Fusion Gamma Research Articles

Research on remote sensing image carbon emission monitoring based on deep learning

Carbon emission monitoring is the key to achieving global emission reduction. This paper proposes a carbon emission identification method based on remote sensing images. Based on the regional satellite remote sensing image data set, the convolutional neural network model is used to extract the carbon emission characteristics of the region. The multi-model fully connected layer fusion algorithm and gamma correction data augmentation strategy are designed to analyze the accuracy of carbon emission monitoring. The results show that the results will be different when the image can not be preprocessed. In the case of Gamma correction, the model's accuracy is affected, but the robustness of the model is improved. The single-model local image cascade fusion algorithm has higher environmental adaptability than the single-model non-cascade algorithm. The recognition accuracy of the multi-model fusion algorithm is more than 7% higher than that of the single-model local image cascade fusion algorithm. The fully connected layer fusion accuracy is more than 1% higher than that of the feature map fusion, and its recognition accuracy for the data set reaches 87.21% and 88.35%, respectively.

An effort to enhance the threshold contrast index of gas Cherenkov detectors

Because gas Cherenkov detectors can exclude most interference from secondary gamma rays, they have been the primary candidate for detection of fusion gamma rays. It is a goal worthy of long-term efforts to enhance the threshold contrast index used for evaluating the ability of gas Cherenkov detectors to exclude below-threshold interference. This paper presents a way of enhancing the index through ultraviolet reflection selective suppression of scintillation signals in the detectors. Both theoretical estimation and experimental verification demonstrate that the threshold contrast index can be enhanced by 5.5 times after applying this method. This provides possibilities of obtaining better fusion gamma-ray detection waveforms and higher confidence diagnostic information.

Total fusion yield measurements using deuterium–tritium gamma rays

The deuterium–tritium (DT) fusion reaction, D(T,γ)5He, has a rare (4.2 ×10−5) branching ratio that releases a ∼16 MeV gamma ray instead of the more common 14.1 MeV fusion neutron. These fusion gamma rays can be used as a complementary source of measuring the net fusion yield of experiments. Fusion gamma rays have the advantage of having negligible Doppler broadening, being isotropic and less down-scattered compared to fusion neutrons. At the National Ignition Facility, the DT fusion gamma rays are measured by the Gamma Reaction History diagnostic that thresholds to only measure >10 MeV gamma rays. After removing a ∼12% contribution from neutron capture interactions in deuterium, D(n,γ)T, and carbon, 12C(n,γ)13C, the deviation between GRH measurements and neutron-based yield measurements has been reduced to 10%. Further improvements are needed for detailed physics comparison.

Monte Carlo analyses of the fusion neutron and gamma signals from the chromium self-powered detector.

To test the applicability of self-powered detectors (SPDs) for radiation monitoring in fusion reactor blankets, several irradiation tests have been undertaken with the ad hoc designed Cr-SPD, which presents the novelty of using chromium as the emitter material. This detector was exposed to an intense 60Co gamma-ray source, and to the 14MeV neutrons produced by the D-T fusion reaction. Detailed analyses of the measured signals have been done here using a Monte Carlo modeling technique. We describe the simulations of the fusion neutron and gamma tests of the Cr-SPD, and compare their results with the experimental ones. Keeping in view the difficulty in computational reproduction of the sophisticated nuclear-electrical phenomena behind low-level SPD signals, our model is found to perform well, giving correct electrical polarities and orders of magnitude of the signals, as well as valuable insights into their different components. Our experience has highlighted the deficits and the needed improvements for the traditional SPD simulation techniques for prompt signal analyses.

Preliminary assessment of genotoxic effects induced by radiation from EAST using Vicia faba micronucleus assay

