[en] Current trend of diagnostic instrument for large scale Tokamak is going in the direction to utilize integrated nonperturbative technology with 3-dimensional data processing. For the fusion grade plasma, i. e or high temperature and large plasma dimension, produced in the large Tokamaks the progress of such technology depends on the power of computers. Apparently these sophisticated non-intrusive diagnostic methods will be advanced in parallel with the development of future computer technology. We expect this advance will change the I and C concept in the next generation Tokamak working in the power reactor regime

[en] This paper describes the simulation of the global orbit feedback system using the singular value decomposition (SVD) method, the error minimization method, and the neural network method. Instead of facing unacceptable correction result raised occasionally in the SVD method, we choose the error minimization method for the global orbit feedback. This method provides minimum orbit errors while avoiding unacceptable corrections, and keeps the orbit within the dynamic aperture of the storage ring. We simulate the Pohang Light Source (PLS) storage ring using the Methodical Accelerator Design (MAD) code that generates the orbit distortions for the error minimization method and the learning data set for neural network method. In order to compare the effectiveness of the neural network method with others, a neural network is trained by the learning algorithm using the learning data set. The global response matrix with a minimum error and the trained neural network are used to the global orbit feedback system. The simulation shows that a selection of beam position monitors (BPMs) is very sensitive in the reduction of rms orbit distortions, and the random choice gives better results than any other cases. (author)

[en] Spin-polarized electrons have been generated from a GaAs crystal whose surface was coated with a NEA (negative electron affinity) layer. The electron polarization was measured using the Mott polarimeter. The work was done utilizing the photocathode test-stand in the Pohang Accelerator Laboratory. That stand was constructed to characterize GaAs photocathodes for use in PES (polarized electron source) development. The test-stand consists of a GaAs crystal, devices for NEA surface production, an electrostatic bend, and a Mott polarimeter. All components, except the polarimeter are contained in a extremely high vacuum (XHV) chamber that can provide a vacuum better than 5 X 10^-10 Torr. Circularly polarized photons are provided by a multi-color laser with quarter-wavelength plates. In order to have a clean surface on the GaAs crystal, which is essential for successful production of a NEA layer, we have adopted the method of hydrogen glow-discharge cleaning. With careful cathode cleaning and activation (NEA surface production), spin-polarized electrons are routinely generated with a quantum efficiency of 3.01 % and a polarization of 30.4 %.

[en] Identification and demining of landmines are a very important issue for the safety of the people and the economic development. To solve the issue, several methods have been proposed in the past. In Korea, National Fusion Research Institute (NFRI) is developing a landmine detector using prompt gamma neutron activation analysis (PGNAA) as a part of the complex sensor-based landmine detection system. In this paper, the Monte Carlo calculation results for this system are presented. Monte Carlo calculation was carried out for the design of the landmine detector using PGNAA. To consider the soil effect, average soil composition is analyzed and applied to the calculation. This results has been used to determine the specification of the landmine detector

[en] A prototype 5-GHz 500-kW CW klystron (model E3762 provided by Toshiba Electron Tubes and Devices Co. Ltd.) has been operating as the RF source for the lower hybrid current drive (LHCD) system in the KSTAR tokamak. A cavity design study is being carried out with a simulation code based on the main klystron’s operation parameters in order to investigate how the efficiency of the 5-GHz 500-kW CW klystron prototype can be enhanced. This is being done by simulating the klystron’s performances for various cavity parameters, including the number of cavities, the inter-cavity distance, and the cavity’s tuning frequencies. The simulation has been done with the FCI (field charge interaction) code aided by a matlab script for scanning input parameters. The initial set of scan parameters was obtained by benchmarking the E3762 klystron, and we are able to obtain optimized design parameters for a cavity system with better efficiency by adopting a multi-cell output cavity. However, the multi-cell output cavity is prone to self-oscillations due to the prolonged (several half RF periods) beam-field interaction along its multiple gaps. We have checked the feasibility of the optimization by evaluating the stability of the output cavity system. The stability is given by the ratio of a beam-loading conductance to the circuit conductance.

