Use of a subminiature storage ring in a weak-current regime

The use of a subminiature electron storage ring in the weak-current regime (I _b = 0.02 mA) as a source of coherent mm-range synchrotron radiation and a laboratory facility for studying electron scattering in a bunch is studied. The weak-current regime considerably simplifies the construction of a magnetic system and decreases the likelihood of the development of bunch instabilities. To make a more accurate assessment of some basic parameters of a subminiature storage ring, a calculation of the effective accelerating voltage was performed taking account of the transit factor of the rf-system cavity.     

Possible source of terahertz coherent synchrotron radiation based on an ultraminiature synchrotron

The possibility of using a weak-focusing ultraminiature synchrotron for generating stable coherent synchrotron radiation at wavelengths 0.5–5 mm is examined. An ultraminiature synchrotron has the following optimized working parameters: electron enegy E = 24 MeV, radius of curvature of the beam orbit R₀ = 0.01592 m, average working beam current I_work = 0.022 A, beam lifetime τ = 1000 sec, injection frequency f_inj = 0.1 Hz, number of bunches in a beam K = 1, and bunch length σ _L = 0.283·10⁻³ m. The use of a source greatly simplifies user access to stable coherent synchrotron radiation and expands the range of applications of this radiation. __________ Translated from Atomnaya énergiya,Vol. 101, No. 5, pp. 388–394, November, 2006.     

Calculation of the effective delayed-neutron fraction and prompt-neutron lifetime in IBR-2M

The main parameters of IBR-2M are presented: the effective delayed-neutron fraction β_eff and the promptneutron lifetime τ, calculated using the DORT two-dimensional multigroup neutron-transport compute code and the SCALE4 code with a system of multigroup nuclear constants. For a regular IBR-2M regime β_eff = 0.00216 ± 0.00007, τ = (6.5 ± 0.5)·10^–8 sec, the delay-neutron value γ = 0.980, the prompt-neutron decay constant in the critical state α = 3.5·104 sec^–1. The calculations showed that the effective delayed-neutron fraction for IBR-2M is identical, within the error limits, to the measured value for IBR-2, the prompt-neutron lifetime is approximately 5% longer (β_eff = 0.00216, τ = (6.2 ± 0.2)·10^–8 sec). It is shown that β_eff and τ increase somewhat as the IBR-2 core size increases in the radial direction.     

Medium-scale experiment with production of prototypical ~100 kg melt and an analysis of its interaction with concrete

The results of a medium-scale experiment in which a prototypical melt is produced by combustion of a chemically active substance in the course of the reaction 2Fe₂O₃ + 3Zr = 3ZrO₂ + 4Fe + 2840 kJ/kg in a ~6·10⁻² m³ concrete container are presented. It is shown that the ~100 kg melt, whose temperature is 2700–3200 K, so obtained produces heat fluxes 100–150 kW/m2 into the walls and bottom of the concrete container for ~10 min. The ablation of the walls of the concrete container was 2.5–3 cm at the completion of the experiment.     

<Superscript>243</Superscript>Am neutron fission cross section and resonance parameters

The SVZ-100 lead moderation time neutron spectrometer at the Institute of Nuclear Physics of the Russian Academy of Sciences was used to measure the fission cross section for ²⁴³Am in the neutron energy range E_n = 0.3 eV – 10 keV. The resonance fission integrals and the area and fission width of the resolved resonances were calculated. The properties of the intermediate-structure resonances were evaluated. The results were compared with existing data and recommended evaluations.     

