High-energy Particle Accelerators Research Articles

Characterization of centrifugal compressors operating in FRIB’s sub-atmospheric compression system

Helium cryogenic systems operating below the normal boiling point (of 4.22 K) are required for many modern high-energy particle accelerators to achieve the necessary performance criteria. Temperatures below the normal boiling point are established by lowering saturation pressure below atmospheric conditions using vacuum equipment. FRIB operates a multi-stage string of cryogenic compressors (or ‘cold-compressors’) to achieve the sub-atmospheric pressures required (30 mbar) for the accelerator operating conditions of approximately 2 K. Housed within a vacuum insulated vessel (i.e., the sub-atmospheric cold box), the cold-compressor system re-pressurizes the helium from approximately 30 mbar to above atmospheric pressure condition before injecting the flow back into the helium refrigerator. Despite the implementation of cold-compressors in several existing large-scale cryogenic systems, openly available literature is insufficient to provide the information necessary for a general characterization of the performance and stability for these cold compressors. A one dimensional steady-state model to predict the performance of cryogenic centrifugal compressors has been developed. This model enables performance prediction by using optimally selected enthalpy loss correlations and basic impeller and diffuser geometrical data. The present work provides an initial comparison of the estimated performance of the individual and string of cryogenic centrifugal compressors to the operational / test data. With appropriate validation, the model is anticipated to allow assessment and prediction of optimal operational envelops that ensure stable and efficient operation at different operating conditions.

Negative Cosmic Evolution of BL Lac Objects from the Sloan Digital Sky Survey

Abstract BL Lacertae (BL Lac) objects are a type of active galactic nucleus (AGN) characterized by featureless optical spectra, where a relativistic jet is oriented toward the observer. By studying BL Lacs objects, we improve our understanding of accretion processes, high-energy particle acceleration, magnetic field structures in extreme environments, and galaxy formation and evolution. Generally, luminous AGNs (i.e., quasars) exhibit “positive” evolution. This means that, on average, quasars are more numerous and/or more luminous in the early Universe, at higher redshifts, than they are today. However, the evolution of BL Lacs has been long disputed, in part due to selection biases and small sample sizes. Here we perform the luminosity–volume test of BL Lac evolution on a uniformly selected sample and find that BL Lacs instead exhibit mild negative evolution. We conclude by putting our results into context with previous studies on BL Lac evolution.

Efficiency of solar microflares in accelerating electrons when rooted in a sunspot

Context. The spectral shape of the X-ray emission in solar flares varies with the event size, with small flares generally exhibiting softer spectra than large events, indicative of a relatively lower number of accelerated electrons at higher energies. Aims. We investigate two microflares of GOES classes A9 and C1 (after background subtraction) observed by STIX onboard Solar Orbiter with exceptionally strong nonthermal emission. We complement the hard X-ray imaging and spectral analysis by STIX with co-temporal observations in the (E)UV and visual range by AIA and HMI to investigate what makes these microflares so efficient in high-energy particle acceleration. Methods. We made a preselection of events in the STIX flare catalog based on the ratio of the thermal to nonthermal quicklook X-ray emission. The STIX spectrogram science data were used to perform spectral fitting to identify the non-thermal and thermal components. The STIX X-ray images were reconstructed to analyze the spatial distribution of the precipitating electrons and the hard X-ray emission they produce. The EUV images from SDO/AIA and SDO/HMI LOS magnetograms were analyzed to better understand the magnetic environment and the chromospheric and coronal response. For the A9 event, EOVSA microwave observations were available, allowing for image reconstruction in the radio domain. Results. We performed case studies of two microflares observed by STIX on October 11, 2021 and November 10, 2022, which showed unusually hard microflare X-ray spectra with power-law indices of the electron flux distributions of δ = (2.98 ± 0.25) and δ = (4.08 ± 0.23), during their non-thermal peaks and photon energies up to 76 keV and 50 keV, respectively. For both events under study, we found that one footpoint is located within a sunspot covering areas with mean magnetic flux densities in excess of 1500 G, suggesting that the hard electron spectra are caused by the strong magnetic fields the flare loops are rooted in. Additionally, we revisited a previously published unusually hard RHESSI microflare and found that in this event, there was also one flare kernel located within a sunspot, which corroborates the result from the two hard STIX microflares under study in this work. Conclusions. The characteristics of the strong photospheric magnetic fields inside the sunspot umbrae and penumbrae where flare loops are rooted play an important role in the generation of exceptionally hard X-ray spectra in these microflares.

Experimental study on the an-isotropic critical current of REBCO tape.

