Accelerator Experiments Research Articles

Constraints on the coupling with photons of heavy axion-like-particles from Globular Clusters

We update the globular cluster bound on massive (ma up to a few 100 keV) axion-like particles (ALP) interacting with photons. The production of such particles in the stellar core is dominated by the Primakoff γ+Ze→Ze+a and by the photon coalescence process γ+γ→a. The latter, which is predominant at high masses, was not included in previous estimations. Furthermore, we account for the possibility that axions decay inside the stellar core, a non-negligible effect at the masses and couplings we are considering here. Consequently, our result modifies considerably the previous constraint, especially for ma≳50keV. The combined constraints from Globular Cluster stars, SN 1987A, and beam-dump experiments leave a small triangularly shaped region open in the parameter space around ma∼0.5−1MeV and gaγ∼10−5GeV−1. This is informally known as the ALP “cosmological triangle” since it can be excluded only using standard cosmological arguments. As we shall mention, however, there are viable cosmological models that are compatible with axion-like particles with parameters in such region. We also discuss possibilities to explore the cosmological triangle experimentally in upcoming accelerator experiments.

Target normal sheath acceleration and laser wakefield acceleration particle-in-cell simulations performance on CPU & GPU architectures for high-power laser systems

We present an integrated study on the scalability and performance of particle-in-cell (PIC) code simulations on CPU and GPU architectures of high parallelization focused on target normal sheath acceleration (TNSA) and laser wakefield acceleration (LWFA) experiments. The developed models follow the experimental specifications of the high-power lasers systems hosted at the infrastructures of the Institute of Plasma Physics & Lasers of the Hellenic Mediterranean University in Crete, Greece and the Extreme Light Infrastructure - Nuclear Physics in Romania. The simulations are implemented on the High-Performance Computer for Advanced Research Information System of the Greek National Infrastructures for Research and Technology. Two representative experiments for TNSA and for LWFA are initially simulated by 2D models with the minimum computational resource demands and the results are used as a reference for the scalability and performance investigation. We further extend our study to 3D models aiming to reproduce the physics involved in both laser-plasma particle accelerators. A detailed analysis of the simulation results, accompanied with the computational demands, scalability and performance of the CPU and the GPU architectures, is provided. Our research findings highlight the key features and parameters of the physical and numerical models which drive simulations to converge to reliable results by means of physics, computational and runtime demands and shed light on their influence on the efficiency and performance of the PIC simulations.

Analysis of the Results of the Neutrino-4 Experiment on the Search for the Sterile Neutrino and Comparison with Results of Other Experiments

We present new results of measurements of reactor antineutrino flux and spectrum dependence on the distance in the range 6-12 meters from the center of the reactor core at SM-3 reactor (Dimitrovgrad, Russia). Additional measurements were carried out and set of data to perform statistical analysis was almost doubled since the previous report. Using all collected data we performed the model independent analysis on the oscillation parameters $\Delta m^2_{14}$ and $\sin^2(2\theta_{14})$. The method of coherent summation of results of measurements allows us to directly observe the effect of oscillations. We observed an oscillation effect in vicinity of $\Delta m^2_{14} = (7.25\pm0.13_{st}\pm1.08_{sys}) \text{eV}^2$ and $\sin^2(2\theta_{14}) =0.26\pm0.08_{st}\pm 0.05_{sys}$. We provide a comparison of our results with results of other experiments on search for sterile neutrino. Combining the result of the Neutrino-4 and the results of measurements of the gallium anomaly and reactor anomaly we obtained value $\sin^2(2\theta_{14})\approx 0.19\pm0.04(4.6\sigma)$. Also was performed comparison of Neutrino-4 experimental results with results of other reactor experiments NEOS, DANSS, STEREO, PROSPECT and accelerator experiments MiniBooNE, LSND and the IceCube experiment also. Sterile neutrino mass which can be calculated using the Neutrino-4 data in assumption that $m^2_4 \approx \Delta m^2_{14}$ is $m_4 = (2.68 \pm 0.13)\text{eV}$. Considering estimations of mixing angles obtained in other experiments we can calculate masses of electron neutrino, muon neutrino and tau neutrino: $m^{\text{eff}}_{\nu_e} = (0.58 \pm 0.09)\text{eV}, m^{\text{eff}}_{\nu_{\mu}} = (0.42 \pm 0.24)\text{eV}, m^{\text{eff}}_{\nu_{\tau}} \leq 0.65\text{eV}$. Extended PMNS matrix for (3 + 1) model with one sterile neutrino is provided, neutrino flavor mixing scheme with sterile neutrino and global fit of reactor experiments.

