Erosion yield of Ti from TiC-deposited graphite by hydrogen ion bombardment at high temperatures

Erosion yields of Ti atoms from a TiC-deposited graphite by bombardment with 1 keV hydrogen ion beam of various current densities at 900°C have been investigated by means of the Rutherford backscattering (RBS) technique. It has been observed that the sputtering yields for Ti atoms at 900°C are almost zero below a critical ion flux of 1 × 10¹⁵/cm²·s, compared with the sputtering yield of Ti atoms at room temperature which has been measured to be 1 × 10⁻²atoms/ion. No sputtering of Ti atoms observed at 900°C is explained in terms of self-sustaining coating of the TiC surface with segregated carbon layer. The condition for the self-sustaining coating is discussed.     

Calculation of Excitation Function of Some Structural Fusion Material for (n, p) Reactions up to 25 MeV

Fusion serves an inexhaustible energy for humankind. Although there have been significant research and development studies on the inertial and magnetic fusion reactor technology, Furthermore, there are not radioactive nuclear waste problems in the fusion reactors. In this study, (n, p) reactions for some structural fusion materials such as ²⁷Al, ⁵¹V, ⁵²Cr, ⁵⁵Mn and ⁵⁶Fe have been investigated. The new calculations on the excitation functions of ²⁷ Al(n, p) ²⁷ Mg, ⁵¹ V(n, p) ⁵¹ Ti, ⁵² Cr(n, p) ⁵² V, ⁵⁵ Mn(n, p) ⁵⁵ Cr and ⁵⁶ Fe(n, p) ⁵⁶ Mn reactions have been carried out up to 30 MeV incident neutron energy. Statistical model calculations, based on the Hauser–Feshbach formalism, have been carried out using the TALYS-1.0 and were compared with available experimental data in the literature and with ENDF/B-VII, T = 300 K; JENDL-3.3, T = 300 K and JEFF-3.1, T = 300 K evaluated libraries.     

Effects of External Resonant Fields on the Tokamak Edge Plasma Fluctuations

In this contribution, the effects of external resonant electric and magnetic fields on the tokamak edge plasma fluctuations have been investigated. For this purpose, the radial and poloidal electric fields and ion saturation current have been measured by two arrays of the Langmuir probes. An external resonant electric field was applied with the limiter biasing system. The biased electric voltage has been restricted to 0 < V _bias  < +320 and it has been applied with the limiter that is fixed in the r/a = 0.9. Moreover, the power spectra of particle flux Γ _r , Γ _p , Reynolds stress, coherency between E _p and I _s have been calculated. Fourier-based techniques have been employed to analyze the frequency of the Reynolds stress and particle flux. The results show that after positive biasing application (V _bias  = +200v), the Reynolds stress increases about 50 % while it doesn’t change remarkability after positive biasing with V _bias  = +320v. The Reynolds stress power spectrum confirms these results. The effect of positive biasing on Γ _r has been displayed a decrease about 60, 20 % by V _bias  = +200v, V _bias  = +320v respectively. Γ _p and I _s increase about 30 and 4 % in the present of biased (V _bias  = +200v) while they don’t change remarkability in another voltage. The power spectrum of Γ _r decreases about 15 and 10 % while the power spectrum of Γ _p increases about 80 and 20 % after positive biasing (V _bias  = +200v, V _bias  = +320v). Consequently, a better confinement obtained for biased with V _bias  = +200v. It means that, the magnitude of biased is important factor in modifying and control plasma turbulence. Also, results were compared with the effects of external resonant magnetic field.     

Spatial distribution of defects in ion-implanted and annealed Si: The RP/2 effect

Gettering of metal impurities in ion-implanted Si occurs midway between the surface and the projected ion range, R_P, after annealing at temperatures in the range of 700–1000°C and vanishes at higher temperatures. This phenomenon, called the R_P/2 effect, seems to be a common feature of ion-implanted and annealed Si. The gettering ability of the damage at R_P/2 is commensurate with or may exceed that of the damage at R_P. The defects around R_P/2 acting as gettering sites have not yet been identified by other analysis techniques. They are formed after ion implantation in the process of defect evolution during annealing and, probably, consist of small complexes of intrinsic defects (vacancies or/and self-interstitials).     

