Pulsed Fusion Research Articles

FPGA Remote Update for Nuclear Environments

In recent years there has been a growing interest to use reconfigurable modules, based on field-programmable gate array (FPGA) devices, in nuclear environments. One of the requirements for these types of modules, when operating in complex future nuclear power experiments, is their remote update capability. The operational needs of pulsed fusion reactors will lead to a large production of very high energy neutrons (MeV range). The current procurement policies for nuclear installations do not allow exposure of electronics to radiation, except following very strict rules. However, considering the “as low as (is) reasonably achievable” (ALARA) principle with respect to human exposure to radiation, the access to cubicles might be restricted, requiring the remote update of FPGA codes. FPGAs are volatile devices, and their programming code is usually stored in dedicated flash memories for proper configuration during module power-on. This paper presents an alternative method for FPGA remote update, capable to store new FPGA codes in inboard Serial Peripheral Interface (SPI) flash memories. The new method, based on the Xilinx Quick Boot application note and adapted to PCIe protocol, was developed with the KC705 Evaluation Kit from Xilinx and successfully tested in the in-house Advanced Mezzanine Card (AMC) prototype, installed on the ATCA-PTSW-AMC4 carrier module from the ITER Fast Plant System Controller catalogue.

The effects of combining fusion imaging, low-frequency pulsed fluoroscopy, and low-concentration contrast agent during endovascular aneurysm repair

This study evaluated the effects of a combined imaging protocol using low-frequency pulsed fluoroscopy, fusion imaging, and low-concentration iodine contrast for endovascular aneurysm repair (EVAR) of aortic aneurysms of varying complexity. The study retrospectively reviewed the data of 103 patients treated between May 2013 and November 2014 with the combined imaging protocol (group A) with low-dose fluoroscopy at 3.75 frames/s, fusion imaging, and iodine contrast of 140mg iodine/mL. A control group (group B) consisted of 123 consecutive patients who underwent EVAR before the combined imaging protocol was introduced by matching the type of procedure. In group B, low-dose 7.5frames/s fluoroscopy, no fusion imaging, and 200mg iodine/mL contrast were used. All patients were reviewed for preoperative, intraoperative, and postoperative variables, with emphasis on intraoperative radiation (dose area product) and iodine exposure, fluoroscopy, and operation times, as well as technical success. Values are presented as median and interquartile range (IQR) when not stated otherwise. Group A included 22 infrarenal EVARs, 17 iliac branch devices, 10 thoracic endovascular aortic repairs, 21fenestrated EVARs, and 33 thoracoabdominal branched/fenestrated EVARs. Groups A and B were similar in types of procedure, body mass index (P > .05), and intraoperative technical success (92% and 92%, respectively; P > .05). Operation time (230 [IQR, 138-331] minutes vs 235 [IQR, 158-364] minutes) and fluoroscopy time (66 [IQR, 33-101] minutes vs 72 [IQR, 42-102] minutes) were similar in both groups (P > .05), but radiation exposure (19,934 [IQR,11,340-30,615] μGym(2) vs 32,856 [IQR, 19,562-55,677] μGym(2); P< .0001), contrast volume usage (63[IQR,103-145] mL vs 215 [IQR, 166-280] mL; P< .0001), and iodine dose (14.5 [IQR, 8.8-20.4] g iodine vs 43.0 [IQR, 32.2-56.0] g iodine; P< .0001) were lower in group A than in group B. The differences were uniform throughout the different procedure types, with the exception of fenestrated grafts, where radiation exposure was similar between group Aand B; however, group A had a much higher involvement of the superior mesenteric artery in the repairs (81% vs 17%; P< .0001) explaining this finding. Fluoroscopic frame rate reduction contributed to a median reduction of the dose area product by 22%. Only four of the group A patients (3.9%) showed a decrease in the glomerular filtration rate ≥30% after EVAR, although 32% of the entire group had at least moderately impaired renal function preoperatively. Combining low-frequency pulsed fluoroscopy, fusion imaging, low-concentration, and iodine contrast medium during EVAR reduces the exposure to radiation and iodine.