Numerical Experiments on Soft X-ray Emission Optimization of Nitrogen Plasma in 3 kJ Plasma Focus SY-1 Using Modified Lee Model

The X-ray emission properties of nitrogen plasmas are numerically investigated using corona plasma equilibrium model. The X-ray emission intensities of nitrogen Ly _α , Ly _β and He _α , He _β lines are calculated. The optimum plasma temperature for nitrogen X-ray output is concluded to be around 160 eV. The Lee model is modified to include nitrogen in addition to other gasses (H₂, D₂, He, Ne, Ar, Xe). It is then applied to characterize the 2.8 kJ plasma focus PF-SY1, finding a nitrogen soft X-ray yield (Ysxr) of 8.7 mJ in its typical operation. Keeping the bank parameters and operational voltage unchanged but systematically changing other parameters, numerical experiments were performed finding the optimum combination of pressure = 0.09 Torr, anode length = 7.2 cm and anode radius = 2.58 cm. The optimum Ysxr was 64 mJ. Thus we expect to increase the nitrogen Ysxr of PF-SY1 sevenfold from its present typical operation; without changing the capacitor bank, merely by changing the electrode configuration and operating pressure.     

Design calculation of an epithermal neutronic beam for BNCT at the Syrian MNSR using the MCNP4C code

This article describes the design calculation of an epithermal neutronic beam for the boron neutron capture therapy at the Syrian MNSR by using the MCNP4C code and ENDF/B-V cross-section library. To produce a high flux of epithermal neutrons at the beam exit, the moderator/filter from Al, Cd, Fluental and Bi was used with Pb as reflector for neutrons along the beam. In addition, the Bi lined collimator with Li₂CO₃-PE and Pb at the end. The calculated beam parameters under 30.0 kW of reactor power at the beam exit are Ф_epi = 2.83 × 10⁸ n/cm² s, D_f/Ф_epi = 7.98 × 10⁻¹¹ cGy cm²/n, D_γ/Ф_epi = 1.70 × 10⁻¹¹ cGy cm²/n, Φ_epi/Φ_the = 0.05 and J_n⁺/Ф_n = 0.77. As well as, the calculated values of the advantage depth and advantage ratio are 7.51 cm and 3.49, respectively. If such beam was built into the Syrian MNSR the scientific applications of the reactor would increase.     

Results of the Inner Electrode Modification on the ZaP Flow Z-Pinch

The ZaP Flow Z-Pinch is a basic plasma physics experiment that uses sheared flows to stabilize an otherwise unstable configuration. The inner electrode is replaced with a larger version (15 cm diameter presently versus 10 cm previously). The goal of this modification is to increase temperature through increased adiabatic compression and to allow greater flexibility of neutral-gas injection through a greater number of gas-puff valves. Results are presented regarding the effect of neutral-gas injection characteristics and charge voltage on pinch stability. Increasing capacitor bank voltage and mass of gas injected increases stability and proximity to the machine axis. A four-chord HeNe interferometer is used to determine density at z = 0 cm and total temperature using magnetic field information from the z = 0 azimuthal array of magnetic probes. Total temperatures of 100–150 eV and densities of 2–3 × 10²² m⁻³ are calculated; temperatures are consistent with measured electron and ion temperatures.     

Gamma-ray attenuation method as an efficient tool to investigate soil bulk density spatial variability

The spatial variability of soil bulk density (ρ_b) was measured by using the volumetric ring method (VRM) and the gamma-ray attenuation method (GAM). Collimated radiation from 3.7 GBq of ²⁴¹Am was used to evaluate the soil mass attenuation coefficient and its bulk density. Circular lead collimators were adjusted and aligned between source (D = 1, 2 and 3 mm) and detector (D = 4.5 mm). Results of GAM for average ρ_b provided good agreement with the corresponding values obtained gravimetrically. Variations in bulk density for different collimator dimensions can be attributed to multiple scattering after photons interaction with soil, mainly for 3 mm collimator size. The best result of ρ_b by the nuclear technique was obtained when ρ_b represents an average of the measurements for collimators of 1 and 2 mm. Another cause for the differences in ρ_b by GAM and VRM is the heterogeneity of soil when the collimated beam can interact with stones or large air-filled holes or channels present in the sample. Therefore, the pattern of spatial variability obtained by VRM was confirmed by GAM for all collimator sizes. This result is a good indication that GAM can be used with success to analyze soil spatial variability.     

