Flux Shape Research Articles

Calibration of Large Photonis Fission Chambers in Standard Neutron Fields of the BR1 Reactor

Small fission chambers manufactured by Photonis, Reuter-Stokes, CEA, and Centronic are routinely calibrated in standard neutron fields of the BR1 reactor at SCK CEN in Mol, Belgium. Two irradiation fields are available: fast spectrum in the MARK3 convertor and thermal spectrum in the Empty Cavity. In this work, for the first time the calibration procedure of larger fission chambers (Photonis CFUL01 and CFUM21 type) with the deposit length exceeding the length of the convertor is presented. Spatial energy correction factors taking into account the neutron flux shape beyond the convertor and radial gradient of the neutron flux were calculated with MCNP and experimentally validated. The combination of calibration (i.e., effective mass measurement) in fast and thermal irradiation fields allows for determination of the purity of ²³⁸U deposit. This is demonstrated on three CFUL01-type fission chambers with purity between 99.8% and 99.998%.

The Solitary Wave in Advanced Nuclear Energy System

The solitary wave naturally arises in many areas of mathematical physics, including in nonlinear optics, plasma physics, quantum field theory, and fluid mechanics. In the past few years, for an advanced nuclear energy system, a particular class of traveling wave reactor called the Constant Axial shape of Neutron flux, nuclide number densities and power shape During Life of Energy production (CANDLE) reactor has been proposed, and an analytical solution has been desired since it could reveal the global characters of the solution. In this study, from the perspective of the solitary wave, the analytical solution of this advanced nuclear energy system is demonstrated through coupling the one-group neutron diffusion equation with the burnup equation. The tanh-function method is applied to solve that nonlinear partial differential equation. The relationship between the velocity of the solitary wave, wave amplitude, or neutron flux and the evolution of the nuclide is revealed by the analytical method. The results demonstrate that the neutron flux is proportional to the wave velocity. The results also imply that the amplitude of the neutron flux is proportional to the square root of the diffusion coefficient but is inversely proportional to the initial 238U density.

MAXI and NuSTAR Observations of the Faint X-Ray Transient MAXI J1848-015 in the GLIMPSE-C01 Cluster

Abstract We present the results of Monitor of All-sky X-ray Image (MAXI) monitoring and two Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the recently discovered faint X-ray transient MAXI J1848015. Analysis of the MAXI light curve shows that the source underwent a rapid flux increase beginning on 2020 December 20, followed by a rapid decrease in flux after only ∼5 days. NuSTAR observations reveal that the source transitioned from a bright soft state with unabsorbed, bolometric (0.1–100 keV) flux F = 6.9 ± 0.1 × 10−10 erg cm−2 s−1, to a low hard state with flux F = 2.85 ± 0.04 × 10−10 erg cm−2 s−1. Given a distance of 3.3 kpc, inferred via association of the source with the GLIMPSE-C01 cluster, these fluxes correspond to an Eddington fraction of the order of 10−3 for an accreting neutron star (NS) of mass M = 1.4M ⊙, or even lower for a more massive accretor. However, the source spectra exhibit strong relativistic reflection features, indicating the presence of an accretion disk that extends close to the accretor, for which we measure a high spin, a = 0.967 ± 0.013. In addition to a change in flux and spectral shape, we find evidence for other changes between the soft and hard states, including moderate disk truncation with the inner disk radius increasing from R in ≈ 3 R g to R in ≈ 8 R g, narrow Fe emission whose centroid decreases from 6.8 ± 0.1 keV to 6.3 ± 0.1 keV, and an increase in low-frequency (10−3–10−1 Hz) variability. Due to the high spin, we conclude that the source is likely to be a black hole rather than an NS, and we discuss physical interpretations of the low apparent luminosity as well as the narrow Fe emission.