Time-stability of a Single-crystal Diamond Detector for fast neutron beam diagnostic under alpha and neutron irradiation

Single-crystal Diamond Detectors (SDDs), due to their good charge carrier transport properties, low leakage and therefore good energy resolution, are good candidates for fast neutron measurement on pulsed spallation sources and fusion plasma experiments. Moreover, diamonds are known to be resistant to neutron irradiation. Nevertheless, measurements show transient effects during irradiation with ionizing particles, as the alpha particle calibration sources. The decrease of the detector counting rate of a counting chain and the pulse height are interpreted as due to a charge trapping inside the detector, which modifies the drift electric field. These instabilities are strongly dependent on the specific type of the interaction. Measurements have been carried out with both alpha particles in the laboratory and neutrons at the ISIS neutron spallation source. We show that these polarization effects are not permanent: the detector performances can be restored by simply inverting the detector bias high voltage. Prime Novelty StatementThe measurements described in the paper were performed in order to study the polarization effect in Single-crystal Diamond Detector. This effect was observed under alpha particle and neutron irradiation. With the Transient Current Technique an interpretation of the effect is given.

The Role of Magnetized Liner Inertial Fusion as a Pathway to Fusion Energy

We discuss the possible impacts of a new magnetized liner inertial fusion concept on magneto-inertial fusion approaches to fusion energy. Experiments in the last 1.5 years have already shown direct evidence of magnetic flux compression, a highly magnetized fusing fuel, significant compressional heating, a compressed cylindrical fusing plasma, and significant fusion yield. While these exciting results demonstrate several key principles behind magneto-inertial fusion, more work in the coming years will be needed to demonstrate that such targets can scale to ignition and high yield. We argue that justifying significant investment in pulsed inertial fusion energy beyond target development should require well-understood, significant fusion yields to be demonstrated in single-shot experiments. We also caution that even once target ideas and fusion power plants have been demonstrated, historical trends suggest it would still be decades before fusion could materially impact worldwide energy production.

Basic considerations on the pump-down time in the dwell phase of a pulsed fusion DEMO

In order to allow an efficient and economically attractive operation scenario of a pulsed fusion power plant, the length of the plasma pulses (burn phase) shall be maximized and the time in between the pulses (dwell phase) must be reduced to an absolute minimum. The time needed for evacuation of the vacuum vessel in the dwell phase to provide the necessary start vacuum for the next plasma discharge is mainly given by outgassing of helium and hydrogen isotopes that were adsorbed on or dissolved in the plasma facing materials in the previous plasma discharges. The paper shows that a reliable calculation of the pump-down time appears critical in view of the insufficient knowledge of the needed material properties whereas an empirical model of the outgassing term in the pump-down equation works better. This is validated by a comparison with existing pump-down data from ASDEX Upgrade with tungsten wall. Results of experiments on the mobile part of outgassing of tungsten surfaces are reported, which are evaluated to extract the decay factor in the empirical model of the outgassing rate. In conclusion, a window of expected minimum pump-down times is derived, which shows that the current DEMO target of approximately 20min may be very difficult to meet. In view of the paucity of much of the data needed for a realistic assessment, a multidisciplinary R&D programme should be pursued.

The influence of ion beam rastering on the swelling of self-ion irradiated pure iron at 450 °C

Ion beam scanning or “rastering” is a technique that is frequently used to uniformly cover a larger specimen area during ion irradiation. In this study, we addressed the effects of rastered and defocused beams, using 3.5 MeV iron ions to irradiate pure iron at 450 °C to peak doses of 50 and 150 dpa. We focused on a frequency range relevant to pulsed fusion devices and show its importance to ion irradiation experiments used for simulating neutron damage. The beam was scanned at 15.6, 1.94, and 0.244 Hz and the resulting microstructure was compared with that produced by a non-rastered, defocused beam. At 150 dpa, the defocused beam case resulted in the highest observed void swelling of ∼12% at a depth of ∼700 nm, a depth short of the peak dose position at 1000 nm. The swelling at the peak dose position was significantly reduced by the defect imbalance phenomenon. A maximum swelling rate of ∼0.12%/dpa was measured in this specimen at a depth of 600 nm below the ion-incident surface. Rastering led to much lower swelling levels achieved at significantly lower swelling rates, with the greatest rate of decrease occurring below ∼1 Hz. Furthermore, the impact of the defect imbalance arising from interstitial injection and spatial distribution difference of initial interstitial and vacancy defects was strongly pronounced in the non-rastered case with a lesser effect observed with decreasing raster frequency.

