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The latest progress of the 1st NBI beamline on HL–2M Tokamak
G Model
ARTICLE IN PRESS
FUSION-9179; No. of Pages 5
Fusion Engineering and Design xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
The latest progress of the 1st NBI beamline on HL–2M Tokamak He Liu ∗ , Jianyong Cao, Huiling Wei, Guiqing Zou, Xianming Zhang, Xianfu Yang Southwestern Institute of Physics, Chengdu, China
h i g h l i g h t s • • • •
The design of the largest NBI beamline of China is described. A non-standard cryopump group with total 1.4 million L/s pumping speed is mentioned. An ion source with 4-grid acceleration system is described. Experimental result of ion source on test bed is briefly shown.
a r t i c l e
i n f o
Article history: Received 22 September 2016 Received in revised form 22 February 2017 Accepted 28 February 2017 Available online xxx Keywords: NBI beamline Vacuum chamber Beam profile Ion source Tokamak
a b s t r a c t HL–2M tokamak is under construction in Southwestern Institute of Physics in China, then leading fusion plasma experiment with advanced tokamak configuration will be performed with up to 31 MW auxiliary heating power, including 15 MW NBI power provided by three neutral beam injection (NBI) systems. The 1st NBI beamline for HL–2M tokamak, employing 4 arc-driven ion sources, which can extract 14.4 MW ion beam power, is being developed. The vacuum chamber and main water-cooled components (i.e. ion dumps, calorimeter, deflection magnet, etc.) have been manufactured and assembled. An ion source test bed had been built and testing experiments were carried out and, after testing and optimization, the configuration of ion source was optimized and the experimental maximum extraction parameters for H+ reached 75 kV × 35 A. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Recognized as the most efficient heating method for fusion plasma, NBI is widely used in controlled magnetic confinement nuclear fusion devices. The HL–2M Tokamak, which is under construction in Southwestern Institute of Physics in China, with major radius 1.78 m, minor radius 0.65 m, toroidal field 2.2 T and plasma current of 3000 kA [1], will be equipped with three NBI beamlines with 5 MW neutral beam power for each beamline. The 1st 5 MW NBI beamline employs four multi-cusp bucket arcdriven positive ion sources with maximum operation parameters of 80 kV/45 A/5 s. With auxiliary gas puff in neutralizer and ion energy at 80 keV, the neutralization efficiency reaches 50% for H+ and 70% for D+ , and transmission efficiency, defined as the ratio of injection neutral beam power to extraction ion beam power, is 35%–40% at good beam optical performance condition. The beam focal length is
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (H. Liu).
6150 mm in horizontal direction and 6283 mm in vertical direction and the tangential injection angle is 38.6◦ [2]. Up to now, the 1st NBI beamline has been designed, optimized, manufactured, assembled and finally tested. The injector is 11.26 m in height and nearly 50 ton in weight. Sub-systems such as cooling water system, controlling system, protection system, data acquisition system and analysis system will be prepared in the next step.
2. Mechanical design of 5 MW NBI beamline As shown in Fig. 1, on the HL–2M Tokamak, two NBI beamlines are of the co-direction with plasma current and one beamline is of the anti-direction with plasma current. The 1st NBI beamline, shown in Fig. 2, mainly consists of 4 ion sources, a magnetic shield box, a vacuum chamber, a deflection magnet, 4 neutralizers, a calorimeter and a drift duct. It is worth mentioning that two non-standard cryopumps, installed on both sides of the vacuum chamber, have been designed with a total pumping speed of more than 1.4 × 106 l/s.
http://dx.doi.org/10.1016/j.fusengdes.2017.02.109 0920-3796/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
G Model FUSION-9179; No. of Pages 5
ARTICLE IN PRESS H. Liu et al. / Fusion Engineering and Design xxx (2017) xxx–xxx
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Fig. 1. The layout of NBI beamlines on HL–2M tokamak.
Fig. 3. Design of the ion source.
Fig. 2. Configuration of the 5 MW NBI beamline.