Performance evaluation of AHWR flux mapping system during normal operational scenarios

In large nuclear reactors, a number of appropriately distributed in-core neutron detectors are used for monitoring and control of neutron flux distribution in the core. In Advanced Heavy Water Reactor (AHWR) too, a set of 168 self-powered neutron detectors installed vertically at 6 locations in 28 in-core detector housing units has been proposed to be used. This configuration arrived at using the K-means clustering approach, has been found to reconstruct the core neutron flux distribution for a number of steady-state flux shapes. For practical application, in addition to steady-state, the optimized set of in-core detectors should provide reasonably accurate core monitoring for regular reactor operations as well. This paper investigates the accuracy characteristics of flux mapping using the proposed set of 168 in-core self-powered neutron detectors in the reconstruction of time-varying flux shapes encountered during normal reactor operations. Time-dependent flux shapes arising due to perturbations such as the movement of reactivity devices, refuelling and xenon spatial oscillations are considered for this study. Flux reconstruction is performed using the well-known flux synthesis method. From the analysis, it can be observed that the proposed set of in-core detectors reliably reconstructs the flux distribution in the reactor even during the normal operational scenarios. The maximum RMS error in mesh flux using 168 SPNDs and 35 eigenmodes is found to be 4.45% across all the operational scenarios considered.

Galaxies lacking dark matter produced by close encounters in a cosmological simulation

Electrons accelerated on Earth by a rich variety of wave scattering or stochastic processes generate hard non-thermal X-ray bremsstrahlung up to >~ 1 MeV and power Earth's various types of aurorae. Although Jupiter's magnetic field is an order of magnitude larger than Earth's, space-based telescopes have previously detected X-rays only up to ~7 keV. On the basis of theoretical models of the Jovian auroral X-ray production, X-ray emission in the ~2-7 keV band has been interpreted as thermal (arising from electrons characterized by a Maxwell-Boltzmann distribution) bremsstrahlung. Here we report the observation of hard X-rays in the 8-20 keV band from the Jovian aurorae, obtained with the NuSTAR X-ray observatory. The X-rays fit to a flat power-law model with slope 0.60+/-0.22 - a spectral signature of non-thermal, hard X-ray bremsstrahlung. We determine the electron flux and spectral shape in the keV to MeV energy range using coeval in situ measurements by the Juno spacecraft's JADE and JEDI instruments. Jovian electron spectra of the form we observe have previously been interpreted to arise in stochastic acceleration, rather than coherent acceleration by electric fields. We reproduce the X-ray spectral shape and approximate flux observed by NuSTAR, and explain the non-detection of hard X-rays by Ulysses, by simulating the non-thermal population of electrons undergoing precipitating electron energy loss, secondary electron generation and bremsstrahlung emission in a model Jovian atmosphere. The results highlight the similarities between the processes generating hard X-ray auroras on Earth and Jupiter, which may be occurring on Saturn, too.

Observation and origin of non-thermal hard X-rays from Jupiter

Electrons accelerated on Earth by a rich variety of wave-scattering or stochastic processes1,2 generate hard, non-thermal X-ray bremsstrahlung up to ~1 MeV (refs. 3,4) and power Earth’s various types of aurorae. Although Jupiter’s magnetic field is an order of magnitude larger than Earth’s, space-based telescopes have previously detected X-rays only up to ~7 keV (ref. 5). On the basis of theoretical models of the Jovian auroral X-ray production6,7,8, X-ray emission in the ~2–7 keV band has been interpreted as thermal (arising from electrons characterized by a Maxwell–Boltzmann distribution) bremsstrahlung5,9. Here we report the observation of hard X-rays in the 8–20 keV band from the Jovian aurorae, obtained with the NuSTAR X-ray observatory. The X-rays fit to a flat power-law model with slope of 0.60 ± 0.22—a spectral signature of non-thermal, hard X-ray bremsstrahlung. We determine the electron flux and spectral shape in the kiloelectronvolt to megaelectronvolt energy range using coeval in situ measurements taken by the Juno spacecraft’s JADE and JEDI instruments. Jovian electron spectra of the form we observe have previously been interpreted as arising in stochastic acceleration, rather than coherent acceleration by electric fields10. We reproduce the X-ray spectral shape and approximate flux observed by NuSTAR, and explain the non-detection of hard X-rays by Ulysses11, by simulating the non-thermal population of electrons undergoing precipitating electron energy loss, secondary electron generation and bremsstrahlung emission in a model Jovian atmosphere. The results highlight the similarities between the processes generating hard X-ray aurorae on Earth and Jupiter, which may be occurring on Saturn, too.