High-Beta Steady-State FRC Plasma Sustained by Rotating Magnetic Field with Spatial High-Harmonic Components

Field-reversed configurations (FRCs) driven by rotating magnetic fields (RMFs) with spatial high-harmonic components have been studied in the metal flux conserver of the FRC injection experiment (FIX). The high-harmonic RMF method has some unique features; (1) field lines of the RMF do not penetrate or cross the vessel wall, (2) selective penetration/exclusion of the fundamental/high-harmonic RMF component will result in a generation of effective magnetic pressure near the separatrix, which helps to keep the separatrix away from the vessel wall, (3) strong azimuthal non-uniformity of the RMF will cause the n = 4 deformation of the core FRC plasma, which will eliminate the destructive modes caused by the rotation of the plasma column. The RMF method with high harmonics will provide quasi-steady current drive of high-beta FRC plasmas without destructive n = 2 rotational mode and will be helpful in reducing the particle loss and thermal load when applied to the fusion core plasma.     

Gettering layer for oxygen accumulation in the initial stage of SIMOX processing

A cavity layer or nano-bubble layer introduced by He implantation before the oxygen implantation collects the implanted oxygen and increases the oxygen concentration. The average size and density of the oxygen precipitates formed in the initial stage of the separation-by-implanted-oxygen (SIMOX) process is conform with the size and density of the cavities pre-formed by He implantation and annealing. The gettering ability of the cavity layer for oxygen is directly related to the area of the internal surface of the cavities. A nano-bubble layer accumulates oxygen in a very narrow range occurring between the damage maximum, D_P, and the mean projected ion range, R_P. Such a nano-bubble layer is most efficient in oxygen gettering due to their larger area of the internal surface and the small size of the oxide precipitates initially formed at the bubbles.     

Defects remaining in MeV-ion-implanted and annealed Si away from the peak of the nuclear energy deposition profile

Damage has been observed in MeV-ion-implanted Si away from the maximum of the nuclear energy deposition profile, mainly around the half of the projected ion range, R_P/2. Cu gettering has been used for the detection of irradiation defects which are formed during annealing at temperatures between 700°C and 1000°C. This damage is primarily created by the implanted ions on their trajectory and consists of intrinsic defects remaining so small that they have not yet been resolved. These defects undergo a defect evolution during annealing which results in a decrease of the width of the damage layer with increasing temperature and prolonged time of the annealing.     

Effects of Resonant Helical Field on Plasma Internal Inductance in IR-T1 Tokamak

Measurement of plasma internal inductance is important in tokamak plasma experiments (plasma internal inductance relates to the plasma current profile). In this paper we present an experimental investigation of effects of Resonant Helical Field (RHF) on the plasma internal inductance in IR-T1 tokamak. For this purpose, four magnetic probes and also a diamagnetic loop with its compensation coil were constructed and installed on outer surface of the IR-T1 tokamak, and Shafranov parameter, poloidal Beta, and then the internal inductance determined. In order to investigate the effects of RHF on internal inductance, we measured it in presence and also in absence of different modes of the RHF (L = 2, L = 3, L = 2&3). Experimental results show that L = 3 mode can flat the plasma current and increase the plasma internal inductance.     

“Ultimate” Configurations of the L = 1, m = 13 Torsatron and the “VINT-20” Torsatron as a Possibility of Creating a Tandem Stellarator–Mirror Trap Hybrid System

The paper is concerned with numerical investigation of various magnetic configurations of a single-pole toroidal L = 1, m = 13 “ultimate” torsatron having a low aspect ratio A _h = 4.345 and the modulation factors (?0.23) ≤ α ≤ 0.71 (K = 1, β = 0) of the helix law ?mφ = θ?αKSinθ?βKSin2θ. The extremums of the basic properties of closed magnetic surfaces as functions of the coefficient α in the neighborhood of α ≈ 0.4, as well as the structures of the edge magnetic field (substructures of virtual current) and the separatrix have been first determined for the L = 1, m = 13 “ultimate” torsatrons and the “Vint-20” torsatron. Unusual positions of the separatrix X-points in the cross sections for 1/4- and 3/4- magnetic field periods have been identified. The formula that takes into account the modulation factor α of the helix law was first derived to determine the average vertical magnetic field on the geometrical axis of the torus.     

High efficiency gettering of Au in Si(1 1 1) by MeV C implantation

A study of MeV C implantation induced effects on gettering of Au (2.2 × 10¹⁵ cm⁻²), implanted into Si(1 1 1), has been carried out using Rutherford backscattering spectrometry. A 2 h anneal in Ar at 850 °C has been found to result in a gettering efficiency close to 55%. It increases beyond 80% with a further 2 h anneal at 900 °C. The C dose (0.3–1.5 × 10¹⁶ cm⁻²) dependence of Au gettering is also presented and discussed.     

