2nd International Workshop on Gas Dynamic Trap based Fusion Neutron Source (GDT-FNS)

18 Nov 2019, 08:45 → 19 Nov 2019, 18:30 Asia/Novosibirsk

Conference Hall (Budker INP)

More photos by N. Kupina, Budker INP, are available here.

Gas-Dynamic Trap (GDT) is one of the most promising concepts to be a high-flux Fusion Volumetric Neutron Source (FVNS) for fusion nuclear science and technology development, and for driving fusion-fission hybrid reactor. Based on the development orientation of the Budker Institute of Nuclear Physics (BINP), the Siberian Branch of the Russian Academy of Sciences (SB RAS). and the Institute of Nuclear Energy Safety Technology (INEST), Chinese Academy of Sciences (CAS), the two institutes have jointly initiated an international mega science program on Gas Dynamic Trap based Fusion Neutron Source (GDT-FNS). The 1st international GDT-FNS Workshop was jointly held in November of 2018 in Hefei, China by the two institutes as the first step to attract more partners to join in this work. It resulted in a project of Compact Volumetric Neutron Source (CVNS). 2nd GDT-FNS workshop to be help in Novosibirsk, Russia will involve discussing various topics related to GDT-FNS development such as: o Cooperation partners and research bases o Proposed requirements of GDT-FNS o Advantages and drawbacks of GDT-FNS o Concept design of GDT-FNS o Engineering design of GDT-FNS o Development of key technologies o GDT experiments and development status o Steady-state operation of GDT o FVNS mega-science project o Applications of FVNS o Physical issues of FVNS; o E.t.c.

Announcements 2nd International Workshop on GDT-FNS, Novosibirsk 2nd International Workshop on GDT-FNS, Novosibirsk

Conference flyer 2nd International Workshop on GDT-FNS, Novosibirsk

Monday, 18 November

08:45 → 09:00 Transfer

Bus from the «Golden Valley» hotel to the Budker INP main bldg

09:00 → 09:30 Registration

09:30 → 09:40 Opening ceremony

09:40 → 13:00 Axisymmetric LInear Advanced Neutron sourCE

Convener: Olov Ågren (Uppsala University)

09:40 ALIANCE: A Route to Fusion Volumetric Neutron Source

This presentation is contributed by the Institute of Nuclear Energy Safety Technology (INEST), Chinese Academy of Sciences and the Budker Institute of Nuclear Physics (BINP), Russian Academy of Sciences. It will be presented the development strategy and plan of construction of a GDT-based fusion volumetric neutron source project named Axisymmetric LInear Advanced Neutron sourCE (ALIANCE). The goal of ALIANCE project, jointly undertaken by BINP, INEST, and other institutions, is the accelerated development and realization of continuously operating fusion volumetric neutron source for specific applications.

Speakers: Prof. Yican Wu (Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences) , Prof. Zhibin Chen (Institute of Nuclear Energy Safety Technology, CAS)

10:30 Future perspectives and status of magnetic mirror studies in Novosibirsk

The report presents an update on the continuing work on open magnetic traps in BINP RAS. It discusses the construction of a gas-dynamic trap with improved longitudinal confinement named GDMT, as well as the experiments on existing (GDT, SMOLA) and newly constructed (GOL-NB, CAT) devices. The report highlights the main experimental achievements obtained on the facilities of previous generation such as formation of thermal barriers, plasma stabilization by sheared rotation and others, outlining their importance for the GDMT project.

Speaker: Prof. Alexander Ivanov (Budker Institute of Nuclear Physics)

11:20 Coffee

11:40 Neutron Shielding Analysis and Activation Calculation of GDT-based Fusion Neutron Source

The report presents results of neutron shielding calculation for ALIANCE project, especially for ALIANCE-2. We used the Monte Carlo transport program SuperMC with data library FENDL 2.1. The calculation results show that the 5cm thickness of the shielding layer of ALIANCE-2 is enough. The highest nuclear thermal deposition is at Coil-3 (C3) with a value 0.92W/m3. It is much lower than ITER's nuclear thermal deposition limit for superconducting conductors, which is 1KW/m3. Special attention has been paid to the shielding of the mirror coils. Materials activation calculation is ongoing.

