Beam Monitoring Research Articles

Optimal sensor placement for strain sensing of a beam of high-speed EMU

Aiming at the strain sensing of a beam of high-speed EMU, optimal sensor placement (OSP) is studied based on the information gain and modal expansion method within the Bayesian framework. In addition, the role of the prediction error in OSP and strain reconstruction is investigated in detail. Two new prediction errors are proposed: the measurement error weighted by modal strain energy and the modeling error based on the change of element stiffness. The covariance matrix of prediction error is obtained by probability method, which improves the calculation efficiency. Also, a method to determine the number of modes based on the change rate of modal strain energy is proposed. With reference to a case study of a beam, the effect of the prediction error on OSP and strain sensing is described and the reliability and the robustness of the proposed method are tested. Finally, the proposed method is further validated through a case study of full-scale beam monitoring systems based on Fiber Bragg grating (FBG) sensors. The errors between the real and reconstructed strains are compared through the measured data. The results show that the errors between the reconstructed strain and the real strain are very small, which illustrates that this method can be used for strain sensing.

Status and perspectives of hydrogenated amorphous silicon detectors for MIP detection and beam flux measurements

Hydrogenated amorphous silicon (a-Si:H) particle detectors have been considered as alternatives to crystalline silicon detectors (c-Si) in high radiation environments, due to their excellent radiation hardness. However, although their capability for particle flux measurement in beam monitoring applications is quite satisfactory, their minimum ionizing particle (MIP) detection has always been problematic because of the poor signal-to-noise ratio caused by a low charge collection efficiency and relatively high (compared to crystalline silicon) leakage current. In this article, after a review of the status of technological research for a-Si:H detectors, a perspective view on MIP detection and beam flux measurements with these detectors will be given.

Ion beam induced luminescence (IBIL) analysis of europium-activated phosphate glass micro-beads scintillators at clinical carbon beam therapy field

The possibility of real-time monitoring of clinical carbon beams was investigated by analyzing ion beam induced luminescence (IBIL) using phosphate glass (PG) with a dopant of europium (Eu). Phosphate glass with a silver activator (PG: Ag) is known as a substrate for personal dosimeters. Several trials are being made by utilizing PG: Ag as an in-situ diagnostic tool for the clinical radiation therapy field. However, silvers are not actively responding to the radiation during the irradiation because of their build-up effect. In this study, we introduced a co-activator of europium, which is expected to coexist with silvers and have a scintillator property for real-time response. IBIL was successfully visualized with each bunch of 290 MeV/n from synchrotron under different beam intensity from 6.0×106 to 3.0×109 (clinical beam condition) counts/spill. IBIL measurement at each position of Bragg peak suggested that developed PG:Ag-beads with Eu co-activators have successfully demonstrated real-time radiation monitoring of clinical carbon beams.

Additive manufacturing of fine-granularity optically-isolated plastic scintillator elements

Plastic scintillator detectors are used in high energy physics as well as for diagnostic imaging in medicine, beam monitoring on hadron therapy, muon tomography, dosimetry and many security applications. To combine particle tracking and calorimetry it is necessary to build detectors with three-dimensional granularity, i.e. small voxels of scintillator optically isolated from each other. Recently, the 3DET collaboration demonstrated the possibility to 3D print polystyrene-based scintillators with a light output performance close to that obtained with standard production methods. In this article, after providing a further characterization of the developed scintillators, we show the first matrix of plastic scintillator cubes optically separated by a white reflector material entirely 3D printed with fused deposition modeling. This is a major milestone towards the 3D printing of the first real particle detector. A discussion of the results as well as the next steps in the R&D is also provided.

Damage Monitoring of Engineered Cementitious Composite Beams Reinforced with Hybrid Bars Using Piezoceramic-Based Smart Aggregates.