Validation of fast neutron reactors fertile blanket depletion calculations through the analysis of the DOUBLON experiment in Phenix with TRIPOLI-4® and DARWIN3-SFR

A reliable assessment of the final inventory in the fertile blanket of a Fast Neutron Reactor is an important issue for fuel cycle physics, as it impacts safety, reprocessing and design studies. The performances of fertile blankets neutronics calculations is a long standing issue, as there as specificities in these regions that are quite challenging, especially for depletion codes.The new CEA fuel depletion calculation package is DARWIN3-SFR, which incorporates the deterministic neutronics code APOLLO3® and the depletion module MENDEL. This paper details the validation of DARWIN3-SFR for fertile blanket calculations through the re-interpretation of the DOUBLON pin-irradiation in the Phenix reactor.During this irradiation, nine pins are studied through isotopic ratios, which give us information about the depletion and, indirectly, the neutron flux calculations inside the blanket. This environment is especially challenging for neutronics codes, since there is a strong variation of the neutron energy and population over a short distance. Our recent analysis of TRAPU - which is a similar experiment, but in the core center - has proven DARWIN3-SFR to be reliable for the fuel depletion calculations of fissile subassemblies; nevertheless, its performances in the fertile blankets still require validation.We observe that, once the calculated neutron flux level has been adjusted to the experiment through the 148Nd/238U ratio, DARWIN3-SFR provides results similar to the reference stochastic code TRIPOLI-4®. However, both codes have difficulties to reproduce some of the measured isotopic ratios inside the fertile blanket. Whilst DARWIN3-SFR produces identical results for most of the isotopes analysed (234U, 235U, 236U, 238Pu, 239Pu, 240Pu), variations of the neutron spectrum lead to some disparities for the production of 241Pu and 242Pu. Indeed, the low-energy flux estimation is higher with TRIPOLI-4® than with DARWIN3-SFR in the energy range where the 240Pu has a high capture cross section, which increases the calculated production of 241Pu and 242Pu.DARWIN3-SFR and its predecessor DARWIN-2 are efficient at calculating the average neutron flux level over the entire fertile blanket. However, the results of the two codes show a strong pin-to-pin dispersion, resulting in a different shape of the neutron flux inside the blanket. With DARWIN3-SFR, the estimated neutron spectrum is softer than in DARWIN-2, which impacts the 238U capture and fission reaction rates and hence the production of plutonium.

The CANDLE burnup strategy applied to small modular pressurized water reactor loading with fully ceramic microencapsulated fuel

Abstract For post-Fukushima nuclear power plants, there has been interested in accident-tolerant fuel (ATF) since it has better tolerant in the event of a severe accident. The fully ceramic microencapsulated (FCM) fuel is one kind of the ATF materials. In this study, the small modular pressurized water reactor (PWR) loading with FCM fuels was investigated, and the modified Constant Axial shape of Neutron flux, nuclide number densities and power shape During Life of Energy producing reactor (CANDLE) burnup strategy was successfully applied to such compact reactor core. To obtain ideal CANDLE shape, it’s necessary to set the infinity or enough length of the core height, but that is impossible for small compact core setting infinity or enough length of the core height. Due to the compact and finite core, the equilibrium state can only be maintained short periods and is not obvious, other than infinitely long active core to reach the long equilibrium state for ideal CANDLE. Consequently, the modified CANDLE shape would be presented. The approximate characteristics of CANDLE burnup are observed in the finite and compact core, and the power density and fuel burnup are selected as main characteristic of modified CANDLE burnup. In this study, firstly, lots of optimization schemes were discussed, and one of optimization schemes was chosen at last to demonstrate the modified CANDLE burnup strategy. Secondly, for chosen compact small rector core, the modified CANDLE burnup strategy is applied and presented. Consequently, the new characteristics of this reactor core can be discovered both in ignition region and in fertile region. The results show that application of CANDLE burnup strategy to small modular PWR loading with FCM fuels suppresses the excess reactivity effectively and reduces the risk of small PWR reactivity-induced accidents during the whole core life, which makes the reactor control more safety and simple.