Speaker: Dr Qiusun Zeng (Institute of Nuclear Energy Safety Technology, CAS)

12:10 A draft design of first and second prototype ALIANCE devices

The report presents the design ideas behind the low- and moderate-power prototypes of continuously operating volumetric fusion neutron sources based on gas-dynamic magnetic mirror devices with neutral beam injection. A possible arrangement of vacuum, magnetic, plasma stabilization and sustainment, and neutron shielding subsystems is presented, along with their required parameters that are defined by the existing calculations of plasma performance in these machines.

Speaker: Dr Dmitry Yakovlev (BINP)

12:40 Numerical simulation of plasma parameters for ALIANCE project by DOL code

An international mega-science project named ALIANCE (Axisymmetric LInear Advanced Neutron sourCE) was jointly initiated by INEST CAS and BINP RAS. It is aimed at the development of fusion volumetric neutron sources based on the GDT concept of plasma confinement. The report reviews the results of numerical simulations of plasma parameters for ALIANCE project done by DOL code. Three devices are considered within the project. The first one will demonstrate the continuous confinement of deuterium plasma in linear device sustained by injection of neutral beam with relatively low power of 0.1 MW. The injection power will rise up to 2 MW in the second device, while the third one will confine D-T plasma heated by the neutral beams with a power of 50 MW. Neutron yield for these devices is expected to reach $4{\cdot}10^{9}$ 1/s and $5{\cdot}10^{13}$ 1/s of D-D neutrons for the first two devices, respectively, and $10^{18}$ 1/s of D-T neutrons for the last one.

Speaker: Dr Vadim Prikhodko (Budker Institute of Nuclear Physics)

13:00 → 14:25 Lunch

14:25 → 16:05 GDT: resent results of studies in support of the ALIANCE project

Convener: Prof. Yican Wu (Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences)

14:25 Axial confinement of electrons in mirror trap with expander divertor

Axial confinement of electrons in mirror trap was studied. The formation of electrostatic potential in expander divertors was examined. The numerical simulations was used to verify the theoretical estimations. The influence of secondary emission of cold electrons from end plate on plasma confinement was studied.

Speaker: Dr Dmitriy Skovorodin (BINP)

14:45 Axial plasma confinement in open magnetic trap - experiments on GDT

The presented work is part of the fundamental research on the implementation of a controlled thermonuclear reaction in open-type magnetic traps. The interest in such systems is defined by the development of powerful neutron sources, which are necessary, in particular, to control hybrid fusion-fission reactors, and, with further development, the creation of purely fusion reactors for energy production. The main parameter from the applications point of view is the energy efficiency of the system, which rapidly increases with increasing of electron temperature. One of the factors limiting the electron temperature is the high thermal conductivity of the plasma along the magnetic field lines, which is determined by a number of complex kinetic processes in the expanders — regions of the expanding magnetic flux behind the magnetic plugs. The main goal of the work is to study this loss channel in detail and determine conditions under which these losses could be suppressed to levels acceptable for thermonuclear applications of mirror magnetic traps. All the experiments were performed on GDT [1] device in Budker Institute of Nuclear Physics. In previous work [2] experimental results describing the electric potential in the Debye layer near the surface of the plasma absorber and the average electron energy along the longitudinal coordinate were presented. The present work is devoted to measuring of energy carried out from the trap by one ion-electron pair along the length of the expander using a set of probes namely pyroelectric bolometer and ion flux probe. This dependence on the residual gas density in the expander tank has also been investigated. These data will make it possible to complete the theoretical model currently being developed [3], which describes the kinetics of processes in the expander of mirror trap. 1. A. Ivanov and V. Prikhodko, Plasma Phys. Controlled Fusion 55, 063001 (2013). 2. E. Soldatkina, et al. Physics of Plasmas 24, 022505 (2017). 3. D. Skovorodin, Physics of Plasmas 26, 012503 (2019).