In order to explore the crack development mechanism and damage self-repairing capacity of ECC beams reinforced with hybrid bars, the smart aggregate-based active sensing approach were herein adopted to conduct damage monitoring of ECC beams under cyclic loading. A total of six beams, including five engineered cementitious composite (ECC) beams reinforced with different bars and one reinforcement concrete counterpart, were fabricated and tested under cyclic loading. The ultimate failure modes and hysteresis curves were obtained and discussed herein, demonstrating the multiple crack behavior and excellent ductility of ECC material. The damage of the tested beams was monitored by smart aggregate-based (SA) active sensing method, in which two SAs pasted on both beam ends were used as actuator and sensor, respectively. The time domain analysis, wavelet packet-based energy analysis and wavelet packet-based damage index analysis were performed to quantitatively evaluate the crack development. To evaluate the self-repairing capacity of the beams, a self-repairing index defined by the difference of damage index at loading and unloading peak points was proposed. The results in time domain and wavelet packed analysis were in close agreement with the observed crack development, revealing the feasibility of smart aggregate-based active sensing approach in damage detection for ECC beams. Especially, the proposed damage self-repairing index can describe the same structural re-centering phenomena with the test results, showing the proposed index can be used to evaluate the damage self-repairing capacity.

Nonlinear deformation monitoring of elastic beams based on isogeometric iFEM approach

Shape sensing plays a key role in Structural Health Monitoring (SHM) and has become an excellent methodology for large-scale engineering structures to achieve significant improvement in their safety, reliability, and affordability. The inverse finite element method (iFEM) is an accurate and efficient method for shape sensing to reconstruct the three-dimensional displacements using in situ surface strain data. This study proposes a novel shape sensing method for large deformation monitoring based on strain gradient theory and iFEM method. Initially, the nonlinear displacement fields are described, and Green–Lagrange strain theory is employed to deduce the theoretical section strains, and then the strain–displacement relation is established by using a least-squares variational principle. Next, isogeometric displacement functions and the measured section strain formulations are deduced, and a decoupling method for high order section strains is proposed. Finally, a cantilever beam is used to demonstrate the accuracy and effectiveness of the refined isogeometric iFEM method for large deformations. The numerical results show the superior reconstruction capability and potential applicability of the proposed model for accurate shape prediction of the non-linear deformation of beam structure.

Characteristic analysis of wideband beam monitor with high-frequency pickups.

The signal transmission characteristics of a wideband beam monitor (WBM) with feedthrough electrodes are discussed in the frequency region up to 13.5GHz on the basis of a coupled-mode analysis using an equivalent circuit model with electromagnetically coupled transmission lines. It is demonstrated that in the signal transmission characteristics based on an electromagnetic induction method, electromagnetic couplings for fundamental and higher-order rf waves play an important role depending on the spatial configuration and geometrical structure of the electrodes mounted on the WBM with a cylindrical structure. The physical prospect in the calibration procedure of feedthrough electrodes is improved in terms of the signal transmission characteristics over the frequency region. In this report, the modal analyses and experimental investigations of the signal transmission characteristics in the WBM are described in detail. An alternative method of gain calibration for each electrode is also demonstrated.

Absolute beam monitor: A novel laboratory device for neutral beam calibration.

Instruments recording Energetic Neutral Atoms (ENAs) for space applications require thorough laboratory calibration in a dedicated test facility providing a neutral atom beam. Accurate knowledge of the neutral beam intensity and energy is central for the laboratory calibration procedure. However, until recently, the quantification of the neutral atom beam intensity in the low-energy range below a few 100eV was based on relative measurements with standard detectors of approximately known detection efficiencies for neutral atoms. We report on the design and development of a novel calibration device dedicated to determining the ENA beam flux in an absolute manner in the energy range from 3keV down to about 10eV. This is realized by applying ENA scattering at a surface and coincident detection of scattered particles and created secondary electrons. Moreover, the neutral beam energy is determined by a time-of-flight measurement. The applied measurement principle relies on very low background signals. The observed background count rates are in the range 10-2 s for the individual channels and about 10-5 s for coincidence events. The background is, thus, at least two, typically four, orders of magnitude lower than the signal rate for neutral atom beams in the foreseen energy range. We demonstrate a concrete application using the absolute flux calibration of a laboratory neutralization stage.

