Campbelling Mode Research Articles

A comprehensive study on natural characteristics and dynamic responses of a dual-rotor system with inter-shaft bearing under non-random uncertainty

Aeroengines are usually designed with a dual-rotor configuration for the rotating part. A dual-rotor system has coupling characteristics introduced by an inter-shaft bearing, and the rotating direction of the rotors has critical influences on the performance. It becomes more complicated when the inevitable uncertainties of the dual-frequency excited dynamical system are considered. This paper delivers a comprehensive study of the natural characteristics and dynamic responses of a dual-rotor system with an inter-shaft bearing considering the non-random parametric uncertainties under co- and counter-rotating conditions. To this end, the finite element modeling and the deterministic solutions of a dual-rotor system are established. Then, the polynomial surrogate function is constructed for the desired natural characteristics and dynamic responses under non-random uncertainty. The polar interpolation technique is implemented to compute uncertain shaft orbits, overcoming difficulties in the traditional frequency-sense measure. Intensive case studies for different interval uncertain parameters are carried out and the results are comparatively discussed. It is found that the mass unbalance uncertainties only affect the respective modes excited by the rotor where the unbalance is located. The shaft stiffness has global uncertainty effects on the Campbell diagram, mode shapes, time history, shaft orbit and responses. Uncertainties in the inter-shaft bearing stiffness and speed ratio generally influence higher-order modes. The results of the present work gain insights into the modal characteristics and dynamical behaviors of the dual-rotor system under complex parametric uncertainties.

Investigation of Campbell mode with automatic calibration operated in fission chamber-based neutron flux monitoring system on EAST

To satisfy the wide-range requirement for the fission chamber-based neutron flux monitoring (NFM) system on experimental advanced superconducting tokamak (EAST), the pulse-counting and Campbell modes were combined to expand the measurement range. However, to obtain the neutron yields, the results of the Campbell mode should first be converted into neutron count rates via linear calibration. During the plasma experiment, the non-neutron backgrounds vary with respect to different experimental conditions, which leads to a baseline dynamic change in the Campbell mode. In future research, NFM system need provide real-time feedback parameters regarding the operational status of the fusion device. Therefore, an automatic calibration method was developed to automatically deduct various baselines of the Campbell mode and obtain the neutron yields in real time. This method continuously updates the average value of each sub-interval (multiple sub-intervals are set in the calibration region) using a linear superposition averaging method. In addition, to optimize the dual-mode switching threshold, ensure the calibration region and define the upper limit of Campbell mode, a simulated neutron signal generator was designed and applied. The switching threshold of the dual modes was set to 400 kcps, the calibration region of the Campbell mode was selected as 50–500 kcps, and the upper limit of the equivalent count rate in the Campbell mode reached to 108cps with a relative error of<4%. Finally, the automatic calibration method was tested using experimental data from the NFM system on EAST. The automatic calibration results basically overlapped with the reference results and superior to the offline fixed calibration results. Under different experimental conditions, the relative root mean square error (RRMSE) values of the automatic calibration results were lower than those of the offline fixed calibration results. Therefore, the proposed automatic calibration method is accurate and reliable, and can satisfy the real-time measurement requirements of wide-range NFM system.

Fission chamber data acquisition system for neutron flux measurements on the Mega-Amp Spherical Tokamak Upgrade.

Neutron flux measurements are important in fusion devices for both safety requirements and physics studies. A new system has been built for the Mega-Amp Spherical Tokamak Upgrade (MAST Upgrade) that provides neutron count, DC, and Campbell mode measurements for a 1 µs period at 1MHz. The acquisition system uses a Red Pitaya board to sample current from two fission chambers mounted on the side of the MAST-U vessel. The system-on-chip design of the Zynq-7020 on the Red Pitaya also allows a web server implementation using Flask for data retrieval and diagnostic configuration over the MAST Upgrade network.