Speaker: Dr Elena Soldatkina (BINP)

15:05 Electron-cyclotron and electron-beam plasma startup

The report provides a review of research results aimed at developing a method for generating preliminary plasma in open type magnetic traps using ECR gas breakdown. This method has proven positively itself in a number of experiments with plasma heating by neutral beam and auxiliary ECR heating at the GDT device. In addition, the results of recent studies on the development of a method for generation a preliminary plasma using an electron beam injected through a magnetic mirror into a trap pre-filled with gas are presented. This method also showed high efficiency, while demonstrating ease of implementation and high reliability. The developed methods are compared with each other and with the traditional method for injecting preliminary plasma through a magnetic plug using an arc-type gas discharge source. The main conclusion of the work is that both recently developed methods can be effectively used in installations of the next generations based on ostrong textpen-type magnetic traps with a linear configuration.

Speaker: Dr Peter Bagryansky (Budker Institute of Nuclear Physics)

15:25 Diagnostic instrumentation for the next generation of GDT devices

Devices of the GDT type belonging to the next generation are being proposed for a vast range of scientific and technological applications, including fusion neutron sources, hybrid fission-fusion power plants and others. The next step GDT-like system is deemed as a large-scale installation sustaining plasmas with a significant fusion power generation in a stationary or long-pulse regime. The paper describes several new diagnostics and physical data acquisition and processing systems developed in the Budker Institute for forthcoming fusion plasma experiments. The combined diagnostic based on the motional Stark effect and laser induced fluorescence (MSE-LIF) inherits advantages of the spectral and polarimetric MSE versions to measure the magnetic field value and direction. The presented project of the MSE-LIF diagnostic at GDT is close to the final assembling and commissioning. The recently upgraded diagnostic of laser Thomson scattering at GDT has six spatial points for measurements of the electron temperature and density. The scattered light is analyzed by filter spectrometers of the innovative design using time-stretch digitizers. The planned second phase of the diagnostic enhancement is installation of the multi-pulse Nd:YAG laser for a sub-millisecond time resolution in every plasma shot. The paper discusses the development of series of data acquisition and analysis electronic devices for physical experiments. The instruments range from the compact isolated ADC with the optical fiber data link to the complete data collection and processing system for the vertical neutron camera (VNC) for the ITER project and similar large-scale machines with high radiation conditions.

Speaker: Dr Andrej Lizunov (Budker Institute of nuclear physics)

15:45 Divertor for steady-state GDT

An analysis is made of possibility of using a device topologically equivalent to a nonparaxial MHD stabilizer as a divertor for the projected ALIANCE source of fusion neutrons on the gas-dynamic trap, which should operate in a continuous mode. A side effect of adding a divertor to a linear trap is the expected improvement in plasma MHD stability, which was previously observed at TARA [Phys. Fluids 31 (1988) 2009] and HIEI [Fus. Tech. 39 (2001) 350] facilities. To assess the effect of MHD stabilization by a divertor, the article indicates a method for finding stability rings, and also calculates the degree of expansion of the plasma flux in the divertor. The analysis showed that a good divertor, which provides a high degree of expansion, cannot be a good MHD stabilizer, which provides a large margin of stability. The divertor configurations made up of two and three coils are studied, their advantages and disadvantages are described. The final part of the article presents the calculations of the magnetic field in an end cell with a superconducting divertor designed for the GDMT gas-dynamic multi-core trap project [Fus. Sci. Tech. 63 (2013) 46].

Speaker: Prof. Igor Kotelnikov (Budker INP)

16:05 → 16:25 Coffee

16:25 → 17:45 The use of neutron sources based on linear traps and related technologies

Convener: Prof. Zhibin Chen (Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences)