A Vibration Similarity Model of Converter Transformers and Its Verification Method

According to the vibration characteristics of converter transformers, considering the Maxwell equation, magnetostrictive effect, Lorentz force and structural mechanics, the similarity criterion suitable for converter transformers is deduced in this paper. Using the finite element simulation platform, the multi physical field coupling model of converter transformers is constructed, and the scale coefficient is 0.1. The magnetic flux density distribution, stress distribution, shape variable and vibration characteristics of the model before and after the similarity are analyzed. The results show that the variation law of the model before and after the similarity conforms to the similarity criterion, and the correctness of the similarity criterion is verified. The converter transformer vibration similarity model and its verification method can effectively reduce the unnecessary waste of resources before the preparation of converter transformers and have important reference value for the analysis and improvement of converter transformer vibration characteristics.

Axial Shuffling on Pebble Bed Reactor using PRAKTIK 3D-HTR

With moving fuel, the pebble bed reactor (PBR) provides flexibility in the fuel management process due to the capability of online fuel refueling. This capability allows the reactor to operate at any given time without the need to shut down for refueling. The complexity of the depletion and burnup analysis requires the problem to be solved with sophisticated and robust computer codes that can handle the fuel shuffling. Since the fuel refueling is conducted from top to bottom, the shuffling and fuel movement in the axial direction should be modeled with acceptable accuracy. The purpose of the simulation is to obtain the equilibrium or even a critical condition of the reactor. The model used is based on the simplified pebble bed reactor with 200 MWt of thermal reactor power, 3 meters of core diameter, and 10 meters of core height. To model the axial shuffling on the reactor, a neutronic computer code called PRAKTIK 3D-HTR is used. The code utilizes the diffusion method in a three-dimensional cylindrical geometry to model the neutronic phenomena in the reactor. Moreover, PRAKTIK 3D-HTR is equipped with the burnup calculation and depletion analysis to be able to handle fuel movement. Finally, the axial shuffling mechanism is implemented using the once-through-then-out (OTTO) method. Implementing this method to the reactor, an equilibrium condition can be obtained. In this condition, the reactor condition in terms of criticality and flux shape is relatively constant. The critical condition can also be searched using PRAKTIK 3D-HTR to obtain the condition when the multiplication factor is equal to unity. The criticality search is conducted by changing the fuel movement speed. If the multiplication factor is less than 1, then the shuffling speed needs to be increased. Otherwise, if it is more than 1, the shuffling speed will be decreased.

Neutronics performances of gas-cooled fast reactor for 300-600 MWt Output Power with Modified CANDLE burn-up scheme in radial direction

Gas-Cooled Fast Reactor-GFR is a Generation IV reactor that is helium-cooled and has a closed fuel cycle. Due to the target operation on 2022-2030, this reactor type still needs further research and development technologies. We investigated the neutronics performances of a GFR balance type core with some modification of CANDLE (Constant Axial shape of Neutron flux, nuclide densities and power shape During Life of Energy production) burn-up scheme in the radial direction. The output power varied from 300 to 600 MWt. The neutronics calculation was performed using SRAC 2002 with JENDL 4.0 nuclear data library. The analysis indicate the reactor could operate critically for ten years without refueling with burn-up level 20% HM.