2.1. Design of the ion source Ion source is the key component that supplies high-energy ion beam. A complete arc-driven ion source includes an arc chamber and an acceleration system [3]. The model of the ion source with 16 filaments, 7 loops of magnets and a 4-grid acceleration system for 5 MW NBI beamline is shown in Fig. 3. Between the horizontal grid holes arrays, there are fine cooling water channels with diameter of 2 mm, which are manufactured by the deep hole drilling process. The arc power is around 100 kW at 2000 A filament current, the max extraction parameter is 80 kV × 45 A × 5 s and the minimum
divergence angle is 1◦ . Each grid of the acceleration system consists of 2 plates with 282 extraction holes. The diameter of each hole is 6–8 mm. The material of the plasma grid is molybdenum, and the material of gradient grid, suppression grid, and ground grid is oxygen-free copper. The extraction area is 420 mm × 135 mm and the transparency is about 38.29%. The detailed dimensions of acceleration system are shown in Fig. 3(b). The potential of plasma grid, gradient grid, suppression grid and ground grid are designed to be 80 kV, 70 kV, −5 kV and 0 V, respectively. See Fig. 4, a large flange is installed between the ion sources and the neutralizers with the purpose of adjusting the beam focus distance and setting the angle between beam axis and horizontal plane to be 3.35◦ , and the angle between beam axis and vertical plane to be 4.55◦ . Four valves between the flange and ion sources are added to keep the main vacuum chamber at vacuum condition when it is necessary to replace ion sources or filament plates.
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
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Fig. 6. The structure of the W-shaped calorimeter.
Fig. 4. The large flange configuration.
Fig. 7. The vacuum chamber and magnetic shield box. Fig. 5. Configuration of deflection magnet.
2.2. Design of the deflection magnet The deflection magnet of the 1st 5 MW NBI beamline, which is made of winding copper pipe with inner cooling channel, provides strong enough magnetic field to ensure 180◦ deflection of 80 keV ions. The design of the deflection magnet is as Fig. 5. 2.3. Design of the calorimeter The calorimeter is placed in a position where it can totally cut off all beams in order to diagnose beam energy, beam profile and beam divergence and also to absorb beam power during individual test of NBI [4]. The calorimeter of 1st 5 MW NBI beamline consists of a target, supports and a lifting structure. The W-shaped target consists of 40 copper belts (Fig. 6). At designed extraction parameters, i.e. 80 kV × 45 A, the max power density deposited on each copper strip is 1 kW/cm2 . 112 thermocouples, 10 for each of 4 strips corresponding to beam center and 2 for each of the other 36 strips, were embedded in calorimeter to measure the temperature of key
points during beam extraction. Using max temperature rise data, a curve fitting method can be adopted to calculate the beam profile. 2.4. Design of the vacuum chamber and the magnetic shield box The vacuum chamber of 5 MW NBI beamline is 26 m3 in volume, of which the leakage rate is less than 1 × 10−9 pa l/s. The magnetic shield for ion sources is a pure iron room without front wall, which can be lifted and removed during the installation of ion sources. The configuration of vacuum chamber and magnetic shield box is shown in Fig. 7. 2.5. Design of the customized cryopumps It is planned to install two same non-standard cryopumps on both sides of the vacuum chamber with total pumping speed of 1.4 × 106 l/s. As shown in Fig. 8, the cryopumps have three-stage adsorption type baffle structure. Each baffle consists of a plate for liquid helium absorption and two plates for heat radiation shielding
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
G Model FUSION-9179; No. of Pages 5
ARTICLE IN PRESS H. Liu et al. / Fusion Engineering and Design xxx (2017) xxx–xxx
4
Fig. 8. Structure of the customized cryopumps.
Fig. 11. The deflection magnet.
Fig. 9. The assembled NBI beamline.
Fig. 12. The customized cryopumps.
Fig. 10. The calorimeter.
of liquid nitrogen, which work at about 10 K and 60–80 K, respectively. In order to increase pumping speed, active carbon is bonded to the surface of baffles and, during dewar test, 1.4 × 106 l/s pumping speed at 7 g/s liquid helium consumption was achieved. Fig. 13. Ion source on test bed.
3. Manufactured components Presently, the 1st 5 MW NBI beamline for HL–2M has been manufactured and assembled. Fig. 9 shows the magnetic shield room
for ion sources and the vacuum chamber with installed inner components. In the case of pumping with two mechanical-molecular pump groups, the pressure achieved the order of magnitude of 10−4 Pa.