Development of a high-temporal resolution neutron flux measurement system for the HL-2M tokamak

To enhance the understanding of the physics of energetic ions in fusion plasma, a high-temporal resolution neutron flux measurement (HTRNFM) system, which is equipped with a fast-neutron scintillation detector embedded with ZnS:Ag phosphor, has been developed for the HL-2M tokamak. It has a temporal resolution of 10 μs during conventional operations. Its dynamic range is sufficiently wide for neutron flux measurements by adopting the combination use of the scalar mode and the Campbell mode. Based on the Monte Carlo calculations, the applicable count rate ranges of both the scalar mode and the Campbell mode are respectively 0.1–10 Mcps and 10–200 Mcps. The performance validation of the HTRNFM system has been performed by neutron flux measurements in magnetohydrodynamic (MHD) quiet plasmas in the HL-2A tokamak. In another plasma with abundant MHD instabilities, both the continuous neutron flux decreases and the rapid neutron flux decreases caused by different MHD instabilities are observed in a more detailed manner for the first time with the HTRNFM system than with other neutron flux measurement (NFM) systems that have a lower temporal resolution of 1 ms. The HTRNFM system will serve as a powerful diagnostic tool for research on energetic ion confinement quality in the HL-2M tokamak.

Development of a wide-range and fast-response digitizing pulse signal acquisition and processing system for neutron flux monitoring on EAST

The neutron count rate fluctuation reaches six orders of magnitude between the ohmic plasma scenario and high power of auxiliary heating on an experimental advanced superconducting tokamak (EAST). The measurement result of neutron flux monitoring (NFM) is a significant feedback parameter related to the acquisition of radiation protection-related information and rapid fluctuations in neutron emission induced by plasma magnetohydrodynamic activity. Therefore, a wide range and high time resolution are required for the NFM system on EAST. To satisfy these requirements, a digital pulse signal acquisition and processing system with a wide dynamic range and fast response time was developed. The present study was conducted using a field-programmable gate array (FPGA) and peripheral component interconnect extension for instrument express (PXIe) platform. The digital dual measurement modes, which are composed of the pulse-counting mode and AC coupled square integral’s Campbelling mode, were designed to expand the measurement range of the signal acquisition and processing system. The time resolution of the signal acquisition and processing system was improved from 10 to 1 ms owing to utilizing high-speed analog-to-digital converters (ADCs), a high-speed PXIe communication with a direct memory access (DMA) mode, and online data preprocessing technology of FPGA. The signal acquisition and processing system was tested experimentally in the EAST radiation field. The test results showed that the time resolution of NFM was improved to 1 ms, and the dynamic range of the neutron counts rate was expanded to more than 10^{6} counts per second. The Campbelling mode was calibrated using a multipoint average linear fitting method; subsequently, the fitting coefficient reached 0.9911. Therefore, the newly developed pulse signal acquisition and processing system ensures that the NFM system meets the requirements of high-parameter experiments conducted on EAST more effectively.

Design and performance of an wide-range real-time NFM system using higher order Campbell mode

This paper reports the design of a neutron flux monitor (NFM) system based on field-programmable gate array (FPGA) with a temporal resolution of 1 ms, and a faster time response of 0.2 ms. Notably, the NFM system completes the automatic calibration of the Campbell algorithm based on the least square method of relative error and obtains the real-time neutron count rate with a wide measurement range of 109 cps. Simultaneously, higher-order Campbell algorithms (HOC) are proposed and the performance is investigated. Inevitably, simulated neutron pulse waveforms with known pulse counting were utilized to assess the performance of the HOC algorithms. Furthermore, an FPGA-based high-speed neutron pulse signal generator capable of generating different count rates is designed to study the HOC algorithms and verify the reliability of the NFM system. Combining the results of simulation and actual testing, we optimized the counting algorithm at a low count rate, the Campbell algorithm at a high count rate, and ultimately reduced the relative error of the NFM system to less than 2%.

