Edge localized modes (ELMs) in high-confinement mode plasmas were completely suppressed in KSTAR by applying n=1 nonaxisymmetric magnetic perturbations. Initially, the ELMs were intensified with a ...reduction of frequency, but completely suppressed later. The electron density had an initial 10% decrease followed by a gradual increase as ELMs were suppressed. Interesting phenomena such as a saturated evolution of edge T(e) and broadband changes of magnetic fluctuations were observed, suggesting the change of edge transport by the applied magnetic perturbations.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Deuterium-tritium reaction is the most promising one in term of the highest nuclear fusion cross-section for the reactor. So it is one of urgent issues to develop materials and components that are ...simultaneously resistant to high heat flux and high energy neutron flux in realization of the fusion energy. 2.45 MeV neutron production was reported in D-D reaction in KSTAR and regarded as beam-target is the dominant process. The feasibility study of KSTAR to wide area neutron source facility is done in term of D-D and D-T reactions from the empirical scaling law from the mixed fast and thermal stored energy and its projection to cases of heating power upgrade and DT reaction is done.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Achieving and sustaining long pulse and ultimately steady-state operation of a fusion reactor in terms of physics and engineering parameters beyond transient period is essentially one of key ...requirements in present non Deuterium Tritium (DT) discharge tokamaks. Since the successful long pulse operation for 25 s at the plasma current of 0.5 MA in 2013, the duration of the H-mode pulse length has been extended to over 70 s, which corresponds to a few multiples of the current diffusion time. In addition to long pulse operation, the plasma performance is enhanced further to high poloidal beta discharge. This characterizes a fully noninductive discharge longer than 12 s, and also achieves both ion and electron temperatures of over 5 keV simultaneously for a line-integrated electron density of 5 x 10¹⁹/m³ and the plasma current of 0.8 MA. Recently, KSTAR reported the long pulse operation beyond 1 min at the injected power of about 5 MW and the plasma current of ~ 0.5 MA. The normalized beta was about 1.5 and the total injected energy to the plasma reached to about 300 MJ. It is also shown that the bootstrap current fraction is about 40% so that sufficient conditions are met for 100-s operation in terms of physics requirements of fully noninductive state. The plasma-facing components overheating issues due to prompt ion loss in the low plasma current operation was overcome by enlarging the outer gap between the plasma and outer poloidal limiter. An advanced tokamak scenario via profile control would be achieved with the new 6-MW neutral beam injection-2, and it is expected that 100-s operation can be possible in a fully noninductive manner at KSTAR. However, a reliable and innovative steady-state heating and current drive source is strongly recommended for achieving the final goal of the KSTAR.
In this study, a 5.8 MW high voltage power supply was developed for two 1.2 MW klystrons to operate the upgraded KSTAR helicon current drive system. The developed power supply was configured to ...connect 180 pulse step modulator (PSM) modules using semiconductor switches connected in series to produce an output with a rating of −92 kV and 64 A for 300 s. To operate the klystron individually, the output of the cathode power supply (CPS) is divided into two high voltage switches (HVSs). The HVS not only operates as an individual switching, but also cuts off the energy from being transferred to the load within 5 μs in case of an arc or short circuit. At this time, the energy should be 5 J or less. The individual PSM of the power supply is controlled by optic shifting distributor controller, and the overall control and protection are controlled by the CPS controller. Currently, this power supply is installed at KSTAR, and has been tested up to the maximum voltage of −92 kV for performance verification. In addition, the arc energy blocking performance was verified through the wire burning test of HVS. Furthermore, an actual load test was conducted on one klystron installed for operation; an RF test was conducted up to −70 kV, and the maximum output was measured up to 620 kW
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In the 2015 Annual Plasma Campaign of the Korea Superconducting Tokamak Advanced Research (KSTAR), which mainly used neutral beam injection (NBI) as auxiliary heating, the yield by the ...Deuterium–Deuterium (D–D) fusion neutrons of 2.45 MeV energy from the KSTAR plasma was estimated to have reached about 1014 n/s. Apart from the primary goal, which is energy production by nuclear fusion, these fusion neutrons may be used in other applications such as aerospace, defense, material, and electronic component research and testing, as well as battery and fuel cell research in the fields of archeology and security. This is because the tokamak is huge and intense as a volumetric neutron source.
This work aims to investigate the feasibility of fast neutron imaging using the D–D fusion neutrons emitted from the KSTAR tokamak. For this work, we adopted a fast neutron imaging technique based on a CCD camera in combination with a fiber–optical scintillator (FOS). The first experimental results about the feasibility of fast neutron imaging obtained from the KSTAR Tokamak will be described in this paper.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A compact ICRF antenna (CIA) for KSTAR was developed.•Design method for the generalized conjugate-T was developed and incorporated in the design of CIA.•Optimization method for the impedance ...transformer was developed for the design of CIA.
