Damavand Tokamak Research Articles

Supercapacitors Based Power Supply Design for Toroidal Field Coil of Upgrade Damavand Tokamak

در این مقاله سیستم تأمین انرژی و تخلیه جریان در سیم‌­پیچ چنبره‌ای توکامک دماوند به منظور افزایش زمان میدان‌های مغناطیسی با هدف افزایش زمان ماندگاری پلاسما، طراحی و شبیه‌سازی شده است. در حال حاضر در این توکامک جریان سیم­‌پیچ چنبره‌ای دارای نیم سیکل سینوسی با مدت زمان ms 100 و پیک جریان kA 12 است که میدان مغناطیس تقریباً T 1/1 در مرکز چنبره تولید می‌کند و ناحیه تخت آن در حدود ms 20 می‌باشد که برای تشکیل و محصورسازی پلاسما استفاده می‌گردد. با هدف ارتقاء توکامک دماوند به منظور افزایش مدت زمان ماندگاری پلاسما به ms 200، ضروری است که سیستم‌های تأمین انرژی و کنترل مربوط به جریان سیم‌­پیچ‌های قطبی و چنبره‌ای جدید طراحی و ارتقاء یابد. برای رسیدن به هدف مذکور، در این مقاله سیستم تأمین انرژی اصلی بر پایه منابع انرژی ذخیره‌ساز ابر خازن با ظرفیت F21، ولتاژ تحمل V900 و چیدمان 7 شاخه سری، 8 شاخه موازی طراحی شده است. هم‌چنین جهت تأمین و تثبیت جریان سیم‌پیچ چنبره‌ای، مبدل چاپر با 7 ماژول موازی به همراه سیستم کنترل حلقه بسته با کنترل‌کننده هیسترزیس طراحی و شبیه‌سازی شده است. سیستم کلی قابیلت تأمین و تثبیت میدان مغناطیسی از محدوده 7/0 تا 2/1 تسلا با ریپل کم‌تر از %2/0 و مدت زمان ms 200 برای ناحیه تخت دارد. هم‌چنین سیستم شارژ بانک ابر خازنی بر اساس مبدل یکسوساز 12 پالسه و مبدل باک با روش جریان ثابت، طراحی و شبیه‌سازی شده است که نتایج مطلوبی را حاصل کرده است.

Modification of visible spectrometer of Damavand tokamak and study of plasma impurities

ناخالصی ­های پلاسما یکی از عوامل اتلاف انرژی محصور شده در توکامک‌­ها به شمار می‌­روند که از این منظر مطالعه و بررسی آن­ها در راستای حفظ پایداری پلاسمای توکامک و بهبود کیفیت محصورسازی امری ضروری خواهد بود. در این کار تحقیقاتی به منظور مطالعه ناخالصی‌­های پلاسمای توکامک دماوند، تکفام­‌ساز نوری موجود در آزمایشگاه توکامک دماوند به همراه یک آرایه خطی CCD در ساختار یک طیف‌سنج نور مریی به کار گرفته شد. سامانه طیف‌­سنج جدید توسط طول موج­‌های مشخصه یک لامپ جیوه کالیبره شده و در رژیم پلاسمای نرمال توکامک دماوند جهت ثبت و تحلیل تابش‌­های گسیلی در بازه طول موجی 7000 – 3000 آنگستروم مورد استفاده قرار گرفت. کم­ترین قدرت تفکیک ابزاری طیف‌­سنج حاصل در پهنای شکاف ورودی μm 50 در حدود A° 9/0 به دست آمد که برای تابش‌­های پرشدت پلاسمای هیدروژن نظیر Hα و Hβ به کار گرفته شد. برای مطالعه تابش‌­های حاصل از ناخالصی­‌ها با توجه به شدت پایین آن­ها از پهنای شکاف ورودی μm 100 و در نتیجه قدرت تفکیک A° 8/1 استفاده گردید. نتایج به دست آمده نشان داد که ناخالصی­‌های غالب در پلاسمای توکامک دماوند عبارتند از اکسیژن، نیتروژن و کربن که منشأ آن­ها عموماً از مولکول‌­های هوای به دام افتاده در دیواره محفظه خلأ و ادوات مجاور با پلاسما هستند و ناخالصی آهن نیز در نتیجه برهم‌­کنش پلاسمای داغ با لیمیتر و ادوات داخل محفظه خلأ تولید می‌­شود.