Experimental analysis of the optical loss of a dusty Fresnel lens with a novel solar flux test system

The effect of dust deposition on a point-focus Fresnel lens is experimentally analyzed using a novel outdoor solar flux test system. The solar flux maps of the concentration region of the Fresnel lens are obtained. A detailed mathematical heat transfer model of the thermocouple is developed to calculate the solar flux density at a given spot temperature. The solar flux intensity and shape, spot temperature, dust deposition density, and imaging distance are analyzed. The flux spot exhibits an ellipsoidal Gaussian distribution. As the dust density increases from 0 g/m2 to 5 g/m2, the peak flux exhibits a decrease of 57.4%, and the spot temperature decreases from 307 °C to 98.1 °C. An average optical loss of 16.69% is obtained for each 1 g/m2 increase in the dust density. Error sources and estimates of the system are analyzed. The experimental measurements are in good agreement with the theoretical values. The deviation is within 8.33%, and the maximum deviation is 18.39 kW/m2.

Standardization and validation of k0-based Neutron Activation Analysis using Apsara-U reactor and its application to pure iron metal and coal sample for trace element determination

The k0-NAA method has been standardized by characterizing the G4 irradiation position of the upgraded Apsara (Apsara-U) reactor. The sub-cadmium to epithermal neutron flux ratio (f) and epithermal neutron flux shape factor (α) were determined taking dual (197Au and 94Zr), triple (197Au, 94Zr and 96Zr) and multi (197Au, 59Co, 64Zn, 68Zn, 96Zr and 94Zr) flux monitors using Cadmium ratio method. The value of f was found to be 19.94 ± 1.02 with average value of α as −0.027 ±0.004. The method was validated by analysing SMELS-II (synthetic multielemental standards) and geological certified reference material (Andesite, AGV-1), wherein results are in good agreement with certified or recommended values. The k0-based NAA method was applied for chemical characterization of pure Iron metal and coal samples. The results obtained were further compared with ICP-OES analysis and the values are found to be in good agreement (t<tcritical) for all the elements determined. F-test was also performed in order to show the reliability of the results in terms of standard deviations.

Neutronic Study of Fast Reactor with Modified CANDLE Burnup Scheme Using natural Pb, Pb(nat)-Bi Eutectic, 208Pb, and 208Pb-Bi Eutectic as Coolant

About 96% of reactors in the world consume enriched uranium. However, enrichment technology is costly and a sensitive issue related to nuclear non-proliferation. Whereas, without the technology, it is difficult to obtain the optimal benefits from the nuclear reactor. The long-life reactor designs that can consume natural uranium and minimize initial fue l loading are needed. Therefore, the design study of long-life Pb(208)-Bi eutectic cooled reactor with modified CANDLE (Constant Axial shape of Neutron flux, nuclide densities, and power shape During Life of Energy Energy production) burn up scheme has performed. Modified CANDLE burnup scheme can use natural Uranium (without enrichment) as fuel and also can reprocess LWR (Light-Water Reactor) spent fuel. In Modified CANDLE scheme, a reactor core is divided into 10 regions in an axial direction which has the same volume. Region 1 is filled by fresh natural uranium and after 10 years burnup, it is then shifted to region 2. These mechanisms are applied to all the regions. Coolant for LFR (Lead-cooled Fast Reactors) have some requirements such as has low neutron absorption, low melting point, high boiling point and non-reactive with air and water. Pb(208)-Bi eutectic is a promising coolant for LFR due to its properties. The Neutronic calculation was performed by SRAC and FITB.ch1 using JENDL 4.0 as nuclear data library. The Important neutronic parameter such as k-eff is discussed in the present study. Initial k-eff of the reactor using Pb-natural, Pb-Bi, Pb(208), and Pb(208)-Bi as coolant are 0.99973, 1.0020, 1.0089, and 1.0059, respectively.

