Japan Atomic Energy Research Institute Annual Report : April 1998-March 1999

7. Nuclear Fusion Research and Development



JAERI is conducting research and development of nuclear fusion according to the "Third Phase Basic Program of Nuclear Fusion Research and Development," which was established by the Japan Atomic Energy Commission in June 1992 and the "Long Term Program of Development and Utilization for Nuclear Energy," which was established in June 1994. The Third Phase Program aimed primarily at achievement of the self-ignition condition, realization of a long burn, and establishment of the reactor technology basis required for the development of a prototype fusion reactor. A tokamak experimental reactor is being developed as the core of research and development (R & D) for the achievement of these goals. The purpose of this R & D is to obtain sufficient knowledge and experience for the fourth and subsequent phases. In FY 1992, JAERI started the engineering design activities (EDA) of the International Thermonuclear Experimental Reactor (ITER), which aimed at self-ignition and extended burn (lasting about 1000 s or longer) in cooperation with the U. S., the EU, and Russia, in accordance with the Third Phase Program. Simultaneously, JAERI has been performing R & D of fusion plasma with the aim of establishing the physics basis for ITER and fusion reactor technology. In the ITER engineering design activity, the Final Design Report of February 1998 has been approved in the four Parties' domestic review and accepted by the ITER Council of July. In July, the original program of engineering design activity was extended another three years, and the design of a low-cost ITER is being investigated. Japan has played major role in low-cost ITER design activity for the establishment of the guidelines and the direction of the activity in the three-year extension phase.

7.1 Research and Development of Fusion Plasmas

To establish the scientific basis towards the realization of a steady-state tokamak fusion reactor and to conduct the physics R & D for ITER-EDA, experimental and theoretical researches have progressed significantly in JT-60 and JFT-2M.