High-precision and wide-range real-time neutron flux monitor system through multipoint linear calibration

The neutron flux monitor (NFM) system is an important diagnostic subsystem introduced by large nuclear fusion devices such as international thermonuclear experimental reactor (ITER), Japan torus-60, tokamak fusion test reactor, and HL-2A. Neutron fluxes can provide real-time parameters for nuclear fusion, including neutron source intensity and fusion power. Corresponding to different nuclear reaction periods, neutron fluxes span over seven decades, thereby requiring electronic devices to operate in counting and Campbelling modes simultaneously. Therefore, it is crucial to design a real-time NFM system to encompass such a wide dynamic range. In this study, a high-precision NFM system with a wide measurement range of neutron flux is implemented using real-time multipoint linear calibration. It can automatically switch between counting and Campbelling modes with variations in the neutron flux. We established a testing platform to verify the feasibility of the NFM system, which can output the simulated neutron signal using an arbitrary waveform generator. Meanwhile, the accurate calibration interval of the Campbelling mode is defined well. Based on the above-mentioned design, the system satisfies the requirements, offering a dynamic range of 108 cps, temporal resolution of 1 ms, and maximal relative error of 4% measured at the signal-to-noise ratio of 15.8 dB. Additionally, the NFM system is verified in a field experiment involving HL-2A, and the measured neutron flux is consistent with the results.

Development of a wide-range neutron flux monitoring system in EAST

A wide measurement range for a neutron flux monitoring (NFM) system is developed in the Experimental Advanced Superconducting Tokamak (EAST) for fusion neutron yield measurement, comprising an 3He proportional counter, a 235U fission chamber (FC), and a wide dynamic range signal-processing circuit. Two high-sensitivity 3He detectors operate in counting mode, which is suitable for low neutron yield (Yn) conditions with ohmic and radio-frequency heating of plasma. Two other FCs are adapted with newly developed digitizers, operating in counting and campbelling modes to satisfy the conditions of wide dynamic range measurement required by neutral beam injection (NBI) experiment. The anti-magnetic-field interference of the FC is examined using two permanent magnets, whose efficiency are calibrated with 2.46 MeV neutrons produced by a Van de Graaff accelerator. Furthermore, the NFM system is implemented in-situ calibration with a 252Cf neutron source and a remote handling. As a routine diagnostic, the NFM system is successful obtaining the fusion neutron yield for ion cyclotron resonance heating (ICRH) and NBI heating performance evaluation in EAST plasma experiment.

In-Pile Qualification of a Fast-Neutron-Detection-System

In order to ensure the quality and the relevance of irradiation programs in the future Jules Horowitz Reactor (JHR), the French Alternative Energies and Atomic Energy Commission (CEA) has significantly increased its research and development effort in the field of in-pile instrumentation during the last decade. Major progress has been achieved in the capability to perform accurate in-pile measurements using reliable and updated techniques. A significant part of this effort has been conducted in the framework of the Joint Instrumentation Laboratory between the CEA and the Belgian Nuclear Research Centre (SCK $\cdot$ CEN). In order to improve measurement techniques for neutron flux assessment, a unique system for online measurement of fast neutron flux has been developed and recently qualified in-pile. The fast-neutron-detection-system (FNDS) has been designed to monitor accurately high-energy neutron flux (E > 1 MeV) in typical material testing reactor (MTR) conditions, where neutron flux levels can be as high as $10^{15}\,\,\text {N}\cdot \text {cm}^{-2}\cdot \text {s}^{-1}$ and are generally dominated by thermal neutrons. Moreover, the neutron flux is coupled with a high gamma flux of typically a few $10^{15} \gamma \cdot \text {cm}^{-2}\cdot \text {s}^{-1}$ , which can be highly disturbing for the online measurement of neutron fluxes. The patented FNDS system is based on two detectors allowing the simultaneous detection of both thermal- and fast-neutron flux. Thermal neutrons can be measured using a self-powered neutron detector or a 235U miniature fission chamber, while fast neutron detection requires a miniature fission chamber with a special fissile material presenting an energy threshold near 1 MeV, which can be 242Pu for MTR conditions. Fission chambers are operated in Campbelling mode for an efficient gamma rejection. FNDS also includes a specific software that processes measurements to compensate online the fissile material depletion and to adjust the sensitivity of the detectors, in order to produce a precise evaluation of both thermal and fast neutron flux even after long-term irradiation. FNDS has been validated through a two-step experimental program. A first set of tests was performed at BR2 reactor operated by SCK $\cdot$ CEN in Belgium. Two FNDS prototypes were operated in-pile during nearly 1000 h. These tests exhibited the consistency of the measurement of thermal to fast neutron flux ratio with Monte Carlo neutron and photon transport calculations, as well as the right compensation of fissile material depletion. This paper describes a second test recently completed at ISIS reactor operated by CEA in France. For this irradiation, FNDS signal was compared to reference thermal- and fast-neutron flux measurements using activation dosimeters analyzed under COFRAC Quality Certification. During this latter test, FNDS proved its ability to measure online the fast neutron flux with an overall accuracy better than 5%. FNDS is now operational and is assumed to be the first and unique acquisition system able to provide an online measurement of the fast neutron flux in MTR conditions. This system will be used to perform spectral neutron characterization of JHR channels, but it may also be implemented in future irradiation experiments, for a better and real-time evaluation of the fast neutron flux received by material and fuel samples.

