High-energy Accelerators Research Articles

Big Science: before and after the Manhattan Project

Abstract Although the concept of Big Science is not well defined, it is often identified with expensive and government-funded post-World-War II projects in physics and space research. However, this definition is too narrow both with regard to chronology and with regard to the sciences in question. Apart from offering some general comments on the notion of Big Science this paper adopts a historical perspective by singling out a few cases of pre-twentieth century Big Science projects in physics and astronomy. These were exceptions, however, and it was only with the Manhattan Project and the early generations of high-energy accelerators that the Big Science era truly started. As argued the development involved new forms of organisation as well as new ethical problems relating to the role and responsibility of the individual scientist.

Broadband multi-wavelength properties of M87 during the 2018 EHT campaign including a very high energy flaring episode

The nearby elliptical galaxy M87 contains one of only two supermassive black holes whose emission surrounding the event horizon has been imaged by the Event Horizon Telescope (EHT). In 2018, more than two dozen multi-wavelength (MWL) facilities (from radio to gamma -ray energies) took part in the second M87 EHT campaign. The goal of this extensive MWL campaign was to better understand the physics of the accreting black hole M87*, the relationship between the inflow and inner jets, and the high-energy particle acceleration. Understanding the complex astrophysics is also a necessary first step towards performing further tests of general relativity. The MWL campaign took place in April 2018, overlapping with the EHT M87* observations. We present a new, contemporaneous spectral energy distribution (SED) ranging from radio to very high-energy (VHE) gamma -rays as well as details of the individual observations and light curves. We also conducted phenomenological modelling to investigate the basic source properties. We present the first VHE gamma -ray flare from M87 detected since 2010. The flux above 350 GeV more than doubled within a period of approx 36 hours. We find that the X-ray flux is enhanced by about a factor of two compared to 2017, while the radio and millimetre core fluxes are consistent between 2017 and 2018. We detect evidence for a monotonically increasing jet position angle that corresponds to variations in the bright spot of the EHT image. Our results show the value of continued MWL monitoring together with precision imaging for addressing the origins of high-energy particle acceleration. While we cannot currently pinpoint the precise location where such acceleration takes place, the new VHE gamma -ray flare already presents a challenge to simple one-zone leptonic emission model approaches, and it emphasises the need for combined image and spectral modelling.

Generalized N-Dimensional Effective Temperature for Cryogenic Systems in Accelerator Physics

Investigations into the properties of generalized effective temperature are conducted across arbitrary dimensions. Maxwell–Boltzmann distribution is displayed for one, two, and three dimensions, with effective temperatures expressed for each dimension. The energy density of blackbody radiation is examined as a function of dimensionality. Effective temperatures for non-uniform temperature distributions in one, two, three, and higher dimensions are presented, with generalizations extended to arbitrary dimensions. Furthermore, the application of generalized effective temperature is explored not only for linearly non-uniform temperature distributions but also for scenarios involving the volume fraction of two distinct temperature distributions. The effective temperature is determined for a cryogenic system supplied with both liquid nitrogen and liquid helium. This effective temperature is applied to the Coefficient of Performance (COP) in cryogenic systems and can also be applied to high-energy accelerator physics, including high-dimensional physics.

Study of the effect of detector to front-end electronics distance on the spectrometric performances of solid-state detectors

Solid-state detectors are used for charge particles detection and spectrometry with front-end electronics located, usually, next to the detectors. Therefore, in some applications, due to high-level radiation, high temperature and/or electro-magnetic noises (e.g. in nuclear fusion energy experiments, high energy accelerators, etc.) there could be the need to locate the front-end electronics far away from the detector. To solve the problem a matching sensitive charge amplifier (MSCA) with AC coupled input was designed by Roberto Cardarelli (former INFN scientist) for measurements at the fusion JET tokamak (U.K.). The prototype, composed of two amplification stages, was “ad hoc” designed for use with Diamond detectors and resulted very reliable. A commercial version of the MSCA was then developed and is now available on the market. Its novelty and main advantage, with respect to the former version, is to be used also with other fast detectors e.g. Resistive Plate Chamber (RPC) with high counting speed and Silicon detectors. The commercial MSCA features input impedance very close to 50 Ohm, which can be matched to a 50-Ohm transmission line. This allows locating the amplifier at variable distances from the detector and up to 100 m. These claimed performances result very interesting for solid state detectors, therefore, up to now a few applications of MSCA are reported in the literature and a systematic study of its performances is missing. In this work, an analysis of the spectrometric performances of Diamond and Silicon detectors coupled to MSCA located at various distances (up to 48 m) from the detectors is reported. Pulse height spectra of a multi-peaks alpha source were measured using MSCA amplifier and compared with those obtained using a standard charge sensitive preamplifier (CA). Then, the effect of the distance between detectors and amplifiers was investigated using standard RG58 and double shielded RG214 coaxial cables. The results are presented and discussed.