Case and Development Path for Fusion Propulsion

This paper discusses the importance of fusion propulsion for interplanetary space travel, illustrates why the magnetoinertial fusion parameter space may facilitate the most rapid, economic path for development, justifies the choice of pulsed Z pinch, and provides a potential development path leading up to a technical readiness level 9 system. Round trips of less than one year to Mars are only possible using fusion propulsion systems. Such a system will require an onboard nuclear fission reactor for reliable startups, and so fission and fusion developments for space are mutually beneficial. The paper reviews the more than 50 year history of fusion research and summarizes results from a recent study of the fusion parameter space for terrestrial power, which suggests magnetoinertial fusion can provide the smallest, most economical approach for a fusion propulsion system. Emerging experimental data and theory show pulsed Z-pinch fusion solves some of the most deleterious instabilities and scales to fusion breakeven within reach of current pulsed power facilities. The paper illustrates a potential development path to a technical readiness level 9 flight system, starting from an assumed technical readiness level 2 for the current state of fusion propulsion.

Note: Experimental platform for magnetized high-energy-density plasma studies at the omega laser facility.

An upgrade of the pulsed magnetic field generator magneto-inertial fusion electrical discharge system [O. Gotchev et al., Rev. Sci. Instrum. 80, 043504 (2009)] is described. The device is used to study magnetized high-energy-density plasma and is capable of producing a pulsed magnetic field of tens of tesla in a volume of a few cubic centimeters. The magnetic field is created by discharging a high-voltage capacitor through a small wire-wound coil. The coil current pulse has a duration of about 1 μs and a peak value of 40 kA. Compared to the original, the updated version has a larger energy storage and improved switching system. In addition, magnetic coils are fabricated using 3-D printing technology which allows for a greater variety of the magnetic field topology.

Determination of oxygen in oxides with high dissociation pressure by inert gas fusion method

A procedure for determination of oxygen in oxides with high pressure of dissociation (NiO, CuO, CoO, Fe2O3, SnO2), including volatile (MoO3, WO3), by pulsed reductive fusion (evaporation) in carrier-gas flow at 2500 K in double graphite capsules (with Ni-Sn bath or graphite powder) on an apparatus with simultaneous IR detection of CO and CO2 is described. The validity of the protocol and its metrological characteristics were evaluated in a series of calibration experiments with a set of pure stoichiometric oxides, including a NiO certified reference material with certified oxygen content. The expanded uncertainty of analysis for the developed procedure was 0.1 wt %. The working range was 2–15 mg of oxygen.

Pulsed eddy current and ultrasonic data fusion applied to stress measurement

Stress measurement and its variation are key problems in the operating performance of materials. Stress can affect the material properties and the life of components. There are several destructive and nondestructive techniques that are used to measure stress. However, no single nondestructive testing (NDT) technique or method is satisfactory to fully assess stress. This paper presents an NDT data fusion method to improve stress measurement. An aluminum alloy 2024 specimen subjected to stress simulation is nondestructively inspected using pulsed eddy current and ultrasonic techniques. Following these nondestructive examinations, the information gathered from these two NDT methods has been fused using a suitable fuzzy combination operator. The results obtained with these processes are presented in this paper and their efficiency is discussed. It is shown that the fusion of NDT data with a suitable fuzzy operator can be adequate to improve the reliability of stress measurements.

FRESCO, a simplified code for cost analysis of fusion power plants

FRESCO (Fusion REactor Simplified COsts) is a code based on simplified models of physics, engineering and economical aspects of a TOKAMAK-like pulsed or steady-state fusion power plant. The experience coming from various aspects of ITER design, including selection of materials and operating scenarios, is exploited as much as possible.Energy production and plant power balance, including the recirculation requirements, are derived from two models of the PPCS European study, the helium cooled lithium/lead blanket model reactor (model AB) and the helium cooled ceramic one (model B). A detailed study of the availability of the power plant due, among others, to the replacement of plasma facing components, is also included in the code.The economics of the fusion power plant is evaluated through the levelized cost approach. Costs of the basic components are scaled from the corresponding values of the ITER project, the ARIES studies and SCAN model. The costs of plant auxiliaries, including those of the magnetic and electric systems, tritium plants, instrumentation, buildings and thermal energy storage if any, are recovered from ITER values and from those of other power plants.Finally, the PPCS models AB and B are simulated and the main results are reported in this paper.

