A Spectrometer for Proton Driven Plasma Accelerated Electrons at AWAKE - Recent Developments

The SHiP experiment (Search for Hidden Particles) is a beam dump experiment proposed at the CERN SPS with the submission of a Technical Proposal in April 2015. SHiP aims at the observation of long lived particles very weakly coupled with ordinary matter. These particles are mostly produced in the decay of charmed hadrons whose production is therefore enhanced through the definition of the characteristics of both the beam and the proton target. This makes the SHiP experiment a Standard Model neutrino factory too, in particular of tau neutrinos produced by the Ds decay chain. My studies have mainly focused on the design of the neutrino detector and on the evaluation of its performances. The Neutrino Detector is placed in a magnetic field and it exploits the Emulsion Cloud Chamber Technology with the micrometric position resolution needed to disentangle the tau lepton decay vertex from the neutrino interaction vertex. This peculiarity, together with the high electron identification efficiency, makes this detector also suitable to search for sub-GeV Dark Matter (produced in the decay of the dark photon) through its scattering with the electrons in the emulsion target. The main unit of the Neutrino Detector is the brick (lead plates interleaved with emulsion films) followed downstream by a Compact Emulsion Spectrometer (CES, 3 emulsion films interleaved with light material) needed to measure the charge and momentum of hadrons produced in neutrino interactions and short lived particles decays. A Muon Magnetic Spectrometer is placed immediately downstream to measure the charge and the momentum of muons produced in charged current muon neutrino interactions or in tau to muon decays. In this thesis the signal and background yield for all the different neutrino flavours are presented: more than twenty thousand nutau and nutau-bar charged current interactions are expected in five years of data taking. This unprecedented statistics of tau neutrinos will allow to measure the structure functions F4 and F5 entering the neutrino-nucleon cross section. The SHiP performances in the measurement of the tau neutrino anomalous magnetic moment are also reported with the estimation of the background yield for this searches. A preliminary estimate of the background events expected for LDM searches is also shown. Detailed studies will be performed with more general assumptions on the dark photon and the dark matter masses. Thanks to the large flux of electron and muon neutrinos interacting in the neutrino target, the measurement of the strange quark content of the nucleon has also been studied. The second to last chapter of the thesis is devoted to the description of the optimisation studies which are on going in view of the production of a Comprehensive Design Report to hand in to the CERN SPS Committee by the end of 2018. In this optimised version of the SHiP detector, the Neutrino Detector is roughly 20 m closer to the proton target, with a resulting increment in the incoming neutrino flux. However, being closer to the proton target has also generated the need for a complete redesign of the detector layout to fit the muon free region. A study of muon background rates on the Neutrino Detector and on the downstream Muon Magnetic Spectrometer is also reported. The last chapter describes the Test Beam activities conducted at CERN to study the performances of both the Compact Emulsion Spectrometer and of the gaseous electronic detectors (GEM) which complement the Neutrino Detector. The data analysis was carried out in the Napoli Emulsion Laboratory. The test beam for the CES has led us to discard the option of using the Rohacell as a light material interleaved to the emulsion films. The test beam with the GEM-emulsion coupled detector has shown a rapid degradation of the GEM performances in terms of position resolution when dealing with inclined tracks also in absence of magnetic field. The degradation is enhanced when the polarisation of the magnetic field contributes to the avalanche displacement. In case of a compensating magnetic field, the position resolution shows the same behaviour as in absence of field, except for a phase-shift of 15 degrees corresponding to the Lorentz angle of the generated electron avalanche.

The Time Dependent Schrödinger Equation In A Strong Laser Field

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) is a project at CERN aiming to accelerate an electron bunch in a plasma wakefield driven by a proton bunch. The plasma is induced in a 10 m long rubidium vapor cell using a pulsed Ti:Sapphire laser, with the wakefield formed by a proton bunch from the CERN Super Proton Synchrotron (SPS). A 16 MeV electron bunch is simultaneously injected into the plasma cell to be accelerated by the wakefield to energies in the GeV range over this short distance. After successful runs with the proton and laser beams, the electron beam line was installed and commissioned at the end of 2017 to produce and inject a suitable electron bunch into the plasma cell. To achieve the goals of the experiment, it is important to have reliable beam instrumentation measuring the various parameters of the proton, electron and laser beams. This contribution presents the status of the beam instrumentation in AWAKE and reports on the performance achieved during the AWAKE runs in 2017.

The interaction of the witness beam with the surrounding plasma particles and wakefields was studied. The implications of the elastic scattering process on beam emittance and, emittance evolution under the focusing and acceleration provided by plasma wakefields were discussed. Simulations results from GEANT4 are presented in this paper.

