- Email: [email protected]
Deployment of multiple shattered pellet injection systems in KSTAR
Fusion Engineering and Design 154 (2020) 111535
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Deployment of multiple shattered pellet injection systems in KSTAR a,
a
b
b
a
SooHwan Park *, KunSu Lee , Larry R. Baylor , Steven J. Meitner , HyunMyung Lee , JaeIn Songa, Trey E. Gebhartb, SangWon Yuna, Jayhyun Kima, KwangPyo Kima, KapRai Parka, SiWoo Yoona a b
T
National Fusion Research Institute, Daejeon, Republic of Korea Oak Ridge National Laboratory, TN, USA
ARTICLE INFO
ABSTRACT
Keywords: Plasma Disruption Mitigation Shattered Pellet
Shattered pellet injection is of the most attractive way to mitigate the plasma disruption in fusion research facilities up to now. DIII-D has already utilized it and achieved very positive results. ITER has decided to adopt this technology for the DMS (disruption mitigation system) for PFPO-1 (Pre-Fusion Power Operation phase 1). The validation between simulation code and experiment, and continuous engineering development need to be carried out to meet the DMS’s requirement and reliability. KSTAR (Korea Superconducting Tokamak Advanced Research) is a possible candidate to test the urgent issues of plasma disruption for ITER. KSTAR can install two injectors in toroidal opposite positions. For this work, ORNL (Oak Ridge National Laboratory) will provide the two injectors, the shatter tubes and auxiliary systems. NFRI (National Fusion Research Institute) is preparing the infrastructure of a pumping system, control and data acquisition system, and arranging the location of diagnostic and the heating systems. This presentation describes the basic requirements and the engineering challenges to be solved for successful deployment and operation of multiple SPI injectors in 2019.
1. Introduction The plasma disruption is one of the urgent issues in ITER now. The way to protect the machine from this is that a large increase of plasma density during disruption can lower the plasma temperature and decrease effects of thermal damage during thermal quench (TQ). Particles must also penetrate into the current channel during the current quench (CQ) to prevent runaway electron (RE) formation. If runaway electrons form, then material can be injected to stimulate collisional dissipation [1]. There are several ways to increase the density and mitigate disruptions. First, gas injection is possible to provide large amount of gas by using fast valves. Second is pellet injection which forms and accelerates the solid and intact pellets into the plasma. And a third more favorable approach is solid particle injection using shattered cryogenic pellets. In ITER, large thermal loads can occur during the TQ [2] and large mechanical loads are also concentrated on plasma facing components (PFC) and vacuum vessel (VV) during the CQ. The decay time of the CQ must be controlled within limits of 50 ∼150 ms. REs can be generated during the CQ and any resulting RE current must be suppressed or
⁎
dissipated to less than 2 MA. It is necessary to radiate more than 90 % of thermal energy to protect the first wall because of potential radiation asymmetry. Excessive radiation peaking can result in melting of Be PFCs. Dissipation and control of REs is possible by high-Z impurity injection during CQ formation of REs. In the initial design for ITER, the candidates of mitigation were the massive gas injection (MGI) and the shattered pellet injection (SPI). The shattered pellet injector (hybrid SPI/MGI) was located in 3 upper ports to shatter pellet near plasma edge. SPI has multiple- barrels for redundancy and adjusting amount injected. Multiple-barrel SPI was located in 1 equatorial port for runaway electron mitigation. The SPI has benefits over MGI such as assimilation efficiency, deeper penetration and easier implementation to ITER than MGI through the experiments and simulations [3–5] so it has been considered as the technology for the DMS now. The recent decision of DMS configuration is below in Fig. 1. Pre-TQ by Ne and D2 injection from upper and equatorial ports is for thermal load mitigation (TQ and CQ), electromagnetic load mitigation (CQ) and RE avoidance (TQ). Post-TQ by Ar or Ne injection from equatorial ports is for runaway energy dissipation (CQ). Post-TQ by Ne (+D2) injection
Corresponding author. E-mail address: [email protected] (S. Park).
https://doi.org/10.1016/j.fusengdes.2020.111535 Received 22 September 2019; Received in revised form 3 February 2020; Accepted 3 February 2020 0920-3796/ © 2020 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 1. Equatorial and upper ports in ITER [6].
from upper ports is for thermal load mitigation (CQ), electromagnetic load mitigation (CQ) and runaway electron avoidance (CQ) [6].
barrel even though the pellet velocity is decreasing. The pellet from exit of shatter tube was viewed by the fast camera. All of the species of pellets were tested in this geometry and found to result in suitable fragmentation [7].
