Neutron emission in neutral beam heated KSTAR plasmas and its application to neutron radiography

KSTAR team,Kwak, J.G.,Kim, H.S.,Cheon, M.S.,Oh, S.T.,Lee, Y.S.,Terzolo, L. North-Holland ; Elsevier Science Ltd 2016 Fusion engineering and design Vol.109 No.1

The main mission of Korea Superconducting Tokamak Advanced Research (KSTAR) program is exploring the physics and technologies of high performance steady state Tokamak operation that are essential for ITER and fusion reactor. Since the successful first operation in 2008, the plasma performance is enhanced and duration of H-mode is extended to around 50s which corresponds to a few times of current diffusion time and surpassing the current conventional Tokamak operation. In addition to long-pulse operation, the operational boundary of the H-mode discharge is further extended over MHD no-wall limit(β<SUB>N</SUB>~4) transiently and higher stored energy region is obtained by increased total heating power (~6MW) and plasma current (I<SUB>p</SUB> up to 1MA for ~10s). Heating system consists of various mixtures (NB, ECH, LHCD, ICRF) but the major horse heating resource is the neutral beam(NB) of 100keV with 4.5MW and most of experiments are conducted with NB. So there is a lot of production of fast neutrons coming from via D(d,n)<SUP>3</SUP>He reaction and it is found that most of neutrons are coming from deuterium beam plasma interaction. Nominal neutron yield and the area of beam port is about 10<SUP>13</SUP>-10<SUP>14</SUP>/s and 1m<SUP>2</SUP> at the closest access position of the sample respectively and neutron emission could be modulated for application to the neutron radiography by varying NB power. This work reports on the results of quantitative analysis of neutron emission measurements and results are discussed in terms of beam-plasma interaction and plasma confinement. It also includes the feasibility study of neutron radiography using KSTAR.

Experiment and simulation of tearing mode evolution with electron cyclotron current drive in KSTAR

김경진,나용수,김민화,Y.M. Jeon,K.D. Lee,J.G. Bak,M.J. Choi,윤건수,S.G. Lee,S. Park,J. H. Jeong,L. Terzolo,D.H. Na,M.G. Yoo,KSTAR Team 한국물리학회 2015 Current Applied Physics Vol.15 No.4

The tearing mode (TM) plasma instability was observed in low confinement (L-mode) plasmas when non-axisymmetric magnetic perturbation (MP) was applied using external coils during 2011 campaign of KSTAR. Based on the collected information of the magnetic island location in a plasma, a discharge was designed for suppression of a (2,1) TM mode by adjusting electron cyclotron (EC) launcher angles to the estimated island position. Here, the (m,n) notation describes the poloidal mode number and the toroidal mode number of the TM, respectively. The discharge is analysed with experimental observations and numerical simulations. Mirnov coil (MC) arrays and electron cyclotron emission (ECE) are used for analysis of the island width and the location as well as the mode number. The EC deposition and its alignment with the island are estimated by X-ray imaging crystal spectroscopy (XICS) and ECE measurements. An integrated numerical system is employed for modelling of this discharge to analyse a temporal evolution of the mode activity by integrating plasma equilibrium, transport, heating and current drive, and the magnetic island evolution, in a self-consistent way. The effect of EC current drive is discussed by comparing with another TM discharge but without ECCD. Some possibilities for classifying this mode to neoclassical tearing mode (NTM) and stabilisation effect of ECCD are suggested based on the experimental observation and the simulation results.