The Topmetal-CEE prototype, a direct charge sensor for the beam monitor of the CSR external-target experiment

The Cooler-Storage-Ring External-target Experiment (CEE) which is being constructed since 2020 is a spectrometer to study the properties of nuclear matter at high baryon density region. We present the design and simulation results of a sensor named Topmetal-CEE which is being developed for an online beam monitor of the CEE. A prototype of the Topmetal-CEE has been designed in a standard CMOS 130 nm process and is being fabricated. The Topmetal-CEE prototype has 180 channels with a pitch of 100 μm. In each channel, electrons are collected by a charge collection electrode which is a top-most metal exposed to the surrounding media, amplified by a charge sensitive amplifier, and then fed into a discriminator. The output of the discriminator is split into two paths which record Time of Arrival (ToA) and Time over Threshold (ToT) of the collected signal, respectively. In order to reduce the dead time, 180 channels are split into two separate parts and then the information in each part is read out by a data-driving priority readout scheme independently. Each channel has its own address encoded by an address encoder. The ToA, ToT and address of each channel are framed and encoded, and then transferred off chip with a serial speed of 4.4 Gbps.

Readout Electronics of the Prototype Beam Monitor in the HIRFL-CSR External-Target Experiment

The External-target Experiment (CEE) at the Cooling Storage Ring of the Heavy-Ion Research Facility in Lanzhou (HIRFL-CSR) will be the first large-scale experiment in nuclear physics independently developed in China covering the GeV energy regime. The beam monitor located at the center front of the CEE accurately measures the position of the particles with a few tens of um accuracy in a non-interceptive way. This unique advantage significantly improves the accuracy of the particle track reconstructions. This beam monitor’s readout electronics consist of the Front-end module (FEM), Readout Control Module (RCM), and Clock Synchronization module (CSM). Twhe novel Topmetal series pixel sensors directly collect the ionized charge along the track of the ion beam while it passes through the gas in the beam monitor. Lab test proves that the readout electronics have an INL of less than 1%. In addition, the prototype beam monitor can measure the position of the 40Ar beam of 320 MeV/u with a resolution of ~6.9 μm. This paper will discuss the design, characterization, and test of the readout electronics.

Split Ring Resonator Network and Diffused Sensing Element Embedded in a Concrete Beam for Structural Health Monitoring.

The aim of this work is to propose two different and integrated sensors for the structural health monitoring of concrete beams. In particular, a diffused sensing element and a split ring resonator network are presented. The first sensor is able to detect the variations in the dielectric properties of the concrete along the whole beam length, for a diffuse monitoring both during the important concrete curing phase and also for the entire life cycle of the concrete beams. The resonators instead work punctually, in their surroundings, allowing an accurate evaluation of the permittivity both during the drying phase and after. This allows the continuous monitoring of any presence of water both inside the concrete beam and at points that can be critical, in the case of beams in dams, bridges or in any case subject to a strong presence of water which could lead to deterioration, or worse, cause serious accidents. Moreover, the punctual sensors are able to detect the presence of cracks in the structure and to localize them.

PLASTIC SCINTILLATOR BASED 2D DETECTOR FOR PHOTON RADIOTHERAPY: PRELIMINARY RESULTS

A proof-of-concept study of a new detector based on a thin plastic scintillator monitored by a Charge-Coupled Device (CCD) camera designed for monitoring and characterisation of Linac photon beams is presented. The response of the detector is compared with radiochromic film using 6 and 18 MV radiotherapeutic beams. We have observed: (i) all instruments survived the secondary radiation fields during Linac operation, (ii) it was possible to process the measured data using statistical techniques and (iii) the processed data from the CCD camera qualitatively correspond to film dosimetry results. A statistical technique based on the selection of minimal values provides the clearest results. Quantitatively, CCD and film results can only be compared as 6 to 18 MV response rates. We have observed that the rates from the CCD data are systematically higher than the rates from film dosimetry. Differences are not too high, namely 1.9-2.4 times the combined standard deviation.