Design and simulation of the high efficiency ion source for Damavand NBI heating system

Neutral beam injection (NBI) is known as one of the important methods of plasma auxiliary heating and current drive in fusion reactors. Optimization of the ion sources, as one of the main components of NBI systems, with high current and minimum divergence, can be very effective in order to reach more optimal dimensions of NBI systems. A high efficiency ion source designed using a helicon plasma source for neutral beam injection system (NBI) of Damavand Tokamak. The extraction system has the ability to extract a positive hydrogen ion beam with the current and voltage of 7A and 4.5 kV, respectively. In this paper, an ion source with optimized helicon plasma and optimized beam extraction system is developed using the COMSOL software. All parameters, including RF power, magnetic field, gas pressure, antenna length, and RF frequency, for the production of helicon plasma and ion beam extraction system with optimal geometry are investigated in the most effective way, in order to reduce the beam divergence and beam current increment. Finally, the helicon plasma with density of 4.12×1018m−3, electron temperature of 2.8eV and hydrogen beam extraction system consists of three Accel-Decel grid, each grid with 280 apertures of 3.5mm diameter, has been designed for neutral beam injection system of Damavand Tokamak. This ion production system has an extractor grid with very large transparency (60%) and the minimum single beamlet divergence of 27 mrad.

Modeling and robust decentralized control system design for plasma current and position in Damavand tokamak

This paper presents a linear dynamic model for the current and position of plasma in Damavand tokamak (DT) based on the RZIP methodology. Experimental data shots of DT are employed to validate the model and to show its accuracy. Since there are uncertainties in the model parameters, a robust decentralized control system is designed by considering the interaction between the input-output channels. Robust proportional and proportional-integral controllers are designed to obtain robust closed-loop stability and performance based on the Kharitonov theorem. The simulation results of the closed-loop system in two scenarios are presented to show the effectiveness of the introduced control system.

Imaging of hard x-ray radiations using Gafchromic™ dosimetry film in Damavand tokamak

In the present study, a series of experiments were performed to study collisions of runaway electrons in the Damavand tokamak by imaging hard x-ray radiations, as one of the secondary effects of these electrons, using radiochromic films. For these experiments, GAFCHROMIC™EBT2 dosimetry films were selected due to their high resolution imaging capability. These instruments were installed in two strip and screen structures for one- and two-dimensional imaging in high-dose areas of the Damavand tokamak, and after irradiation on the device, the recorded data were extracted using a flatbed scanner. The results showed that in runaway discharges of the Damavand tokamak, if active plasma position control system is off, predominant collision of the runaway electrons column occurs with outer wall of the vacuum chamber. Also, the recorded images indicated that dimensions of temporary sources of hard x-rays in the Damavand tokamak are about 10 cm × 10 cm. Two-dimensional imaging in these experiments showed that toroidal field coils are exposed to significant hard x-ray radiations, making the use of radiation-sensitive diagnostic systems in this area questionable. The results obtained from measurements also indicated that the highest radiation dose in the Damavand tokamak is in the limiter region and reaches up to 300 mSv shot−1.

Fractional order Multiple Modeling for Plasma Vertical Position in Damavand tokamak

Fractional order Multiple Modeling for Plasma Vertical Position in Damavand tokamak

Optimal estimation of plasma boundary shape using magnetic probe measurements in Damavand tokamak

This paper introduces an optimal estimation methodology to estimate the boundary shape of plasma in Damavand tokamak (DT). The first step of the introduced methodology is determining an initial guess of the plasma center. An accurate initial guess of the plasma center can improve the performance of the boundary shape estimation. A methodology to find the best arrangement of filaments around the plasma center and their current values for different numbers of plasma filaments is introduced. The Tikhonov regularization method is used to estimate the current values of assumed filaments as an ill-conditioned linear least squares problem. The simulation results show that the Tikhonov has a better performance than the other regularization methods from the computation time and estimation error performance perspectives. In two circular and elongated scenarios, experimental datasets of DT are employed to show the effectiveness of the method.

Measurement of plasma current in Damavand tokamak using magnetic probes assembly as a discrete Rogowski coil

In this paper, the pickup coils assembly in vacuum vessel of Damavand tokamak is used as a discrete Rogowski coil. An important advantage of this approach is the insensitivity of discrete Rogowski coil to magnetic fields created by the external excitation and equilibrium coils. Three interpolation methods are compared to evaluate the magnetic field between pickup coils with experimental data. The lowest error for estimating current is obtained by piecewise quadratic interpolation method. Moreover, the sensitivity to magnetic noise of this approach is investigated by introducing statistical error. According to the results, this array can measure plasma current with considerably better accuracy than a continuous external Rogowski coil.