Particle Trajectories and Energy Distribution from a New IEC Fusion Device: A Many-Body Approach

This paper reports the explorations on the particle dynamics, ion distribution, energy spectra and temperature in a new-designed inertial electrostatic confinement fusion device in case of low azimuthal magnetic field. The proposed design has six bar-sized cathodes at the vicinity of the central region and a central DC current-carrying bar injects a homogeneous azimuthal magnetic flux on the particles. The cylindrical device is simulated in the fully ionized Deuterium media. Following the 3D design of the chamber, the real-time simulations have been performed by the time integration of the electrical and magnetic forces. The model uses the many-body approach with the particle–particle and particle–chamber interactions. To implement the particle–chamber interaction, the finite difference method has been applied. Besides, the model includes reflection effects of particles from the electrically grounded chamber wall. According to the simulations, the particle trajectories exhibit complex fluctuations in the central region and nearby the chamber walls. The ion temperature has been calculated around T _i  = 35 keV for the source potential V = ?150 kV. In addition, the ion distribution indicates that 68 % of ions can be collected in the central region. According to the velocity distribution, there exists a double Gaussian distribution with a low velocity peak. In addition, nearly 61 % of ions stay in the energy scale between 2 keV ≤ E ≤ 39 keV. The averaged neutron rate is estimated as 5.96 × 10⁵ n/s.     

Analysis of titanium coatings deposited and exposed in macrotor and microtor

Metal coatings of Ti are vapor-deposited (200 A/day) in MACROTOR and MICROTOR during low temperature H₂-discharge cleaning and operated far away from the gettering threshold for plasma impurity control. Several methods of analysis (X-ray diffraction, ESCA, AES, SEM) show that after several months of deposition two major effects have an impact on the coating: (a) formation of a porous microstructure which enhances H₂,-gas trapping: (b) formation of Ti-hydride of a 100 Å crystallite size and with large microstrain present. Both effects are responsible for a mechanically and chemically unstable first wall. H/D-exchange and H-retention are affected most by the existing wall condition. These difficulties may be avoided by using a hot (≈400°C) liner.     

Measurement of Plasma Energy Confinement Time in Presence of Resonant Helical Field in IR-T1 Tokamak

Plasma energy confinement time is one of the main parameters of tokamak plasma and Lawson criterion. In this paper we present an experimental method especially based on diamagnetic loop (toroidal flux loop) for measurement of this parameter in presence of resonance helical field (RHF) in IR-T1 tokamak. For this purpose a diamagnetic loop with its compensation coil constructed and installed on outer surface of the IR-T1. Also in this work we measured the plasma current and plasma voltage from the Rogowski coil and poloidal flux loop measurements. Measurement results of plasma energy confinement time with and without RHF (L = 2, L = 3, L = 2 & 3) show that the addition of a relatively small amount of RHF could be effective for improving the quality of tokamak plasma discharge by flatting the plasma current and increasing the energy confinement time.     

2-D temperature distribution and heat flux of PFC in 2011 KSTAR campaign

KSTAR has reached a plasma current up to 630 kA, plasma duration up to 12 s, and has achieved high confinement mode (H-mode) in 2011 campaign. The heat flux of PFC tile was estimated from the temperature increase of PFC since 2010. The heat flux of PFC tiles increases significantly with higher plasma current and longer pulse duration. The time-averaged heat flux of shots in 2010 campaign (with 3 s pulse durations and I_p of 611 kA) is 0.01 MW/m² while that in 2011 campaign (with 12 s pulse duration and I_p of 630 kA) is about 0.02 MW/m². The heat flux at divertor is 1.4–2 times higher than that at inboard limiter or passive stabilizer. With the cryopump operation, the heat flux at the central divertor is higher than that without cryopump. The heat flux at divertor is proportional to, of course, the duration of H-mode. Furthermore, a software tool, which visualizes the 2D temperature distribution of PFC tile and estimates the heat flux in real time, is developed.     

