Fusion Test Facility Research Articles

TRITIUM CONCENTRATION IN MONTHLY PRECIPITATION NEAR THE FUSION TEST FACILITY IN JAPAN BEFORE AND AFTER THE DEUTERIUM PLASMA EXPERIMENT.

In Japan, the deuterium plasma experiment using the Large Helical Device was started at the National Institute for Fusion Science (NIFS) in March 2017 to investigate high-temperature plasma physics and hydrogen isotope effects in research leading towards the realisation of fusion energy. The deuterium plasma experiment produces small amount of tritium by fusion reactions. To understand any impacts by the experiment to the surrounding environment, monthly precipitation samples have been collected at the NIFS site since November 2013 to assess the relationship between isotope composition and chemical species in precipitation including tritium. By comparing data before and after the deuterium plasma experiment start, it was found that tritium released from the main stack of the fusion test facility had no impact on the environment surrounding NIFS.

A New Wide-Area Monitoring System of Electromagnetic Fields Around Megawatt-Class Amplifiers for Ion Cyclotron Range of Frequency Heating at a Fusion Test Facility

Nuclear fusion research requires the production of high-temperature plasma. One of the plasma heating methods is the use of radio frequency (RF) waves. The RF wave heating system uses a high-power amplifier, which poses a concern about the leakage electromagnetic fields. Therefore, a new wide-area multipoint electromagnetic monitoring system using personal RF monitors has been developed. The developed monitoring system was applied to the megawatt-class amplifiers for the “ion cyclotron range of frequency” (ICRF) heating system in the frequency range of ion cyclotron resonance from 30 to 40 MHz. As a result, the leakage magnetic field was less than the measurement sensitivity during the plasma experiment, in which the leakage electric field was detected with sufficient sensitivity. The leakage electric field becomes larger as the RF forward power increases, and thus the electric field would be radiated through the stub and/or high voltage supply line connected to the anode of tetrode in the ICRF amplifier. The electric field around the ICRF amplifiers did not exceed the reference level of International Commission on Non-Ionizing Radiation Protection (ICNIRP). The developed wide-area multipoint monitoring system will be useful for monitoring the leakage RF electromagnetic fields around the ICRF heating system at the future fusion devices.

Monitoring and Recovery of Tritium in a Fusion Test Facility

In a large fusion test facility, when a deuterium-plasma experiment is conducted a small amount of tritium is produced by the d(d, p)t reaction. From the viewpoints of radiation management and public acceptance, the tritium monitoring and recovery systems were developed and installed for the fusion test device. As for the tritium monitoring equipment, an expiratory test system of tritium was utilized for the internal dose assessment of workers. Active tritium samplers were operated continuously to monitor the amount of tritium released from the stack. As for the tritium recovery equipment, an exhaust detritiation system (EDS) for the plasma experiment has been developed and installed at the downstream of the vacuum pumping system in the fusion test device. All of the exhausted tritium from the vacuum vessel was treated by the EDS during the deuterium-plasma experimental campaign. Then, the tritium recovery rate achieved was more than 95%.

Isotope Composition and Chemical Species of Monthly Precipitation Collected at the Site of a Fusion Test Facility in Japan.

The deuterium plasma experiment was started using the Large Helical Device (LHD) at the National Institute for Fusion Science (NIFS) in March 2017 to investigate high-temperature plasma physics and the hydrogen isotope effects towards the realization of fusion energy. In order to clarify any experimental impacts on precipitation, precipitation has been collected at the NIFS site since November 2013 as a means to assess the relationship between isotope composition and chemical species in precipitation containing tritium. The tritium concentration ranged from 0.10 to 0.61 Bq L−1 and was high in spring and low in summer. The stable isotope composition and the chemical species were unchanged before and after the deuterium plasma experiment. Additionally, the tritium concentration after starting the deuterium plasma experiment was within three sigma of the average tritium concentration before the deuterium plasma experiment. These results suggested that there was no impact by tritium on the environment surrounding the fusion test facility.

ENVIRONMENTAL TRITIUM AROUND A FUSION TEST FACILITY.