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
G Model FUSION-9179; No. of Pages 5
ARTICLE IN PRESS H. Liu et al. / Fusion Engineering and Design xxx (2017) xxx–xxx
5
Fig. 14. Typical extraction curve.
established. Fig. 13 shows the installation of an ion source on the test bed. One typical extraction curve is shown in Fig. 14. In this shot, the arc current is 820 A, the arc voltage is 76 V, the potential of plasma grid is 66 kV, the potential of gradient grid is 51 kV, the extraction current is 32.3 A and the extraction pulse width is 35 ms. A flat copper target with blackening process at back surface was set at 3.28 m from acceleration grid surface and an infrared camera was used to monitor its temperature variation through a special quartz window, the beam profile was obtained, which is shown in Fig. 15. Acknowledgments The authors would like to express their gratitude to NBI group of IPP Garching and the NIFS. Our engineers including the authors have visited the two labs, and have learned a lot of experiences in the design of NBI beamline. Fig. 15. Beam profile at 3.28 m from the acceleration grid. (a) Original image measured by infrared camera, (b) Experimental isotherm distribution.
The main water-cooled components are shown in Figs. 10–12. These devices and those not shown in the article, as ion dumps, neutralizers, scrapers, etc., all passed the tests of dimensions and installation accuracy. Laser beam were used to simulate ion beam trajectory and measured focus point was coincident with the designed focus point.
References [1] Q. Li, et al., The component development status of HL–2 M tokamak, Fusion Eng. Des. 96–97 (2015) 338–342. [2] J.Y. Cao, et al., Conceptual design of 5MW-NBI injector for HL-2 M, Fusion Eng. Des. 88 (6–8) (2013) 872–877. [3] G.Q. Zou, G.J. Lei, et al., Optics of ion beams for the neutral beam injection system on HL-2A Tokamak, Rev. Sci. Instrum. 83 (2012) 073307. [4] H. Liu, J.Y. Cao, et al., HL-2A NBI beam profile and beam power measurement, Plasma Sci. Technol. 11 (2009) 613.
4. Experimental results The 5 MW neutral beam injector has not been connected onto HL–2M tokamak yet. For this reason an ion source test bed was
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
ARTICLE IN PRESS
FUSION-9179; No. of Pages 5
Fusion Engineering and Design xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
The latest progress of the 1st NBI beamline on HL–2M Tokamak He Liu ∗ , Jianyong Cao, Huiling Wei, Guiqing Zou, Xianming Zhang, Xianfu Yang Southwestern Institute of Physics, Chengdu, China
h i g h l i g h t s • • • •
The design of the largest NBI beamline of China is described. A non-standard cryopump group with total 1.4 million L/s pumping speed is mentioned. An ion source with 4-grid acceleration system is described. Experimental result of ion source on test bed is briefly shown.
a r t i c l e
i n f o
Article history: Received 22 September 2016 Received in revised form 22 February 2017 Accepted 28 February 2017 Available online xxx Keywords: NBI beamline Vacuum chamber Beam profile Ion source Tokamak
a b s t r a c t HL–2M tokamak is under construction in Southwestern Institute of Physics in China, then leading fusion plasma experiment with advanced tokamak configuration will be performed with up to 31 MW auxiliary heating power, including 15 MW NBI power provided by three neutral beam injection (NBI) systems. The 1st NBI beamline for HL–2M tokamak, employing 4 arc-driven ion sources, which can extract 14.4 MW ion beam power, is being developed. The vacuum chamber and main water-cooled components (i.e. ion dumps, calorimeter, deflection magnet, etc.) have been manufactured and assembled. An ion source test bed had been built and testing experiments were carried out and, after testing and optimization, the configuration of ion source was optimized and the experimental maximum extraction parameters for H+ reached 75 kV × 35 A. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Recognized as the most efficient heating method for fusion plasma, NBI is widely used in controlled magnetic confinement nuclear fusion devices. The HL–2M Tokamak, which is under construction in Southwestern Institute of Physics in China, with major radius 1.78 m, minor radius 0.65 m, toroidal field 2.2 T and plasma current of 3000 kA [1], will be equipped with three NBI beamlines with 5 MW neutral beam power for each beamline. The 1st 5 MW NBI beamline employs four multi-cusp bucket arcdriven positive ion sources with maximum operation parameters of 80 kV/45 A/5 s. With auxiliary gas puff in neutralizer and ion energy at 80 keV, the neutralization efficiency reaches 50% for H+ and 70% for D+ , and transmission efficiency, defined as the ratio of injection neutral beam power to extraction ion beam power, is 35%–40% at good beam optical performance condition. The beam focal length is
∗ Corresponding author. E-mail addresses: [email protected], [email protected] (H. Liu).