Superconducting magnets are widely used in nuclear fusion reactors, high-energy particle accelerators, steady-state high magnetic fields, etc. Higher magnetic fields and higher operating temperatures are two application trends. High temperature superconducting (HTS) materials are the only choice for high temperature and high field magnets in the future. The first- and second-generation HTS materials have a typical tape structure; their critical performance is magnetic field angle and temperature dependent. A new test facility is developed for an experimental study on the an-isotropic critical current. The field angle can be changed from 0° to 360° with a resolution of 1°. The rotation deviation angle is measured to be 0.2° when the upper part rotates 90°. The temperature can be changed from 4.2 to 80K. The temperature errors are ±50, ±80, and ±135 mK for 4.2-20, 20-40, and 40-80K, respectively. The angle dependence of critical current (Ic) of the tested rare-earth barium copper oxide tape within 0°-30° is strong. From 30° to 90°, the sample Ic almost does not change with the magnetic field angle. The implementation of the project will not only promote the structural optimization of HTS tapes but also promote the miniaturization and economical application of HTS magnets.

CRaTeBo: a high-speed, radiation-tolerant and versatile testing platform for FPGA radiation qualification for high-energy particle accelerator applications

The CHARM Radiation Tolerant FPGA Tester Board (CRaTeBo) is a FPGA testing platform for the CERN High-energy Accelerator (CHARM) irradiation facility. It is meant to ease the radiation testing of FPGA-based systems by providing users with a radiation-tolerant carrier card featuring an FPGA interface, a high-speed communication interface, a flexible power supply, and an HPC-FMC connector for additional front-end electronics. It is foreseen to be a permanent installation in the CHARM facility at CERN, giving users the possibility to carry out radiation tests of their system with minimum effort on the test setup development.

Future high energy colliders and options for the U.S.

The United States has a rich history in high energy particle accelerators and colliders — both lepton and hadron machines, which have enabled several major discoveries in elementary particle physics. To ensure continued progress in the field, U.S. leadership as a key partner in building next generation collider facilities abroad is essential; also critically important is to prepare to host an energy frontier collider in the U.S. once the construction of the LBNF/DUNE project is completed. In this paper, we briefly discuss the ongoing and potential U.S. engagement in proposed collider projects abroad and present a number of future collider options we have studied for hosting an energy frontier collider in the U.S. We also call for initiating an integrated national R&D program in the U.S. now, focused on future colliders.

Speed and Acceleration of Coronal Mass Ejections Associated with Sustained Gamma-Ray Emission Events Observed by Fermi/LAT

The sustained gamma-ray emission (SGRE) from the Sun is a prolonged enhancement of >100 MeV gamma-ray emission that extends beyond the flare impulsive phase. The origin of the >300 MeV protons resulting in SGRE is debated, with both flares and shocks driven by coronal mass ejections (CMEs) being the suggested sites of proton acceleration. We compared the near-Sun acceleration and space speed of CMEs with “Prompt” and “Delayed” (SGRE) gamma-ray components. We found that “Delayed”-component-associated CMEs have higher initial accelerations and space speeds than “Prompt Only”-component-associated CMEs. We selected halo CMEs (HCMEs) associated with type II radio bursts (shock-driving HCMEs) and compared the average acceleration and space speed between HCME populations with or without SGRE events, major solar energetic particle (SEP) events, metric, or decameter-hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs associated with a DH type II radio burst and/or a major SEP event have higher space speeds and especially initial accelerations than those without an SGRE event. We estimated the radial distances and speeds of the CME-driven shocks at the end time of the 2012 January 23 and March 7 SGRE events using white-light images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES. The shocks were at the radial distances of 0.6–0.8 au and their speeds were high enough (≈975 km s−1 and ≈750 km s−1, respectively) for high-energy particle acceleration. Therefore, we conclude that our findings support the CME-driven shock as the source of >300 MeV protons.

Conceptual Design of a 20 T Hybrid Cos-Theta Dipole Superconducting Magnet for Future High-Energy Particle Accelerators

High energy physics research will need more and more powerful circular accelerators in the next decades. It is therefore desirable to have dipole magnets able to produce the largest possible magnetic field, in order to keep the machine diameter within a reasonable size. A 20 T dipole is considered a desired achievement since it would allow the construction of an 80 km machine, able to circulate 100 TeV proton beams. In order to reach 20 T, a hybrid Low-Temperature Superconductor (LTS) - High-Temperature Superconductor (HTS) magnet is needed, since LTS technology is presently limited to ∼16 T for accelerator magnet applications. In this paper, we present the design of a 6 layers 20 T hybrid dipole magnet using Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn (LTS) and Bi2212 (HTS). We show that it is possible to achieve this magnetic field with accelerator field quality, with sufficient margin on a realistic conductor, keeping the stresses within safe limit, avoiding conductor degradation.

