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Design of an ion extractor system for a prototype ion source experiment for SST-1 neutral beam injector
Fusion Engineering and Design 85 (2010) 122–125
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Design of an ion extractor system for a prototype ion source experiment for SST-1 neutral beam injector M.R. Jana ∗ , M. Bandyopadhaya, N.P. Singh, S.K. Sharma, A.K. Chakraborty, U.K. Baruah, S.K. Mattoo Institute for Plasma Research, Nr. Indira Bridge, Bhat Village, Gandhinagar, Gujarat 382428, India
a r t i c l e
i n f o
Article history: Received 15 October 2008 Received in revised form 3 August 2009 Accepted 20 August 2009 Available online 12 September 2009 PACS: 52.75.−d 29.25.Lg.Ni Keywords: Ion source Extraction system Neutral beam injector SST-1
a b s t r a c t An ion extractor system has been designed for the steady state superconducting tokamak (SST-1) neutral beam injector (NBI) for an experiment using a prototype ion source with fully integrated regulated high voltage power supply (RHVPS) and data acquisition and control system (DACS) developed at Institute for Plasma Research (IPR) to obtain experience of NB operation. The extractor system is capable of extracting positive hydrogen ion beam of ∼10 A current at ∼20 kV. This paper presents the beam optics study for detailed design of an ion extraction system which could meet this requirement. It consists of 3 grid accel–decel system, each of the grid has 217 straight cylindrical holes of 8 mm diameter. Grids are placed on a specially designed G-10 block; a fiber reinforc plastic (FRP) isolator of outer diameter of 820 mm and 50 mm thickness. Provisions are made for supplying high voltage to the grid system through the embedded feed-throughs. Extractor system has been fabricated, mounted on the SST-1 neutral beam injector and has extracted positive hydrogen ion beam of 4 A at 20 kV till now. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Neutral beam injection (NBI) is a well established technique for heating and current drive in tokamak fusion plasma [1,2]. Major components of NBI system (Fig. 1) include ion source, extractor system, neutralizer, bending magnet, ion dump, V-target, cryo pumps, power supply, data acquisition and control system (DACS). In SST-1 machine (R = 1.2 m, a = 0.2 m, ne = 2 × 1019 m−3 , Te = 1 keV), D-shaped plasma shall be produced for 1000S [3,4]. To raise the ion temperature of ∼1 keV, a neutral hydrogen beam power of 0.5 MW at 30 kV is required. Future upgrade of the SST-1 will require 1.7 MW of H◦ at 55 kV [5,6].As a part of the SST-1 NBI program, an experiment with positive hydrogen ion beam of ∼10 A at 20 kV is planned with prototype ion source integrated with RHVPS and DACS developed at IPR. This experiment would give us the information about performance of RHVPA and DACS needed for operation of PINI ion source. To fulfill this requirement an ion extractor system has been designed based on beam optics calculation using AXCELINP [7] code which takes into account the space charge effects of the ions. The output of this beam optics calculation is used for engineering design of multi-aperture 3 grid accel–decel extractor system. Three grids are made up of stainless steel fabricated at IPR work-
∗ Corresponding author. Tel.: +91 79 23962168; fax: +91 79 23962277. E-mail address: [email protected] (M.R. Jana). 0920-3796/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2009.08.004
shop. These grids are housed on G-10 block. Single insulator block made of G-10 FRP of 50 mm thickness, 820 mm OD and 250 mm ID is chosen for grid holder (GH), where machined grooves are provided for placement of grids. The paper is organised in the following way. The ion extractor system is described in Section 2. Beam optics calculation for design of extractor grid is discussed in Section 3 and finally summary is given in Section 4.
2. Ion extractor system Extractor system contains 3 grids and a grid holder which is made up of G-10 FRP insulator. Selected parameters of the extractor system are mentioned in Table 1. The acceleration grid plate has 430 mm outer diameter, thickness 4 mm and 217 straight cylindrical apertures each of radius 4 mm as shown in Fig. 2. Both deceleration grid of thickness 8 mm and earth grid of thickness 4 mm have same number of apertures. For holding the grids with requisite inter-grid distances we have designed grid holder system made up of single block of G-10 insulator shown in Fig. 3. Grooves are machined for fixing the grids and provision has been made for electrical connection to each grid through a specially designed vacuum tight connector made up of SS304 knurled rod of 8 mm diameter bonded with G-10 insulator. The extractor system along with all grids (Fig. 4) is mounted on NBI vacuum vessel. Then prototype ion source is attached with the extractor system shown in Fig. 5.