6150 mm in horizontal direction and 6283 mm in vertical direction and the tangential injection angle is 38.6◦ [2]. Up to now, the 1st NBI beamline has been designed, optimized, manufactured, assembled and finally tested. The injector is 11.26 m in height and nearly 50 ton in weight. Sub-systems such as cooling water system, controlling system, protection system, data acquisition system and analysis system will be prepared in the next step.
2. Mechanical design of 5 MW NBI beamline As shown in Fig. 1, on the HL–2M Tokamak, two NBI beamlines are of the co-direction with plasma current and one beamline is of the anti-direction with plasma current. The 1st NBI beamline, shown in Fig. 2, mainly consists of 4 ion sources, a magnetic shield box, a vacuum chamber, a deflection magnet, 4 neutralizers, a calorimeter and a drift duct. It is worth mentioning that two non-standard cryopumps, installed on both sides of the vacuum chamber, have been designed with a total pumping speed of more than 1.4 × 106 l/s.
http://dx.doi.org/10.1016/j.fusengdes.2017.02.109 0920-3796/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
G Model FUSION-9179; No. of Pages 5
ARTICLE IN PRESS H. Liu et al. / Fusion Engineering and Design xxx (2017) xxx–xxx
2
Fig. 1. The layout of NBI beamlines on HL–2M tokamak.
Fig. 3. Design of the ion source.
Fig. 2. Configuration of the 5 MW NBI beamline.
2.1. Design of the ion source Ion source is the key component that supplies high-energy ion beam. A complete arc-driven ion source includes an arc chamber and an acceleration system [3]. The model of the ion source with 16 filaments, 7 loops of magnets and a 4-grid acceleration system for 5 MW NBI beamline is shown in Fig. 3. Between the horizontal grid holes arrays, there are fine cooling water channels with diameter of 2 mm, which are manufactured by the deep hole drilling process. The arc power is around 100 kW at 2000 A filament current, the max extraction parameter is 80 kV × 45 A × 5 s and the minimum
divergence angle is 1◦ . Each grid of the acceleration system consists of 2 plates with 282 extraction holes. The diameter of each hole is 6–8 mm. The material of the plasma grid is molybdenum, and the material of gradient grid, suppression grid, and ground grid is oxygen-free copper. The extraction area is 420 mm × 135 mm and the transparency is about 38.29%. The detailed dimensions of acceleration system are shown in Fig. 3(b). The potential of plasma grid, gradient grid, suppression grid and ground grid are designed to be 80 kV, 70 kV, −5 kV and 0 V, respectively. See Fig. 4, a large flange is installed between the ion sources and the neutralizers with the purpose of adjusting the beam focus distance and setting the angle between beam axis and horizontal plane to be 3.35◦ , and the angle between beam axis and vertical plane to be 4.55◦ . Four valves between the flange and ion sources are added to keep the main vacuum chamber at vacuum condition when it is necessary to replace ion sources or filament plates.
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
G Model FUSION-9179; No. of Pages 5
ARTICLE IN PRESS H. Liu et al. / Fusion Engineering and Design xxx (2017) xxx–xxx
3
Fig. 6. The structure of the W-shaped calorimeter.
Fig. 4. The large flange configuration.
Fig. 7. The vacuum chamber and magnetic shield box. Fig. 5. Configuration of deflection magnet.