A novel digital neutron flux monitor for international thermonuclear experimental reactor

A novel full-digital real-time neutron flux monitor (NFM) has been developed for the International Thermonuclear Experimental Reactor. A measurement range of 109 counts per second is achieved with 3 different sensitive fission chambers. The Counting mode and Campbelling mode have been combined as a means to achieve higher measurement range. The system is based on high speed as well as parallel and pipeline processing of the field programmable gate array and has the ability to upload raw-data of analog-to-digital converter in real-time through the PXIe platform. With the advantages of the measurement range, real time performance and the ability of raw-data uploading, the digital NFM has been tested in HL-2A experiments and reflected good experimental performance.

In-Pile Qualification of the Fast-Neutron-Detection-System

In order to improve measurement techniques for neutron flux assessment, a unique system for online measurement of fast neutron flux has been developed and recently qualified in-pile by the French Alternative Energies and Atomic Energy Commission (CEA) in cooperation with the Belgian Nuclear Research Centre (SCK•ECEN). The Fast-Neutron-Detection-System (FNDS) has been designed to monitor accurately high-energy neutrons flux (E &gt; 1 MeV) in typical Material Testing Reactor conditions, where overall neutron flux level can be as high as 1015 n.cm-2.s-1 and is generally dominated by thermal neutrons. Moreover, the neutron flux is coupled with a high gamma flux of typically a few 1015 γ.cm-2.s-1, which can be highly disturbing for the online measurement of neutron fluxes. The patented FNDS system is based on two detectors, including a miniature fission chamber with a special fissile material presenting an energy threshold near 1 MeV, which can be 242Pu for MTR conditions. Fission chambers are operated in Campbelling mode for an efficient gamma rejection. FNDS also includes a specific software that processes measurements to compensate online the fissile material depletion and to adjust the sensitivity of the detectors, in order to produce a precise evaluation of both thermal and fast neutron flux even after long term irradiation. FNDS has been validated through a two-step experimental program. A first set of tests was performed at BR2 reactor operated by SCK•CEN in Belgium. Then a second test was recently completed at ISIS reactor operated by CEA in France. FNDS proved its ability to measure online the fast neutron flux with an overall accuracy better than 5%.

The development of Campbell integration system applied in high particle flux measurement

Campbell Mode is a method widely used in nuclear signal processing. In this article, we introduce the design of the new system based on the Campbell integration measurement applied in NFM (neutron flux measurement) systems for ITER plasma diagnose. In this article, we introduce a digital particle flux measurement system based on Campbell integration theory. A subsequent series of experiment are conducted to test the digital Campbell system performance, which proves that the Campbell integration system is competent for the plasma diagnose in ITER.

A digital wide range neutron flux measuring system for HL-2A**Contributed paper, published as part of the Proceedings of the 3rd Domestic Electromagnetic Plasma Diagnostics Workshop, September 2016, Hefei, China.