During long-pulse deuterium plasma operations in the Experimental Advanced Superconducting Tokamak (EAST), a mixed radiation field is generated, which is mainly composed of fusion neutrons, gamma rays, and x-rays. More accurate and effective dose monitoring methods have been developed and established to determine the ionizing radiation intensity both for the stable operation of the device and for the radiation safety of personnel. As far as we know, there are few reports about the biological effects of radiation induced by fusion neutrons and γ radiation, which are of vital importance for the assessment of radiation hazards presented by fusion devices, such as EAST, to human beings and the environment. In this study, three positions in the EAST hall were selected to detect genotoxic effects induced by nuclear fusion radiation using a Vicia faba micronucleus (MN) test for the first time. The doses of neutrons and gamma rays at these places were measured by thermoluminescence dosimeters four times between June 2019 and May 2020. The radiation doses decreased as the distances from the EAST device shell gradually increased from S1 to S3. The radiation in the EAST hall resulted in a significant induction of MN in the Vicia faba root tip cells compared to a negative control, which was different from the MN frequency induced by fission neutrons, γ-rays and other kinds of radiation in previous studies. These results indicate the existence of potential genotoxic effects induced by radiation from EAST which is different from other radiation and suggest that personnel should not be permitted to enter the experimental hall during the discharge process, and that radiation protection measures should be taken during necessary maintenance to avoid radiation damage. These newly acquired results will certainly increase our knowledge about the biological effects induced by radiation from nuclear fusion and provide good data support for developing more effective environmental and personnel fusion radiation protection.

Time resolved ablator areal density during peak fusion burn on inertial confinement fusion implosions

Near peak compression, inertial confinement fusion implosions release both deuterium–tritium (DT) fusion gamma rays and neutron induced gamma rays from carbon from the areal density of the remaining ablator shell. The gamma reaction history diagnostic makes a time resolved measurement of both. Across many recent implosions, the carbon gamma ray peak arrives systematically 11 ± 10 ps later compared to DT fusion burn. The timing shift is consistent with the carbon areal density increasing throughout the peak of the fusion burn, implying that the carbon portion of the capsule continues to converge. A model finds that the observed timing shift is consistent with a 4π averaged carbon ablator inward velocity of 80 μm/ns for the contemporary National Ignition Facility implosions. The timing shift is possibly related to the energy balance of the implosion, with the expectation that a high performing, igniting capsule would see the carbon gamma rays arrive before the DT fusion peak.

Design and performance study of a gas-Cherenkov detector with an off-axis parabolic reflector for inertial confinement fusion experiments

In this work, the gas-Cherenkov detector with an off-axis parabolic reflector (OprGCD) is designed using the Geant4 Monte Carlo simulation toolkit, which is helpful to improve the collection efficiency of Cherenkov photons. The method to study the performance of OprGCD based on femtosecond laser-wakefield-accelerated electron beams is presented. Cherenkov signals with high signal-to-noise ratio were obtained, and the measured Cherenkov signals changing with the CO2 pressure were consistent well with the simulation results. The design and study of this OprGCD system lay the foundation for the application of fusion gamma diagnostics system in large laser facilities of China.

Preliminary investigation of the shutdown radioactivity for EAST based on gamma ray spectrometry

• The HPGe spectrometer system was placed inside the vacuum vessel to measure the characteristic γ-rays emission from radionuclides after EAST shutdown. • The identification and pathway analysis of radionuclides were discussed based on structural materials and radiation sources of EAST. • Activity of radionuclides and time evolution of dose rate, preliminary activation results, were discussed. Experimental Advanced Superconducting Tokamak (EAST) is capable of operating with long-pulse deuterium plasma, which will generate a lot of radiation such as fusion neutrons, gamma rays and hard X-rays. Since the structure material of the device was activated, work around and inside the tokamak would be limited from a radiation protection point of view after shutdown. Identification of radionuclides and evaluation of dose rate inside the vacuum vessel are needed to develop a guiding principle for radiation protection during maintenance. In this paper, a gamma ray spectrometer based on high purity germanium (HPGe) detector and digitizer was placed inside the vacuum vessel to measure the characteristic gamma ray emission from radionuclides. 7 Be, 46 Sc, 51 Cr, 54 Mn, 58 Co, 60 Co, 59 Fe, 88 Y, 91 Y, 91m Nb, 99 Mo, 124 Sb and 110m Ag produced by photonuclear reactions and neutron-induced reactions were identified. The activities of radionuclides was calculated respectively with the uncertainty not exceed 6.05 %. The dose rate for 10 days after shutdown was mainly contributed by 60 Co, 58 Co, 54 Mn, 110m Ag, 59 Fe, 51 Cr, 88 Y, 99 Mo, 7 Be and 124 Sb, total dose rate were 3.62 × 10 −9 Sv/h(Port E) and 3.40 × 10 −9 Sv/h(Port I).