Deuterium plasma operations using a large fusion test device have been carried out since 2017 at the National Institute for Fusion Science. A small amount of tritium was produced by the fusion reaction, d(d, p)t. Then, a part of the tritium was released into the environment. Thus, monitoring the level of tritium in the environment around the fusion test facility is important. This is done before starting the deuterium plasma experiment. The environmental tritium concentrations indicated that they are at background levels in Japan. After starting the deuterium plasma experiment, the environmental tritium around the fusion test facility was within the range of environmental variation. This suggests that there was no impact of tritium on the environment during the first deuterium plasma experimental campaign.

Expiratory Testing as a Simple and Effective Bioassay Method for Screening Workers for Tritium Exposure in Fusion Test Facilities

Expiratory Testing as a Simple and Effective Bioassay Method for Screening Workers for Tritium Exposure in Fusion Test Facilities

Monitoring of Tritium Concentration by Simplified Active Sampler in a Fusion Test Facility

Monitoring of Tritium Concentration by Simplified Active Sampler in a Fusion Test Facility

Development of an active tritium sampler for discriminating chemical forms without the use of combustion gases in a fusion test facility

A new type of active tritium sampler that can discriminate between chemical forms in a fusion test facility without the use of combustion gases was developed. The proposed tritium sampler was operated using water vapour instead of combustion gases. To test the operation and performance of the device when water vapour is used, we evaluated the catalytic oxidation properties, and the evaporation and collection of water vapour under actual sampling conditions. The properties of the added water mass and the operation temperature of catalysts in the proposed sampling system were then determined. Thereafter, we carried out air sampling for tritium monitoring. The levels of tritium concentration measured by the proposed tritium sampling system were similar to the values measured by the conventional sampling system. Our findings show that the proposed tritium sampling system without combustion gases is a good replacement for the conventional tritium sampling system in a fusion test facility.

Plant integration of MITICA and SPIDER experiments with auxiliary plants and buildings on PRIMA site

This paper presents a description of the PRIMA (Padova Research on ITER Megavolt Accelerator) Plant Integration work, aimed at the construction of PRIMA Buildings, which will host two nuclear fusion test facilities named SPIDER and MITICA, finalized to test and optimize the neutral beam injectors for ITER experiment. These activities are very complex: inputs coming from the experiments design are changing time to time, while the buildings construction shall fulfill precise time schedule and budget. Moreover the decision process is often very long due to the high number of stakeholders (RFX, IO, third parties, suppliers, domestic agencies from different countries). The huge effort includes: forecasting what will be necessary for the integration of many experimental plants; collecting requirements and translating into inputs; interfaces management; coordination meetings with hundreds of people with various and different competences in construction and operation of fusion facilities, thermomechanics, electrical and control, buildings design and construction (civil plants plus architectural and structural aspects), safety, maintenance and management.The paper describes these activities and also the tools created to check and to validate the building design, to manage the interfaces and the organization put in place to achieve the required targets.

Variation of atmospheric tritium concentration in three chemical forms at Toki, Japan: 2004-12.

Atmospheric tritium concentrations of HTO, HT and CH3T have been measured at Toki, Japan, for the environmental impact assessment of tritium for a fusion test facility. According to the data from 2004 to 2012, the concentrations of HT and HTO in water vapour tend to increase in spring. The seasonal variation in HT concentration at Toki was compared with the H2 concentration between 1990 and 2005 at Tae-ahn Peninsula, Republic of Korea, which is at approximately the same latitude as Toki. The monthly average of HT-specific activity varied from 1.24 × 10(5) to 1.76 × 10(5) TU. The peak of the monthly average H2 concentration did not match that of HT. This indicates that the mechanism of the production or the source of HT might be different from the production mechanism of H2.

Electromagnetic Fields Measurement and Safety Consideration in Magnetic Confinement Fusion Test Facilities

Electromagnetic Fields Measurement and Safety Consideration in Magnetic Confinement Fusion Test Facilities

Performance test of personal RF monitor for area monitoring at magnetic confinement fusion facility

For safety management at a magnetic confinement fusion-test facility, protection from not only ionising radiation, but also non-ionising radiation such as the leakage of static magnetic and electromagnetic fields is an important issue. Accordingly, the use of a commercially available personal RF monitor for multipoint area monitoring is proposed. In this study, the performance of both fast- and slow-type personal RF monitors was investigated by using a transverse electromagnetic cell system. The range of target frequencies was between 10 and 300 MHz, corresponding to the ion cyclotron range of frequency in a fusion device. The personal RF monitor was found to have good linearity, frequency dependence and isotropic response. However, the time constant for the electric field sensor of the slow-type monitor was much longer than that for the fast-type monitor. Considering the time-varying field at the facility, it is found that the fast-type monitor is suitable for multipoint monitoring at magnetic confinement fusion test facilities.