This thesis presents a complete set of proton-impact ionization cross section data of DNA constituents determined at the Physikalisch-Technische Bundesanstalt (PTB). The cross section data describe the probabilities for the ionization of gas-phase tetrahydrofuran, pyrimidine and trimethyl phosphate that are structural analogues to the base, sugar, and phosphate residue of the DNA, respectively. Total, single-differential and double-differential ionization cross sections were determined, whereby the differential description refers to the energy or angular dependence of electron emission. Double-differential cross sections were measured for impact energies between 75 keV and 3000 keV over an angular range between 15бу and 150бу in 15бу intervals. Both single-differential and total ionization cross sections were derived by integration of the measured double-differential cross sections. The measurements of double-differential cross sections were carried out using a crossed-beam arrangement in a high-vacuum chamber. The proton beam, which perpendicularly crosses an effusive gas jet target of DNA constituents inside the chamber, was generated either by the 3.75 MV Van de Graaff accelerator of the PTB ion accelerator facility (PIAF) or a newly developed 155 kV ion accelerator. In the measurement a newly constructed electron spectrometer was used to detect the secondary electrons produced by proton collisions with the target molecules. The energy of the secondary electrons was selected by a hemispherical electron energy analyzer, which was mounted on a turntable to allow the spectrometer to rotate around the axis of the gas jet. Hence, the energy spectra could be recorded at defined observation angles with respect to the proton beam. These spectra were converted into absolute cross section values via a normalization procedure based on previously published absolute electron-impact cross section data.

Via three-dimensional particle-in-cell simulations, the self-mode-transition of a laser-driven electron acceleration from laser wakefield to plasma-wakefield acceleration is studied. In laser wakefield accelerator (LWFA) mode, an intense laser pulse creates a large amplitude wakefield resulting in high-energy electrons. Along with the laser pulse depletion, the electron bunch accelerated in the LWFA mode drives a plasma wakefield. Then, after the plasma wakefield accelerator mode is established, electrons are trapped and accelerated in the plasma wakefield. The mode transition process and the characteristics of the accelerated electron beam are presented.

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.

In this article, we present the underlying physics and the present status of high gradient and high-energy plasma accelerators. With the development of compact short pulse high-brightness lasers and electron and positron beams, new areas of studies for laser/particle beam-matter interactions is opening up. A number of methods are being pursued vigorously to achieve ultra-high-acceleration gradients. These include the plasma beat wave accelerator (PBWA) mechanism which uses conventional long pulse ( approximately 100 ps) modest intensity lasers (I approximately 10(14)-10(16) W cm(-2)), the laser wakefield accelerator (LWFA) which uses the new breed of compact high-brightness lasers (<1 ps) and intensities >10(18) W cm(-2), self-modulated laser wakefield accelerator (SMLWFA) concept which combines elements of stimulated Raman forward scattering (SRFS) and electron acceleration by nonlinear plasma waves excited by relativistic electron and positron bunches the plasma wakefield accelerator. In the ultra-high intensity regime, laser/particle beam-plasma interactions are highly nonlinear and relativistic, leading to new phenomenon such as the plasma wakefield excitation for particle acceleration, relativistic self-focusing and guiding of laser beams, high-harmonic generation, acceleration of electrons, positrons, protons and photons. Fields greater than 1 GV cm(-1) have been generated with monoenergetic particle beams accelerated to about 100 MeV in millimetre distances recorded. Plasma wakefields driven by both electron and positron beams at the Stanford linear accelerator centre (SLAC) facility have accelerated the tail of the beams.

Plasma wakefield acceleration has the potential to dramatically shrink the size and cost of particle accelerators. Research at the SLAC National Accelerator Laboratory has demonstrated that plasmas can provide 1,000 times the acceleration in a given distance compared with current technologies. Developing revolutionary and more efficient acceleration techniques that allow for an affordable high-energy collider is the focus of FACET, a National User Facility at SLAC. The existing FACET National User Facility uses part of SLAC’s two-mile-long linear accelerator to generate high-density beams of electrons and positrons. FACET-II is a new test facility to develop advanced acceleration and coherent radiation techniques with high-energy electron and positron beams. It is the only facility in the world with high energy positron beams. FACET-II provides a major upgrade over current FACET capabilities and the breadth of the potential research program makes it truly unique. It will synergistically pursue accelerator science that is vital to the future of both advanced acceleration techniques for High Energy Physics, ultra-high brightness beams for Basic Energy Science, and novel radiation sources for a wide variety of applications. The design parameters for FACET-II are set by the requirements of the plasma wakefield experimental program. To drive the plasma wakefield requires a high peak current, in excess of 10kA. To reach this peak current, the electron and positron design bunch size is 10μ by 10μ transversely with a bunch length of 10μ. This is more than 200 times better than what has been achieved at the existing FACET. The beam energy is 10 GeV, set by the Linac length available and the repetition rate is up to 30 Hz. The FACET-II project is scheduled to be constructed in three major stages. Components of the project discussed in detail include the following: electron injector, bunch compressors and linac, the positron system, the Sector 20 sailboat and W chicanes, and experimental area and infrastructure.

We propose a Plasma Accelerator Research Station (PARS) based at proposed FEL test facility CLARA (Compact Linear Accelerator for Research and Applications) at Daresbury Laboratory. The idea is to use the relativistic electron beam from CLARA, to investigate some key issues in electron beam transport and in electron beam driven plasma wakefield acceleration, e.g. high gradient plasma wakefield excitation driven by a relativistic electron bunch, two bunch experiment for CLARA beam energy doubling, high transformer ratio, long bunch self-modulation and some other advanced beam dynamics issues. This paper presents the feasibility studies of electron beam transport to meet the requirements for beam driven wakefield acceleration and presents the plasma wakefield simulation results based on CLARA beam parameters. Other possible experiments which can be conducted at the PARS beam line are also discussed.

