiten in diesem Anwendungsbereich. Ihre Ansätze bleiben jedoch dem Anwender meist verborgen, oder es fehlen wichtige Details zur genauen Abbildung des vorliegenden Konzepts. Daher bestand eine Hauptaufgabe dieser Arbeit darin, einen speziellen Multi-Particle-Tracking-Beam-Dynamics-Code (BCDC) zu entwickeln, bei dem der Raumladungseffekt während des Bunch-Vorgangs, ausgehend von einem DC-Strahl berechnet wird. Der BCDC - Code enthält elementare Routinen wie Drift und Beschleunigungsspalt oder magnetische Linse für die transversale Strahlfokussierung und Raumladungsberechnungen unter Berücksichtigung der Auswirkungen der nächsten Nachbar-Bunche (NNB). Der Raumladungsalgorithmus in BCDC basiert auf einer direkten Coulomb- Gitter-Gitter-Wechselwirkung und Berechnungen des elektrischen Feldes durch Lokalisierung der Ladungsdichte auf einem kartesischen Gitter. Um Genauigkeit zu erreichen, werden die Feldberechnungen in Längsrichtung symmetrisch um das zentrale Bucket (βλ-Größe) erweitert, so dass das Simulationsfeld dreimal so groß ist. Die zentrale Teilchenverteilung wird dann nach jedem Schritt in die benachbarten Buckets kopiert. Anschließend werden die resultierenden Felder im Hauptgitterfeld neu berechnet, indem die elektrischen Felder im Hauptgitterfeld mit denen aus den benachbarten Regionen überlagert werden. Ohne diese Methode würde z. B. ein kontinuierlicher Strahl, welcher jedoch in der Simulation nur innerhalb einer Zelle der Länge βλ definiert ist, zu einer resultierenden Raumladungsfeldkomponente Ez an beiden Rändern der Zelle führen. Ein solches unphysikalisches Ergebnis konnte durch die Anwendung der NNB-Technik bereits weitgehend eliminiert werden. Zusätzlich zum NNB-Feature verfügt das BCDC über eine weitere Besonderheit nämlich die sogenannte Raumladungskompensation (SCC). Aufgrund der Ionisierung des Restgases kommt es entlang des Niederenergiestrahltransports zu einer teilweisen Raumladungskompensation, und zwar am und hinter dem Bunchersystem mit unterschiedlichen Prozentsätzen. Eines der Hauptziele des DDHB-Konzepts besteht darin, es für Hochstromstrahlanwendungen zu entwickeln. Dabei ermöglicht die teilweise Raumladungskompensation, dass das Design in der Praxis höhere Stromniveaus erreicht. Dadurch ist das BCDC-Programm ein leistungsstarkes Werkzeug für Simulationen in künftigen, stromstarken Projekten. Proof-of-Principle-Designs wurden in dieser Arbeit entwickelt.
In this thesis, we use lattice QCD to study a part of the QCD phase diagram, specifically the QCD phase transition at mu=0, where the QCD matter changes from hadron gas to quark-gluon plasma (QGP) with increasing temperature.
This phase transition takes place as a crossover, but when theoretically changing the masses of the quarks, the order of the phase transition changes as well.
We focus on the region of heavy quark masses with Nf=2 flavours, where we investigate the critical quark mass at the second order phase transition in the form of a Z2 point between the first-order and the crossover region.
The first-order region is positioned at infinitely heavy quarks. As the quark masses decrease, the associated Z3 centre symmetry breaks explicitly, causing the first-order phase transition to weaken until it turns into the Z2 point and finally into a crossover.
We study this Z2 point using simulations at Nf=2 and lattices of the sizes Nt = {6, 8, 10, 12}, partially building on previous work, in which the simulations for Nt = {6, 8, 10} were started.
The simulations for Nt=12 are not finished yet though, but we were able to draw some preliminary conclusions. These simulations are run on GPUs and CPUs, using the codes Cl2QCD and open-QCD-FASTSUM, respectively. Afterwards, the data goes through a first analysis step in the form of the Python program PLASMA, preparing it for the two techniques we use to analyse the nature of the phase transition.
As a first, reliable analysis method, we perform a finite size scaling analysis of the data to find the location of the Z2 point. Since we are using lattice QCD, performing a continuum extrapolation is necessary to reach the continuum result.
In regard to this, the finite size scaling analysis method is hampered by the excessive amount of simulated data that is needed regarding statistics and the total number of simulations, which is why this thesis is only an intermediate step towards the continuum limit.
This also leads to the second analysis technique we explore in this thesis.
We start to design a Landau theory which describes the phase boundary for heavy masses at Nf=2 based on the simulated data.
We develop a Landau functional for every Nt we have simulation data for.
Albeit the results are not at the same precision as the ones from the finite size scaling analysis, we are able to reproduce the position of the Z2 point for every Nt.
Even though we are not able to take a continuum extrapolation right now, after more development takes place in future works, this approach might, in the long run, lead to a continuum result that won't need as many simulations as the finite size scaling analysis.