Large Tokamak Device JT-60

The new W-shape divertor relevant to that in a fusion reactor was effective in purifying plasma in JT-60. Using this, the world's highest equivalent fusion gain, 1.25, was achieved in a reversed magnetic shear configuration. Application of this device is promising for fusion reactor development. Many high-performance discharges that exceeded the equivalent break-even condition were also achieved with high reproducibility. Furthermore, in extensive studies on the formation and sustainment in reversed magnetic shear plasmas, high-performance plasma was stably sustained for about 6 s in a reversed magnetic shear configuration by a noninductive current drive. With respect to a high-poloidal beta H-mode operation, the plasma stability was improved by increasing the triangularity of the plasma cross-section and optimizing the current and pressure profiles. Consequently, long sustainment of a high normalized beta (beta N~2.5-2.8) was successfully obtained in a low safety factor regime (~3.2), which exceeded the design value of beta N 2.2 required in the ITER-FDR (final design report) for ITER. In the use of the W-shape divertor, the suppression effect on chemical sputtering was confirmed as an important function of the W-shape divertor. Authenticated by spectroscopic measurements for hydrocarbons produced in the divertor region, the suppression is consistent with the prediction from a computer simulation. A significant reduction in the amounts of impurities in the main plasma was demonstrated by simultaneous application of gas puffed into the main plasma and particles pumped from the divertor, which is called a puff and pump technique. The efficiency of exhausting helium ash when pumping particles from the inner divertor was evaluated. The results satisfied the conditions required for a fusion reactor. When making plasma edge measurements, a particle back flow from the lower divertor to the upper plasma was observed. This was useful to investigate the generation mechanism for particle flow. In experiments to develop heating and current drive methods for ITER, an ELMy H-mode, which is considered an ITER standard operation mode, was produced for the first time by the use of the negative-ion based neutral-beam injector (N-NBI). The electron temperature was 1.4 times higher than the ion temperature, and the confinement improvement factor against the L-mode scaling was 1.64. Such plasma plays an important role on in the study of the H-mode since electron heating by alpha particles is dominant in fusion reactor plasma. A current drive experiment using N-NBI was also carried out, which showed that a high beam-driven current, 0.6 MA, was achieved. Furthermore, an N-NBI experiment to induce a toroidal Alfven eigenmode, which results in degrading the confinement of injected beam ions, was continued since first observed last year. The excitation conditions of the mode were clarified. In diagnostic development, the electron density fluctuations in reversed magnetic shear plasmas were newly measured by a millimeter wave reflectometer, which was developed under collaboration with the Princeton Plasma Physics Laboratory. The results showed that the correlation length of the density fluctuations is dramatically reduced in the region of an internal transport barrier for a reversed magnetic shear discharge. Thus, a substantial suppression of fluctuation enhanced diffusion phenomena was measured for the first time in the world. Laser guiding optics of the "CO2 laser collective scattering diagnostic" were installed. This diagnostic device is under collaborative development by the Oak Ridge National Laboratory and Kyushu University. In theoretical studies of plasma, development of an analysis method for magnetohydrodynamic (MHD) stability in an ideal mode was extended, and a new method to analyze an ideal and a nonideal mode synthetically was developed. For plasma computing science, a particle simulation study for MHD modes progressed. It was shown that a radial electric field forms when internal kink modes appear, and this could not be predicted by a conventional fluid model. The importance of electric field formation on MHD phenomena was identified from clarification of significant effects of the radial electric field on the magnetic configuration for plasma confinement and disruption processes. In the design study of JT-60SU, a conceptual design was carried out for a device more compact than the previous design and with an increase in design margin, a reduction of construction costs, and the advancement of the reactor concept. This study showed that high-performance experiments having the objectives of steady-state operation, an equivalent energy multiplication factor of QDT 1, and an induction operation with QDT 5, are possible with a smaller superconducting tokamak having a plasma current of 8 MA, a major radius of 3.9 m, and a toroidal magnetic field of 5.8 T. This would be slightly larger than JT-60U. In the JFT-2M experiments, to develop a new fuel supply method, a compact toroid injection experiment was performed in collaboration with the Himeji Institute of Technology. Fuel supplied into an H-mode plasma was successfully demonstrated