Ionization injection in a plasma wakefield accelerator was investigated experimentally using two lithium plasma sources of different lengths. The ionization of the helium gas, used to confine the lithium, injects electrons in the wake. After acceleration, these injected electrons are observed as a distinct group from the drive beam on the energy spectrometer. They typically have a charge of tens of pC, an energy spread of a few GeV, and a maximum energy of up to 30 GeV. The emittance of this group of electrons can be many times smaller than the initial emittance of the drive beam. The energy scaling for the trapped charge from one plasma length to the other is consistent with the blowout theory of the plasma wakefield.

As part of the LHC Injector Upgrade (LIU) project, the Super Proton Synchrotron (SPS) must be upgraded in order to inject in the LHC 25 ns bunch spaced beams of higher intensity. To mitigate the Electron Multipacting (EM) phenomenon in the SPS, CERN developed thin film carbon coatings with a low Secondary Electron Yield (SEY). The development went from coating small samples, up to coating of 6 m long vacuum chambers directly installed in the magnets. To deposit the low SEY amorphous carbon (aC) film on the vacuum chamber inner wall of SPS ring components, a modular hollow cathode train was designed. The minimization of the logistical impact requires a strategy combining in-situ and ex-situ coating, depending on the type of components. To validate the implementation strategy of the aC thin films and the in-situ coating process along the 7 km long SPS beamline, approximately 2 cells of B-type bending dipoles and 9 focussing quadrupoles are foreseen to be treated with the aC coating during the Extended Year End Technical Stop (EYETS) 2016-2017. We will discuss the coating technique and evaluate both the implementation process and the resulting coating performance.

Muon beams of low emittance provide the basis for the intense, well-characterised neutrino beams necessary to elucidate the physics of flavour at the Neutrino Factory and to provide lepton-antilepton collisions at energies of up to several TeV at the Muon Collider. The International Muon Ionization Cooling Experiment (MICE) will demonstrate ionization cooling, the technique by which it is proposed to reduce the phase-space volume occupied by the muon beam at such facilities. In an ionization-cooling channel, the muon beam passes through a material (the absorber) in which it loses energy. The energy lost is then replaced using RF cavities. The combined effect of energy loss and re-acceleration is to reduce the transverse emittance of the beam (transverse cooling). A major revision of the scope of the project was carried out over the summer of 2014. The revised project plan, which has received the formal endorsement of the international MICE Project Board and the international MICE Funding Agency Committee, will deliver a demonstration of ionization cooling by September 2017. In the revised configuration a central lithium-hydride absorber provides the cooling effect. The magnetic lattice is provided by the two superconducting focus coils and acceleration is provided by two 201 MHz single-cavity modules. The phase space of the muons entering and leaving the cooling cell will be measured by two solenoidal spectrometers. All the superconducting magnets for the ionization cooling demonstration are available at the Rutherford Appleton Laboratory and the first single-cavity prototype is under test in the MuCool Test Area at Fermilab. The design of the cooling demonstration experiment will be described together with a summary of the performance of each of its components. The cooling performance of the revised configuration will also be presented.

The work I carried out in the last three years was focused on the development and test of purification systems and data analysis techniques for the Borexino experiment, a detector specifically designed for low energy neutrino spectroscopy. I participated to the study of the adsorption technique based on activated carbons for removing krypton from nitrogen and to the investigation of the purity of nitrogen available on the market. I analyzed the data from the third campaign of the Borexino prototype detector, the Counting Test Facility (CTF), to identify each contamination source in the scintillator and to evaluate the efficiency of the purification system. 11C represents the main background source in the CNO and pep neutrino energy range. I investigated on the possibility to apply the three-fold coincidence technique with the parent muon track and the subsequent neutron capture on protons in Borexino in order to tag and remove 11C nuclides on a one-by-one basis. Furthermore, I implemented and tested such technique on the CTF data.

In order to identify design weaknesses and improve reliability for a product as soon as possible, accelerated life-testing is extensively used. Accelerated life-testing (ALT) is either to accelerate the number of cycle per unit time (frequency acceleration) or to increase the stress-levels when operating (stress acceleration). In this paper, Constant-stress accelerated life-testing is used construct the accelerated function. Singly right censoring is considered to form the failure distributions at various stress levels. The characteristic parameters (location and scale) for each distribution are estimated by incorporating the methods of best linear unbiased estimators with the theory of order statistics. The scale parameter being minimum variance is derived out using the technique of Lagrange Multiplier. A log-linear life-stress relationship is suggested to formulate the accelerated equation. The unknown coefficients the accelerated equation are obtained using Gauss-Markov theorem. Once the scale parameter and the unknown coefficients determined, the life normal operating condition and the related reliability measures could then be evaluated. Typically, several cases involving various failure distributions are used as examples to depict the estimated procedures ALT.