Development and operation of fast protection for KSTAR

KSTAR Operation Research Team,Hong, J.,Lee, W.,Lee, T.,Han, H.,Han, S.H.,Park, K. North-Holland ; Elsevier Science Ltd 2016 Fusion engineering and design Vol.112 No.-

Protection for the Korea superconducting tokamak advanced research (KSTAR) is somewhat more complicated than for the previous tokomak generation. External reasons for this increased complexity are the initial and maintenance costs, and internal reasons relate to various characteristics of the tokamak and long pulse operation. KSTAR has two protection mechanisms: the device protection system protects damage to superconducting coils etc. from events within the other systems, and the fast protection system protects the internal vacuum vessel components against damage from heating and the long pulse plasma. The fast protection system initially contained the plasma control system (PCS), central control system (CCS), and the heating devices. In 2012, a fast interlock interface was implemented for PCS fail-safe. This detected the absence of plasma current using the diagnostic signals and discharge operation gate windows of the timing synchronized system (TSS), and activates the operation gates and heating stop from the CCS. Additional fast interlock logic was implemented to reduce damage to the plasma facing components (PFC) and other materials by overheating and improper operational state of heating systems after starting the discharge sequence. However, the fast interlock interface system has failed to protect the heating during PCS malfunctions since 2013. This paper introduces the KSTAR protection system, and describes the fast protection interface, with testing and operational results, then discusses future plans for a more effective and safer protection system.

(Review Article) Status of the KSTAR Project

KIM, Keeman,OH, Yeong-Kook,S. BAK, Joo,KWON, Myeun,LEE, Gyung-Su,KSTAR team, The 低溫工學協會 2006 低溫工學 Vol.41 No.5

<P>The KSTAR project was started in 1996 and conducted in three phases, the conceptual design phase (1996-1998), the R&D and engineering design phase (1998-2002), and the construction phase (2002-2007). The mission of the Korea Superconducting Tokamak Advanced Research (KSTAR) Project is to develop a steady-state-capable advanced superconducting tokamak for establishing a scientific and technological basis for an attractive fusion reactor. Since the KSTAR mission includes the achievement of a steady-state-capable operation, the use of superconducting coils is an obvious choice for the magnet system and the long pulse current drive and heating systems are also the important aspect of the KSTAR design features. The advanced tokamak aspect of the mission is incorporated in the design features associated with flexible plasma shaping, double-null divertor and passive stabilizer, internal control coils. All the major components are in the stage of the fabrication and assembly for the completion of the KSTAR construction in the year 2007.</P>

Fast Reciprocating Probe Assembly for the KSTAR

Bak, J. G.,Lee, S. G.,KSTAR project team WILEY-VCH Verlag 2006 CONTRIBUTIONS TO PLASMA PHYSICS Vol.46 No.5

<P>A fast reciprocating probe assembly (FRPA) that can scan a distance of up to 32.5 cm with a maximum speed of 1.7 m/s was fabricated to obtain the spatial profile of basic plasma parameters in the edge region of the KSTAR plasma during a plasma discharge of 20 s. The probe driving mechanism consists of two parts; first a slow movement driven by a servo motor system and then a fast reciprocating movement actuated by a pneumatic system. A performance test of the drive system, which is remotely controlled by a PC, was carried out. The prototype of the probe head for the KSTAR FRPA was fabricated as a modular type for easy replacement. It was installed in the fast injection probe assembly (FIPA) in the Hanbit magnetic mirror device, and a radial plasma parameter profile measurement was carried out. The performance test results of the drive system and the profile measurements using the probe head are presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

Measurement of the Electric Properties of the KSTAR CS Model Coil

Hirofumi Yonekawa,G. M. Moon,G. S. Lee,J. S. Bak,J. S. Kim,박갑래,K. W. Cho,박수환,W. S. Han,W. W. Park,Y. Chu,Y. J. Lee,Y. K. Oh,Y. M. Park,Y. S. Kim,KSTAR Team 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.2