16:25 Assessment of Gas-dynamic Trap Magnetic Fusion for Space Propulsion

The space propulsion system of high performance is required for deep space exploration missions such as Mars and Jupiter exploration. The fusion propulsion system has excellent performance of ultra-high specific impulse, high specific power, and moderate thrust so that it can reflect their advantages in future manned and unmanned deep space exploration. In this paper, preliminary analysis has been conducted in order to investigate the technical requirements of a fusion propulsion system for the Earth-to-Mars mission. The analytic model based on the Williams assumption was adopted and solved using MATLAB. Key parameters such as specific impulse, specific power mission time, and payload ratio for Mars rendezvous missions were analyzed. The preliminary results through qualitative and quantitative analysis show that in order to arrive the Mars in one month with more than 10% of optimal payload ratio, the specific power in the range of 5-15kW/kg is more reasonable, and the specific impulse need to reach 10000 seconds for make full use of inherent advantage of fusion propulsion system, furthermore, the fusion propulsion system can operate in optimal condition in a wide specific power range (1-100kW/kg) at about 10000-20000 seconds. The future fusion space propulsion system can operate in different modes according to the actual mission requirements, the concept of fusion space propulsion system based on GDT can exhaust the high-temperature plasma easily to obtain moderate thrust with high specific impulse, due to its own linear structure. Meanwhile, compared with other fusion propulsion concepts, it has the advantages of simple and compact configuration, plasma steady operation, low technical difficulty, and construction cost, it is very suitable for deep space exploration. In this paper, the research development of GDT-based fusion space propulsion system is investigated, we also clear the key technologies required. the overall calculation and analysis can provide a certain reference for the development of the future fusion space propulsion system.

Speaker: Mr Jun Song (Institute of Nuclear Energy Safety Technology, CAS)

16:45 Medium Power Thorium Hybrid Plant with GDT-FNS for Long operation time.

The GDT-FNS medium-power hybrid thorium plant is an innovative nuclear fission-fusion facility constructively consisting of an assembly of hexagonal graphite blocks of a uniform design and a long magnetic trap for plasma confinement, which serves as a source of additional thermonuclear neutrons. The active zone of the analyzed hybrid plant consists of areas with different enrichment, contains units to control and management, as well as other spatially distributed components perturbing the system, which are affecting the criticality of the assembly and the evolution of the nuclear fuel composition. Research conducted as part of this work is aimed at solving two key problems. The first task is to study the effect of Pa-233 protactinium on the fulfillment of the condition k=const under conditions of excess reactivity + dk/k, which is created using "starting" fission nuclides, which is necessary for the reactor to operate in the first day at starting its operation. Another task is related to the modeling of neutron-physical parameters during long-term operation of the assembly in stationary and cyclically changing non-stationary operating modes. The results obtained in the course of solving the tasks set in the work will improve the safety of a hybrid thorium reactor with an elongated neutron source based on a magnetic trap in a long working cycle.

Speakers: Prof. Andrey Arzhannikov (Novosibirsk State University) , Prof. Igor Shamanin (National Research Tomsk Polytechnic Univ.)

17:05 The neutron field in a hybrid reactor operating with GDT-FNS in a pulse-periodic mode.

To study three-dimensional neutron flux and heat generation fields in a reactor facility with a modified axial region operating in a subcritical mode with thermonuclear neutrons generated by an extended plasma neutron source, a computational model has been developed under utilizing a Serpent-Prizma program code. The studies are conducted for a radially profiled reactor core consisting of areas with different composition of nuclear fuel and containing elements of control and management of sub-criticality. The evolution of the sub criticality of the assembly and the nuclide composition of nuclear fuel is studied as well as the influence of these factors on the nuclear and technological safety of a hybrid system is analyzed when operating in a pulse-periodic mode.

Speaker: Dr Vladimir Shmakov (All-Russian Research Center VNIITF)

17:25 The dynamics of energy release in a hybrid reactor operating with GDT-FNS in a pulse-periodic mode.

Results of our studies of the dynamics features of energy release in a hybrid thorium reactor facility with an extended neutron source based on a long magnetic trap are presented in the paper. In the studied configuration of the active zone, a high-temperature plasma column is formed in a pulse-periodic mode, and with certain combinations of the “thermonuclear combustion” pulse duration and duty cycle. We should expect the formation of the fission reaction that is diverging from the axial part of the system and spreading over the volume of the fuel assembly (blanket) in the radial direction. In such conditions, in order to level the resulting offset of energy release, there is a need to optimize the fuel composition of the assembly in order to achieve most appropriate radial distribution of physical parameters. The studies are carried out on the basis of a full-scale model of the reactor core in which axial region is modified by a long magnetic trap operating with plasma as the source of fusion neutrons.

Speaker: Prof. Igor Shamanin (National Research Tomsk Polytechnic Univ.)