2. Shattered pellet injection 2.1. Pipe-gun pellet injector
3. SPI system in KSTAR
The pipe-gun uses liquid helium (LHe) or cryocooler (ex. GiffordMcMahon refrigerator) to form a pellet in situ in a stainless steel (STS) barrel. Gas is supplied into the STS barrel and then it starts to freeze where the cold block is attached. A fast propellant gas valve is pulsed to release high pressure gas behind the formed pellet that accelerates it out of the barrel into the injection line to the plasma [7].
3.1. Multiple injections It is important to determine the effectiveness of multiple pellet injections to achieve radiation symmetry and RE avoidance with optimum TQ, and a suitable CQ duration according to the recent ITER research plan. To extrapolate from different sizes and plasma parameters to ITER, at least two injectors toroidally well separated are needed. Up to now, most other SPI systems were installed as single injector or multiple injectors with asymmetric locations. KSTAR has become a first test bed for symmetric multiple injections even though it was difficult to find suitable symmetric location for two identical injectors.
2.2. SPI for other tokamaks The 3-barrel SPI concept was originally proposed for ITER DMS. Such a system called SPI2 was installed on DIII-D in 2017 and initial experiments are under way [8]. 3 pellets from each barrel can be injected together or serially depending on the purpose. 3-barrel SPI2 on DIII-D is mounted horizontally above a mid-plane port and is cooled from a LHe dewar near the injector [9]. JET now also has an SPI system based on SPI2 design [10]. The pellet size is limited to 12.5 mm. Major difference is tritium compatibility, so more strict regulations are required than DIII-D, but it will be a good reference for ITER. The 3-barrel SPI of JET can make different sizes of pellet. The pellet is formed by pure D2, Ne, Ar or the mixture of D2 and Ne. The pellet can be injected independently and accelerated 100 ∼ 250 m/s (max800 m/ s with D2). The total flight time is between 20 and 50 ms and the arrival time from shatter tube exit to plasma edge is predictable less than 2 ms. A microwave cavity diagnostic can detect the pellet mass, velocity and intactness. The shatter tube for the SPI2 has a 20-degree bend that results in good collimation and the resulting fragments are too small to damage PFCs. KSTAR has chosen to implement this same shatter tube geometry. This shatter tube was tested at ORNL using argon pellets launched with a prototype mechanical punch because pure high-Z pellet has high shear strength and is difficult to fire with propellant gas pressure only. The mechanical punch helps to break the pellet free from the cold
3.2. Key parameters Duplication of the SPI2 design was chosen to reduce the cost and risk within restricted budget and time schedule [11]. It has 3 different size barrels for D2, Ne and Ar that can form and inject pellets individually (Fig. 2). Barrels can be quickly replaced for pellet size changes in a day. A mechanical punch can be added for injecting nonshell pellets (pure Ne and Ar) [12]. The cryocooler (Sumitomo RDK-415D) cools down the SPI system instead of LHe cooling. It is a new attempt for an SPI system however conventional fueling pellet injection systems already have adopt it. The cryocooler makes it more convenient to install and operate the SPI systems in KSTAR. Pellet formation is achieved by a barrel connection to the cold head of the cryocooler and then pellet is accelerated by the fast propellant gas valve with helium gas of 5 MPa. The injected pellet is transported to the plasma through the ∼10 m long external guide tube and an internal shatter tube. The end part of the shatter tube is changeable from inside of vacuum vessel for research flexibility so multiple tubes for fragment size variation are also available. The length of the shatter tube with bend just fits inside mid-plane 2
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 2. Pellet injector, cubes and guide tube (courtesy of L. Baylor).