[en] Ion distributions in expanding collisionless sheaths of two-dimensional (2D) grid electrodes were studied by using XOOPIC (particle-in-cell) simulations when short pulses of negative high-voltage were applied to electrodes immersed in plasmas. 2D grid electrodes consist of a periodic array of cylindrical electrodes, and the opening ratio of the grid electrodes is defined by the ratio of the spacing between cylindrical electrodes to the periodic length of the grid electrodes. In this paper, we introduce a normalized ion distribution function in normalized coordinates, and it is shown by simulation that the normalized ion distribution function depends only on the opening ratio of the grid electrodes. When the opening ratio of the grid electrodes is fixed, the ion distribution in expanding sheaths can be easily found in various conditions using only a single run of a PIC simulation, and the computation time can be significantly reduced. (paper)

[en] The Pohang Neutron Facility, which is based on an electron linear accelerator, has been equipped with a new CAMAC data acquisition system consisting of a neutron-gamma separation circuit and a four-position sample changer for nuclear data production and for basic science experiments using neutrons. The system has been tested by measuring the neutron flux and the neutron total cross-sections of natural W and Ti samples with the ⁶Li-ZnS (Ag) scintillator by using the neutron time-of-flight method. The measured neutron total cross-sections are compared with other measured data and the evaluation data in ENDF/B-VI. The present measurements are in generally good agreement with other data and the evaluated data.

[en] Photocathode rf gun, the high-brightness electron source with extremely low emittance is highly required for future light sources such as X-ray free electron lasers (XFEL). The coupling hole between the waveguide and the cavity of a photocathode rf gun causes asymmetries in the rf fields at the coupler cell. The dipole and quadruple fields are the dominant sources of the transverse rf emittance growth. In the BNL Gun-III, the dipole field is reduced by adding a symmetric pumping hole at the opposite side of the waveguide coupling hole. The dipole field can be reduced further by adjusting the size of the pumping hole. However, the quadruple field cannot be suppressed by the single pumping hole. We have designed new rf cavity in which the quadruple field as well as the dipole one are suppressed. In this design, two additional pumping ports are placed at the 90deg positions with respect to the coupling hole and the pumping holes. Beam dynamics simulation for newly designed rf gun shows that the vertical transverse emittance is reduced by about 60% compared to the old one. (author)

[en] In the third generation light source, photon beam position stability is critical issue on user experiment. Generally photon beam position monitors have been developed for the detection of the real photon beam position and the position is controlled by feedback system in order to keep the reference photon beam position. In the PLS-II, photon beam position stability for front end of particular beam line, in which photon beam position monitor is installed, has been obtained less than rms 1μm for user service period. Nevertheless, detail analysis for photon beam position data in order to demonstrate the performance of photon beam position monitor is necessary, since it can be suffers from various unknown noises. (for instance, a back ground contamination due to upstream or downstream dipole radiation, undulator gap dependence, etc.) In this paper, we will describe the start to end study for photon beam position stability and the Singular Value Decomposition (SVD) analysis to demonstrate the reliability on photon beam position data.

[en] A major upgrade of KSTAR LHCD system to 4 MW is planned for 2021. The system will be composed of eight 5-GHz 500-kW klystrons, low loss transmission lines with oversized circular waveguides, and a passive active multijunction launcher. Circular TE₀₁ mode will be adopted for transmission lines longer than 50 m because it has extremely low loss in oversized waveguide, but mode converters from rectangular TE₁₀ to circular TE₀₁ mode are not easy to design. Mock-ups of two types of mode converters were developed. One is serpentine type, and the other is symmetric sidewall coupling type. The TE₀₁ mode purities were demonstrated by measuring the transmission efficiencies between two identical mode converters at various angles between symmetric planes. A sidewall coupling mode converter with a refined design, which showed better circular symmetry and higher transmission efficiency than serpentine type, is under fabrication for prototype. The prototype mode converter is calculated to have 99.5% transmission efficiency, with 0.16% diffraction loss and 0.35% resistive loss, according to the simulation.