Phase-contrast visualization of human tissues using superimposed wavefront imaging of diffraction-enhanced x-rays.

Phase-contrast computed tomography (CT) using high-brilliance, synchrotron-generated x-rays enable three-dimensional (3D) visualization of microanatomical structures within biological specimens, offering exceptionally high-contrast images of soft tissues. Traditional methods for phase-contrast CT; however, necessitate a gap between the subject and the x-ray camera, compromising spatial resolution due to penumbral blurring. Our newly developed technique, Superimposed Wavefront Imaging of Diffraction-enhanced x-rays (SWIDeX), leverages a Laue-case Si angle analyzer affixed to a scintillator to convert x-rays to visible light, capturing second-order differential phase contrast images and effectively eliminating the distance to the x-ray camera. This innovation achieves superior spatial resolution over conventional methods. In this paper, the imaging principle and CT reconstruction algorithm based on SWIDeX are presented in detail and compared with conventional analyzer-based imaging (ABI). It also shows the physical setup of SWIDeX that provides the resolution preserving second-order differential images for reconstruction. We compare the spatial resolution and the sensitivity of SWIDeX to conventional ABI. To demonstrate high-spatial resolution achievable by SWIDeX, the internal structures of four human tissues-ductal carcinoma in situ, normal stomach, normal pancreas, and intraductal papillary mucinous neoplasm of the pancreas-were visualized using an imaging system configured at the Photon Factory's BL14B beamline under the High Energy Accelerator Research Organization (KEK). Each tissue was thinly sliced after imaging, stained with hematoxylin and eosin (H&E) for conventional microscope-based pathology. A comparison of SWIDeX-CT and pathological images visually demonstrates the effectiveness of SWIDeX-CT for biological tissue imaging. SWIDeX could generate clearer 3D images than existing analyzer-based phase-contrast methods and accurately delineate tissue structures, as validated against histopathological images. SWIDeX can visualize important 3D structures in biological soft tissue with high spatial resolution and can be an important tool for providing information between the disparate scales of clinical and pathological imaging.

Beam dynamics simulations at the high energy accelerator section in the RAON accelerator

Beam dynamics simulations at the high energy accelerator section in the RAON accelerator

Challenges of radiation measurements in an institute with various large-scale research facilities

The Paul Scherrer Institute is a unique Swiss research institute that operates five large-scale research facilities in which different types of particles, such as electrons, protons, neutrons, pions and muons, are accelerated or produced. Depending on the facility and location, the operational radiation protection has to deal with challenging measurements of mixed radiation fields, which can be in addition pulsed and of high-energy. In this article, we provide insight into the associated demands and challenges using two examples with different requirements for the monitoring technology. Using the example of the high-intensity proton accelerator (HIPA), the measurement technology around high-energy accelerators is examined in more detail. On the other hand, the problems of measuring technology for pulsed radiation and its dynamic range are discussed using the example of the Swiss X-ray free electron laser SwissFEL. The aim of this paper is to highlight the different requirements and technical challenges in radiation measurements for such complex facilities and, thus, to raise awareness and provide a stimulus for further developments in measurement technology.

Investigation of the neutron radiation fields inside the accelerator tunnel during operation of the Swiss Light Source (SLS)

The Swiss Light Source (SLS) is a third-generation synchrotron light source with an electron energy of 2.4 GeV. It consists of a linear accelerator, a booster and a storage ring providing light for various applications. As SLS is a high-energy accelerator, its operation is accompanied with production of ionizing radiation fields, including neutrons. This leads to additional challenges from a radiation protection point of view. The long-term investigation of the radiation fields at this accelerator facility can provide useful information for the residual activation studies and optimization of shielding. This work describes measurements of the neutron radiation fields inside the tunnel and results of this study.