Fig. 3. Shatter tube (green) and angle of pellet dispersion (beige) at G port (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).
port before touching the plasma. G port and O port are already occupied by an ECEI diagnostic housing and ECH waveguide frame respectively (Figs. 3 and 4). The shatter tube for G port could only be installed after disassembly of ECEI housing. All shatter tubes have already been installed at each port before reinstallation of ECEI and ECH components.
applied to protect the guide tubes in Fig. 6. The vacuum pumping system for guard vacuum chamber, cubes and guide tube is installed. This is a 2- stage differential pumping system (DPS) to prevent the propagation of the propellant gas into the tokamak because the propellant gas is an impurity to plasma and can reach the plasma before pellet and affect the SPI plasma interaction. The gas manifold with the valves and reservoirs provides the all of gas to the injector. The junction box contains terminals for the various signal lines from injector to the control rack. The control rack and DAQ system are ready to connect.
3.3. Deployment of SPI Two identical SPIs will be installed at KSTAR in 2019 (Fig. 5). The injector, pumping cubes, microwave cavity, guide tube, shatter tube and the related electronics are supplied from ORNL. For more stable installation, a rigid structure for the pellet injector and cubes are prepared. The guide tube can be damaged during assembly and disassembly of other equipment, so the tube support is
3.4. Commissioning at ORNL The commissioning of injector and shatter tube with 32 mm inner diameter was carried out at ORNL before delivery to KSTAR (Fig. 7).
Fig. 4. Shatter tube (green) and angle of pellet dispersion (beige) at O port (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.). 3
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 5. Multiple and symmetric injections in KSTAR.
out with pellets accelerated by only the fast propellant gas valve. This test shows that the 16.5 degree of dispersion angle from the center of the shatter tube is acceptable with other interference such ECEI, ECH and the inner liner. 4. Further works The first SPI has already been installed at O Port of KSTAR. Control and DAQ system (Fig. 8) will be connected to SPI and the junction box by the end of September. The PLC and HMI program are under development. Integration testing will be carried out with ORNL’s collaboration in early October 2019. The second SPI has been already assembled at ORNL. It is ready to ship to KSTAR and will be installed between the end of October and early November 2019. Single SPI experiments are planned at November and multi SPI experiments will be started at the end of 2019. For this experiment, bolometers based on toroidal filtered silicon absolute extreme ultraviolet (AXUV) Arrays (TFAA) and poloidal filtered AXUV arrays (PFAA) are installed at KSTAR and more diagnostic systems such as an infrared sensor-based fast bolometer, fast visible camera and compact dispersion interferometer are under development now [13].
Fig. 6. First SPI at O port of KSTAR.
CRediT authorship contribution statement SooHwan Park: Conceptualization, Investigation, Validation, Supervision, Writing - original draft, Resources. KunSu Lee: Software, Visualization, Investigation. Larry R. Baylor: Conceptualization, Formal analysis, Writing - review & editing, Data curation, Resources. Steven J. Meitner: Software, Investigation, Visualization, Data curation. HyunMyung Lee: Visualization, Investigation. JaeIn Song: Visualization, Investigation. Trey E. Gebhart: Data curation, Investigation. SangWon Yun: Software, Data curation. Jayhyun Kim: Validation. KwangPyo Kim: Investigation, Project administration. KapRai Park: Project administration, Funding acquisition. SiWoo Yoon: Funding acquisition.
Fig. 7. Commissioning of first SPI at ORNL (courtesy of L. Baylor).
Each size (∅ 4.5, 7, 8.5 mm) of pure pellet is formed and fired successfully and the PLC and HMI program work well to control SPI system and acquire data. The shatter tube tested for KSTAR has 0.241 m of straight length and a 20-degree of bend. Mixture pellets of D2-Ne pellets (up to 750 m/s) and pure D2 pellet (up to 900 m/s) were successfully fired during commissioning. The dispersion of the shattered pellet has been characterized as a function of different shatter tube lengths after the bend. An aluminum foil located at 0.355 m from the shatter tube exit is used to check the impact of the shattered pellet with a fast camera. This test was carried
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This study was supported by Korean Ministry of Science and ICT under the Korea Superconducting Tokamak Advanced Research (KSTAR) Project. This work was supported by the Oak Ridge National 4
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 8. SPI control and DAQ scheme.
Laboratory managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725 and by the ITER Organization.