M.R. Jana et al. / Fusion Engineering and Design 85 (2010) 122–125
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Fig. 1. Schematic of neutral beam injection system [5]. Table 1 Parameters of the extractor system.
Fig. 3. Insulator G-10 FRP.
Parameter
Value
Beam current (A) Acceleration voltage (kV) Deceleration voltage (kV) Aperture radius of acceleration grid (mm) Aperture radius of deceleration grid (mm) Aperture radius of earth grid (mm) Acceleration gap (mm) Deceleration gap (mm) Diameter of acceleration grid (mm) Thickness of acceleration grid (mm) Diameter of deceleration grid (mm) Thickness of deceleration grid (mm) Diameter of earth grid (mm) Thickness of earth grid No. of aperture Extraction area (cm2 ) Current density (mA/cm2 )
10 20 −0.8 4 4 4 8 2 430 4 346 8 284 4 217 109 100 Fig. 4. Assembled extractor system mounted on SST-1 NBI vacuum vessel.
3. Beam optics calculation and design of grid geometry As mentioned above, the aim of this prototype ion source experiment was to test the performance of in-house made regulated high voltage power supply (RHVPS) integrated with data acquisition and
control system. So it was decided to design a simple ion extractor system with 3 grids each consisting of straight cylindrical apertures maintaining thickness and inter-grid distances same as actual ion extractor designed for SST-1 NBI [5,6]. It is to be noted that this prototype ion source shall be replaced by PINI ion source during actual SST-1 NBI operation. Ion beam optics calculation has been done using axis symmetry single aperture AXCEL-INP code for design of the above mentioned prototype ion extractor system consisting of 3 grids. The first grid in contact with plasma is called acceleration grid maintained at positive potential ∼20 kV. This grid separates
Fig. 2. Arrangement of apertures in acceleration grid.
Fig. 5. Prototype ion source mounted with SST-1 NBI vacuum vessel.
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M.R. Jana et al. / Fusion Engineering and Design 85 (2010) 122–125
Fig. 6. Ion trajectory plot for single aperture 3 Grid accel–decel system.
ions from the plasma source and accelerates them towards earth grid at ground potential. The deceleration grid is maintained at negative potential of −800 V to prevent back-streaming electron beam leaking from the plasma neutralizer. The acceleration gap (d) length is 8 mm and deceleration gap length is 2 mm. These gaps have been chosen to keep the aspect ratio (S = r/d) of 0.5 which is same as actual design of ion extractor system [5,6]. This would also help us to test the performance of RHPVS integrated with DACS designed for actual beam operation. The other parameters are: extracted hydro-
gen ion current density ∼1000 A/m2 , electron temperature ∼5 eV, ion temperature ∼0.1 eV, species fractions H1 + :H2 + :H3 + :27:23:50%. Calculated ion beamlet trajectory from single aperture is shown in Fig. 6. This shows that at beam axis ion density of the plasma meniscus is not uniform and ion trajectories are hollow. This is due to the fact that apertures are not shaped (Pierce or Quasi-Pierce) properly to reduce aberration field near acceleration grid aperture. Presence of higher aberration field near beam axis due to straight cylindrical aperture in acceleration grid caused non-uniform ion density
Fig. 7. Radial emittance plot.