The EXTraS project: Exploring the X-ray transient and variable sky

Temporal variability in flux and spectral shape is ubiquitous in the X-ray sky and carries crucial information about the nature and emission physics of the sources. The EPIC instrument on board the XMM-Newton observatory is the most powerful tool for studying variability even in faint sources. Each day, it collects a large amount of information about hundreds of new serendipitous sources, but the resulting huge (and growing) dataset is largely unexplored in the time domain. The project called Exploring the X-ray transient and variable sky (EXTraS) systematically extracted all temporal domain information in the XMM-Newton archive. This included a search and characterisation of variability, both periodic and aperiodic, in hundreds of thousands of sources spanning more than eight orders of magnitude in timescale and six orders of magnitude in flux, and a search for fast transients that were missed by standard image analysis. All results, products, and software tools have been released to the community in a public archive. A science gateway has also been implemented to allow users to run the EXTraS analysis remotely on recent XMM datasets. We give details on the new algorithms that were designed and implemented to perform all steps of EPIC data analysis, including data preparation, source and background modelling, generation of time series and power spectra, and search for and characterisation of different types of variabilities. We describe our results and products and give information about their basic statistical properties and advice on their usage. We also describe available online resources. The EXTraS database of results and its ancillary products is a rich resource for any kind of investigation in almost all fields of astrophysics. Algorithms and lessons learnt from our project are also a very useful reference for any current and future experiment in the time domain.

Transient Multilevel Scheme with One-Group CMFD Acceleration

The Transient Multilevel (TML) scheme in the MPACT code has reduced the computational burden for three-dimensional, full-core, time-dependent reactor simulations with pin-resolved detail. However, the total computational cost is still large for practical applications. In this paper, we present a new method that uses a one-group coarse mesh finite difference (1GCMFD) approach to further accelerate the TML scheme. Since multigroup coarse mesh finite difference (MGCMFD) calculations in TML dominate the simulation run time, the 1GCMFD method developed here is shown to reduce the overall computational time by as much as 50% for some large-scale applications. The 1GCMFD method accelerated the calculation primarily by accelerating the convergence of the source for MGCMFD calculations through 1G/MGCMFD iteration. A new 1GCMFD level was implemented in the TML scheme (TML-4) assuming that the energy distribution of the scalar flux shape varies more slowly than the energy-integrated amplitude of the scalar flux. Various numerical cases were used to investigate the practicality of the 1G/MGCMFD iteration and TML-4 scheme. Numerical results show that using the 1G/MGCMFD iteration with a dynamic iteration strategy alone does better capture the evolution of the amplitude function when the scalar flux distribution in energy space varies rapidly and thus provides more accurate results. However, TML-4 is more efficient in capturing the variation of the energy-integrated amplitude when cross-section changes are small and feedback dominates the change of the reactivity. For smaller problems, the 1G/MGCMFD iteration and the new TML-4 scheme can reduce the run time of the coarse mesh finite difference (CMFD) solver by 50% and the total run time by at least 16%. For large-scale, full-core problems, the run time of the CMFD solver can be reduced by 78% and the total run time by as much as 47%.

Numerical investigation of heat flux distribution on the welding groove face in magnetic oscillation arc narrow gap GTAW

Obtaining uniform penetration on welding groove faces is one urgent problem in oscillation arc narrow gap welding; however, the heat flux distribution on the groove face under the deflected welding arc is difficult to investigate by the experimental method. In this article, a unified three-dimensional model is developed to study the heat flux distribution on groove faces. The model includes the electrode, welding arc, workpiece, and their coupling. The plasma arc profile, heat flux characteristics, and weld pool formation were simulated. Based on the simulation results, the following conclusions were contained. The deflecting degree of the welding arc axis is increased with the increasing of extra magnetic-field intensity, and this leads to the change of the distribution of conduction heat flux and electric heat flux. At the groove bottom, both heat fluxes move to one side, and their distribution shape changes from circular to elliptical. At the sidewall, the distribution shape of conduction heat flux is triangular, and that of electrical heat flux is elliptical. The maximum value of heat flux density decreased, and the affected area was increased with the associate of the extra magnetic field. The simulation welding bead was in agreement with the experimental result.