[6] M. Lehnen, Update on DMS Status/Strategy for DMS Design Validation, ITPA-CC, (2019). [7] L.R. Baylor, et al., Shattered pellet injection technology design and characterization for disruption mitigation experiments, Nucl. Fusion 59 (2019) 066008. [8] D. Shiraki, et al., Results from recent shattered pellet injection research on DIII-D, Theory and Simulation of Disruptions Workshop, PPPL (2017). [9] S. Meitner, et al., Design and commissioning of a three-barrel shattered pellet injector for DIII-D disruption mitigation studies, Fusion Sci. Technol. 72 (2017) 318–323. [10] L.R. Baylor, et al., Developments in shattered pellet technology and implementation on JET and ITER, Theory and Simulation of Disruptions Workshop, PPPL (2017). [11] L.R. Baylor, et al., Shattered pellet injection for disruption mitigation in KSTAR, KSTAR Conference 2018 (2018). [12] T.E. Gebhart, et al., Development of solenoid-driven and pneumatic punches for launching high-Z cryogenic pellets for Tokamak disruption mitigation experiments, Fusion Sci. Technol. (2019). [13] Jayhyun Kim, Status and plan of shattered pellet injection in KSTAR for studying ITER disruption mitigation, SPI Progress Meeting (2019).
References [1] T.C. Hender, et al., Chapter 3: MHD stability, operational limits and disruptions, Nucl. Fusion 47 (2007) S128–S202. [2] M. Lehnen, et al., Disruptions in ITER and strategies for their control and mitigation, J. Nucl. Mater. 463 (2015) 39–48. [3] N. Commaux, et al., Novel rapid shutdown strategies for runaway electron suppression in DIII-D, Nucl. Fusion 51 (2011) 103001. [4] E.M. Hollmann, et al., Status of research toward the ITER disruption mitigation system, Phys. Plasmas 22 (2015) 021802. [5] N. Commaux, et al., First demonstration of rapid shutdown using neon shattered pellet injection for thermal quench mitigation on DIII-D, Nucl. Fusion 56 (2016) 046007.
5
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Deployment of multiple shattered pellet injection systems in KSTAR a,
a
b
b
a
SooHwan Park *, KunSu Lee , Larry R. Baylor , Steven J. Meitner , HyunMyung Lee , JaeIn Songa, Trey E. Gebhartb, SangWon Yuna, Jayhyun Kima, KwangPyo Kima, KapRai Parka, SiWoo Yoona a b
T
National Fusion Research Institute, Daejeon, Republic of Korea Oak Ridge National Laboratory, TN, USA
ARTICLE INFO
ABSTRACT
Keywords: Plasma Disruption Mitigation Shattered Pellet
Shattered pellet injection is of the most attractive way to mitigate the plasma disruption in fusion research facilities up to now. DIII-D has already utilized it and achieved very positive results. ITER has decided to adopt this technology for the DMS (disruption mitigation system) for PFPO-1 (Pre-Fusion Power Operation phase 1). The validation between simulation code and experiment, and continuous engineering development need to be carried out to meet the DMS’s requirement and reliability. KSTAR (Korea Superconducting Tokamak Advanced Research) is a possible candidate to test the urgent issues of plasma disruption for ITER. KSTAR can install two injectors in toroidal opposite positions. For this work, ORNL (Oak Ridge National Laboratory) will provide the two injectors, the shatter tubes and auxiliary systems. NFRI (National Fusion Research Institute) is preparing the infrastructure of a pumping system, control and data acquisition system, and arranging the location of diagnostic and the heating systems. This presentation describes the basic requirements and the engineering challenges to be solved for successful deployment and operation of multiple SPI injectors in 2019.