Real‐Time THz Beam Profiling and Monitoring via Flexible Vertically Aligned Carbon Nanotube Arrays

AbstractIn terahertz (THz) quasi‐optical systems, the real‐time profiling and visualization of THz beams is of great importance for beam focusing and collimation applications. Herein, a cost‐effective and room‐temperature‐operated THz imaging device for this purpose is demonstrated experimentally using a flexible and broadband THz absorber based on a vertically aligned carbon nanotube (VACNT) array. Excellent THz absorption performances with an average power absorptance >96.8% are achieved within 0.1 and 2.5 THz. The energy of the incident THz wave is absorbed by the THz absorber and converted into heat that will re‐radiate and can be detected by an infrared (IR) camera as a result of the THz‐to‐IR conversion mechanism. Real‐time THz beam imaging and monitoring applications are demonstrated by a series of experiments at both 0.1 and 0.3 THz, providing an alternative approach for real‐time beam profiling and monitoring of THz waves.

The FlashDC project: Development of a beam monitor for FLASH radiotherapy

FLASH Radiotherapy is currently being studied and actively explored by medical and radiobiology communities as one of the most promising technological break-through in the future of cancer treatment as it could considerably improve the sparing of healthy tissues when compared to conventional radiotherapy. However, the FLASH effect activation mechanism still needs a thorough investigation before the characteristics of a therapeutic beam could be properly defined. In this manuscript, a new method for the on-line monitoring of therapeutic beams at FLASH intensities, based on air fluorescence and developed within the FlashDC project, is presented.

Displacement reconstruction of beams subjected to moving load using data fusion of acceleration and strain response

Displacement response induced by moving load is important for health monitoring and safety assessment of beams. It contains displacement representing the high frequency part and pseudo-static displacement (PSD) representing the low frequency part. It is normally difficult to reconstruct the PSD due to its approximately zero frequency and inaccurate assumption of the neutral axis position of the structural cross-section. This paper presents a moving load induced displacement reconstruction method using data fusion of acceleration and strain response with special attention on PSD extraction. Firstly, the displacements are derived from the acceleration and strain, which are deemed as the acceleration-derived displacement (ADD) and the strain-derived displacement (SDD), respectively. Subsequently, a correction factor is proposed based on the ADD and SDD to determine the neutral axis position of the structural cross-section. Then the PSD is extracted from the SDD based on the correction factor and a designed low-pass filter. Finally, the performance of proposed method is investigated by numerical and experimental examples. The results manifest that the correction factor can determine the neutral axis position with high accuracy, and the proposed method can obtain more accurate reconstructed displacement than using the acceleration or the strain alone.

A novel methodological study for monitoring proton beam spot using back-streaming secondary neutrons from the high-power target

The power of the proton beam of a high-power spallation neutron source generally ranges from 100 kW to several MW. The distribution of the power density of the beam on the target is critical for the stable operation of the high-power spallation target. This study proposes a beam monitoring method that involves restoring the image of a high-power proton beam spot on a target based on the principle of pinhole imaging by using the back-streaming of secondary neutrons from the spallation target. Fast and indirect imaging of the beam spot can be achieved at a distance of tens of meters from the target. The proposed method of beam monitoring can flexibly adjust the size of the pinhole and the measurement distance to control the intensity of flux of the secondary neutrons according to the demands of the detection system, which is far from the high-radiation target area. The results of simulations showed that the proposed method can be used to restore the beam spot of the incident proton by using the point response function and images of the secondary neutrons. Based on the target and the Back-n beamline in the CSNS, the effectiveness of this method has also been confirmed by means of Monte Carlo simulation.

Pearson Correlation and Discrete Wavelet Transform for Crack Identification in Steel Beams

Discrete wavelet transform is a useful means for crack identification of beam structures. However, its accuracy is severely dependent on the selecting mother wavelet and vanishing moments, which raises a significant challenge in practical structural crack identification. In this paper, a novel approach is introduced for structural health monitoring of beams to fix this challenge. The approach is based on the combination of statistical characteristics of vibrational mode shapes of the beam structures and their discrete wavelet transforms. First, this paper suggests using regression statistics between intact and damaged modes to monitor the health of beam structures. Then, it suggests extracting quasi-Pearson-based mode shape index of the beam structures to use them as an original signal in discrete wavelet transforms. Findings show that the proposed approach has several advantages compared with the conventional mode shape signal processing by the discrete wavelet transforms and significantly improves damage detection’s accuracy.