Scaling laws for direct laser acceleration in a radiation-reaction dominated regime

We study electron acceleration within a sub-critical plasma channel irradiated by an ultra-intense laser pulse (a0 > 100 or I > 1022 W cm−2). In this regime, radiation reaction significantly alters the electron dynamics. This has an effect not only on the maximum attainable electron energy but also on the phase-matching process between betatron motion and electron oscillations in the laser field. Our study encompasses analytical description, test-particle calculations and two-dimensional particle-in-cell simulations. We show single-stage electron acceleration to multi-GeV energies within a 0.5 mm-long channel and provide guidelines how to obtain energies beyond 10 GeV using optimal initial configurations. We present the required conditions in a form of explicit analytical scaling laws that can be applied to plan the future electron acceleration experiments.

Modeling the interaction of an ultra-high intensity laser pulse with an ultra-thin nanostructured foil target

New plastic nanostructured foil targets interacting with an ultra-high intensity laser pulse are investigated by performing particle-in-cell simulations. The thickness of the ultra-thin planar and nanostructured foil target is in the range of tens of nanometers. Complementary numerical simulations which use the finite-difference time-domain method without considering plasma generation have been performed. The laser pulse has the parameters of the two 10 PW lasers from ELI-NP. The circularly polarized laser pulse has the twice intensity of the linearly polarized (LP) laser pulse. We show a strong dependence of the maximum proton energy on the nanospheres diameter. But, the carbon ion maximum energy varies very weak with the nanospheres diameter. We prove that the acceleration regime of the protons is a combination of the radiation pressure acceleration and target normal sheath acceleration regimes. The carbon ions experience the target normal sheath acceleration. This study is a very useful tool for the preparation of laser-ion acceleration experiments with nanostructured foil targets at ELI-NP and other PW laser facilities.

A novel method to predict the stiffness evolution of in-service wind turbine blades based on deep learning models

Since wind turbines operate in a complex environment for long term, the fatigue behavior of the blades can be influenced by wind, illumination, moisture, temperature, and so forth. For wind turbine blade manufacturers, the determination of their fatigue limit before delivery is necessary and fatigue acceleration experiments usually require a lot of labor and experimental costs. As a machine learning paradigm, deep learning focuses on the inherent hierarchical models of data and has achieved notable success in computer vision, speech recognition, natural language processing, etc. Aimed at reducing the time and the costs during fatigue tests, this paper studies a training-based method for wind turbine blade stiffness prediction using time series stiffness data under fatigue tests. Based on deep learning methods including convolutional neural network, long-short term memory network and the hybrid network, the residual stiffness of the blade with fatigue life under fatigue tests is obtained by combining the fatigue historical data. The obtained results show that the developed models can learn features directly from raw stiffness data and complete the residual stiffness prediction in succession. White Gaussian noise with different signal-to-noise ratios is also added to all stiffness data to demonstrate the models’ feasibility of stiffness prediction.

Feasibility study for a THz acceleration experiment on the PHIL accelerator at LAL

We present a feasibility study for an experiment aiming to post-accelerate an electron bunch, coming from the PHIL (Photo-Injecteur au LAL) photoinjector at LAL (Laboratoire de l’Accélérateur Linéaire), in a circular partially dielectric-loaded waveguide (DLW) driven by a multicycle THz pulse generated by the infrared laser coming from the LASERIX (Installation laser XUV/IR de l’Université Paris Sud) facility. We first discuss the considerations taken into account to fix the DLW design and the THz pulse properties, especially the choice of a 160 GHz THz pulse frequency, and then provide a set of values for their main parameters. We then perform start-to-end simulations of the acceleration experiment, taking into account the current achievable range of parameters at PHIL and the THz pulse properties already achieved with LASERIX with some margins for the coupling losses. They demonstrate the possibility to obtain a 1.2 MeV energy gain for a 10 pC bunch, without charge losses, with a clear shift of the energy spectrum, which would represent a significant improvement compared to the current state-of-the-art of THz acceleration. An overview of the upcoming steps towards the realization of the experiment is finally given.