Investigation of Hydrogen Glow Discharge Cleaning Side Effects on Tungsten

Hydrogen glow discharge cleaning (H-GDC) is a routine conditioning procedure for the modern tokamaks and the future fusion machines, including ITER. Due to the low energy of hydrogen ions in glow discharge plasmas, the probability of any considerable damage to the plasma-facing components was mainly ignored. In this work, Tungsten, as the primary candidate for the plasma-facing materials in tokamaks, is considered for studies regarding effects of the H-GDC procedure on the material during a routine vacuum vessel conditioning in Damavand tokamak. After performing routine H-GDC using pure hydrogen, the formation of loosely attached nanostructured bundles (NSBs) on the surface of the tungsten samples was observed. The presence of the NSBs, which can be a source of dust, would be significant due to their possible effects on the functionality of the future fusion plasma devices. The NSBs are observed on the tungsten samples with the surface temperature of <370 K after 2.5–4 hours of hydrogen ion bombardment with incident energy of ≈120 eV and fluence of ≈(2–3.5) × 1022 m–2. The surface modifications of specimens exposed to H‑GDC were examined using a material probe experiment and several surface analysis techniques such as SEM, EDX, XRD, and ERDA. Therefore, the formation of loose nanostructures on the wall of plasma confinement vessels due to H-GDC draws attention to probable damaging effects of this phenomenon upon functionality and outcomes of tokamaks.

Time-Dependent Thermo-Electro-Magneto-Mechanical Analysis of the TF Coil in Damavand Upgrade Tokamak With Longer Pulse Operation

To reach a more efficient plasma operation, a new configuration is planned for Damavand tokamak toward a longer pulse scenario. The current pulses in the magnetic system will be ten-times extended. This introduces major thermal impacts on the toroidal field (TF) coils due to Joule heating in addition to electromagnetic loads. Each TF coil consists of a winding pack (WP) with epoxy-impregnated glass-mica tape enclosed in an aluminum case. In this work, the combined thermo-electro-magneto-mechanical behavior of the TF coil components is investigated in the long pulse operation. A computational fluid dynamics (CFD) model has been involved to simulate a water cooling in the TF coil using COMSOL. Therefore, the study involves various analyses on the Lorentz force density, thermal load due to the Joule heat, stabilized temperature, heat dissipation, stresses and strains, and TF deviation in vacuum vessel due to the TF coil deformation. Every shot introduces a rise in the temperature of the coil. Thus, depending on the cooling conditions, in a series of consecutive shots, the temperature reaches a limit which is crucial for the mechanical analysis. As a result, although the thermal stress on the WP is highly increased in every long pulse, the total stress (i.e., combined thermal-magnetic stress) decreases compared to the value in the presently short pulse operation. The total stress in the WP can be lower than its magnetic stress due to an increase in elasticity of the coil during the longer pulses, while this result is the opposite for the casing and the epoxy resin.

Conceptual design of 30 kW-NBI injector using a multi-cusp ion source for heating of D-shaped Damavand tokamak plasma

A conceptual design is presented for a neutral beam injection system using the parameters of Damavand tokamak plasma. The design is of a multi-cusp ion source, an efficient large-scale multi-aperture system, a high-energy beam neutralizer cell and a bending magnet for the Damavand neutral beam injector. It is shown that, when taking the tokamak parameters and the amount of beam absorption into consideration, the ion source must deliver an ion beam for which the critical energy, ion beam power and current are 4.5 keV, 30 ± 1.5 kW and 6.7 A, respectively. The extractor system has three electrodes, each with a radius of 35 mm, and 69 apertures, each with a radius of 3 mm, for extraction of a proton beam with a radius of 35 mm. The extractor transparency was 50%, magnetic fields near the ion source of electron emission and ion extraction areas was less than 0.0003 T, the ion source dead space thickness was 38.4 mm, acceleration gap was 6 mm and the optimum voltage of the extractor suppressor electrode was -2.5 kV. The results show that the neutralization efficiency increased with an increase in the outgassing flux, which is equivalent to a decrease in the neutralizer length at a fixed input flux rate. The maximum efficiency obtained was about 83% at an input flux rate of 37.5 sccm. Considering the hydrogen gas pressure and density in the charge exchange cell, this was compatible with the theoretical relation and the Damavand tokamak vacuum. Iron magnets, a steel transmission chamber and a deviation angle of 180° were considered. The uniform magnetic field along the path of the beam was 0.03 T, number of coils was 112 and the current of was 18.2 A.