Monte Carlo intercomparison and benchmark of the neutron streaming in the ramified access maze of the CERN High-energy AcceleRator Mixed field (CHARM) facility at CERN

Experiments of high-energy neutron streaming were performed in the access maze of the CERN High-energy AcceleRator Mixed-field (CHARM) facility where high-intensity proton beams of 24 GeV/c impact on a copper target. The streaming of the secondary neutrons through the various legs of the ramified access maze of the facility was measured using aluminium activation detectors installed at 12 different locations: for the first time, the extended coverage of measurement locations allowed to assess the streaming in more distant areas of the maze. The attenuation profile along the maze measured via the production of 24Na was also used to benchmark results from Monte Carlo calculations performed with FLUKA, PHITS, and GEANT4: over almost the five orders of magnitude of the measured production yield, an agreement within a factor 1.4, 1.7, and 2.5 respectively was found for the three codes.

Study and analysis of high-power coupler failure due to asymmetric electric field distribution

Microwave vacuum electronics play a vital role in numerous applications, and high-power couplers are a critical component. However, coupler failure is a common problem in high-energy accelerators, especially in situations involving high continuous wave (CW) power operation, leading to costly downtime and reduced performance. This paper focuses on addressing the issue of coupler failure in high-power scenarios by studying the specific case of the Circular Electron-Positron Collider (CEPC) 650 MHz high-efficiency klystron, designed for a power of 800 kW and tested up to 700 kW. The failure was attributed to the cracking of the coupler ceramics due to asymmetric electric field distribution, a previously unnoticed issue. Consequently, this study describes the coupler testing process, analyzes the problem, and proposes corresponding solutions to achieve symmetrical electric field distribution and reduce thermal stress. After evaluating three approaches, we recommend the T-bar coupler with water cooling and forced air cooling as the most viable option. This research is significant for the future development of high-power couplers, as it offers references for overcoming technical challenges and optimizing structural designs. As a result, other high-power coupler designers may find inspiration in the suggested solutions as they strive for increased dependability and performance.

Neutron dose evaluation inside high-energy accelerator irradiation vault using LR-115

Recently, a new radiation therapy using a high-energy accelerator irradiation vault has attracted significant attention. This therapy is very effective in destroying cancer cells because it uses much higher energy than conventional radiation therapy. Nevertheless, it also has disadvantages due to its high energy and dose, resulting in the generation of secondary radiation such as X-rays and neutrons. In particular, neutrons have a higher radiation weighting factor than photons; therefore, they are more harmful to normal tissues. However, the popular neutron dosimeter CR-39 cannot evaluate high-dose neutrons.This paper proposes a novel method for measuring high-dose neutrons generated during cancer treatment. LR-115, which has low detection efficiency but is expected to be useful for evaluating high-dose neutrons, was used to evaluate the effective dose of neutrons in a high-energy accelerator irradiation room. The results were verified using MCNP 6.2, a Monte Carlo-based particle transport code. This study provides the lower limit for evaluating neutron effective dose using LR-115. The experimental results showed that the neutron effective dose increased linearly with beam current. These findings provide basic data for evaluating neutron effective dose for radiation protection.

Activity estimates of localised gamma emitting radionuclides using a GR-135 survey meter

During the operation of high energy accelerators activated materials are commonly created. The activity and isotopes present in these materials must be characterised for their clearance and release from the facility, or to ascertain their duration of stay in a radiological storage area. An activity estimate method using a gamma detecting GR-135 survey meter, which has the ability to collect an energy spectrum, is presented. Using several reference radioactive sources the detection efficiency and dead time of the survey meter were characterised. This information combined with the physical properties of the survey meter, the counting time and the properties of the measured photon energy emissions can be used to calculate an accurate activity estimate for localised activation on accelerator components, or loose contamination on isolated waste materials.