Multiterawatt Ti:Sapphire/KrF laser GARPUN-MTW as a test bench facility for verification of combined amplification of nanosecond and subpicosecond pulses

The possibility of the same large-aperture KrF laser driver to amplify simultaneously both nanosecond pulses for thermonuclear target implosion and picosecond ones for fuel ignition is discussed relative to KrF-based Fusion Test Facility. In this way experiments were performed at hybrid Ti:Sapphire/KrF GARPUN-MTW facility on amplification of subpicosecond pulses. 2-TW, 330-fs pulses were produced with beam divergence 20 μrad in direct double-pass amplification scheme. Peak power as high as 30–40 TW can be achieved in 50-fs pulses, being combined with long pulses (of a few ns to 100 ns) of ∼1 GW power.

A Remote Monitoring System of Environmental Electromagnetic Field in Magnetic Confinement Fusion Test Facilities

A remote, continuous environmental electromagnetic field monitoring system for use in magnetic confinement fusion test facilities is developed. Using this system, both the static magnetic field and the high frequency electromagnetic field could be measured. The required frequency range of the measurement system is from 25 to 100 MHz for the ICRF (Ion Cyclotron Range of Frequencies) heating system. The outputs from the measurement instruments are measured simultaneously by custom-built software using a laptop-type personal computer connected to a local area network. In this way, the electromagnetic field strength could be monitored from a control room located about 200 m from the fusion device building. Examples of measurement data from the vicinity of a high-frequency generator and amplifier and the leakage static magnetic field from a fusion test device are presented.

A Laser Based Fusion Test Facility

The Fusion Test Facility (FTF) is a high repetition rate ignition facility that would bridge the gap between single shot facilities (such as NIF and LMJ) and a fully functioning laser fusion power plant. It would allow development of science and technologies so that follow-on power plants could have predictable performance. The FTF would need to have enough fusion power, about 100 MW, to rigorously test materials and components for the power plants. Because inertial fusion provides a “point” source for neutrons, it can provide very high fluxes for test objects placed close to the target, while the reaction chamber walls remain at conservatively large distances. Simulations indicate that direct-drive designs can achieve 100 MW fusion power with laser energies well below 1 MJ with a 5 Hz driver. High-resolution 2-D simulations of high-velocity direct-drive implosions utilizing a Krypton-Fluoride (KrF) laser give gains of >60× at 500 kJ, and shock-ignited targets may allow higher gains at even lower driver energy. Utilizing designs that require relatively small driver energy is the most straightforward path to reducing cost and development time for a practical laser fusion energy power plant. A program to develop an FTF would build upon the science and technologies developed in the existing National Ignition Campaign and the High Average Power Laser (HAPL) program, as well as the magnetic fusion technology program.

Design and Testing of Helium Cooled Components for DEMO and Synergies with Gen4 Reactor

The apparent fundamental movements in the world wide energy market risen by (i) the dramatic increase in world energy demand, (ii) the perceived danger of an ongoing world climate change and (iii) the predicted price and resource trends in fossil resources have risen discussions on the possibilities to significantly further accelerate the development of pure fusion power stations under the headline ‘fast track’ in the recent past. In contrast at the same time strong fusion specific challenges are being recognized in the light of some issues with the ITER project in terms of schedule, technologies and cost. Therefore, it seems to be appropriate to reappraise the role of DEMO and fusion energy in the overall context and consider readjusting or redefining the medium-term mission in nuclear fusion and its relation to nuclear fission.Firstly, the current paper assesses synergies with nuclear fission Gen4 reactors. It is ascertained that the development of efficiently helium cooled high temperature components and reactor systems allows for strong collaboration between fission and fusion. Furthermore, it could be concluded that an integrated nuclear strategy for the 21st century should be developed including all important aspects of the possible interplay between fusion and fission. It is briefly discussed whether hybrid fusion-fission systems could be a central point of such an integrated strategy in the world wide context.The second emphasis of the current paper is on the description of the current progress made in Karlsruhe in the fields of design and testing of helium cooled components for fusion power stations and test facilities. Efficient helium cooling methods for divertor and blanket structures were found by applying the state of the art jet impingement and rib turbulator heat transfer enhancement techniques. The low pressure and the high pressure TBM section of the HELOKA facilities are under assembly. HELOKA is the main experimental tool for out of pile testing and qualification of in-vessel components at Forschungszentrum Karlsruhe.