Tuesday, 19 November

08:30 → 08:45 Transfer

Bus from the «Golden Valley» hotel to the Budker INP main bldg

09:00 → 11:10 Development of the basic technologies for the ALIANCE project

Convener: Dr Alexander Ivanov (Budker Institute of Nuclear Physics)

09:00 Minimum B mirror trap with guiding center motion on magnetic surface

A properly shaped quadrupolar mirror magnetic field, in combination with a controllable weak radial electric field, is predicted to force each guiding center to move close to its mean magnetic surface. A neoclassical increase of radial transport would then be practically eliminated. The radial electric field may be controlled by biased end plates placed at the end tank outside the confinement region where the magnetic field lines intersect. A radial invariant, the radial Clebsch coordinate of the gyro center, can be used to derive Vlasov equilibria with a finite plasma beta. The minimum B property of the trap is a strong indicator of MHD stability. For a magnetic field ended by two expanders, magnetic field shaping is made aiming at minimum drift and ellipticity. The corresponding magnetic field can be reproduced by superconducting coils up to a mirror ratio of 4 or somewhat higher. Mirror ratios exceeding 10 may be reachable with finite beta effects included. Analytical expressions in closed form are derived. The study addresses potentials for the concept as a fusion neutron source.

Speaker: Prof. Olov Ågren (Uppsala University)

09:45 Problems to be addressed in the development of steady state NBIs

To build-up and sustain a population of high energy ions of hydrogen isotopes in the GDT-based neutron sources, injection of a steady-state powerful focused neutral beams with energies up to 100 keV is required. Problems arising at update of the high power NBIs developed at the Budker Institute with a duration of up to 2 s to the stationary operation mode are discussed in the report. All the injector elements that operate under high heat loads or/and intense fluxes of energetic particles should be protected against those and water cooled to provide reasonable time between replacements and services. Here, the key problem is development of ion-optical systems with spherically formed electrodes operated in DC mode, which are most sensitive to these severe conditions. The RF plasma boxes of the ion sources require some redesign and optimization of Faraday screens to reliably protect the ceramic parts of plasma box exposed to plasma loads. Other elements of the injectors such as neutralizer, cryo-pumps, bending magnets, beam dumps should be also modified for operation in steady-state regime. For these injector elements the required modifications are quite straightforward. To increase the energy efficiency of the injectors, application of steady-state energy recuperator of the residual ions, which are deflected by the bending magnet, is very promising.

Speaker: Dr Vladimir Davydenko (Budker Institue of Nuclear Physics)

10:10 Continuously operated high performance vacuum-pumping systems for Gas-Dynamic Trap

Estimation shows that powerful Gas-Dynamic Trap operated for generating neutrons at continuous rate 1E18 1/s will release high particle flux (∼3E22 1/s of D/T mixture) out of confinement region. The vacuum vessel of the Gas-Dynamic Trap consists of central cylindrical confinement volume and two plasma expansion vessels. In order to sustain the adequate vacuum conditions in the expansion vessels (<0.04 Pa) a continuously operating pumping system has to be incorporated into their design. The required pumping speed for each expansion vessel is estimated as 750 m^3/s. In addition, the vacuum system has to remove selectively He atoms (∼1E18 1/s). The report considers possible variants of the neutron source vacuum system with respect to its reliability, safety and cost.

Speaker: Dr Alexander Krasnov (BINP)

10:30 Features of GDMT design relevant to the development of ALIANCE

Gas-dynamic multi-mirror trap (GDMT) is an ongoing project in development at Budker Institute of Nuclear Physics, which aims to demonstrate a leap in performance for linear axisymmetric magnetic plasma confinement systems and lay the groundwork for a full-scale development of fusion neutron sources (NS) based on gas-dynamic plasma confinement. As a multipurpose facility, GDMT is being designed to experimentally evaluate a number of concepts, which promise a dramatic improvement in plasma confinement in linear systems. Superconducting magnet system of GDMT consists of a confinement region with magnetic field strength up to 3 T which is terminated by either single high-field (up to 18 T) magnetic mirrors or advanced multi-mirror modules, which provide necessary plasma flux suppression. Owing to its modular design, the system length can change from 6 m for studies of high-β plasma regimes to several tens of meters to accommodate for NS studies with maximized confinement zone length and most advanced multi-mirror modules. The design goal is to build a modular superconducting magnet system, which enables an easy reconfiguration of the confinement zone and attachment of mirror sections, while being mechanically robust and cryogenically efficient. The report outlines the scientific program of GDMT and reviews the experimental possibilities it provides to study a set of problems that are most critical to accelerated development of practical volumetric fusion neutron sources.