Development of a 90–600 MHz Meter-wave Solar Radio Spectrometer

Radio observation is important for understanding coronal mass ejections (CMEs), coronal shock waves, and high-energy electron acceleration. Here, we developed a new Chashan broadband solar radio spectrometer at a meter wavelength for observing the (super)fine structure of the solar radio burst spectrum. In the signal-receiving unit, we adopt an antenna system consisting of a 12 m large-aperture parabolic reflector and dual-line polarized logarithmic periodic feed source, as well as a high-precision Sun-tracking turntable system, all of which ensure the high-precision acquisition of solar radiation signals. For the digital receiver, we use a high-speed analog-to-digital converter with a sampling rate of 1.25 GSPS to directly sample the signal amplified and filtered by the analog receiver, simplifying the structure of the analog receiver, and design a 16k-point fast Fourier transform algorithm in the field programmable gate array to perform time–frequency transformation on the sampled signals. The default frequency and temporal resolution of the system are 76.294 kHz and 0.839 ms (up to 0.21 ms), respectively. The noise coefficient of the system is less than 1 dB, the dynamic range is more than 60 dB, and the sensitivity is as high as 1 sfu. We have observed a large number of radio bursts, including type I radio storms, hundreds of type III, ∼20 type II, and ∼15 type IV bursts in the past year. These high-quality data are useful in the further study of CMEs and associated particle acceleration and the origins of solar radio bursts.

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.

HVE ion sources for medium and high-energy accelerator systems

Since decades, High Voltage Engineering (HVE) manufactures particle accelerator systems for research and industry. HVE’s product line includes Singletron and Tandetron accelerator systems with terminal voltages of up to 6 MV. They are dedicated to a wide range of applications including ion implantation and irradiation, Ion Beam Analysis (IBA), Accelerator Mass Spectrometry (AMS), and neutron reference fields. In this paper, we give an overview of the different positive and negative ion sources that are applied in these systems. We focus especially on the recent development and the performance of a compact 2.45 GHz permanent magnet ECR bipolar ion source (HVE Model SO-160), used for negative light-ion injection into tandem accelerators. It generates high-current, low-emittance light-ion beams at 30 keV energy. The novelty in the design of this ion source is that it combines direct negative extraction for H − with positive extraction for He + that is followed by charge exchange to He − in a Na-based electron donor canal. The source produces in excess of 250 eµA of H − and more than 20 eµA of He −. It is expected the design allows for substantially higher currents, especially for H −.

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.

Revisiting the Luce diode in the context of recent research on multi-vircators with dielectric reflectors

Recently, in a series of articles Mumtaz, Choi, and others [i.e., S. Mumtaz and E. Choi, IEEE Electronic Device Lett. 43, 1756 (2022)] studied a relativistic gridded vircator with one or more dielectric anodes, in which considerable increase in the efficiency of high-power microwave (HPM) generation compared to ordinary vircators was observed. This is very important since the main disadvantage of vircators is their low efficiency. It was suggested that the repelling of electrons by the initial impacting electron charge collected on the dielectric reflectors forms a multi-vircator, which increases HPM production. The present article reports the results of experiments and numerical simulations, which show that this mechanism does not result in high multi-vircator efficiency. Similar dielectric anodes were investigated 50 years ago in a configuration known as the Luce diode, in which collective acceleration of ions was studied. It was also known that the operation of the Luce diode is accompanied by a HPM burst, which was never measured. Results of experiments and simulations in various configurations based on a gridded vircator and dielectric reflectors confirm the existence of high-energy ion acceleration. Unfortunately, none of these configurations produce HPM of higher efficiency than a regular gridded vircator.

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.

Effect of the second curing cycle on performance of superconducting magnet insulating system

In large-scale, high-field superconducting magnets used for magnetic confinement fusion, high energy accelerators, and magnetic resonance imaging, the insulating system made from glass fiber reinforced resin-based composites is the key component, which mainly plays the role of mechanical support, fixing and protecting superconducting conductors, as well as electrical insulation. Vacuum Pressure Impregnation (VPI) approach is widely used in the manufacturing of the insulation system. The second curing cycle is generally required after the first VPI and curing process. For example, after the superconducting coil is cured in the mold, the de-molding process requires the superconducting coil to be reheated according the curing temperature. Moreover, for large-scale superconducting magnets, the superconducting coil needs to undergo a second VPI process after the first VPI process to fix the coil in the coil case. In this work, the tensile and shear properties of pure epoxy resin and the glass fiber reinforced resin-based composite, were investigated at both room and cryogenic temperatures and the effect of the second curing cycle on the mechanical properties was analyzed. Additionally, the strain evolution of the Nb-Ti superconducting coil during the second curing cycle was measured using the Fiber Bragg Grating (FBG) sensors embedded in the composite. The results indicate that the second curing cycle will not introduce additional strain to the previously cured resin matrix, but the defective or weak parts of the resin matrix may be affected by the new added epoxy resin and a little extra strain has been observed.