An Overview of Multibeam Klystron Technology

The multibeam klystron (MBK) is a compact high-power microwave vacuum electronic device that features low beam voltage, high efficiency, wide bandwidth, and low volume and weight. Since the 1960s, high-performance broadband MBKs have been developed that cover the entire microwave frequency band with relative instantaneous bandwidths <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 15%, peak power <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 1 MW, average power up to 40 kW, and efficiencies <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> 40%. In recent years, driven by the needs of high-energy particle accelerators, ultra high frequency (UHF) and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\textit{L}$</tex-math> </inline-formula> -band MBKs with peak powers of more than 20 MW and efficiencies of nearly 80% are being developed. This article presents an overview of the development of broadband MBKs used in microwave electronic systems, such as radar and communication, and high-power MBKs used in the RF systems of particle accelerators. It also introduces the latest progress and development trends in MBKs leading to higher frequency, output power, bandwidth, efficiency, and lifetime.

Development of superconducting model dipole magnets beyond 12 T with a combined common-coil configuration

The superconducting magnet group at IHEP (the Institute of High Energy Physics, Chinese Academy of Sciences, China) has been engaging in the R&D of high field accelerator magnets since 2014 for the pre-study of the next-generation high energy particle accelerators like CEPC-SPPC (Circular Electron Positron Collider-Super Proton Proton Collider), FCC (Future Circular Collider), etc. A superconducting model dipole magnet named LPF1 was first fabricated with NbTi and Nb3Sn in a combined common-coil configuration in 2017 and tested in 2018, a main field of 10.23 T was reached within two 10 mm apertures. The magnet was reassembled with higher pre-stress in 2019 to investigate the influence of the pre-stress loading level on the performance of common-coil dipole magnets. The main field of this upgraded magnet named LPF1-S was increased to 10.71 T within two 12 mm apertures. By improving the key processing technologies in Rutherford cable fabrication, coil winding, Nb3Sn & NbTi splices soldering and coil impregnation, the recently fabricated model dipole magnet named LPF1-U attained a 12.47 T main field in two 14 mm apertures in 2021. To fully take advantage of Nb3Sn and NbTi superconductors in different field regions, LPF1-U was still designed and developed with a combined coil configuration with Nb3Sn for the inner two coils and NbTi for the outer four coils. Additionally, graded coil topology and different coil LSS (length of straight section) settings were adopted in the optimization of LPF1-U layouts. Bladder and key technology was used for the support structure, and fiber optic sensors based on FBG (fiber Bragg grating) were utilized to monitor the stress distribution and variation in the structures and coils through the whole process from magnet assembly to cool-down and excitation. During the performance test, a relatively large number of trainings were carried out and LPF1-U became more stable after the thermal cycle. A peak field of 12.7 T in the coils (12.47 T main field in apertures) corresponds to an operating current of 6865 A and a load line ratio of 90% was finally attained. It is worth mentioning that LPF1-U is the first hybrid—Nb3Sn, NbTi—common coil dipole magnet that has achieved a main field of more than 12 T in two apertures. The design, fabrication and performance analysis of the LPF series dipole magnets are presented in this paper.

X-ray fluorescence (XRF) analysis and prediction of induced radioactivity components for high-energy electron accelerator

The objective of this research was to predict the induced activation in high-energy particle accelerator components to determine the isotope inventories and remanent dose rates for considering the replacement materials. The long-lived radionuclides produced by nuclear reactions caused biological health effects to human as well as environmental impacts. The bremsstrahlung photon beam by the high-energy electron accelerator produced the radioactive nuclei from direct interactions or indirect interactions. The study highlighted the determination of chemical compositions and the estimation of induced activation in particle accelerator components. The elemental compositions of materials were investigated by the X-ray fluorescence (XRF) technique. The heavy metal elements were detected with different percentages, i.e., Zr, Zn, Ti, Pb, Ni, Mn, Fe and Cu. To calculate the induced activation in the materials, the FLUKA simulation was performed. The 1.2 GeV high-energy electron beam had been defined to irradiate the materials for this simulation. The daughter nuclei were obtained, and their decay followed. The estimation of the residual dose rate in activated materials after various cooling times from the end of the irradiation was presented.