1. Introduction The plasma disruption is one of the urgent issues in ITER now. The way to protect the machine from this is that a large increase of plasma density during disruption can lower the plasma temperature and decrease effects of thermal damage during thermal quench (TQ). Particles must also penetrate into the current channel during the current quench (CQ) to prevent runaway electron (RE) formation. If runaway electrons form, then material can be injected to stimulate collisional dissipation [1]. There are several ways to increase the density and mitigate disruptions. First, gas injection is possible to provide large amount of gas by using fast valves. Second is pellet injection which forms and accelerates the solid and intact pellets into the plasma. And a third more favorable approach is solid particle injection using shattered cryogenic pellets. In ITER, large thermal loads can occur during the TQ [2] and large mechanical loads are also concentrated on plasma facing components (PFC) and vacuum vessel (VV) during the CQ. The decay time of the CQ must be controlled within limits of 50 ∼150 ms. REs can be generated during the CQ and any resulting RE current must be suppressed or
⁎
dissipated to less than 2 MA. It is necessary to radiate more than 90 % of thermal energy to protect the first wall because of potential radiation asymmetry. Excessive radiation peaking can result in melting of Be PFCs. Dissipation and control of REs is possible by high-Z impurity injection during CQ formation of REs. In the initial design for ITER, the candidates of mitigation were the massive gas injection (MGI) and the shattered pellet injection (SPI). The shattered pellet injector (hybrid SPI/MGI) was located in 3 upper ports to shatter pellet near plasma edge. SPI has multiple- barrels for redundancy and adjusting amount injected. Multiple-barrel SPI was located in 1 equatorial port for runaway electron mitigation. The SPI has benefits over MGI such as assimilation efficiency, deeper penetration and easier implementation to ITER than MGI through the experiments and simulations [3–5] so it has been considered as the technology for the DMS now. The recent decision of DMS configuration is below in Fig. 1. Pre-TQ by Ne and D2 injection from upper and equatorial ports is for thermal load mitigation (TQ and CQ), electromagnetic load mitigation (CQ) and RE avoidance (TQ). Post-TQ by Ar or Ne injection from equatorial ports is for runaway energy dissipation (CQ). Post-TQ by Ne (+D2) injection
Corresponding author. E-mail address: [email protected] (S. Park).
https://doi.org/10.1016/j.fusengdes.2020.111535 Received 22 September 2019; Received in revised form 3 February 2020; Accepted 3 February 2020 0920-3796/ © 2020 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 1. Equatorial and upper ports in ITER [6].
from upper ports is for thermal load mitigation (CQ), electromagnetic load mitigation (CQ) and runaway electron avoidance (CQ) [6].
barrel even though the pellet velocity is decreasing. The pellet from exit of shatter tube was viewed by the fast camera. All of the species of pellets were tested in this geometry and found to result in suitable fragmentation [7].
2. Shattered pellet injection 2.1. Pipe-gun pellet injector
3. SPI system in KSTAR
The pipe-gun uses liquid helium (LHe) or cryocooler (ex. GiffordMcMahon refrigerator) to form a pellet in situ in a stainless steel (STS) barrel. Gas is supplied into the STS barrel and then it starts to freeze where the cold block is attached. A fast propellant gas valve is pulsed to release high pressure gas behind the formed pellet that accelerates it out of the barrel into the injection line to the plasma [7].
3.1. Multiple injections It is important to determine the effectiveness of multiple pellet injections to achieve radiation symmetry and RE avoidance with optimum TQ, and a suitable CQ duration according to the recent ITER research plan. To extrapolate from different sizes and plasma parameters to ITER, at least two injectors toroidally well separated are needed. Up to now, most other SPI systems were installed as single injector or multiple injectors with asymmetric locations. KSTAR has become a first test bed for symmetric multiple injections even though it was difficult to find suitable symmetric location for two identical injectors.