The maximum current, the self inductance and the lap joint resistance of a split-pair superconducting pulse magnet were experimentally inspected. The pulse magnet mainly consists of two KSTAR central solenoid (CS) model coils, which are wound, continuous Nb₃Sn cable-in-conduit conductors (CICC) with Incoloy 908 jackets. The pulse magnet initially could not achieve its rated current over several days whereas the temperature of the magnet surfaces and coolant outlets stayed at 5 ~ 8 K. A training effect and a ramp rate limitation were suspected of being the cause at the beginning. However the magnet's supporting structure was found to have been exceedingly warm in that period, and the maximum current clearly corresponded to the temperature of the supporting structure. The self inductance of the pulse magnet was measured with an LCR meter at 0.1 ~ 1 kHz at room temperature, but the inductance was nearly double the design value. The self inductance was also measured by means of a decay time constant method at 5 K and, at values of current above 200 A, was found to be originally the same as the design value, however, it dynamically increased below that current. Supplemental calculation showed that the permeability of Incoloy 908 could have a detrimental impact upon the dynamic variation of the self inductance. The lap joint resistance was successfully obtained by measuring the voltage drops between two CICCs at 5 K. Another trial measuring the voltage drops between the two outer surfaces of the lap joint resulted in a nonphysical result that violated Ohm's law.

핵융합 디지털 트윈 기술과 V-KSTAR 개발

권재민(Jae-Min KWON),V-KSTAR 개발팀(V-KSTAR Development Team) 한국물리학회 2022 물리학과 첨단기술 Vol.31 No.4

Electric Probe Measurements at Edge Region During H‐Mode Discharges in KSTAR

Bak, J.G.,Oh, Y.S.,Kim, H.S.,Hahn, S.H.,Yoon, S.W.,Jeon, Y.M.,Xiao, W.W.,Ko, W.H.,Kim, W.C.,Kwak, J.G.,Woo, H.J.,Chung, K.S.,the KSTAR project team, WILEY‐VCH Verlag 2013 Contributions to plasma physics Vol.53 No.1

<P><B>Abstract</B></P><P>Electrical probe measurements are carried out at the scrape‐off‐layer (SOL) and divertor regions in order to investigate the characteristics of edge plasmas during H‐mode discharges in the Korea Superconducting Tokamak Advanced Research (KSTAR) device. Radial profiles of plasma parameters such as electron temperature T<SUB><I>e</I></SUB>, plasma density n<SUB><I>e</I></SUB>, and parallel flow velocity v<I><SUB>‖</SUB></I> are measured by using a fast reciprocating Langmuir probe assembly (FRLPA) at the SOL region. From the FRLPA measurements, it is found that the decay length of temperature λ<I><SUB>Te</SUB></I> and that of density λ<I><SUB>ne</SUB></I> are 2 <I>∼</I> 4 cm and 1 <I>∼</I> 3 cm, respectively. The magnitude of v<I><SUB>‖</SUB></I> near the last closed flux surface (LCFS) is 4 <I>∼</I> 15 km/s. The radial flux due to edge turbulence at the SOL region is investigated by using spectra analysis on electrostatic fluctuation levels such as ion saturation current Ĩ<I><SUB>is</SUB></I> and floating potential <TEX>$ \tilde{\rm V}_f$</TEX> obtained from the FRLPA measurement. The value of the flux is estimated as <I>∼</I> 10<SUP>20</SUP> particle m<SUP>−2</SUP> s <SUP>−1</SUP> near the LCFS. The poloidal distribution of the ion saturation current density j<I><SUB>is</SUB></I> is measured by fixed edge Langmuir probe array (ELPA) at the divertor region, and it is found that the positions of strike points from the ELPA measurement agree well with those reconstructed from the EFIT result using magnetic diagnostic data. From the spectrum analysis on the ELPA measurements at the divertor region during edge localized modes (ELMs) control in the H‐mode discharges, it is observed that the magnitude of <TEX>$ \tilde{\rm j}_{is}$</TEX>(<I>ω</I>) near strike point decreases when the ELMs are suppressed or mitigated (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)</P>

KSTAR 진공용기 시작품 제작관련 기술분석

조승연,김형섭,도철진,엄기원,윤병주,인상렬,임기학,임종연,조창호,정영수,허남일,KSTAR Team 한국진공학회 1999 한국진공학회 학술발표회초록집 Vol.- No.-

Surface Analysis of Plasma-Facing Components in Tokamaks

Suk-Ho Hong,KSTAR team 한국표면공학회 2012 한국표면공학회 학술발표회 초록집 Vol.2012 No.11