for the first time in the world. In a confinement physics study using the heavy-ion-beam probe measurement under collaboration with the National Institute for Fusion Science, a fast measurement of the electric field profile of plasma during H-mode transition was successfully obtained for the first time in the world. This provided important experimental data for establishing a transition model. In DIII-D experiments, a study regarding confinement improvement of high-density plasma was extended; high confinement characteristics were achieved by the use of an outer pellet injection at 1.5 times the density of the Greenwald empirical density limit. In a study of a radiative confinement improvement mode by impurity injection, a normalized beta of 4 and a confinement improvement factor of 3~4 were achieved in a density regime having 60% the Greenwald limit. The above results strongly support the operation scenario that utilizes high-density and high-performance plasma in ITER. Engineering activities in JT-60 have included the following plasma-facing component improvements, which were implemented in November and December of 1998 in preparation for experimental operation commencing January 1999: (1) modification of the W-shape divertor to enable particles to be exhausted from both pumping slots, (2) installation of carbon-fiber reinforced-graphite (CFC) tiles that have high-heat pulse resistance to reduce the heat load on the top and outside of the divertor dome, (3) installation of boron carbide (B4C) tiles to suppress carbon impurity generation around gas injection ports. To prevent damage to the toroidal magnetic field coils (TFC), the development of an early detection system for TFC shorting events was completed. It has been in use since January 1999. For the development of electric power supplies and control systems in JT-60, the development of a high-phase-factor converter with pulse-width modulation determined that the observed system instability was attributed to the method used for pulse pattern generation and the associated analogue control circuits. Consequently, the improvement to both the algorithm and the control circuits for pulse pattern generation was achieved. The "Cauchy-condition surface method" was developed as an identification algorithm of the entire image of a plasma cross section, and this can be applied for real-time control. The identification of the last closed plasma surface was successfully obtained with accuracy using real-time signals from electromagnetic probes in JT-60. The seventy-two units of the high-accuracy long-time digital integrator, which were developed and fabricated last year, were installed in the control system and were used for experimental operations in JT-60. In the development of RF heating devices in JT-60, data to determine the antenna-plasma-coupling characteristics in the lower-hybrid wave (LH) device were obtained for reversed shear plasmas. Following adjustment of the injected RF power and refractive indices, the LH device contributed to the success of quasi-steady sustainment of an internal transport barrier in reversed shear plasma by RF current drive. This attracted world attention. On the ion cyclotron wave (IC) device, the unusual intermittent vibrations that occurred in the high-power amplifiers were determined to result from oscillation in a screen circuit. Hence, the prospect for higher gain (increased amplification factor) was obtained. A required system design modification of the RF heating devices to control the local current profile was completed. Additionally, the design, trial manufacture, and acceptance of many components, such as a high voltage power supply, antennas, waveguides, were completed. In the development of the NBI device, the higher power and longer duration of injection (25-MW injection power, 9-s injection pulse duration) were embodied in the positive-ion based NBI device. A monitoring system using an infrared TV camera was installed to monitor temporal behavior of the shine-through rate of an injected beam into the plasma just after the shot. In terms of the N-NBI device, an operational scenario to stabilize a discharge in a negative-ion generator was established by increasing the duration of a pre-arc discharge before the injection. This allows stable injection of a long beam pulse. By the use of this method, the neutral deuterium beam injection was realized without break down for 1.9 s with a beam energy of 350 keV (3 MW) and for 1.5 s with a beam energy of 360 keV (4 MW). In terms of the development of the JFT-2M device, the optimization of the operation conditions of the compact toroid injector progressed. The compact toroid injection was shown to be an effective fuel supply method for a fusion reactor. In the advanced material tokamak experiment, specific engineering considerations were executed in the manufacture of ferritic steel plates to implement a reduction of the fast-ion ripple loss. The installation of the ferritic steel plates between the vacuum vessel and the toroidal field coil was completed in March 1998. In FY 1998, an infrared TV system was also installed to measure the ripple loss particles escaping from the plasma toward the experiments.