Commentary: Let’s send the DOE to Alpha Centauri

The announcement of an Earth-mass planet orbiting the closest Sunlike star has renewed discussion of the costs and benefits of an interstellar probe. The planet, Alpha Centauri Bb, is in an extremely hot orbit, but its existence increases the probability that a planet with a liquid-water ocean orbits Alpha Centauri. Data from NASA’s Kepler telescope now show that there are about as many habitable-zone, Earth-sized planets as stars, and in April NASA decided to fund a follow-up spacecraft, the Transiting Exoplanet Survey Satellite. Before this decade is out, we will probably discover an ocean-bearing planet orbiting a nearby star. When we do, should we send a mission?

Conceptual design for the superconducting magnet system of a pulsed DEMO reactor

A methodology has been developed to consistently investigate, taking into account main reactor components, possible magnet solutions for a pulsed fusion reactor aiming at a large solenoid flux swing duration within the 2–3h range. In a conceptual approach, investigations are carried out in the equatorial plane, taking into account the radial extension of the blanket-shielding zone, of the toroidal field magnet system inner leg and of the central solenoid for estimation of the pulsed swing.Design criteria are presented for the radial extension of the superconducting magnets, which is mostly driven by the structures (casings and conductor jacket). Typical available cable current densities are presented as a function of the magnetic field and of the temperature margin.The magnet design criteria have been integrated into SYCOMORE, a code for reactor modeling presently in development at CEA/IRFM in Cadarache, using the tools of the EFDA Integrated Tokamak Modeling task force.Possible solutions are investigated for a 2GW fusion power reactor with different aspect ratios.The final adjustment of the DEMO pulsed reactor parameters will have to be consistently done, considering all reactor components, when the final goals of the machine will be completely clarified.

Experimental studies on pulsed neutron sensitivity of a fusion neutron spectrometer

A sensitivity optimized magnetic proton recoil (MPROS) spectrometer for measuring both steady and pulsed fusion neutron spectra in several complicated environments is developed. The proton energy-position projection relationship of the spectrometer is measured by utilizing an imaging plate. The energy response to neutron sensitivity of the MPROS spectrometer is studied through a single event count method on an accelerated steady DT neutron source and simulations by a three-dimensional charged particle transport code. The detection efficiency of the spectrometer to DT neutrons reaches a level of 2×10-5 cm2 through high efficiency parameter settings, therefore the experimental data of high statistic accuracy are obtained on a comparatively weak neutron source. Results from simulations and experiments, such as α particle calibrations, and DT neutron calibrations, achieve good consistency. Based on this conclusion, precise solution technique of measured spectra can be developed to increase the sensitivity and energy resolution of measurements of pulsed neutron spectroscopy.

Beryllium neutron activation detector for pulsed DD fusion sources

A compact fast neutron detector based on beryllium activation has been developed to perform accurate neutron fluence measurements on pulsed DD fusion sources. It is especially well suited to moderate repetition-rate (<0.2 Hz) devices, such as the plasma focus or Z-pinch. The detector comprises a beryllium metal sheet sandwiched between two large-area xenon-filled proportional counters. A methodology for calculating the absolute response function of the detector using a “first principles” approach is described. This calibration methodology is based on the 9 Be(n,α) 6 He cross-section, energy calibration of the proportional counters, and numerical simulations of neutron interactions and beta-particle paths using MCNP5. The response function R ( E n ) is determined over the neutron energy range 2–4 MeV. The count rate capability of the detector has been studied and the corrections required for high neutron fluence measurements are discussed. For pulsed DD neutron fluencies >3×10 4 cm −2 , the statistical uncertainty in the fluence measurement is better than 1%. A small plasma focus device has been employed as a pulsed neutron source to test two of these new detectors, and their responses are found to be practically identical. Also the level of interfering activation is found to be sufficiently low as to be negligible.

A comparison between a steady state and a pulsed fusion power plant

In the paper the first results of a simplified code (FRESCO) for the evaluation of capital cost and cost of electricity of a D-T Tokamak fusion power plant are reported. For the scope of this paper, only the main assumptions and features of the code are described and its validation against the figures of the European PPCS plant models are presented. The code is here applied to compare the costs of a steady state and a pulsed fusion power plant.