Plasma Focus Device as a Breeder of Proton to Produce Short Lived Radioisotope <Superscript>18</Superscript>F

In a plasma focus device, the nuclear fusion products are created through the thermal and non-thermal (beam-target) mechanisms. The beam target character of the pinched plasma is used to determine the yield of 3.02 Mev protons (when deuterium filling gas is used) at the optimized regime. For this situation, a combination of “moving boiler” model and a shock wave theory are employed. The numerical simulations for the production of the positron emitter nuclide, ¹⁸F (T _1/2 = 110 min; widely used in positron emission tomography), for two Mather type devices (NX2 and PF1000) show that, the rules of the drift velocity as well as the drive parameters have an high impact on the final yields.     

Stellarator-Mirror Based Fusion Driven Fission Reactor

The version of fusion driven system (FDS), a sub-critical fast fission assembly with a fusion plasma neutron source, theoretically investigated here is based on a stellarator with a small mirror part. In the magnetic well of the mirror part, fusion reactions occur from collision of an RF heated hot ion component (tritium), with high perpendicular energy with cold background plasma ions. The hot ions are assumed to be trapped in the magnetic mirror part. The stellarator part which connects to the mirror part provides confinement for the bulk (deuterium) plasma. Calculations based on a power balance analysis indicate the possibility to achieve a net electric power output with a compact FDS device. For representative thermal power output of a power plant (P _th ≈ P _fis = 0.5–2 GW) the computed electric Q-factor is in the range Q _el = 8–14, which indicates high efficiency of the FDS scheme.     

Dependence of Plasma Focus Argon Soft X-Ray Yield on Storage Energy, Total and Pinch Currents

Numerical experiments are carried out systematically to determine the argon soft X-Ray yield Y_sxr for optimized argon plasma focus with storage energy E₀ from 1 kJ to 1 MJ. The ratio c = b/a, of outer to inner radii; and the operating voltage V₀ are kept constant. E₀ is varied by changing the capacitance C₀. These numerical experiments were investigated on argon plasma focus at different operational gas pressures (0.41, 0.75, 1, 1.5, 2.5 and 3 Torr) for two different values of static inductance L₀ (270 and 10 nH). Scaling laws on argon soft X-Ray yield, in terms of storage energies E₀, peak discharge current I_peak and focus pinch current I_pinch were found. It was found that the argon X-ray yields scale well with \textY_\textsxr = 8 ×10 ^{- 11} \textI_\textpinch^4.12 {\text{Y}}_{\text{sxr}} = 8 \times 10^{ - 11} {\text{I}}_{\text{pinch}}^{4.12} for the high inductance (270 nH) and \textY_\textsxr = 7 ×10 ^{- 13} \textI_\textpinch^4.94 {\text{Y}}_{\text{sxr}} = 7 \times 10^{ - 13} {\text{I}}_{\text{pinch}}^{4.94} for the low inductance (10 nH), (where yields are in joules and current in kilo amperes). While the soft X-ray yield scaling laws in terms of storage energies were found to be as \textY_\textsxr = 0.05 ×\textE₀^0.94 {\text{Y}}_{\text{sxr}} = 0.05 \times {\text{E}}_{0}^{0.94} at energies in the 1–100 kJ region. The scaling ‘drops’ as E₀ is increased, and Y_sxr scales as \textY_\textsxr = 1.01 ×\textE₀^0.33 {\text{Y}}_{\text{sxr}} = 1.01 \times {\text{E}}_{0}^{0.33} at high energies towards 1 MJ for 10 nH at argon gas pressure of 1 Torr. The optimum efficiencies for SXR yield were found to be 0.00077% with a capacitor bank energy of 112.5 kJ for high inductance (270 nH) and 0.005% with a capacitor bank energy of 4.5 kJ for low inductance (10 nH). Therefore for larger devices, it may be necessary to operate at a higher voltage and use higher driver impedance to ensure increasing X-ray yield efficiency beyond the optimum values. As storage energy is changed the required electrode geometry for optimum yield is obtained and the resultant plasma pinch parameters are found. Required values of axial speed for argon soft X-ray emission were found to be in the range 11–14 cm/μs.     