High-energy particle enhancements in the solar wind upstream Mercury during the first BepiColombo flyby: SERENA/PICAM and MPO-MAG observations

Context. The first BepiColombo Mercury flyby offered the unique opportunity to simultaneously characterize the plasma and the magnetic field properties of the solar wind in the vicinity of the innermost planet of the Solar System (0.4 AU). Aims. In this study, we use plasma observations by SERENA/PICAM and magnetic field measurements by MPO-MAG to characterize the source with intermittent features (with a timescale of a few minutes) at ion energies above 1 keV observed in the solar wind upstream of Mercury. Methods. The solar wind properties have been investigated by means of low-resolution magnetic field (1 s) and plasma (64 s) data. The minimum variance analysis and the Lundquist force-free model have been used. Results. The combined analyses demonstrate that the intermittent ion features observed by PICAM at energies above 1 keV can be associated with the passage of an interplanetary magnetic flux rope. We also validate our findings by means of Solar Orbiter observations at a larger distance (0.6 AU). Conclusions. The core of an interplanetary magnetic flux rope, hitting BepiColombo during its first Mercury flyby, produced high-energy (&gt; -pagination1 keV) intermittent-like particle acceleration clearly distinct from the background solar wind, while at the edges of this interplanetary structure compressional low-energy fluctuations have also been observed.

Time-Series Deep Learning Anomaly Detection for Particle Accelerators

High energy particle accelerators rely on superconducting radio frequency cavities to transfer energy and accelerate the beam. Such particle accelerators are complex and expensive systems prone to failures which lead to downtime of the whole experimental facility: it is thus of primary importance to anticipate and prevent these faults to improve the uptime and cost-effectiveness of particle accelerators. Data-driven methods are especially fit for this task as they can leverage all the data recorded and archived by a typical control system. Previous works used classical machine learning (ML) models for anomaly detection to detect early signs of an upcoming fault. We propose here a different approach based on deep learning (DL) models, exploiting the temporal correlation of the raw data. Three different models are tested on data from the ALPI (Linear Accelerator for Ions) linear accelerator in INFN (National Institute for Nuclear Physics) Legnaro National Laboratories in Italy and they are compared with the classical ML approach.

Measurement of anti-3He nuclei absorption in matter and impact on their propagation in the Galaxy

In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of {}^{3}overline{{{{rm{He}}}}} when it encounters matter particles and annihilates or disintegrates within the ALICE detector at the Large Hadron Collider. We extract the inelastic interaction cross section, which is then used as an input to the calculations of the transparency of our Galaxy to the propagation of {}^{3}overline{{{{rm{He}}}}} stemming from dark-matter annihilation and cosmic-ray interactions within the interstellar medium. For a specific dark-matter profile, we estimate a transparency of about 50%, whereas it varies with increasing {}^{3}overline{{{{rm{He}}}}} momentum from 25% to 90% for cosmic-ray sources. The results indicate that {}^{3}overline{{{{rm{He}}}}} nuclei can travel long distances in the Galaxy, and can be used to study cosmic-ray interactions and dark-matter annihilation.

Classifying exploratory experimentation – three case studies of exploratory experimentation at the LHC

Along three measurements at the Large Hadron Collider (LHC), a high energy particle accelerator, we analyze procedures and consequences of exploratory experimentation (EE). While all of these measurements fulfill the requirements of EE: probing new parameter spaces, being void of a target theory and applying a broad range of experimental methods, we identify epistemic differences and suggest a classification of EE. We distinguish classes of EE according to their respective goals: the exploration where an established global theory cannot provide the details of a local phenomenon, exploration of an astonishing discovery and exploration to find a new entity. We find that these classes also differ with respect to the existence of an identifiable target and their impact on the background theory. The characteristics distinguish EE from other kinds of experimentation, even though these different kinds have not yet been systematically studied. The formal rigor and precision of LHC physics facilitates to analyze concept formation in its early state. In particular we emphasize the importance for nil–results for conceptualization and argue that conceptualization can also be achieved from nil–results only.

Dipole Magnets Wound Using YBCO Cables-FEM Stability Issues Modeling

Quench and protection in magnets wound with coated conductors is of great interest for many applications, including high energy particle accelerators. The relatively large slow normal zone propagation and large MQE of coated conductors and the potential of burn out in well insulated coils has led to an interest in non-insulation coils. A stability of block type dipole magnets wound using non-insulated YBCO Roebel and CORC cables has been modeled by FEM. Critical currents of the magnets have been calculated using a self-consistent method based on anisotropic I_c(B) curves of the cables. Advantages and disadvantages of using the Roebel and CORC cables in dipole magnet windings have been discussed. Measured heat disturbances of different size, intensity and duration in a pancake coil wound using a non-insulated YBCO tape have been analyzed from the viewpoint of the magnet quench and stability. The effect of CORC cable magnetization on the field quality of a canted cosine theta dipole was evaluated.