SINBAD-ARES - A Photo-Injector for external Injection Experiments in novel Accelerators at DESY

The accelerator R&D facility SINBAD (Short Innovative Bunches and Accelerators at DESY) will drive multiple independent experiments in the fields of production of ultra-short electron bunches and tests of advanced high gradient acceleration concepts.The SINBAD-ARES (Accelerator Research Experiment at SINBAD) linac has been designed to allow the production of high brightness ultra-short electron bunches with excellent arrival-time stability. The accelerator will be used to study experimentally the optimization of the brightness for fs long electron bunches. Such electron bunches, with tunable characteristics, will be then injected into novel accelerators realized in the context of the ATHENA project, the ACHIP international collaboration and the ARIES program. In this paper we describe the principal characteristics of the linac design, we underline the technical challenges connected to the production and characterization of fs bunches and we report on the status of the installation and commissioning.

First dielectric wakefield experiments at Daresbury Laboratory

The first dielectric wakefield acceleration (DWA) experiments have been conducted at the CLARA/VELA test facility at Daresbury Laboratory, UK. The DWA structures were of planar geometry with variable gap and dielectric thicknesses ranging from 0.025 to 0.2 mm. The facility, in its current state, provided electron bunches with up to 100 pC bunch charge, and variable 0.2-2.0 ps bunch lengths at the beam energy of 35 MeV. All major wakefield effects have been observed including energy modulation in longer bunches, energy dechirping, and transverse streaking and focussing. With a modest bunch charge of ∼ 50 pC, a decelerating field of ~ 8 MV/m was measured. Using this variable gap planar structure, we have also demonstrated generation of continuously tunable narrowband THz. A summary of experimental results and near future developments are presented.

Performance improvement of a 200TW/1Hz Ti:sapphire laser for laser wakefield electron accelerator

For investigations on laser wakefield electron acceleration, there is a strong demand for driving laser exhibiting high stability and good spatial-temporal quality. Here we present an upgraded 200TW/1Hz Ti:sapphire laser with following key characteristics. The fluctuation of pulse energy and beam pointing for consecutive 5400 pulses in 90 min are as low as 0.55% and 1.5μrad respectively. The compressed pulse duration is 23.7 fs, which is about 1.1 times of the Fourier-transform limit. The focal spot obtained by an f/30 off-axis parabolic mirror is 54 μm × 52 μm at 1/e2, which is very close to the diffraction limit. Moreover, in the laser wakefield electron acceleration experiments driven by this upgraded 200TW/1Hz laser, quasi-mono-energetic electron beams are reproduced in consecutive shots. For successive 300 shots, the average peak energy of produced electron beams is 667 MeV, and the peak energy fluctuation is only 3.4%. The progresses on both driving laser and laser wakefield electron acceleration make the realization of compact X-ray free electron laser possible.

Design considerations for permanent magnetic quadrupole triplet for matching into laser driven wake field acceleration experiment at SINBAD

The ARES (Accelerator Research experiment at SINBAD) Linac at SINBAD (Short and INnovative Bunches and Accelerators at DESY) facility at DESY aims to produce high brightness ultrashort electron bunches (sub fs to few fs) at around 100 MeV, suitable for injection into novel accelerators e.g. dielectric Laser acceleration (DLA) and Laser Driven Wakefield acceleration (LWFA). The external injection experiment planned at ARES aims for stable LWFA by combining the reproducible conventional RF-based accelerator technology, with high-power plasma wakefield dynamics. The LWFA experiment demands Twiss parameter β to be of the order of few mm, in order to avoid emittance growth because of high accelerating gradient in the plasma. The ARES Linac is capable of producing ultra-short bunches at around 100-150 MeV, so the effect of space charge is significantly high. To match such a space charge dominated beam, strong transverse focusing is required. A Permanent Magnetic Quadrupole (PMQ) triplet is one promising focusing strategy. In this paper, we report the technical design constraints and findings for stable settings for PMQ triplet to match the requirements of the electron beam properties and study of phase spaces for final focus into LWFA experiment.