Neon Soft X-Ray Yield Optimization from PF-SY1 Plasma Focus Device

Based on the consideration of that for operation of the plasma focus in neon, a focus pinch compression temperature of 200–500 eV (2.3 × 10⁶–5 × 10⁶ K) is suitable for good yield of neon soft X-rays (SXR), numerical experiments have been investigated on the plasma focus device PF-SY1 using the latest version Lee model code. The Lee model code is firstly applied to characterize the PF-SY1 Plasma Focus. Keeping the bank parameters and operational voltage unchanged but systematically changing other parameters, numerical experiments were performed finding the optimum Y _sxr was 0.026 J. Thus we expect to increase the neon Y _sxr of PF-SY1 from its present typical operation; without changing the capacitor bank and the electrode configuration merely by changing the operating pressure. The Lee model code was also used to run numerical experiments on PF-SY1 with neon gas for optimizing soft X-ray yield with reducing L ₀, varying z ₀ and ‘a’. From these numerical experiments we expect to increase the neon Y _sxr of PF-SY1 with reducing L ₀, from the present 0.026 J at L ₀ = 1600 nH to maximum value of near 26 J at an achievable L ₀ = 10 nH.     

Pinch Current and Soft X-Ray Yield Limitations by Numerical Experiments on Nitrogen Plasma Focus

The modified version of the Lee model code RADPF5-15a is used to run numerical experiments with nitrogen gas, for optimizing the nitrogen soft X-ray yield on PF-SY1. The static inductance L ₀ of the capacitor bank is progressively reduced to assess the effect on pinch current I _pinch. The experiments confirm the I _pinch, limitation effect in plasma focus, where there is an optimum L ₀ below which although the peak total current, I _peak, continues to increase progressively with progressively reduced inductance L ₀, the I _pinch and consequently the soft X-ray yield, Ysxr, of that plasma focus would not increase, but instead decreases. For the PF-SY1 with capacitance of 25 μF, the optimum L ₀ = 5 nH, at which I _pinch = 254 kA, Ysxr = 5 J; reducing L ₀ further increases neither I _pinch nor nitrogen Ysxr. The obtained results indicate that reducing the present L ₀ of the PF-SY1 device will increase the nitrogen soft X-ray yield.     

RF calculation and thermal-stress analysis of the ECRH launcher on EAST tokamak

EAST is a medium sized superconducting tokamak with major radius R = 1.8 m, minor radius a = 0.45 m, plasma current I_p ≤ 1 MA, toroidal field B_T ≤ 3.5 T and expected plasma pulse length up to 1000 s. An electron cyclotron resonance heating (ECRH) launcher for four-beam injection is being installed on EAST tokamak. Four electron cyclotron wave beams which are generated from four sets of 140 GHz/1 MW/1000 s gyrotrons will be injected into the plasma by the spherical focusing mirrors and plane mobile mirrors. The focusing mirrors are spherical to focus Gaussian beams after reflection. Four plane mobile mirrors independently steer continuously in the poloidal and toroidal direction controlled by motors. With the suitable distance between mirrors and appropriate focal length of focusing mirror, the beam radius in the resonance layer of plasma is 31.145 mm. The heat from plasma radiation and metal losses is loaded on the mobile mirror. In order to decrease the temperature and thermal stress, the inner equivalent diameter of water channels is 8 mm and the suggested water velocity is 4 m/s.     