2.2. Design of the deflection magnet The deflection magnet of the 1st 5 MW NBI beamline, which is made of winding copper pipe with inner cooling channel, provides strong enough magnetic field to ensure 180◦ deflection of 80 keV ions. The design of the deflection magnet is as Fig. 5. 2.3. Design of the calorimeter The calorimeter is placed in a position where it can totally cut off all beams in order to diagnose beam energy, beam profile and beam divergence and also to absorb beam power during individual test of NBI [4]. The calorimeter of 1st 5 MW NBI beamline consists of a target, supports and a lifting structure. The W-shaped target consists of 40 copper belts (Fig. 6). At designed extraction parameters, i.e. 80 kV × 45 A, the max power density deposited on each copper strip is 1 kW/cm2 . 112 thermocouples, 10 for each of 4 strips corresponding to beam center and 2 for each of the other 36 strips, were embedded in calorimeter to measure the temperature of key
points during beam extraction. Using max temperature rise data, a curve fitting method can be adopted to calculate the beam profile. 2.4. Design of the vacuum chamber and the magnetic shield box The vacuum chamber of 5 MW NBI beamline is 26 m3 in volume, of which the leakage rate is less than 1 × 10−9 pa l/s. The magnetic shield for ion sources is a pure iron room without front wall, which can be lifted and removed during the installation of ion sources. The configuration of vacuum chamber and magnetic shield box is shown in Fig. 7. 2.5. Design of the customized cryopumps It is planned to install two same non-standard cryopumps on both sides of the vacuum chamber with total pumping speed of 1.4 × 106 l/s. As shown in Fig. 8, the cryopumps have three-stage adsorption type baffle structure. Each baffle consists of a plate for liquid helium absorption and two plates for heat radiation shielding
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
G Model FUSION-9179; No. of Pages 5
ARTICLE IN PRESS H. Liu et al. / Fusion Engineering and Design xxx (2017) xxx–xxx
4
Fig. 8. Structure of the customized cryopumps.
Fig. 11. The deflection magnet.
Fig. 9. The assembled NBI beamline.
Fig. 12. The customized cryopumps.
Fig. 10. The calorimeter.
of liquid nitrogen, which work at about 10 K and 60–80 K, respectively. In order to increase pumping speed, active carbon is bonded to the surface of baffles and, during dewar test, 1.4 × 106 l/s pumping speed at 7 g/s liquid helium consumption was achieved. Fig. 13. Ion source on test bed.
3. Manufactured components Presently, the 1st 5 MW NBI beamline for HL–2M has been manufactured and assembled. Fig. 9 shows the magnetic shield room
for ion sources and the vacuum chamber with installed inner components. In the case of pumping with two mechanical-molecular pump groups, the pressure achieved the order of magnitude of 10−4 Pa.
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109
G Model FUSION-9179; No. of Pages 5
ARTICLE IN PRESS H. Liu et al. / Fusion Engineering and Design xxx (2017) xxx–xxx
5
Fig. 14. Typical extraction curve.
established. Fig. 13 shows the installation of an ion source on the test bed. One typical extraction curve is shown in Fig. 14. In this shot, the arc current is 820 A, the arc voltage is 76 V, the potential of plasma grid is 66 kV, the potential of gradient grid is 51 kV, the extraction current is 32.3 A and the extraction pulse width is 35 ms. A flat copper target with blackening process at back surface was set at 3.28 m from acceleration grid surface and an infrared camera was used to monitor its temperature variation through a special quartz window, the beam profile was obtained, which is shown in Fig. 15. Acknowledgments The authors would like to express their gratitude to NBI group of IPP Garching and the NIFS. Our engineers including the authors have visited the two labs, and have learned a lot of experiences in the design of NBI beamline. Fig. 15. Beam profile at 3.28 m from the acceleration grid. (a) Original image measured by infrared camera, (b) Experimental isotherm distribution.
The main water-cooled components are shown in Figs. 10–12. These devices and those not shown in the article, as ion dumps, neutralizers, scrapers, etc., all passed the tests of dimensions and installation accuracy. Laser beam were used to simulate ion beam trajectory and measured focus point was coincident with the designed focus point.
References [1] Q. Li, et al., The component development status of HL–2 M tokamak, Fusion Eng. Des. 96–97 (2015) 338–342. [2] J.Y. Cao, et al., Conceptual design of 5MW-NBI injector for HL-2 M, Fusion Eng. Des. 88 (6–8) (2013) 872–877. [3] G.Q. Zou, G.J. Lei, et al., Optics of ion beams for the neutral beam injection system on HL-2A Tokamak, Rev. Sci. Instrum. 83 (2012) 073307. [4] H. Liu, J.Y. Cao, et al., HL-2A NBI beam profile and beam power measurement, Plasma Sci. Technol. 11 (2009) 613.
4. Experimental results The 5 MW neutral beam injector has not been connected onto HL–2M tokamak yet. For this reason an ion source test bed was
Please cite this article in press as: H. Liu, et al., The latest progress of the 1st NBI beamline on HL–2M Tokamak, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.02.109