Optical transition radiation based transverse beam diagnostics for nonrelativistic ion beams

The usage of optical transition radiation (OTR) for profile monitoring of relativistic electron beams is well known. This paper presents the case for beam diagnostic application of OTR for nonrelativistic ion beams. In addition to expected linearly polarized transition radiation in the plane of observation, a significant component of observed radiation is unpolarized. The unpolarized contribution increases as the target is tilted toward the grazing angles with its intensity, an order of magnitude higher than the polarized radiation. This unpolarized radiation is shown to have the characteristics of OTR and is qualitatively explained as the OTR generated on a rough target surface. This increase in observed radiation can be used advantageously for transverse profile measurements. Further systematic effects such as the dependence of light yield on beam current, comparison of the measured transverse profiles with secondary electron emission based grid, target heating, and prompt nature of observed radiation are reported.

Strip detector array (SDA) for beam monitoring in radiotherapy: reconstruction of MLC parameters from multiple projections of flux

Objective. In this paper we propose and investigate a new detector with multiple strip detector arrays (SDA) for monitoring MLC shaped x-ray beams for radiotherapy treatment. Approach. Each SDA measures 1D dose profiles equivalent to dose projections. The goal of such a detector is to determine individual MLC leaf positions as well as the Monitor Units (MU) per MLC segment during radiotherapy. In the present work we investigate an optimal SDA detector configuration and reconstruction algorithm. We determine the accuracy of SDA for different treatment sites (spine, pelvis, retroperitoneum, prostate, brain SRT, SRS, lung and head and neck). We perform a simulation study accounting for different type of MLC leaf positional errors: random MLC leaf, systematic for the whole leaf bank and systematic for an individual leaf. In a similar fashion, we also account for errors in Monitor Units per segment. Main results. We demonstrate that for a broad range of IMRT treatment plans a robust reconstruction of errors is achievable with only 3 projections (3 sets of SDA oriented at at 0°, 45° and 135°). The SDA is capable of capturing both systematic errors in leaf banks and individual leaves as well as random errors sufficient for practical clinical purposes. Significance. These features of the SDA detector makes it suitable for real-time Quality Control of MLC collimated linac output.

Microdosimetry performance of the first multi-arrays of 3D-cylindrical microdetectors

The present work reports on the microdosimetry measurements performed with the two first multi-arrays of microdosimeters with the highest radiation sensitive surface covered so far. The sensors are based on new silicon-based radiation detectors with a novel 3D cylindrical architecture. Each system consists of arrays of independent microdetectors covering 2 mmtimes2 mm and 0.4 mmtimes12 cm radiation sensitive areas, the sensor distributions are arranged in layouts of 11times11 microdetectors and 3times3 multi-arrays, respectively. We have performed proton irradiations at several energies to compare the microdosimetry performance of the two systems, which have different spatial resolution and detection surface. The unitcell of both arrays is a 3D cylindrical diode with a 25 mum diameter and a 20 mum depth that results in a welldefined and isolated radiation sensitive micro-volume etched inside a silicon wafer. Measurements were carried out at the Accélérateur Linéaire et Tandem à Orsay (ALTO) facility by irradiating the two detection systems with monoenergetic proton beams from 6 to 20 MeV at clinical-equivalent fluence rates. The microdosimetry quantities were obtained with a spatial resolution of 200 mum and 600 mum for the 11times11 system and for the 3times3 multi-array system, respectively. Experimental results were compared with Monte Carlo simulations and an overall good agreement was found. The good performance of both microdetector arrays demonstrates that this architecture and both configurations can be used clinically as microdosimeters for measuring the lineal energy distributions and, thus, for RBE optimization of hadron therapy treatments. Likewise, the results have shown that the devices can be also employed as a multipurpose device for beam monitoring in particle accelerators.