Pulse shaping and energy storage capabilities of angularly multiplexed KrF laser fusion drivers

This paper describes a rep-rated multibeam KrF laser driver design for the 500kJ Inertial Fusion test Facility (FTF) recently proposed by NRL, then models its optical pulse shaping capabilities using the ORESTES laser kinetics code. It describes a stable and reliable iteration technique for calculating the required precompensated input pulse shape that will achieve the desired output shape, even when the amplifiers are heavily saturated. It also describes how this precompensation technique could be experimentally implemented in real time on a reprated laser system. The simulations show that this multibeam system can achieve a high fidelity pulse shaping capability, even for a high gain shock ignition pulse whose final spike requires output intensities much higher than the ∼4MW∕cm2 saturation levels associated with quasi-cw operation; i.e., they show that KrF can act as a storage medium even for pulsewidths of ∼1ns. For the chosen pulse, which gives a predicted fusion energy gain of ∼120, the simulations predict the FTF can deliver a total on-target energy of 428kJ, a peak spike power of 385TW, and amplified spontaneous emission prepulse contrast ratios IASE∕I<3×10−7 in intensity and FASE∕F<1.5×10−5 in fluence. Finally, the paper proposes a front-end pulse shaping technique that combines an optical Kerr gate with cw 248nm light and a 1μm control beam shaped by advanced fiber optic technology, such as the one used in the National Ignition Facility (NIF) laser.

Comparative study of predictive FE methods for mechanical properties of nuclear composites

Carbon fiber reinforced carbon (C/C) composites are candidate materials for plasma facing components in experimental fusion reactors such as: the ITER; the JT-60 – a Tokamak fusion test facility (JAEA); and for control rods in the next generation fission reactors. Therefore, determining their thermo-mechanical properties under irradiation is essential for safe design-cum-operation of future reactors. Development of reliable models which can predict such materials’ behavior is of massive advantage against the conventional experimental verification which is hugely expensive and time-consuming. Three-dimensional finite element (FE) methods are used here for predicting Young’s modulus of two woven C/C composites where tensile tests are performed for validation. Stress distribution results indicate that a novel image-based route for FE meshes compared to a unit cell approach gives stronger agreement with experimental data. The image-based approach captures true porosity as fine microstructural details are converted from X-ray tomographic data. In comparison, the unit cell model represents idealizations of composite architecture that ignores porosities.

On the use of KrF lasers for fast ignition

AbstractThe KrF laser has been considered as an inertial fusion driver alternative to diode-pumped lasers. The possibilities of KrF lasers for fast ignition is supported by their short wavelength and the corresponding larger penetration depth together with the possible use of the same amplifiers for fusion driver and fast ignitor. It is shown that in the case of a fusion test facility both the energy and the intensity requirements can be fulfilled. A fast ignitor using 20 ps KrF pulses requires beam smoothing techniques after angular multiplexing due to the coherence of the beam. A multiple beam fast ignitor is suggested as an alternative in which a high number of beams of 1 ps duration are separately focused on the fuel after polarization demultiplexing. This arrangement allows even the pulse-forming of the ignitor.

Quests for inertial fusion energy conducted at GARPUN KrF laser facility

Some aspects of e-beam-pumped KrF laser physics and technology are considered with an impact on Fusion Test Facility design. These includes fluorescence and transient absorption measurements in KrF gain medium aimed at elaborating the kinetic model of large-scale amplifiers, studying the radiation stability of laser and target chamber optics, development of fluorine-resistant high-optical-strength protective coatings for laser windows.