A Deformation of a Mercury Droplet under Acceleration in an Annular Groove.

Microelectromechanical system (MEMS) liquid sensors may be used under large acceleration conditions. It is important to understand the deformation of the liquid droplets under acceleration for the design and applications of MEMS liquid sensors, as this will affect the performance of the sensors. This paper presents an investigation into the deformation of a mercury droplet in a liquid MEMS sensor under accelerations and reports the relationship between the deformation and the accelerations. The Laminar level set method was used in the numerical process. The geometric model consisted of a mercury droplet of 2 mm in diameter and an annular groove of 2.5 mm in width and 2.5 mm in height. The direction of the acceleration causing the droplet to deform is perpendicular to the direction of gravity. Fabrication and acceleration experiments were conducted. The deformation of the liquid was recorded using a high-speed camera. Both the simulation and experimental results show that the characteristic height of the droplets decreases as the acceleration increases. At an acceleration of 10 m/s2, the height of the droplet is reduced from 2 to 1.658 mm, and at 600 m/s2 the height is further reduced to 0.246 mm. The study finds that the droplet can deform into a flat shape but does not break even at 600 m/s2. Besides, the properties of the material in the domain surrounding the droplet and the contact angle also affect the deformation of the droplet. This work demonstrates the deformation of the liquid metal droplets under acceleration and provides the basis for the design of MEMS droplet acceleration sensors.

Accelerator experiments are closing in on neutrino CP violation

It’s starting to look like neutrinos and antineutrinos aren’t exact mirror images of each other.

Searching for light dark matter at fixed target experiments

Nowadays deciphering the fundamental nature of dark matter is one of the foremost open questions in fundamental science. In the last years the dark matter experimental program is primarily focused on weakly-interacting massive particles (WIMPs), but in the recent years many innovative dark matter candidates have emerged. One of the most viable models takes into account DM particles in MeV-GeV mass range that are completely neutral under Standard Model forces, but interact through a new force. Small-scale fixed-target experiments at accelerators have unique sensitivities to fully explore these models. Indeed, accelerator experiments can both produce and detect new particles, such as dark matter and the particles mediating new interactions. This article reviews the various experimental techniques to search for light dark matter, i.e. beam dump, missing mass/energy, and visible mediator search experiments.

Development of longitudinal beam profile monitor based on Coherent Transition Radiation effect for CLARA accelerator

Coherent Transition Radiation (CTR) has widely been used for longitudinal beam profile diagnostics. Its spectral-spatial properties have been thoroughly theoretically and experimentally investigated. We have decided to develop a longitudinal beam profile diagnostics based on CTR technique to be used for interpreting the experimental results of Dielectric Wakefield Accelerator (DWA) and Coherent Cherenkov Diffraction Radiation (CChDR) experiments. In this paper we present the technical design,tuning and commissioning of the CTR longitudinal bunch profile monitor at CLARA facility.

Laser-heated capillary discharge plasma waveguides for electron acceleration to 8 GeV

A plasma channel created by the combination of a capillary discharge and inverse Bremsstrahlung laser heating enabled the generation of electron bunches with energy up to 7.8 GeV in a laser-driven plasma accelerator. The capillary discharge created an initial plasma channel and was used to tune the plasma temperature, which optimized laser heating. Although optimized colder initial plasma temperatures reduced the ionization degree, subsequent ionization from the heater pulse created a fully ionized plasma on-axis. The heater pulse duration was chosen to be longer than the hydrodynamic timescale of ≈1 ns, such that later temporal slices were more efficiently guided by the channel created by the front of the pulse. Simulations are presented which show that this thermal self-guiding of the heater pulse enabled channel formation over 20 cm. The post-heated channel had lower on-axis density and increased focusing strength compared to relying on the discharge alone, which allowed for guiding of relativistically intense laser pulses with a peak power of 0.85 PW and wakefield acceleration over 15 diffraction lengths. Electrons were injected into the wake in multiple buckets and times, leading to several electron bunches with different peak energies. To create single electron bunches with low energy spread, experiments using localized ionization injection inside a capillary discharge waveguide were performed. A single injected bunch with energy 1.6 GeV, charge 38 pC, divergence 1 mrad, and relative energy spread below 2% full-width half-maximum was produced in a 3.3 cm-long capillary discharge waveguide. This development shows promise for mitigation of energy spread and future high efficiency staged acceleration experiments.