2.2. SPI for other tokamaks The 3-barrel SPI concept was originally proposed for ITER DMS. Such a system called SPI2 was installed on DIII-D in 2017 and initial experiments are under way [8]. 3 pellets from each barrel can be injected together or serially depending on the purpose. 3-barrel SPI2 on DIII-D is mounted horizontally above a mid-plane port and is cooled from a LHe dewar near the injector [9]. JET now also has an SPI system based on SPI2 design [10]. The pellet size is limited to 12.5 mm. Major difference is tritium compatibility, so more strict regulations are required than DIII-D, but it will be a good reference for ITER. The 3-barrel SPI of JET can make different sizes of pellet. The pellet is formed by pure D2, Ne, Ar or the mixture of D2 and Ne. The pellet can be injected independently and accelerated 100 ∼ 250 m/s (max800 m/ s with D2). The total flight time is between 20 and 50 ms and the arrival time from shatter tube exit to plasma edge is predictable less than 2 ms. A microwave cavity diagnostic can detect the pellet mass, velocity and intactness. The shatter tube for the SPI2 has a 20-degree bend that results in good collimation and the resulting fragments are too small to damage PFCs. KSTAR has chosen to implement this same shatter tube geometry. This shatter tube was tested at ORNL using argon pellets launched with a prototype mechanical punch because pure high-Z pellet has high shear strength and is difficult to fire with propellant gas pressure only. The mechanical punch helps to break the pellet free from the cold
3.2. Key parameters Duplication of the SPI2 design was chosen to reduce the cost and risk within restricted budget and time schedule [11]. It has 3 different size barrels for D2, Ne and Ar that can form and inject pellets individually (Fig. 2). Barrels can be quickly replaced for pellet size changes in a day. A mechanical punch can be added for injecting nonshell pellets (pure Ne and Ar) [12]. The cryocooler (Sumitomo RDK-415D) cools down the SPI system instead of LHe cooling. It is a new attempt for an SPI system however conventional fueling pellet injection systems already have adopt it. The cryocooler makes it more convenient to install and operate the SPI systems in KSTAR. Pellet formation is achieved by a barrel connection to the cold head of the cryocooler and then pellet is accelerated by the fast propellant gas valve with helium gas of 5 MPa. The injected pellet is transported to the plasma through the ∼10 m long external guide tube and an internal shatter tube. The end part of the shatter tube is changeable from inside of vacuum vessel for research flexibility so multiple tubes for fragment size variation are also available. The length of the shatter tube with bend just fits inside mid-plane 2
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 2. Pellet injector, cubes and guide tube (courtesy of L. Baylor).
Fig. 3. Shatter tube (green) and angle of pellet dispersion (beige) at G port (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.).
port before touching the plasma. G port and O port are already occupied by an ECEI diagnostic housing and ECH waveguide frame respectively (Figs. 3 and 4). The shatter tube for G port could only be installed after disassembly of ECEI housing. All shatter tubes have already been installed at each port before reinstallation of ECEI and ECH components.
applied to protect the guide tubes in Fig. 6. The vacuum pumping system for guard vacuum chamber, cubes and guide tube is installed. This is a 2- stage differential pumping system (DPS) to prevent the propagation of the propellant gas into the tokamak because the propellant gas is an impurity to plasma and can reach the plasma before pellet and affect the SPI plasma interaction. The gas manifold with the valves and reservoirs provides the all of gas to the injector. The junction box contains terminals for the various signal lines from injector to the control rack. The control rack and DAQ system are ready to connect.
3.3. Deployment of SPI Two identical SPIs will be installed at KSTAR in 2019 (Fig. 5). The injector, pumping cubes, microwave cavity, guide tube, shatter tube and the related electronics are supplied from ORNL. For more stable installation, a rigid structure for the pellet injector and cubes are prepared. The guide tube can be damaged during assembly and disassembly of other equipment, so the tube support is
3.4. Commissioning at ORNL The commissioning of injector and shatter tube with 32 mm inner diameter was carried out at ORNL before delivery to KSTAR (Fig. 7).
Fig. 4. Shatter tube (green) and angle of pellet dispersion (beige) at O port (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.). 3
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 5. Multiple and symmetric injections in KSTAR.
out with pellets accelerated by only the fast propellant gas valve. This test shows that the 16.5 degree of dispersion angle from the center of the shatter tube is acceptable with other interference such ECEI, ECH and the inner liner. 4. Further works The first SPI has already been installed at O Port of KSTAR. Control and DAQ system (Fig. 8) will be connected to SPI and the junction box by the end of September. The PLC and HMI program are under development. Integration testing will be carried out with ORNL’s collaboration in early October 2019. The second SPI has been already assembled at ORNL. It is ready to ship to KSTAR and will be installed between the end of October and early November 2019. Single SPI experiments are planned at November and multi SPI experiments will be started at the end of 2019. For this experiment, bolometers based on toroidal filtered silicon absolute extreme ultraviolet (AXUV) Arrays (TFAA) and poloidal filtered AXUV arrays (PFAA) are installed at KSTAR and more diagnostic systems such as an infrared sensor-based fast bolometer, fast visible camera and compact dispersion interferometer are under development now [13].