Investigating different methods for calculating the lambda equilibrium parameter for the plasma column in the Damavand tokamak

In this paper, various methods of measurement and calculation of the lambda equilibrium parameter (Λ=βp+li2) have been studied and applied. The main purpose is comparing different methods to increase the accuracy of the lambda parameter calculation in the Damavand tokamak. Two general methods have been used to calculate the lambda parameter. The first method is based on the calculation of the external and internal fluxes of the plasma using the Grad-Shafranov equation. Because Damavand is a tokamak with an elongated cross-section and its profile is approximated to the ellipse, the solution of the first order flux due to Grad-Shafranov equation is used in the elliptic cylindrical coordinate system. Also the first order tangential and radial fields are calculated and then the lambda parameter is determined by comparing the values obtained from the analytic relations and the measurement data in cylindrical coordinate. In the second method, the lambda parameter has been calculated using Shafranov integrals and poloidal magnetic field’s expansions. Finally, by using the calculated lambdas for estimating the vertical position of the Damavand plasma, it was observed that the accuracy of the second method is highest.

Design and simulation of NBI heating system using high dense helicon plasma source for Damavand Tokamak

A neutral beam injection system by using standard COMSOL software is designed and simulated for plasma heating of small size Damavand tokamak. In context of theoretical model, the needed heat power for plasma heating of this tokamak to the specified temperature is estimated. The number of particles per second, power and energy of the neutral beam which is needed to reach the intended heat power are calculated. Based on these parameters, all sections of the neutral beam injection system such as the plasma source, the extractor, the accelerator, the neutralizer and the charge particles deflector system, are designed and simulated. A dense helicon plasma source, with nonuniform magnetic field configuration, is employed as a plasma source of the device. This helicon plasma source is designed and simulated according to the estimated parameters. Considering the beam optics and space-charge effects, an ion extractor system is simulated and designed for this device. This extractor system can extract an ion beam with current about 7.5 A. The simulation results show that a neutral beam with energy 4.45 KeV and particle current about 6.6 particle per second can be obtained from our designed NBI system. This neutral beam can heat the electrons of plasma to temperature 300 eV and ions to 150 eV. On the other hand, the results of the simulation indicate that our designed neutralizer system could neutralize about 90.58 percent of the initial input ions. In this context, the proper parameters (the neutral beam energy and power) of the NBI systems are calculated for heating of the electrons and ions of the plasma to temperature 1000 eV and 500 eV, respectively.

Identification of Damavand tokamak using fractional order dynamic neural network

The Damavand tokamak is a small size research machine for fusion-related studies. This paper is motivated by the need to create an accurate nonlinear subspace model that may be used for controller design. The system is identified based on a newly introduced Fractional Order Dynamic Neural Network (FODNN) optimized by evolutionary computation. The proposed method, owing to its rich structure, is appropriate for modeling of the complicated behavior of the plasma and its instability. In the proposed method, a Lyapunov-like analysis is used to derive a stable new learning rule for updating the proposed FODNN weights. To achieve optimal value for fractional order of the proposed FODNN, a Particle Swarm Optimization (PSO) is employed. The performance of the proposed identifier is verified by using experimental data and the results are also compared with the integer order dynamic neural network identifier. The results show that there is a bound for the “identification error” that vanishes to zero as time tends to infinity. Furthermore, the comparison of the results achieved by the proposed method and those of the integer order dynamic neural network depicts higher accuracy of the proposed FODNN.

Design and implementation of new control room system in Damavand tokamak

The aim of this paper is design and implementation of an up-to-date control room. The previous control room had a lot of constraints and it was not apposite to the sophisticated diagnostic systems as well as to the modern control and multivariable systems. Although it provided the best output for the considered experiments and implementing offline algorithms among all similar plants, it needed to be developed to provide more capability for complex algorithm mechanisms and this work introduces our efforts in this area. Accordingly, four leading systems were designed and implemented, including real-time control system, online Data Acquisition System (DAS), offline DAS, monitoring and data transmission system. In the control system, three real-time control modules were established based on Digital Signal Processor (DSP). Thanks to them, implementation of the classic and linear and nonlinear intelligent controllers was possible to control the plasma position and its elongation. Also, online DAS was constructed in two modules. Using them, voltages and currents of charge for the capacitor banks and pressure of different parts in vacuum vessel were measured and monitored. Likewise, by real-time processing of the online data, the safety protocol of plant performance was accomplished. In addition, the offline DAS was organized in 13 modules based on Field Programmable Gate Array (FPGA). This system can be used for gathering all diagnostic, control, and performance data in 156 channels. Data transmission system and storing mechanism in the server was provided by data transmitting network and MDSplus standard protocol. Moreover, monitoring software was designed so that it could display the required plots for physical analyses. Taking everything into account, this new platform can improve the quality and quantity of research activities in plasma physics for Damavand tokamak.