Online multi-objective particle accelerator optimization of the AWAKE electron beam line for simultaneous emittance and orbit control

Multi-objective optimization is important for particle accelerators where various competing objectives must be satisfied routinely such as, for example, transverse emittance vs bunch length. We develop and demonstrate an online multi-time scale multi-objective optimization algorithm that performs real time feedback on particle accelerators. We demonstrate the ability to simultaneously minimize the emittance and maintain a reference trajectory of a beam in the electron beamline in CERN’s Advanced Proton Driven Plasma Wakefield Acceleration Experiment.

Investigation of charge multiplication in irradiated p-type silicon strip sensors designed for the ATLAS phase II tracking detector

Future particle accelerator experiments, for example the High Luminosity-LHC (HL-LHC) in 2025, will demand a much higher radiation hardness of silicon strip sensors due to high fluences and long operation times. New p-type strip sensors have been developed and their charge collection behavior as well as their electrical performance have been investigated. Additionally the long-term behavior under operation has to be investigated and understood. In previous studies of the annealing behavior, the phenomenon of charge multiplication appeared in highly irradiated and/or long-term annealed sensors. This phenomenon is now thoroughly investigated within this study for ATLAS12 strip sensors irradiated to fluences ranging from 5⋅1014neq∕cm2 to 2⋅1015neq∕cm2. Therefore systematic charge collection, leakage current and electric field measurements have been carried out at several annealing temperatures between 23°C and 80°C to investigate the dependence on temperature and fluence. The stability, temperature effects and the maximum amount of multiplication reachable were investigated. Severe changes in the signal pulses in time were observed with increasing amount of annealing. The pulse duration started to increase for enhanced charge multiplication, exceeding the readout shaping time of the ALIBAVA system.

Getting a THUMP from a WIMP

Producing an acceptable thermal relic abundance of dark matter with masses ≫ 102 TeV is a challenge. We propose a novel mechanism where GeV-scale states establish a tiny thermal relic abundance for dark matter, which is later promoted to ultra massive status by a very light scalar. We refer to this dark matter as a THermal Ultra Massive Particle (THUMP). Direct detection of THUMPs can be naturally expected due to large scattering cross sections mediated by low mass states that couple THUMPs to the Standard Model. Our model generically leads to signals for the associated GeV-scale states at accelerator experiments.

Timing System Development for RAON Operation

The Rare Isotope Accelerator complex for ON-line experiments (RAON) is a heavy-ion accelerator experiment facility under construction in Korea. This facility aims at a beam energy of 200 MeV/u and a maximum beam power of 400 kW and is expected to be completed by 2021. A large-scaled experiment facility like RAON requires a timing system for precise-synchronized operation. For this purpose, domestic accelerator facilities mainly use timing systems that are foreign products. The accelerator engineering team of RAON has successfully developed the RAON timing system in cooperation with a domestic company. The signals from the RAON timing system synchronized with an radio frequency (RF) reference clock and a global positioning system (GPS) are distributed throughout the RAON site via the dedicated timing network (3.25 Gbps). The time accuracy of the timing system is 12.3 ns synchronized with the RF reference clock (81.25 MHz). All signals (triggers, pulse delayed clock, and external signals) of the timing system developed using the Experimental Physics and Industrial Control System (EPICS) software module are configurable on a software. In addition, the RAON timing system supports the more flexible system for the various beam operation mode and improves the performance of the control system. This paper describes the results of the design and development of the RAON specific timing system.