Statistical Goodness Factor ‘ᴦ’ for Image Fusion Algorithm Based on UGGD Parameters

In this paper we propose a novel pyramid decomposition based Image fusion metric, Gamma Factor or Goodness of Fit ‘ᴦ’ which describes the statistically amount of information fused by the image fusion algorithm. We first apply steerable pyramid decomposition and then a fitting model for Univariate Generalised Gaussian Distribution (UGGD) parameter estimation. From the UGGD; P and S fitting model coefficients are computed. To estimate the optimum weights for computation a huge data set of complimentary images are used. Using these weights, amount of information contributed by each image to form a fused image can be estimated. Experimental results show the tremendous matching with the quantise information

Improved inertial confinement fusion gamma reaction history 12C gamma-ray signal by direct subtraction.

The Gamma Reaction History (GRH) diagnostic located at the National Ignition Facility (NIF) measures time resolved gamma rays released from inertial confinement fusion experiments by converting the emitted gamma rays into Cherenkov light. Imploded capsules have a bright 4.4 MeV gamma ray from fusion neutrons inelastically scattering with carbon atoms in the remaining ablator. The strength of the 4.4 MeV gamma ray line is proportional to the capsule's carbon ablator areal density and can be used to understand the dynamics and energy budget of a carbon-based ablator capsule implosion. Historically, the GRH's four gas cells use the energy thresholding from the Cherenkov process to forward fit an estimation of the experiment's complete gamma ray spectrum by modeling the surrounding environment in order to estimate the 4.4 MeV neutron induced carbon gamma ray signal. However, the high number of variables, local minima, and uncertainties in detector sensitivities and relative timing had prevented the routine use of the forward fit to generate carbon areal density measurements. A new, more straightforward process of direct subtraction of deconvolved signals was developed to simplify the extraction of the carbon areal density. Beryllium capsules are used as a calibration to measure the capsule environment with no carbon signal. The proposed method is then used to appropriately subtract and isolate the carbon signal on shots with carbon ablators. The subtraction algorithm achieves good results across all major capsule campaigns, achieving similar results to the forward fit. This method is now routinely used to measure carbon areal density for NIF shots.

First measurements of remaining shell areal density on the OMEGA laser using the Diagnostic for Areal Density (DAD).

A glass Cherenkov detector, called the Diagnostic for Areal Density (DAD), has been built and implemented at the OMEGA laser facility for measuring fusion gammas above 430 keV, from which remaining shell ⟨ρR⟩ abl can be determined. A proof-of-principle experiment is discussed, where signals from a surrogate gas Cherenkov detector are compared with reported values from the wedge range filter and charged particle spectrometer and found to correlate strongly. The design of the more compact port-based DAD diagnostic and results from the commissioning shots are then presented. Once absolutely calibrated, the DAD will be capable of reporting remaining shell ⟨ρR⟩ abl for plastic and glass capsules within minutes of a shot and with potentially higher precision than existing techniques.

Extended performance gas Cherenkov detector for gamma-ray detection in high-energy density experiments.

A new Gas Cherenkov Detector (GCD) with low-energy threshold and high sensitivity, currently known as Super GCD (or GCD-3 at OMEGA), is being developed for use at the OMEGA Laser Facility and the National Ignition Facility (NIF). Super GCD is designed to be pressurized to ≤400 psi (absolute) and uses all metal seals to allow the use of fluorinated gases inside the target chamber. This will allow the gamma energy threshold to be run as low at 1.8 MeV with 400 psi (absolute) of C2F6, opening up a new portion of the gamma ray spectrum. Super GCD operating at 20 cm from TCC will be ∼400 × more efficient at detecting DT fusion gammas at 16.7 MeV than the Gamma Reaction History diagnostic at NIF (GRH-6m) when operated at their minimum thresholds.

Design and construction of a Gamma reaction history diagnostic for the National Ignition Facility

Gas Cherenkov detectors have been used to convert fusion gammas into photons to record gamma reaction history measurements. These gas detectors include a converter, pressurized gas volume, relay collection optics, and a photon detector. A novel design for the National Ignition Facility (NIF) using 90° off-axis parabolic mirrors efficiently collects signal from fusion gammas with 8-ps time dispersion. Fusion gammas are converted to Compton electrons, which generate broadband Cherenkov light (response is from 250 to 700 nm) in a pressurized gas cell. This light is relayed into a high-speed detector using three parabolic mirrors. The relay optics collect light from a 125-mm-diameter by 600-mm-long interchangeable gas (CO2 or SF6) volume. The parabolic mirrors were electroformed instead of diamond turned to reduce scattering of the UV light. All mirrors are bare aluminum coated for maximum reflectivity. This design incorporates a 4.2-ns time delay that allows the detector to recover from prompt radiation before it records the gamma signal. At NIF, a cluster of four channels will allow for increased dynamic range, as well as different gamma energy thresholds.