Study of runaway electrons using the conditional average sampling method in the Damavand tokamak

Some experiments for studying the runaway electron (RE) effects have been performed using the poloidal magnetic probes system installed around the plasma column in the Damavand tokamak. In these experiments, the so-called runaway-dominated discharges were considered in which the main part of the plasma current is carried by REs. The induced magnetic effects on the poloidal pickup coils signals are observed simultaneously with the Parail–Pogutse instability moments for REs and hard X-ray bursts. The output signals of all diagnostic systems enter the data acquisition system with 2 Msample/(s channel) sampling rate. The temporal evolution of the diagnostic signals is analyzed by the conditional average sampling (CAS) technique. The CASed profiles indicate RE collisions with the high-field-side plasma facing components at the instability moments. The investigation has been carried out for two discharge modes—low-toroidal-field (LTF) and high-toroidal-field (HTF) ones—related to both up and down limits of the toroidal magnetic field in the Damavand tokamak and their comparison has shown that the RE confinement is better in HTF discharges.

Identification of the plasma boundary shape and position in the Damavand tokamak

A series of experiments and numerical calculations have been done on the Damavand tokamak for accurate determination of equilibrium parameters, such as the plasma boundary position and shape. For this work, the pickup coils of the Damavand tokamak were recalibrated and after that a plasma boundary shape identification code was developed for analyzing the experimental data, such as magnetic probes and coils currents data. The plasma boundary position, shape and other parameters are determined by the plasma shape identification code. A free-boundary equilibrium code was also generated for comparison with the plasma boundary shape identification results and determination of required fields to obtain elongated plasma in the Damavand tokamak.

Application of poloidal beta and plasma internal inductance in determination of input power time of Damavand tokamak

In this study, magnetic measurement of poloidal fields were used to determine poloidal beta and plasma internal inductance of Damavand tokamak combination of poloidal beta and plasma internal inductance ( $$\beta _p+\dfrac{l_i}{2}$$ ), known as Shafranov parameter, was obtained experimentally in terms of normal and tangential components of the magnetic field. Plasma internal inductance and poloidal beta were obtained using parametrization method based on analytical solution of Grad-Shafranov equation (GSE) and compared with parabolic-like profile of toroidal current density approach for determination of the plasma internal inductance. Finding evolution of $$\beta _p+\dfrac{l_i}{2}$$ and plasma internal inductance. Finding poloidal beta (Shafranov parameter and internal inductance) and using energy balance equation, thermal energy and energy confinement were determined qualitatively in terms of poloidal beta during a regular discharge of Damavand tokamak.

Study of plasma equilibrium in toroidal fusion devices using mesh-free numerical calculation method

Plasma confinement using external magnetic field is one of the successful ways leading to the controlled nuclear fusion. Development and validation of the solution process for plasma equilibrium in the experimental toroidal fusion devices is the main subject of this work. Solution of the nonlinear 2D stationary problem as posed by the Grad-Shafranov equation gives quantitative information about plasma equilibrium inside the vacuum chamber of hot fusion devices. This study suggests solving plasma equilibrium equation which is essential in toroidal nuclear fusion devices, using a mesh-free method in a condition that the plasma boundary is unknown. The Grad-Shafranov equation has been solved numerically by the point interpolation collocation mesh-free method. Important features of this approach include truly mesh free, simple mathematical relationships between points and acceptable precision in comparison with the parametric results. The calculation process has been done by using the regular and irregular nodal distribution and support domains with different points. The relative error between numerical and analytical solution is discussed for several test examples such as small size Damavand tokamak, ITER-like equilibrium, NSTX-like equilibrium, and typical Spheromak.

Temporal and spatial evolution of runaway electrons at the instability moments in Damavand tokamak

The time and position behavior of runaway electrons at the Parail–Pogutse instability moments has been investigated using experimental observations in plasma current, loop voltage, the Hard X-ray (HXR) radiations, and 18 poloidal pickup coils signals received by data acquisition system simultaneously. The conditional average sampling (CAS) method was used to analyze the output data. Moreover, a filament current code was modified to study the runaway electrons beam movement in the event of instabilities. The results display a rapid drift of runaway beam toward the inner wall of the vacuum vessel and the collision with the wall components at the instability moments. The existence of the collisions in these experiments is evident in the HXR bursts which are considered as the main trigger for CAS Analysis. Also, the variation of HXR bursts with the toroidal magnetic field shows that the hard X-ray bursts drop with increase in the toroidal magnetic field and runaway electrons confinement quality.