Speaker: Dr Dmitry Yakovlev (BINP)

10:50 Numerical simulation of GDT-based neutron source in DCLC-stable regimes by DOL code

The paper devoted to simulation of neutron source based on gas-dynamic trap concept. DOL code was used as a main tool for numerical calculations. Stability against Drift-Cyclotron Loss-Cone (DCLC) and Double Hump (DH) modes is estimated according to [I.A.Kotelnikov, I.S.Chernoshtanov, V.V.Prikhodko. Electrostatic instabilities in a mirror trap revisited. Physics of Plasmas v. 24, p. 122512 (2017)].

Speaker: Dr Vadim Prikhodko (Budker Institute of Nuclear Physics)

11:10 → 11:30 Coffee

11:30 → 11:45 Group photo

11:45 → 13:00 Excursion

Excursion to the experimental facilities of the Budker INP

13:00 → 14:30 Lunch

14:30 → 16:00 Research activities aimed at magnification an energy efficiency of the ALIANCE

Convener: Prof. Igor Kotelnikov (Budker INP)

14:30 Diamagnetic confinement in axially symmetric traps

There is a possibility of enhanced plasma confinement in axially symmetric linear traps due to significant modification of equilibrium close to the upper beta limit. In general this type of equilibrium is highly unstable to ballooning modes while its low internal magnetic field may cause non-adiabatic particle losses. However, under special conditions these problems can be probably overcome. If achieved, the enhanced confinement in the diamagnetic "bubble" equilibrium may drastically improve fusion prospects of linear traps.

Speaker: Dr Alexei Beklemishev (Budker Institute of Nuclear Physics)

15:00 Numerical simulation of plasma equilibrium in a diamagnetic trap

The recently proposed diamagnetic confinement (DC) mode (diamagnetic “bubble”) is designed to increase plasma parameters in open traps due to a significant increase in confinement time. We constructed a numerical stationary model of the diamagnetic “bubble” equilibrium in an axisymmetric open trap. The theoretical model is based on the Grad-Shafranov equilibrium equation and plasma transport equation obtained within the resistive magnetic hydrodynamics (MHD) with isotropic pressure. Numerical solutions corresponding to the DC mode were found; they are in good agreement with analytical estimates. In particular, the equilibrium configurations of the future experiments, such as CAT (DC mode) and GDMT were calculated. The numerical algorithm also allows one to obtain the distribution of the diamagnetic field, which may help to optimize the position of the wall-stabilization plates. Applying this model, we investigated the effect of magnetic field corrugation on the equilibrium. It is shown that the vacuum field corrugation leads to a proportional corrugation of the "bubble" boundary if the period is small enough.

Speaker: Mr Mikhail Khristo (Budker Institute of Nuclear Physics)

15:20 Single-particle confinement in the diamagnetic trap

The collisionless dynamic of ions in the axisymmetric diamagnetic trap is discussed in the report. Smallness of magnetic field leads to non-conservation of magnetic moment of ions. It can results in chaotic movement and fast losses of ions. Two mechanisms allowing ions to confine in the trap unlimited time (if Coulomb collisions and instabilities are neglected): conservation of adiabatic invariant if magnetic field is smooth enough and so-called absolute confinement of ions having large azimuthal velocity. So there are different regimes of plasma confinement in the diamagnetic trap. This regimes and requirements to magnetic system of the trap are discussed.

Speaker: Dr Ivan Chernoshtanov (Budker Institute of Nuclear Physics)

15:40 The optimal scenario for the formation of high beta plasmoid

The formation of high beta plasma by means of neutral beam injection was studied. Energy balance was treated to obtain the scaling of threshold power of the beams required to form high beta equilibrium.

Speaker: Dr Dmitriy Skovorodin (BINP)

16:00 → 17:10 Excursion

17:10 → 17:30 Coffee

17:30 → 18:00 Final discussion

Convener: Dr Alexander Ivanov (Budker Institute of Nuclear Physics)

18:00 → 18:05 Conference closing