ICF gamma-ray reaction history diagnostics

Reaction history measurements, such as nuclear bang time and burn width, are fundamental components of diagnosing ICF implosions and will be employed to help steer the National Ignition Facility (NIF) towards ignition. Fusion gammas provide a direct measure of nuclear interaction rate (unlike x-rays) without being compromised by Doppler spreading (unlike neutrons). Gas Cherenkov Detectors that convert fusion gamma rays to UV/visible Cherenkov photons for collection by fast optical recording systems have established their usefulness in illuminating ICF physics in several experimental campaigns at OMEGA. In particular, bang time precision better than 25 ps has been demonstrated, well below the 50 ps accuracy requirement defined by the NIF. NIF Gamma Reaction History (GRH) diagnostics are being developed based on optimization of sensitivity, bandwidth, dynamic range, cost, and NIF-specific logistics, requirements and extreme radiation environment. Implementation will occur in two phases. The first phase consists of four channels mounted to the outside of the target chamber at ∼6 m from target chamber center (GRH-6m) coupled to ultra-fast photo-multiplier tubes (PMT). This system is intended to operate in the 1013–1017 neutron yield range expected during the early THD campaign. It will have high enough bandwidth to provide accurate bang times and burn widths for the expected THD reaction histories (> 80 ps fwhm). Successful operation of the first GRH-6m channel has been demonstrated at OMEGA, allowing a verification of instrument sensitivity, timing and EMI/background suppression. The second phase will consist of several channels located just inside the target bay shield wall at 15 m from target chamber center (GRH-15m) with optical paths leading through the cement shield wall to well-shielded streak cameras and PMTs. This system is intended to operate in the 1016–1020 yield range expected during the DT ignition campaign, providing higher temporal resolution for the expected burn widths of 10–20 ps associated with ignition. Multiple channels at each phase will allow for increased redundancy, reliability, accuracy and flexibility. In addition, inherent energy thresholding capability combined with this multiplicity will allow exploration of interesting gamma-ray physics well beyond the ignition campaign.

Cherenkov radiation conversion and collection considerations for a gamma bang time/reaction history diagnostic for the NIF

Bang time and reaction history measurements are fundamental components of diagnosing inertial confinement fusion (ICF) implosions and will be essential contributors to diagnosing attempts at ignition on the National Ignition Facility (NIF). Fusion gammas provide a direct measure of fusion interaction rate without being compromised by Doppler spreading. Gamma-based gas Cherenkov detectors that convert fusion gamma rays to optical Cherenkov photons for collection by fast recording systems have been developed and fielded at Omega. These systems have established their usefulness in illuminating ICF physics in several experimental campaigns. Bang time precision better than 25 ps has been demonstrated, well below the 50 ps accuracy requirement defined by the NIF system design requirements. A comprehensive, validated numerical study of candidate systems is providing essential information needed to make a down selection based on optimization of sensitivity, bandwidth, dynamic range, cost, and NIF logistics. This paper presents basic design considerations arising from the two-step conversion process from gamma rays to relativistic electrons to UV/visible Cherenkov radiation.

Gamma bang time/reaction history diagnostics for the National Ignition Facility using 90° off-axis parabolic mirrors

Gas Cherenkov detectors (GCDs) have been used to convert fusion gamma into photons to achieve gamma bang time and reaction history measurements. The GCDs designed for OMEGA used Cassegrain reflector optics in order to fit inside a 10 in. manipulator. A novel design for the National Ignition Facility using 90 degrees off-axis parabolic mirrors will increase light collection efficiency from fusion gammas and achieve minimum time dispersion. The broadband Cherenkov light (from 200 to 800 nm) is relayed into a high-speed detector using three parabolic mirrors. Because light is collected from many source planes throughout the CO(2) gas volume, the detector is positioned at the stop position rather than at an image position. The stop diameter and its position are independent of the light-generation location along the gas cell. The current design collects light from a 100 mm diameter by 500 mm long gas volume. Optical ray tracings demonstrate how light can be collected from different angled trajectories of the Compton electrons as they fly through the CO(2) gas volume. A cluster of four channels will allow for increased dynamic range as well as for different gamma energy threshold sensitivities.