To achieve wide-range, high-integration, and real-time performance on the neutron flux measurement on the HL-2A tokamak, a digital neutron flux measuring (DNFM) system based on the peripheral component interconnection (PCI) eXtension for Instrumentation express (PXIe) bus was designed. This system comprises a charge-sensitive preamplifier and a field programmable gate array (FPGA)-based main electronics plug-in. The DNFM totally covers source-range and intermediate-range neutron flux measurements, and increases system integration by a large margin through joining the pulse-counting mode and Campbell mode. Meanwhile, the neutron flux estimation method based on pulse piling proportions is able to choose and switch measuring modes in accordance with current flux, and this ensures the accuracy of measurements when the neutron flux changes suddenly. It has been demonstrated by simulated signals that the DNFM enhances the full-scale measuring range up to 1.9 × 108 cm−2 s−1, with relative error below 6.1%. The DNFM has been verified to provide a high temporal sensitivity at 10 ms time intervals on a single fission chamber on HL-2A.

Implementing a Neutron-Diagnostic advanced DAQ system use case on a PXIe platform through a 3D remote laboratory

IRIO-3DLab is devised to enhance the learning process and reduce the development time for engineers in charge of designing intelligent DAQ systems based on PXIe technology and distributed control systems such as Experimental Physics In Control Systems (EPICS). IRIO-3DLab consists of an OpenSimulator-based virtual world that aims to promote the understanding of how DAQ systems work. This contribution describes how to use IRIO-3DLab to implement a Neutron-Diagnostic use case using a PXIe platform, which includes setting up the hardware remotely and configuring the EPICS IOC and the interface with the application using Control System Studio (CSS). IRIO-3DLab allows users to connect the real hardware with its virtual replicas and select the application to be implemented in a Field Programmable Gate Array (FPGA). The FPGA addresses Pulse, Campbelling and Current mode measurements of the signals acquired. When the user selects the application, there is an associated EPICS application implementing the data gathering. The virtual world allows the user to first set the waveform generator used to generate predefined signal patterns to check the correct measurement and then to interface with the operator panel to assess the results obtained.

Design of a high order Campbelling mode measurement system using open source hardware

This paper reviews a new real-time measurement instrument dedicated for online neutron monitoring with fission chambers in nuclear reactors. The instrument implements the higher order Campbelling methods and self-monitoring capabilities on an open source development board. The board includes an CPU/FPGA System on a Chip.The feasibility of the measurement instrument was tested both in laboratory with a signal generator and in the Minerve reactor. It is shown that the instrument provides reliable and robust count rate estimation over a wide reactor power range based on the third order statistics of the fission chamber signal. In addition, the system is able to identify whether the measured count rate change is due to the malfunction of the detector or due to the change in the neutron flux. The applied self-monitoring method is based on the spectral properties of the fission chamber signal. During the experimental verification, the considered malfunction was the change of the polarization voltage.

Performance of Higher Order Campbell methods, Part II: calibration and experimental application

Applying Higher Order Campbelling methods in neutron flux monitoring with fission chambers is advantageous due to their capabilities to suppress the impact of unwanted noises and signal contributions (such as gamma radiation). This work aims to verify through experimental results that the basic assumptions behind the Higher Order Campelling methods are valid in critical reactors.The experiments, reported in this work, were performed at the MINERVE reactor in Cadarache. It is shown that the calibration of a fission chamber and the associated electronic system is possible in higher order mode. With the use of unbiased cumulant estimators and with digital processing, it is shown that over a wide count rate range, accurate count rate estimation can be achieved based on signal samples of a few ms, which is a significant progress compared to similar experimental results in the literature. The difference between the count rate estimated by pulse counting and by the Higher Order Campelling is less than 4%.The work also investigates the possibility of monitoring transient events. For this purpose, a control rod drop event was followed in Higher Order Campbelling mode.

Digital Real-Time Multiple Channel Multiple Mode Neutron Flux Estimation on FPGA-based Device

This paper presents a complete custom full-digital instrumentation device that was designed for real-time neutron flux estimation, especially for nuclear reactor in-core measurement using sub-miniature Fission Chambers (FCs). Entire fully functional small-footprint design (about 1714 LUTs) is implemented on FPGA. It enables real-time acquisition and analysis of multiple channels neutron's flux both in counting mode and Campbelling mode. Experimental results obtained from this brand new device are consistent with simulation results and show good agreement within good uncertainty. This device paves the way for new applications perspectives in real-time nuclear reactor monitoring.