Design and Simulation for Pre-amplifier of ITER Radial X-ray Camera

The radial X-ray camera, which is used to measure magnetohydrodynamic phenomenon and monitor edge localised mode events, is a key diagnostic system for physics studies in the international thermonuclear experimental reactor (ITER) tokamak. Considering the special requirements of physics measurements and spatial resolution, 144 detector channels are required. The board card of the pre-amplifier is designed to improve the integration, on which 16 signal channels have been integrated. In order to suppress the noise and improve the stability of the pre-amplifier, the target impedance analysis method is applied in the design of the power supply, the trans-impedance amplifier and a two-stage active low pass filter are applied in the design. Simulation with Cadence OrCAD and ANSYS SIwave has been adopted to optimize the characteristics of the pre-amplifier. A test of the pre-amplifier shows its good performance for ITER application. After optimization of the pre-amplifier, the band width is 270 kHz, the amplification is 10⁷ V/A, and the noise attenuation is ??30 dB, the noise of the pre-amplifier is reduced to 10 mV (noise of the power supply is included).     

Design a 10 kJ IS Mather Type Plasma Focus for Solid Target Activation to Produce Short-Lived Radioisotopes 12C(d,n)13N

A 10 kJ (15 kV, 88 μF) IS (Iranian Sun) Mather type plasma focus device has been studied to determine the activity of a compound exogenous carbon solid target through ¹²C(d,n)¹³N nuclear reaction. The produced ¹³N is a short-lived radioisotope with a half-life of 9.97 min and threshold energy of 0.28 MeV. The results indicate that energetic deuterons impinging on the solid target can produce yield of $ \langle y\rangle $  = 6.7 × 10^?5 with an activity of A = 6.8 × 10⁴ Bq for one plasma focus shut and A _ν  = 4 × 10⁵ Bq for 6 shut per mint when the projectile maximum deuterons energy is E _max = 3 MeV.     

Properties of Active Water Cooling Atmospheric Plasma Spraying Tungsten Coating

Tungsten coating was deposited onto an actively water-cooled oxygen-free copper substrate by atmospheric plasma spraying technique. The properties of the microstructure, porosity, microhardness and oxidation of the active water cooling atmospheric plasma spraying tungsten coating were characterized and measured. High heat load and thermal response tests using an electron beam facility have been carried out on the tungsten coated mock-ups under the water cooling condition. The heat flux is changed from 3 to 10 MW/m² under the condition that the water flow rate is 2.5, 2.0 and 1.5 m³/h, respectively. It is demonstrated that the mock-ups successfully withstood a heat flux of 15.5 MW/m² at steady state.     

Internal Magnetic Field Measurements in the TCSU RMF Current Drive Experiment

Detailed magnetic measurements of Field-reversed configurations (FRC) from the Translation Confinement Sustainment Upgrade (TCSU) experiment are presented. A two-axis probe inserted transversely at the axial midplane provides 24 independent measurements of B _z (r) and B _x (r). Two single-axis 29 channel probes provide axial profiles at the plasma edge. The B _x (r) field profiles, oriented to measure B_θ from the rotating magnetic field (RMF), provide details about RMF penetration into the FRC. B _z (r) profiles, when combined with the high beta nature of the FRC, interferometric density measurements, and assuming uniform temperature, yield radial density and pressure profiles. Time evolution of these profiles gives insight into plasma dynamics and the n = 1 (wobble) and n = 2 instabilities. Data from 123 and 172 kHz RMF frequencies is presented.     

Measurement of Plasma Poloidal Beta in Presence of Resonant Helical Field in IR-T1 Tokamak

Precise measurements of poloidal beta and internal inductance are essential for tokamak plasma experiments. In this paper we present an experimental investigation of effects of Resonant Helical Field (RHF) on the poloidal beta in IR-T1 tokamak. For this purpose, a diamagnetic loop with its compensation coil were constructed and installed on outer surface of the IR-T1 tokamak, and then poloidal beta measured. In order to investigate the effects of RHF on the poloidal beta, we measured it with and without introducing of different modes of the RHF (L = 2, L = 3, L = 2 & 3). Experimental results discussed.     

Study on reaction of 15-15Ti with fission products under various oxygen potential

ABSTRACT

The effect of oxygen potential on the Fuel-Cladding Chemical Interaction (FCCI) of 15-15Ti cladding material was studied in this paper. In the test, the materials have been exposed to simulated fission products at 600?C for 120 h under the oxygen potential in equilibrium with Mo/MoO₂ and Cr/Cr₂O₃.The general corroded depth was roughly 30 µm. Furthermore, the results also show that corroded depth on the cladding surface increase with the increase of oxygen potential. No intergranular attacks were observed, which might be caused by the absence of the high-temperature gradient. A single layer of CrTe is assumed to be formed under low oxygen potential, whereas cesium and oxygen may play an important role under high oxygen potential. Moreover, FCCI may impose a great threat to the integrity of China designed 15-15Ti material.