For the high-power and long-pulse ion cyclotron range of frequencies (ICRF) heating of the KSTAR plasma, we developed the compact ICRF antenna (CIA). The target injection power of CIA is 2 MW for 300 s. In order to continue injecting the power into plasma even if drastic instantaneous changes occur in the plasma condition, such as ELM events, we adopted the internal conjugate-T method for the load resilience. Between antenna heads and the junction point, impedance transformers were inserted to satisfy the condition of conjugate-T in a limited space keeping the electric field on the transformer low enough. To reduce the risk of water leakage into the vacuum chamber, only the backsides of antenna heads are water-cooled in the in-vessel region.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract High-performance long-pulse plasma operation is essential for producing economically viable fusion energy in tokamak devices. To achieve such discharges in KSTAR, firstly, the rapid increase ...in the temperature of plasma-facing components was mitigated. The temperature increase of the poloidal limiter, especially, was associated with beam-driven fast ion orbit loss and the discrepancy of the equilibrium reconstructed with heated magnetic probes of signal drift. The fast ions lost to the poloidal limiter were reduced by optimizing the plasma shape and the composition of neutral beam injection (NBI). This nonlinear signal drift was successfully reduced by a new thermal shielding protector on the magnetic probes. Secondly, a lower loop voltage approach was implemented to reduce a poloidal flux consumption rate. A plasma current of 400 kA and a line-averaged electron density of ∼2.0 × 10 19 m −3 were chosen by considering the L – H power threshold, fast ion orbit loss, and beam shine-through power loss for low loop voltage in KSTAR. In addition, the application of electron cyclotron heating also helped maintain the plasma with low loop voltage (∼25 mV) by enhancing the NBI-driven current and achieving a high poloidal beta ( β P ) state. KSTAR has achieved a long pulse (∼90 s) operation with the high performance of β P ⩽ 2.7, thermal energy confinement enhancement factor (H 98y2 ) ∼ 1.1, and fraction of non-inductive current ( f NI ) ⩽ 0.96. Still, gradual degradation of the plasma performance has been observed over time in the discharges. In one of the long-pulse discharges, β P reduced by ∼18% over the time of ∼8 τ R (current relaxation time, τ R ∼ 5 s) and ∼1067 τ E,th (thermal energy confinement time, τ E,th ∼ 45 ms). The degradation may be closely associated with weak, yet growing, and persistent toroidal Alfvén eigenmodes and their effect on fast ion confinement.
•The plasma startup recipe and each component of auxiliary devices are checked to support the tokamak physics experiments.•This process will conduct regularly for each KSTAR campaign in the future.
...At the beginning of every KSTAR campaign, during the plasma commissioning period, a stable tokamak plasma operation condition is aimed to be established to support various physics experiments throughout the rest of the KSTAR campaign. To achieve this, considering the KSTAR's superconducting operation, the plasma startup recipe is confirmed, and every component of auxiliary devices for fuel, heating, and diagnostics must be checked. A robust plasma startup scenario has been secured at the beginning of every plasma commissioning period for all plasma experiments. Then, the commissioning work deals with the plasma shaping and the auxiliary devices for fueling and heating. As the last stage, the radial profile diagnostics are tested by moving the plasma boundary and varying the operating toroidal magnetic field for cross-validation in a dedicated session. This paper explains in detail the established routine process for plasma commissioning in the KSTAR campaign.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The confinement degradation of the energetic particles during RMP would be a key issue in success of realizing the successful energy production using fusion plasma, because a 3.5 MeV energetic alpha ...particle should be able to sustain the burning plasma after the ignition. As KSTAR recent results indicate the generation of high-performance plasma(βp∼3), the confinement of the energetic particles is also an important key aspect in neutral beam driven plasma. In general, the measured absolute value of the neutron intensity is generally used for to estimating the confinement time of energetic particles by comparing it with the theoretical value based on transport calculations. However, the availability of, but for its calculation process, many accurate diagnostic data of plasma parameters such as thermal and incident fast ion density, are essential to the calculation process. In this paper, the time evolution of the neutron signal from an He3 counter during the beam blank has permitted to facilitate the estimation of the slowing down time of energetic particles and the method is applied to investigate the fast ion effect on ELM suppressed KSTAR plasma which is heated by high energy deuterium neutral beams. Keywords: KSTAR, neutron, fast ion
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A prototype of a midplane passive active multijunction (PAM) antenna was fabricated for the lower hybrid current drive system of KSTAR. The antenna includes a PAM launcher, bidirectional couplers, ...power dividing components, and two RF windows. The RF characteristics of each component, such as the splitting ratio, phase shift, transmission, and reflection, were measured using a network analyzer. A taper adapter and matched load, which can be inserted into the active waveguide of the PAM mouth, were designed and fabricated for the phase shift and power coupling measurement. The maximum error and the standard deviation of measured phase shifts between adjacent active waveguides of the PAM were 6.5° and 2.28°, respectively. The design improvement of the mid-plane PAM launcher is suggested. Multiple round trips of the reflected field in a multijunction provides the advantage of lowering the reflection but, at the same time, it causes the deterioration of directivity and an increase of the electric field in the waveguide. Adding a hybrid splitter at the end of the multijunction structure reduces the reflection by redirecting the reflection to plasma as in multijunction, however, contrary to the multijunction, it does not switch the toroidal direction of phase progression and thus improves the antenna directivity. The directivity of the hybrid PAM increases by more than 10% and the reflection decreases to 1/3–1/100 in comparison with the prototype PAM.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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