7.2 Research and Development in Fusion Reactor Technology

By July 1998, the Engineering R & D Tasks assigned to the Japanese Home Team for the ITER Engineering Design Activities (EDA) were completed, summarized, and submitted to the Joint Central Team. In the following extended three-year period of the ITER-EDA, systems experiments of the major components will be developed, engineering R & D will aim at cost reductions, ITER safety demonstration experiments will be conducted (such as to enhance tritium safety and seismic isolation) and the breeding blanket R & D for the DEMO reactor will move forward. In engineering research on the fueling/pumping system, a detection method for water leakage from the ITER in-vessel water-cooling systems using a water-soluble tracer has been conceptually investigated as an ITER design task. Krypton was selected as the tracer, and the detectability of the effused krypton together with water leakage using a residual gas analyzer was evaluated. In the development of a ceramic coating technique, an alumina coating film produced by the Alchoxide method has been performance tested. The effectiveness of the film in preventing hydrogen permeation was confirmed. In the development of superconducting magnets, a large advanced coil, called the Outer Module of the ITER Central Solenoid (CS) Model Coil, was successfully fabricated. This coil has been under development and fabrication since 1992 by international collaboration through the ITER technology R & D activities. Significant activities carried out in Japan to reach this achievement were 1) assembling the 8 superconducting layers, 2) fabrication of the joints of 46-kA superconductors by diffusion bonding between metals under high pressure (30 MPa) and high temperature (750oC), and finally 3) the fabrication of the ground insulation around the coil by the vacuum impregnation method. In November 1998, the Outer Module was transferred to Naka Fusion Research Establishment of JAERI. In an acceptance test, high voltage (31 kVDC) was applied to the coil. The measured leakage current was only 93microA, which verified the high-quality performance of its electrical insulation. The activation heat treatment of the CS Insert Coil was successfully performed in the U. S. A. under collaboration with the Massachusetts Institute of Technology. The CS Insert Coil will be installed at the inner most layer of the CS Model Coil for testing at 13 T at an operating current of 40 kA. The conductors used for the CS Insert Coil were separately tested. These tests indicated that the coil could maintain its superconductivity up to a temperature of 8.1 K at 13 T and 40 kA. The original target of technology development was to maintain superconductivity up to 7.3 K at 13 T and 40 kA; therefore, an additional margin of 0.8 K in temperature increase was obtained. In the development of NBI heating technology, a high current density, 30 mA/cm2H-, has been successfully extracted from a newly developed, small KAMABOKO source with a seven-aperture extractor. The current density is higher than the required value for the ITER NBI. The seven extracted beamlets were merged to a single beam of 140 mA. In the beam optics study of the negative ions, it was experimentally confirmed that the beamlets repel each other during acceleration by the space charge effect. Beam emittance of the H-ions was confirmed to be as small as 0.3 mm. mrad. For the development of the ITER NBI components, a high-voltage test of a 90% scale model of a multi-conductor bushing for the 1 MV transmission line has been performed. High voltage (900 kVDC), which corresponds to the rated voltage of 1 MV, has been successfully sustained for longer than 1000s. Steady-state operation of a cryogenic pump whose pumping speed is 5 m3/s was also demonstrated. In the development of the plasma-facing components, JAERI fabricated a near-full-scale mock-up, which is completely applicable to the lower half of the ITER divertor plate in the ITER Final Design Report. The mock-up is about 1 m long, and consists of 30 mono-block C/C armors brazed onto a triple-layer dispersion strengthened copper tube with a silver-free braze. Heating tests were conducted in the PBEF facility of JAERI. The mock-up successfully demonstrated its ability to withstand an ITER steady-state heat load of 5 MW/m2 for more than 3000 cycles and an ITER 10 s transient heat load of 20 MW/m2 for more than 1000 cycles. These encouraging results imply that the developed mock-up meets the three-year operation requirement of ITER, which corresponds to one cycle of divertor replacement. In research on Radio-Frequency (RF) Heating Technology, JAERI succeeded in demonstrating the world's first high-efficiency gyrotron that has energy recovery. JAERI also demonstrated a 1-MW output from a super-high-order mode (TE31,8) cavity gyrotron. Based on these successes, the development of the ITER 170 GHz gyrotron for electron cyclotron heating (ECH) has been further advanced. The performance of the ITER gyrotron prototype was restricted to an output of 500 kW/0.7 sec. at 170 GHz due to overheating the Sapphire or Si3N4 output window. To solve this problem, we have developed a synthetic diamond window, which has ideal performance as the ECH window, and have installed it into the ITER gyrotron. The world's first diamond window gyrotron has achieved 520 kW for 6 s, which is more than the task target of 500 kW for 5 s of the ITER EDA. The diamond window gyrotron has also demonstrated an improvement in the required transmission efficiency of 10% because of the Gaussian output profile. The torus window for the ITER EC wave launcher was performance tested. The results demonstrated that the diamond window could withstand a 0.7-MPa-pressure difference, which is far higher than the required value of 0.5 MPa that would occur during a coolant leakage accident. Regarding reactor structure development, elastic-plastic analysis of the field joint welding of the ITER Vacuum Vessel (VV) sector, which was fabricated in the ITER R & D Project, has been performed to develop a simulation method of testing weld deformation. The full-scale, mid-plane port extension fabricated by the Russian Federation (RF) Home Team has been shipped to Japan for remote weld testing with the VV sector. The testing of seismic isolators (rubber bearings), which support high vertical loads and the weld joints of the double-walled vacuum vessel that form part of the radioactivity confinement