Fig. 6. First SPI at O port of KSTAR.
CRediT authorship contribution statement SooHwan Park: Conceptualization, Investigation, Validation, Supervision, Writing - original draft, Resources. KunSu Lee: Software, Visualization, Investigation. Larry R. Baylor: Conceptualization, Formal analysis, Writing - review & editing, Data curation, Resources. Steven J. Meitner: Software, Investigation, Visualization, Data curation. HyunMyung Lee: Visualization, Investigation. JaeIn Song: Visualization, Investigation. Trey E. Gebhart: Data curation, Investigation. SangWon Yun: Software, Data curation. Jayhyun Kim: Validation. KwangPyo Kim: Investigation, Project administration. KapRai Park: Project administration, Funding acquisition. SiWoo Yoon: Funding acquisition.
Fig. 7. Commissioning of first SPI at ORNL (courtesy of L. Baylor).
Each size (∅ 4.5, 7, 8.5 mm) of pure pellet is formed and fired successfully and the PLC and HMI program work well to control SPI system and acquire data. The shatter tube tested for KSTAR has 0.241 m of straight length and a 20-degree of bend. Mixture pellets of D2-Ne pellets (up to 750 m/s) and pure D2 pellet (up to 900 m/s) were successfully fired during commissioning. The dispersion of the shattered pellet has been characterized as a function of different shatter tube lengths after the bend. An aluminum foil located at 0.355 m from the shatter tube exit is used to check the impact of the shattered pellet with a fast camera. This test was carried
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgments This study was supported by Korean Ministry of Science and ICT under the Korea Superconducting Tokamak Advanced Research (KSTAR) Project. This work was supported by the Oak Ridge National 4
Fusion Engineering and Design 154 (2020) 111535
S. Park, et al.
Fig. 8. SPI control and DAQ scheme.
Laboratory managed by UT-Battelle, LLC for the U.S. Department of Energy under Contract No. DE-AC05-00OR22725 and by the ITER Organization.
[6] M. Lehnen, Update on DMS Status/Strategy for DMS Design Validation, ITPA-CC, (2019). [7] L.R. Baylor, et al., Shattered pellet injection technology design and characterization for disruption mitigation experiments, Nucl. Fusion 59 (2019) 066008. [8] D. Shiraki, et al., Results from recent shattered pellet injection research on DIII-D, Theory and Simulation of Disruptions Workshop, PPPL (2017). [9] S. Meitner, et al., Design and commissioning of a three-barrel shattered pellet injector for DIII-D disruption mitigation studies, Fusion Sci. Technol. 72 (2017) 318–323. [10] L.R. Baylor, et al., Developments in shattered pellet technology and implementation on JET and ITER, Theory and Simulation of Disruptions Workshop, PPPL (2017). [11] L.R. Baylor, et al., Shattered pellet injection for disruption mitigation in KSTAR, KSTAR Conference 2018 (2018). [12] T.E. Gebhart, et al., Development of solenoid-driven and pneumatic punches for launching high-Z cryogenic pellets for Tokamak disruption mitigation experiments, Fusion Sci. Technol. (2019). [13] Jayhyun Kim, Status and plan of shattered pellet injection in KSTAR for studying ITER disruption mitigation, SPI Progress Meeting (2019).
References [1] T.C. Hender, et al., Chapter 3: MHD stability, operational limits and disruptions, Nucl. Fusion 47 (2007) S128–S202. [2] M. Lehnen, et al., Disruptions in ITER and strategies for their control and mitigation, J. Nucl. Mater. 463 (2015) 39–48. [3] N. Commaux, et al., Novel rapid shutdown strategies for runaway electron suppression in DIII-D, Nucl. Fusion 51 (2011) 103001. [4] E.M. Hollmann, et al., Status of research toward the ITER disruption mitigation system, Phys. Plasmas 22 (2015) 021802. [5] N. Commaux, et al., First demonstration of rapid shutdown using neon shattered pellet injection for thermal quench mitigation on DIII-D, Nucl. Fusion 56 (2016) 046007.
5