Inverse method to describe crystallization of undercooled water in cold storage tank

The objective of this work is to a physical model to describe the thermal performance of cylindrical tank filled with spherical water capsules during the storage period. A particularity is encountered in this type of storage; it refers to the supercooling phenomenon caused by the delay in the crystallization of the water in the capsules. The originality of this model consists in evaluating the heat flux exchanged between the heat transfer fluid (HTF) and the spherical capsules by using experimental data (here, the temperature) and an inverse method. The inverse method is addressed with a genetic algorithm (GA). The heat flux determined by the inverse method for one case of flowrate condition has been applied for other flowrates to evaluate the temperature of HTF at the outlet of the tank during the storage period. The obtained results are then compared with experimental results from the literature. A good agreement was found between the numerical and the experimental results. The influence of the flowrate of the HTF on the shape of the heat flux released by the capsules during the storage period is also analysed and discussed.

First application of large reactivity measurement through rod drop based on three-dimensional space–time dynamics

Reactivity measurement is an essential part of a zero-power physics test, which is critical to reactor design and development. The rod drop experimental technique is used to measure the control rod worth in a zero-power physics test. The conventional rod drop experimental technique is limited by the spatial effect and the difference between the calculated static reactivity and measured dynamic reactivity; thus, the method must be improved. In this study, a modified rod drop experimental technique that constrains the detector neutron flux shape function based on three-dimensional space-time dynamics to reduce the reactivity perturbation and a new method for calculating the detector neutron flux shape function are proposed. Correction factors were determined using Monte Carlo N-Particle transport code and transient analysis code for a pressurized water reactor at the Ulsan National Institute of Science and Technology and Xi'an Jiaotong University, and a large reactivity of over 2000 pcm was measured using the modified technique. This research evaluated the modified technique accuracy, studied the influence of the correction factors on the modification, and investigated the effect of constraining the shape function on the reactivity perturbation reduction caused by the difference between the calculated neutron flux and true value, using the new method to calculate the shape function of the detector neutron flux and avoiding the neutron detector response function (weighting factor) calculation.

Design and first results of a retractable 1D-CFC beam target for BATMAN upgrade

BATMAN Upgrade (BUG) is a test facility for the production of negative ion beams from an RF driven plasma ion source devoted to supporting the development of the ITER Neutral Beam Injection (NBI). BUG consists of the IPP RF prototype source and a multi-aperture grid system corresponding roughly to a beamlet group of the ITER NBI grid system, i.e. an arrangement of 14 (vertical) ×5 (horizontal) Ø14 mm apertures, meaning the ion beam is comprised of 70 individual beamlets. The beams can be extracted with up to 10 kV and accelerated up to a total voltage of 45 kV for up to 10 s (steady state operation is underway). One of the goals of BUG is a detailed study of the ion beam optics. So far, the permanently installed beam diagnostic consisted of several lines of sight of Beam Emission Spectroscopy (BES) at two different positions and thermocouple measurements on the beam dump calorimeter. Resolving the divergence and deflection of single beamlets is technically exceptionally difficult with the existing diagnostic tools, therefore, a beam target made out of a one-directional carbon fiber composite material (1D-CFC) with dimensions 376×142×20 mm³ has been installed at a distance of 851 mm from the exit of the grid system. The thermal footprints of the beamlets are observed from the back side via infrared imaging with a high spatial resolution (<0.7 mm/pixel) that allows characterization of the beamlets at low divergence. The target can be rotated out of the beam to make it compatible with long pulses and the forthcoming steady state operation. The safety analysis of the target operation for different operational scenarios is presented together with an energy-based interlock. Finally, the accuracy of estimating the shape of the heat flux on the front of the target from the temperature profile at the back is assessed, based on FEM simulations of a single beamlet.