Challenges of Future Accelerators for Particle Physics Research

For over half a century, high-energy particle accelerators have been a major enabling technology for particle and nuclear physics research as well as sources of X-rays for photon science research in material science, chemistry and biology. Particle accelerators for energy and intensity Frontier research in particle and nuclear physics continuously push the accelerator community to invent ways to increase the energy and improve the performance of accelerators, reduce their cost, and make them more power efficient. The accelerator community has demonstrated imagination and creativity in developing a plethora of future accelerator ideas and proposals. The technical maturity of the proposed facilities ranges from shovel-ready to those that are still largely conceptual. At this time, over 100 contributed papers have been submitted to the Accelerator Frontier of the US particle physics decadal community planning exercise known as Snowmass’2021. These papers cover a broad spectrum of topics: beam physics and accelerator education, accelerators for neutrinos, colliders for Electroweak/Higgs studies and multi-TeV energies, accelerators for Physics Beyond Colliders and rare processes, advanced accelerator concepts, and accelerator technology for Radio Frequency cavities (RF), magnets, targets and sources. This paper provides an overview of the present state of accelerators for particle physics and gives a brief description of some of the major facilities that have been proposed, their perceived advantages and some of the remaining challenges.

Influence of Porosity on Ultra-High Vacuum Gas-Tightness in Cold-Sprayed Aluminum Coatings

Vacuum chambers used in high-energy particle accelerator experiments are conventionally made of bulk beryllium, which shows significant drawbacks due to cost and toxicity. An alternative solution could be to develop chambers made of polymer-based composites. Since these materials exhibit high outgassing not compatible with an ultra-high vacuum environment, a suitable gas-tight coating is required. Cold spray deposition of aluminum can be a solution, provided that the coating behaves as a perfect vacuum barrier. Porosity, especially percolating porous networks, is key to coating gas tightness issues. This work addresses the relationship between porosity and gas-tightness in cold spray coatings. To do so, coatings with different porosity were achieved playing with powder morphology, composition, and process parameters. Their gas tightness was evaluated by helium leak tests. Classical microscopy, being essentially a 2D analysis, is strongly limited when dealing with 3D properties as porosity percolation. For this reason, 3D X-ray microtomography images of coatings were obtained and treated by image analysis methods: pores were compared in terms of size and shape. Overall porosity properties, including percolation and a homogeneity criterion, were also investigated. Percolating porosity was highlighted for several samples which showed poor gas-tightness properties. The permeability of percolating pore structures was then numerically computed by a fast Fourier transform-based method, to quantify the mass flow through the coating. Results of those computations were finally compared to experimental coating leak rate measurements, in an effort to elucidate the link between gas tightness and morphology of the pore space.

Investigation on the Effect of Cable Length on Pulse Shape of High Voltage High Pulse Power Supply

In the present scenario of pulse power applications, transmission of high voltage pulses varies as per load condition. In the early days of its application, High Voltage High Pulse Power Supply (HVHPPS) design saw short distance between load and source, where the effect of cable length was not taken into account for design. This paper presents the effect of cable length on pulse shape of High Voltage High Pulse Power Supply. The load under observation is Klystron based high energy particle accelerator system. The performance of pulse power systems were observed continuously on a daily basis throughout the year and detailed analysis was carried out. This paper generates the model of pulse forming system and provides details of pattern distortion of the pulse shape due to various dynamic parameter changes i.e. impedance, Load Voltage, Load Current, Cavity Dimensional Changes (Microwave components) due to temperature variations and performance of the power supply. The results were analysed and validated with hardware results across a range of actual industrial loads.

Cryogenic System Design and Performance Test of Calibration Magnet

According to the requirements of high-energy particle accelerators, a cryostat system was designed and manufactured to provide a low-temperature environment for high uniformity superconducting magnet used for calibration. The performance test of the calibration magnet system including linearity, locking area, stability, and uniformity was completed. This system uses a single 1.5 W @ 4.2 K refrigerator by combining direct conduction cooling with indirect conduction cooling of the gravity heat pipe. The superconducting magnet was cooled to 4 K and entered the superconducting state, and the minimum temperature reached 2.8 K within 40 hours. The maximum excitation current is 300 A and the maximum magnetic field reaches about 6.2 T. At present, the equipment has been running stably for more than 90 days.