Improved gamma bang time measurements on Omega

The time of peak fusion reactivity with respect to the impingement of laser light on an Inertial Confinement Fusion (ICF) capsule is known as Bang Time (BT). For deuterium-tritium fueling, fusion reactivity and BT can be measured using either fusion neutrons or fusion gammas. Initial gamma bang time (GBT) measurements on Omega using a Gas Cherenkov Detector (GCD) have been previously reported [1]. Recent improvements have significantly enhanced the ability to measure GBT precisely. By relating the peak of the GCD gamma signal to laser timing fiducials, and cross calibrating the resulting raw bang time to the neutron bang time obtained using the absolutely calibrated Neutron Temporal Diagnostic (NTD), we demonstrate a precision of better than 25 ps on Omega. Bang time, along with other aspects of reaction history (RH), is an essential component of diagnosing failed attempts at ICF ignition. For the NIF, gammas are preferred over neutrons for this application due to the unacceptably large neutron temporal spreading resulting from detector standoff limitations on the NIF. The NIF System Design Requirement specifies a gamma bang time accuracy of better than 50 ps.

Multiplexed gas Cherenkov detector for reaction-history measurements

A diagnostic is being designed for the National Ignition Facility, using fusion gamma rays to measure highly time-resolved bang times and deuterium-tritium (d-t) interaction rates for imploding inertial fusion capsules. As a complement to neutron-based methods, gas Cherenkov detectors were chosen for this purpose because of proven ultrahigh bandwidth, thresholding versatility, and minimal time-of-flight dispersion. Gas Cherenkov detector prototypes, involving streak cameras and fast photomultiplier, microchannel plate detectors, are being tested using d-t implosions at the Omega Laser Facility. The possibility of simultaneous streak camera and photomultiplier, microchannel plate recordings of a source in one gas Cherenkov detector instrument is advantageous for reasons of independent measurement and extended reaction-history coverage. A multiplexed gas Cherenkov detector system was demonstrated successfully using electron pulses produced by the Idaho State University linear electron accelerator. A reaction-history diagnostic scheme composed of several types of detectors is proposed. The detectors considered reflect current and improving technology that allows coverage over a significant range of a reaction history generated from National Ignition Facility implosions.

Remarks on detecting high-energy deuterium–tritium fusion gamma rays using a gas Cherenkov detector

As fusion ignition conditions are approached using the national ignition facility (NIF), independent high-bandwidth gamma-ray fusion burn measurements become essential complements to information obtained from neutron diagnostics. The 16.75-MeV gamma rays that accompany deuterium–tritium (d+t) fusion can be detected using a high-bandwidth gaseous carbon dioxide Cherenkov threshold detector. The detection energy threshold was set by the CO 2 gas pressure. A 1-GHz detector system was fielded successfully at the Omega laser facility, demonstrating unambiguous detection of high-energy fusion gamma rays from high-yield d+t implosions. An experiment to detect the ∼12.5 MeV d–t fusion gamma ray is described.

Observation of high-energy deuterium–tritium fusion gamma rays using gas Cherenkov detectors

As fusion ignition conditions are approached using the National Ignition Facility (NIF), independent high-bandwidth gamma-ray fusion-burn measurements become essential complements to neutron-based methods. Time resolution ∼20 ps (10–30 GHz), energy discrimination, and significant stand off distance may be needed for credible burn history measurements. The 16.75 MeV gamma rays that accompany deuterium–tritium (d+t) fusion provide a high-bandwidth alternative to 14 MeV fusion neutrons for d+t burn-history measurements. A thresholding detector, based on the Cherenkov effect, resulting from Compton and pair production electron interactions in gaseous carbon dioxide, offers a means of separating the high-energy fusion gamma rays from other background sources. When coupled to appropriate streak camera recorders, a gas Cherenkov system response of 15 GHz is feasible. As a first step toward this goal, a gas Cherenkov system, employing a 1 GHz photodiode detector, was fielded at the Omega laser facility to demonstrate unambiguous detection of fusion gamma rays from high-yield d+t implosions. With the carbon dioxide Cherenkov production threshold at 12 MeV, the observed high-energy gamma-ray signal is proportional to the observed 14 MeV fusion neutron yield and independent of neutron-induced gamma rays.