Effects of base and filler chemistry and weld techniques on equiaxed zone formation in Al–Zn–Mg alloy welds

Equiaxed zone (EQZ) formation in Al–Zn–Mg alloy welds as affected by base metal, filler metal chemistry and weld techniques is studied. Filler metal chemistry and welding techniques have great influence on the formation of EQZ microstructure as base metal composition has. In an effort to characterise the equiaxed grain zone formation in Al–Zn–Mg alloy welds two commercial Al alloys AA7018 and RDE40 were selected. Gas tungsten arc welding in continuous current, pulsed current and arc oscillation mode were applied to weld the base materials. The influence of Sc containing fillers have been studied and compared with the commercial filler material. Mechanical and metallurgical characterisation were carried out in the EQZ. Intergranular corrosion in EQZ was studied according to ASTM G 110-92. Results reveals that RDE40 with low solute contents showed wider EQZ but relatively better corrosion and mechanical properties compared to AA7018 EQZ. Gas tungsten arc welding in pulsed and arc oscillation mode fusion boundary region exhibits better corrosion and mechanical properties compared to continuous current mode welds. Addition of Sc to the AA5556 filler combined with pulsed mode resulted in elimination of EQZ, better corrosion and mechanical properties compared to welds made with conventional AA5556 filler and also the presence of Sc within the EQZ so called unmixed zone has been observed.

Methods to determine the joint strength of C/C to copper joints

The plasma facing high heat flux components to be used in the divertor of long pulsed nuclear fusion experiments like Tore Supra, Wendelstein 7-X, ITER, EAST or NCT require joints between carbon–carbon-composites (C/C) and copper. Beside residual stresses resulting from the manufacture these joints have to sustain thermo-mechanical stresses that are superimposed during the application. Up to now different shear tests of the joint are in use for quality assurance during the manufacture. In addition, thermal fatigue tests of components are employed to qualify this crucial joint in a condition close to the final application. Recent results from high heat flux tests and finite element calculations have suggested that the shear strength level determined after manufacture is not sufficient to predict the performance of the C/C to copper joint under high heat flux. Therefore, different approaches are currently employed by the authors for a better judgement of this particular joint. Firstly, the joint is characterized by a shear test after repeated thermal quenching. It is assumed that such a quenching generates at least microcracks, which reduce the integral capability of the joint to transfer mechanical loads. A comparison of the shear values obtained on quenched samples to the shear value obtained directly after manufacture gives a measure to determine the thermal shock resistance of the joints. In addition, tensile test and shear test samples are employed at different temperatures to characterize the joint. Finally, possibilities have been investigated to characterize the performance of the joint in the presence of a crack. For that purpose, a method based on notched three-point bending tests has been applied to the C/C-copper joints. This allows to determine the fracture toughness of the joint. Besides the description of the different test methods the paper also presents results obtained for selected C/C to copper joints.

Recent FRC Plasma Studies

There are continuing theoretical activities to understand experimentally observed unusual (not explained by the ideal MHD theory) stability of the Field Reversed Configuration (FRC) plasmas and the existence of the FRC-equilibria as a relaxed state. FRC plasma sustainment system based on high energy particles are proposed to exploit their possible good confinement. It is also proposed to realize pulsed fusion system with the particle density between continuous systems (˜1020/m3) and inertial systems (˜1031/m3); the magnetized target fusion (˜1026/m3) and the pulsed high density systems (˜1023/m3). With the aim of overcoming the limitation in producing large scale, continuous FRC plasma, theoretical and experimental studies are intensively carried out on the FRC plasma formation and/or sustainment by the rotating magnetic field (RMF). The technology of the translation made it possible to apply standard method of sustaining the plasma - the neutral beam injection and the wave - to the theta pinch produced FRC plasma. Except for the duration, this plasma has the best performance (density and temperature) and low frequency wave is successfully induced and propagated deep in the FRC plasma.

Theoretical analysis of material removal mechanisms in pulsed laser fusion cutting of ceramics

It is well known that the efficiency of material removal mechanisms has a crucial influence on the performance and quality of the laser cutting process. However, they are very difficult to study since the physical processes and parameters which govern them are quite complicated to observe and measure experimentally. For this reason, the development of theoretical models to analyse the material removal mechanisms is very important for understanding the characteristics and influence of these processes.In this paper, a theoretical model of the pulsed laser fusion cutting of ceramics is presented. The material removal mechanisms from the cutting front are modelled under the assumption that the ceramic material may be, simultaneously, melted and evaporated by the laser radiation. Therefore, three ejection mechanisms are investigated together: ejection of molten material by the assist gas, evaporation of the liquid and ejection of molten material due to the recoil pressure generated by the evaporation from the cutting front.The temporal evolution of the material removal mechanisms and the thickness of the molten layer are solved for several laser pulse modes. Theoretical results are compared with experimental observations to validate the conclusions regarding the influence of frequency and pulse length on the cutting process.