Precise tune determination and split beam emittance reconstruction at the CERN PS synchrotron
(2023)
In accelerator physics, the need to improve the performance and better control the operating point of an accelerator has become, year after year, an increasingly important need in order to achieve higher energies and brightness, as well as point-like particle beams. If this involves increasingly advanced technological developments (in terms, for example, of materials for more intense superconducting magnets), it can not take place in the absence of targeted studies of linear and non-linear beam dynamics. In the context of this Ph.D. thesis in physics, linear and non-linear dynamics of charged particles in circular accelerators is the topic that will be discussed and treated in detail. In particular, the presentation and discussion of the results will be divided in two main topics: the need to know the physical properties of a proton beam; and the development of innovative methods to determine and study the accelerator’s working point. With regard to the first topic, an innovative procedure will be presented to determine the transverse size of the PS beam in the beam extraction phase. Among the different ways the extraction occurs at the PS, the analysed one is based on the transverse splitting of the beam by means of non-linear fields. Thus, the knowledge of the transverse beam size is not trivial since resonant linear and non-linear beam structures (namely, core and islands) arise and, for each of them, the beam size has to be quantified. This parameter is crucial for two main reasons: the accelerator that will receive the beam exiting the upstream accelerator may have restrictions (physical or magnetic) that involve a partial or total loss of the incoming beam; and any experiments located downstream of the considered accelerator may need a beam with a transversal size as constant as possible; consequently, its monitoring and control are essential. The second topic concerns the accurate determination of the working point of an accelerator, defined as the number of transverse oscillations the particle beam travels per unit of accelerator circumference, both horizontally and vertically. This quantity is called horizontal and vertical tune, respectively. Their knowledge is also crucial to understand whether the beam will be stable or unstable. In fact, not all tune values are acceptable, as there are particular values that bring the beam into resonance. In this configuration, the amplitude of the transverse oscillations of the particles increases in an uncontrolled manner and leads to the loss of all or part of the beam. Note that, in particular operating conditions, the resonant conditions are sought and desired to model, in a suitable way, the transversal shape of the beam, such as the above mentioned PS extraction scheme. It is even clearer how much the determination of the machine working point is essential to determine the operating conditions of an accelerator. In this context, several methods (also taken from the field of applied mathematics) to calculate the tune will be demonstrated and tested numerically on different types of synthetic signals. At the end of this description, the use of experimental data will allow to obtain the benchmark of a new method for the direct calculation of some characteristic quantities of non-linear beam dynamics (namely, the amplitude detuning, i.e. the variation of tune as a function of intensity of the perturbation provided to the beam.
Precise intensity monitoring at CRYRING@ESR: on designing a Cryogenic Current Comparator for FAIR
(2023)
In the field of today’s beam intensity diagnostic there is a significant gap in the non-interceptive, calibrated measurement of the absolute intensity of continuous (unbunched) dc beams with current amplitudes below 1 μA. At the Facility for Antiproton and Ion Research (FAIR) low-intensity DC beams will occur during slow extraction from the synchrotrons as well as for coasting beams of highly-charged or exotic nuclei in the storage rings. The lack of adequate beam instrumentation limits the experimental program as well as the accuracy of experimental results.
The Cryogenic Current Comparator (CCC) can close the diagnostic gap with a high-precision dc current reading independent of ion-species and of beam parameters. However, the established detector design based on a core with high magnetic permeability and on a radial shield geometry has well-known weaknesses concerning magnetic shielding efficiency and intrinsic current noise. To eliminate these weaknesses, a novel coreless CCC with a co-axial shield was constructed and combined with a high-performance SQUID contributed by the Leibniz-Institute of Photonic Technology (Leibniz-IPHT Jena). The new axial CCC model was compared to a radial CCC with the established design provided by the Friedrich-Schiller-University Jena. According to numerical simulations prepared at TU Darmstadt and test measurements of the detectors in the laboratory, the new design offered a significant improvement of the shielding factor – from 75dB to 207dB at the required dimensions – and eliminated all noise contributions from the core material, promising an improved current resolution. Although the lower inductance of the pickup coil reduced the coupling to the beam significantly, the noise properties of the new CCC type were comparable to the classical version with a high-permeability core. However, the expected decrease of the low-frequency noise and thus an increase of the current resolution could not be observed at this stage of development.
Consequently, the classical CCC based on the radial shielding and high-permeability core had to be installed in CRYRING@ESR to provide best possible intensity measurements for the upcoming experimental campaign. In CRYRING the CCC was operated with beam currents between 1nA and 20μA and with different ion species (H, Ne, O, Pb, U). It was shown that the CCC provides a noise-limited current resolution of better than 3.2 nArms at a bandwidth of 200 kHz as well as a noise level below 40 pA/√Hz above 1 kHz. During the operation, the main noise sources of the accelerator environment had to be identified and suitable mitigation strategies were developed. Temperature and pressure fluctuations were suppressed with a newly-designed cryogenic support system based on a 70 l helium bath cryostat, developed and built in collaboration with the Institut für Luft- und Kältetechnik Dresden, in combination with a helium re-liquefier. The cryogenic operating time was restricted to around 7 days, which must be expanded significantly in the future. Digital filters were developed to remove the perturbations of the helium liquefier and of the neighboring dipole magnets. Given the promising results the CCC system can be considered as a prototype for future CCCs at FAIR.