barrier, is being continued to establish the technical database for the seismic isolation criteria and the structural design criteria required for ITER construction. The mechanical tests of sub-scale rubber bearings with diameters from 0.2 to 0.7 m have been conducted to evaluate the feasibility of using full-scale rubber bearings with diameters of 1.2 to 1.5 m. For remote assembly/disassembly technology of reactor components, a new control scheme was developed to suppress the dynamic deflection and vibration caused by dead-load transfer during installation and removal of the 4-ton blanket module. The test results obtained by the full-scale mock-up of the vehicle manipulator system have shown that the dynamic deflection of the rail and the acceleration of the manipulator were successfully suppressed to nearly zero by a new control scheme. Regarding divertor cassette maintenance, a Japanese Home Team member joined the integrated test program being continued on the Divertor Test Platform (DTP), which was constructed at ENEA Brasimone in Italy. The remote replacement test of the central cassette carrier (shipped from Japan in January 1998) was performed by using the control system prepared by ENEA. In blanket technology research, high heat-flux cycle tests of the mid-scale mock-up (8-m-high and 0.5-m-wide) ITER shielding blanket module and the small-scale mock-up (0.4-m-high and 49-mm-wide) ITER baffle module were performed under the framework of ITER/EDA. The validity of the first wall thermal design and the integrity of the HIP bonded interfaces were demonstrated. For development of the breeding blanket fabrication technology, a small-scale mock-up (0.1-m-high, 0.03-m-wide, and 0.2-m-deep) breeding blanket box structure made of reduced activation ferritic steel, F82H, was successfully fabricated by the HIP bonding method. Additionally, the effective thermal conductivities of the pebble beds of the tritium breeding materials and the neutron multiplier materials were measured by the hot-wire method. Databases required for the thermal design of the breeding blanket were obtained. As a development in the tritium breeding blanket effort, an experiment addressing the tritium release from the Li2TiO3 packing region was conducted to evaluate the effects of various parameters, i. e., the sweep gas flow rate, the hydrogen content of the sweep gas, the irradiation temperature, etc. Testing was done at the Japan Materials Testing Reactor. From the results obtained, it was clear that the main parameters that affect the tritium release properties are irradiation temperature and hydrogen flow rate. In R & D on tritium safety technology, a study on the spatial diffusion behavior of tritium gas was started using a gas-tight 12-m3 vessel, and engineering data concerning tritium behavior were accumulated. Under the U. S.-Japan collaborative program for tritium safety technology development, valuable data were obtained by measuring the tritium distribution in the plasma-facing graphite tiles of the Tokamak Fusion Test Reactor (TFTR) of the Princeton Plasma Physics Laboratory. In R & D of tritium production, development of production technology for high-purity tritium was advanced through a 0.1-g-level tritium production test using 6Li-Al alloy target material. The ceramic target will accept a variety of nuclear reactor irradiation conditions. Development of a capsule for 6Li ceramic target irradiation was started. A tritium transportation test was carried out successfully. This demonstrated the performance of the developed tritium transportation container, which uses Zr-Co hydrogen getter material. In the design study of fusion reactor systems, the conceptual design of a helium cooling demo fusion reactor (fusion power: 1.5 GW) was completed. Silicon carbide composites were adopted as reactor core material; however, the coolant temperature was selected to be 800oC, which is 100oC lower than that of a commercial reactor, in consideration of the silicon carbide composites now under development. Moreover, loss-of-coolant-accident safety and the radwastes produced by a commercial reactor were investigated. The helium release tank volume required to maintain the integrity of the vacuum vessel in the event of such an accident was determined. The quantities of radwastes for shallow land burial and medium depth burial were also determined. For the study of fusion safety, the following three studies were performed. 1) The TRAC-BF1 code has been adapted to evaluate the ingress coolant event (ICE) for the ITER safety design. The calculation results of this code were compared with those of the ITER reference code, MELCOR, which verified the performance of that code. 2) The thermal-hydraulic analysis code, STREAM, was used to evaluate the flow phenomena inside the vacuum vessel in the case of a loss-of-vacuum accident. 3) A dynamic simulation code, DYNAS, was completed to determine the tritium inventory in the fusion reactor system. ITER EDA was initiated in July 1992 under an agreement between EURATOM, Japan, the RF, and the U. S. A. The Final Design Report was completed in July 1998, and the EDA was supposed to enter an additional three-year extension phase (after the completion of its initially planned six-year activities). However, the U. S. was unable to sign the extension Agreement and gradually began to withdraw from the EDA. The remaining three parties, the EU, JA, and the RF, confirmed their intention to continue the three-year extension at the ITER Meeting held in Yokohama. The Japanese AEC judged the completion of the EDA in three additional years by the three parties to be a sound decision. Along with this decision, the intention of the extension by the other parties was reconfirmed. Substantial EDA activities had been resumed by the end of March, with the expectation of an early completion of the legal procedure. The San Diego Joint Work Site was closed in March due to the withdrawal of the U. S. The Joint Central Team (JCT) then continued design activities at the two remaining Joint Work Sites, Garching and Naka. In March also, it was agreed that the Special Working Group should restart informal discussions on construction-related issues. Japan has made significant contributions to the EDA. It sent designers (a total of 198 man-years effort) to the JCT, and its home team completed design tasks totaling 177 man-years. It expended 182 kIUA (kIUA: million dollars in 1989) performing R & D on fusion related technology.