Preliminary Design of Alborz Tokamak

The Alborz tokamak is a D-shape cross section tokamak that is under construction in Amirkabir University of Technology. The most important part of the tokamak design is the design of TF coils. In this paper a refined design of the TF coil system for the Alborz tokamak is presented. This design is based on cooper cable conductor with 5 cm width and 6 mm thickness. The TF coil system is consist of 16 rectangular shape coils, that makes the magnetic field of 0.7 T at the plasma center. The stored energy in total is 160 kJ, and the power supply used in this system is a capacitor bank with capacity of C = 1.32 mF and V _max = 14 kV.     

CFD code application: calculating heat transfer in a reactor with supercritical parameters

Thermohydraulic calculations of isolated and communicating cells of a rod bundle were performed by the channel method for CANDU-X fuel assemblies and by a three-dimensional method. It was established that in solving the problem for the tightest cell in the case q = const the azimuthal nonuniformity of the temperature was found to decrease by 77°C but it too was inadmissibly large. The temperature distribution along the surface of a fuel element in the case q = const was found to be different from the solution of the adjoint problem. A region with elevated coolant temperature, impeding heat exchange between two neighboring cells, was found between two adjoining cells. It was found that to evaluate computational reliability an experimental study must be performed on rod assemblies with supercritical coolant parameters.     

Effect of Li3+ irradiation on the transport properties of La0.7Pb0.3MnO3 type CMR material

We report the low temperature (below the metal–insulator transition temperature T_im) resistivity and magnetoresistance (MR) behavior of 50 MeV Li³⁺ beam irradiated La_0.7Pb_0.3MnO₃ for three different fluences. Ion beam irradiation causes a decrease of T_im leading to the increase of insulating regime. Resistivity data of the unirradiated as well as irradiated samples fitted well with an equation of the form ρ = ρ₀ + ρ_2.5T^2.5 which indicates predominant contribution from the electron–magnon interaction (second term). The temperature dependent MR data of samples irradiated with different ion fluences follow the simple relation [MR = a + b/(T + C)] showing appreciable effect of radiation on the parameters a, b and C. The physical significance of the radiation effect on these parameters is not yet very clear.     

Spheromak Formation and Current Sustainment Using a Repetitively Pulsed Source

By repeated injection of magnetic helicity (K = 2φψ) on time-scales short compared with the dissipation time (τ_inj << τ _K ), it is possible to produce toroidal currents relevant to POP-level experiments. Here we discuss an effective injection rate, due to the expansion of a series of current sheets and their subsequent reconnection to form spheromaks and compression into a copper flux-conserving chamber. The benefits of repeated injection are that the usual limits to current amplification can be exceeded, and an efficient quasi-steady sustainment scenario is possible (within minimum impact on confinement). A new experiment designed to address the physics of pulsed formation and sustainment is described.     

MHD Properties of Low-aspect Ratio RFP in RELAX

The low-aspect-ratio (A) reversed field pinch (RFP) offers attractive properties such as enhanced bootstrap current and simpler MHD mode dynamics. The RELAX (REversed field pinch of Low-Aspect ratio eXperiment) machine with the world’s lowest A of 2 (R/a = 0.5 m/0.25 m) has been constructed to explore the RFP properties in low-A regime. In flat-topped low-A RFP discharges in RELAX, plasma current of ~50 kA has been attained with discharge duration of ~2 ms. In round-topped discharges with plasma current of ~70 kA, quasi-periodic growth of a single helical mode has been observed. When the dominant m = 1/n = 4 mode grows, the toroidal mode spectrum looks like that of the quasi-single helicity (QSH) RFP state with higher amplitude. MHD equilibrium analyses using a reconstruction code have shown that the bootstrap current fraction is lower than ~5% in the present RELAX plasmas, and it will be ~25% if we could achieve the plasma density of 4 × 10¹⁹ m⁻³ and electron temperature of 300 eV at plasma current of ~100 kA.