Performance investigation of the pulse and Campbelling modes of a fission chamber using a Poisson pulse train simulation code

The detectors of the neutron flux monitoring system of the foreseen French GEN-IV sodium-cooled fast reactor (SFR) will be high temperature fission chambers placed in the reactor vessel in the vicinity of the core. The operation of a fission chamber over a wide-range neutron flux will be feasible provided that the overlap of the applicability of its pulse and Campbelling operational modes is ensured. This paper addresses the question of the linearity of these two modes and it also presents our recent efforts to develop a specific code for the simulation of fission chamber pulse trains. Our developed simulation code is described and its overall verification is shown.An extensive quantitative investigation was performed to explore the applicability limits of these two standard modes. It was found that for short pulses the overlap between the pulse and Campbelling modes can be guaranteed if the standard deviation of the background noise is not higher than 5% of the pulse amplitude. It was also shown that the Campbelling mode is sensitive to parasitic noise, while the performance of the pulse mode is affected by the stochastic amplitude distributions.

Impact of Gas Pressure on Fission Chamber Sensitivity in Campbelling Mode

The study presented in this paper is based on measurements conducted in the MINERVE zero power reactor operated at CEA Cadarache with a CEA-made U-235 miniature fission chamber (8 mm in diameter) and obtained in both pulse and Campbelling modes. Our objective was to investigate the impact of the filling gas mixture and pressure on each operating mode, using the capacity of the chamber to be refilled with gas. Three gas mixtures were tested (pure Ar, Ar+4%N2 and Ar+10%CH4) with pressure ranging from 1 to 9 bars. The Mean Fission Product Charge (MFPC), which is the mean charge deposited in the gas by fission products, was obtained from pulse mode signals for each detector setting. It is shown the MFPC is another key parameter to optimize the detector neutron sensitivity, after the fissile coating cross section. Campbelling mode signal was acquired with the Fast Neutron Detector System (FNDS) recently developed by CEA and SCK·CEN. Interesting results were obtained which improve our knowledge of the detector operation. Firstly, it was found that the measurements obtained in both modes are very consistent. The MFPC as a function of the gas pressure was found to be not monotonic. Instead, it features a maximum between 3 and 4 bars. This behavior is expected if the detector does not operate in saturation regime. Indeed, our standard voltage bias of 300 V appeared to be not high enough so that the saturation regime is established. Saturation curves measured in Campbelling mode were fitted using a detector modeling in order to extrapolate the saturation regime MFPC, which came to be independent from the gas. Secondly, obtained results show that the measuring range in Campbelling mode with this detector starts from fission rates as low as a few thousand counts per second. So the so called overlapping range, in which both pulse and Campbelling modes are usable, is about one decade with our spectroscopy modules and more than two decades with fast counting electronic modules. This feature is of high interest to test and/or calibrate Campbelling mode electronic systems using the MINERVE ZPR.

Comparison of Thermal Neutron Flux Measured by &lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$^{235}{\rm U}$&lt;/tex&gt; &lt;/formula&gt; Fission Chamber and Rhodium Self-Powered Neutron Detector in MTR

Thermal neutron flux is one of the most important nuclear parameter to be measured online in material testing reactors (MTRs). In particular two types of sensors with different physical operating principles are commonly used: self-powered neutron detectors (SPND) and fission chambers with coating. This work aims to compare on one hand the thermal neutron flux evaluation given by these two types of sensors and on the other hand to compare these evaluations with activation dosimeter measurements, which are considered as the reference for absolute neutron flux assessment. This study was conducted in an irradiation experiment, called CARMEN-1, performed during 2012 in OSIRIS reactor (CEA Saclay-France). The CARMEN-1 experiment aims to improve the neutron and photon flux and nuclear heating measurements in MTRs. In this paper we focus on the thermal neutron flux measurements performed in CARMEN-1 experiment. The use of fission chambers to measure the absolute thermal neutron flux in MTRs is not very usual. An innovative calibration method for fission chambers operated in Campbell mode has been developed at the CEA Cadarache (France) and tested for the first time in the CARMEN-1 experiment. The results of these measurements are discussed, with the objective to measure with the best accuracy the thermal neutron flux in the future Jules Horowitz Reactor.