(1) Design Activities in JCT

Japan contributed 44 Japanese members to the JCT, including 25 from industry, and has undertaken a full share of the drafting the Final Design Report and of the preparatory design work for the Outline Design Report of the Reduced-cost ITER. At the end of FY 1998, 45 JCT members were at the Naka Joint Work Site, including 13 Japanese.

(2) Design Activities by the Japanese Home Team

The Japanese Home Team has performed its assigned tasks to contribute to the completion of the Final Design Report and the preparatory design work for the Outline Design Report of the Reduced-cost ITER in collaboration with the JCT. Preparation of the technology R & D tasks was performed until the restart of EDA in March. As a part of preparation for construction, the home team continued to identify technical and safety related issues and to proceed with the examination of seismic isolation, electric power storage, design codes and standards, and so on. Also continued was the study of design basis accidents, analysis of abnormal events, and evaluation of public doses for possible safety licensing of ITER in the future.

(3) Support of the ITER Naka Joint Work Site

JAERI continues to support the ITER Naka Joint Work Site by providing office work space and equipment, including CAD machines and personal computers, and support personnel. It also provides improvement of the social infrastructure.

7.3 Related Research

As for the research on ITER shielding, a straight duct streaming experiment to simulate various port geometries and a decay heat measurement experiment for tungsten divertor plates were performed to verify accuracy of design calculations. Under the IEA collaboration, integral experimental data for lithium titanate, which is a candidate for advanced breeding blanket material, were obtained for the first time. The development of synthetic-diamond radiation detectors has been advanced. Measurements of secondary gamma-ray production cross sections have almost been completed. For the development of tritium breeding materials, the release rates of helium atoms from irradiated single-crystal and sintered-powder Li2O specimens were measured to evaluate the effects of irradiation damage and porosity. For development of ceramic insulators, triple-beam ion-irradiation on a single crystal of alumina (Al2O3) has been performed using the TIARA facility in the Takasaki establishment. The synergistic effect of the displacement damage and transmutation produced gas atoms was evaluated by examining the depth dependence of the damage microstructure. The result indicating that the mobility of hydrogen was strongly reduced by the trapping at the cavities formed with helium atoms and vacancies. SiC/SiC composite material is a promising ceramic structural material for in-vessel components. Improvement of the reaction bonding method to fabricate the composite is in progress. The relation between the amount of free silicon and the raw material composition was evaluated. Also, the parameters affecting the fiber-matrix interface microstructures were examined, and several ways to improve fracture toughness were obtained. Application of the complex oxide as a coating material on the fiber is one such method. Chemical vapor-and polymer-infiltration techniques have been tried in attempts to fabricate three-dimensional fiber fabric composites. Reduced activation ferritic/martensitic steel, F82H, developed by JAERI and the NKK Corporation has been recognized as a candidate alloy for blanket structural materials. Analysis on the damage microstructures in specimens irradiated with the multiple ion-beam using the TIARA facility (located in the Takasaki Establishment) and by neutrons in HFIR at the Oak Ridge National Laboratory (under a collaboration program between JAERI and the U. S. DOE for fusion reactor materials development) has been carried out to obtain the effect of transmutation-produced helium atoms and minor alloying elements. The results indicated the strong effect of heat/mechanical treatment on the distribution of cavities formed during irradiation. In the evaluation of atomic and molecular data, a five-year project, started in 1997, is in progress to produce the fifth volume of the Japanese evaluated atomic and molecular data library for fusion, JEAMDL-5. The main objective of JEAMDL-5 is to provide databases for atomic and molecular collision processes relevant to divertor and edge plasmas and for spectroscopic data of gasses to be injected for divertor plasma cooling. This fiscal year a compilation was completed of the observed cross sections for 207 kinds of collision processes of H2O, CO, CO2, and hydrocarbons (CH4, C2H6, and so forth) by electron impacts. Containing data published before 1998, the cross-section values for each collision process have been compared with each other and evaluated by taking into account the uncertainties of the experimental methods used. Spectral data of Ar I-Ar XVIII, comprising about 5,600 emission lines, have been compiled and evaluated. Research studies on the thermofluid safety of fusion reactors addressed an ingress-of-coolant event, ICE. Controlling factors on the pressure rise process during ICE events were validated numerically by performing preliminary ICE experiments and analyzing two-phase flow behavior with the TRAC-PF1 code. Moreover, an integrated ICE test facility was planned to verify the ITER safety systems during ICE events and to validate the ITER safety analysis codes. The specifications for the integrated ICE test facility were determined and preparation for construction was begun. Another study addressed a loss-of-vacuum-accident event, LOVA. Development of numerical analysis codes was begun. These codes will provide quantitative predictions regarding air ingress behavior, activated dust transport behavior, and buoyancy-driven exchange flow behavior during LOVA events.

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