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as extractor grids designed for 55 kV. During engineering design some of the outer apertures are removed, as these would give large beam divergence due to large plasma density variation of the ion source at outer apertures of the acceleration grid. After considering all these factors, 217 apertures are considered and arranged on extraction plane as shown in Fig. 8. 4. Experiment
Fig. 8. Hydrogen ion beam of 4 A, 20 kV coming out from neutralizer.
at plasma meniscus. As mentioned above the aspect ratio of this geometry is not optimum for beam voltage of 20 kV. All these factors lead to higher beamlet divergence and hollow trajectories near beam axis. It is to be noted that in beam optics calculation for actual design of 55 kV extractor system these problems have been minimized and calculated ion beamlet trajectories are parallel to the beam axis [5]. The emittance of the ion trajectories is calculated at the exit plane of the earth grid shown in Fig. 7. The emittance plot indicates the angular spread (divergence) in phase space for all extracted ion species e.g., H1 + (m/q = 1), H2 + (m/q = 2) and H3 + (m/q = 3) respectively. The calculated RMS beamlet divergence is ∼60 mrad (≈3.5◦ ). The emittance plot also shows that extracted ion beamlet current from single aperture is ∼40 mA. Therefore to obtain ∼10 A ion beam current, the required number of aperture is 250. Single aperture beam optics calculation described here can be used in design grids consisting of multi-aperture. The effect of neighboring beams on the optics is small and can be neglected [8]. Based on single aperture beam optics calculation, extractor grids consisting of multi-aperture have been designed by TFTR, DII-D [8], JET [9] and TEXTOR [10] for neutral beam application. We have also followed the same path for design of prototype extractor grids. Looking into the interface issue of both prototype ion source chamber and flange of gate valve connected to NBI vacuum vessel; apertures are arranged in hexagonal structure on extraction plane of diameter 204 mm as shown in Fig. 8. The distances between the center of two adjacent apertures along horizontal and vertical direction are kept at 11.579 mm and 11.885 mm, respectively which are same
Electrical power connections were made to nine tungsten filaments connected to different locations on the cylindrical wall of the ion source and RHVPS connection is made to the grid system. The pressure inside the vacuum chamber is maintained to ∼1 × 10−4 Torr using Turbo molecular pump of pumping speed ∼3 × 103 l/s. Beam operation has been done by feeding 50 standard cubic centimeter per minute (SCCM) hydrogen gas into the ion source. The corresponding ion source pressure was about 1 × 10−3 Torr. Positive hydrogen ion beam of 20 kV, 4 A has been extracted from the prototype ion source shown in Fig. 8. The extracted beam current and extraction voltage waveform of 800 ms pulse length is shown in Fig. 9. Beam profile is measured with interceptor plate embedded with thermocouples and Dropper Spectroscopy is used for measurement of beam divergence and species fractions. Details of these measurement schemes and analysis of the beam characteristics shall be reported elsewhere. 5. Discussion An ion extractor system capable of extracting positive hydrogen ion beam of 20 kV, 10 A from a prototype ion source is designed. Beam optics is calculated for single aperture 3 grid accel–decel system using AXCEL-INP code. Doppler Spectroscopy measurement shows the beam divergence is ∼4◦ . In this experimental campaign, 20 kV, 4 A positive hydrogen beam has been extracted. This prototype ion source experiment with RHVPS integrated with DACS shall be helpful for actual PINI ion source operation for SST-1 NBI. At present prototype ion source has been removed and assembled PINI ion source is mounted to the vacuum vessel. Commissioning work for various beam line components including water and electrical connections, etc. are under progress. After completion of these commissioning works, operation of PINI ion source shall be undertaken. Acknowledgement Authors are grateful to both reviewers for their valuable comments towards improving the quality of the work. References
Fig. 9. Current and voltage waveform of 20 kV, 4 A positive hydrogen ion beam of 800 ms pulse.
[1] T. Ohkawa, Nuclear Fusion 10 (1970) 185–188. [2] M. Menon, Proceedings of the IEEE 69 (1981) 1012–1028. [3] Y.C. Saxena, Present status of the SST-1 project, Nuclear Fusion 40 (2000) 1069–1082. [4] D. Bora, Test results on systems developed for SST-1 tokamak, Nuclear Fusion 43 (2003) 1748–1758. [5] M.R. Jana, S.K. Mattoo, A.K. Chakraborty, U.K. baruah, G.B. Patel, P.K. Jayakumer, Long pulse characteristics of 5 MW ion source for SST-1 neutral beam injector, Fusion Engineering and Design 83 (2008) 729. [6] M.R. Jana, P.K. Jayakumar, N. Bisai, U. Baruah, P.J. Patel, N.P. Singh, et al., A high current ion accelerator system for neutral beam injector, Indian Journal of Physics 53S (2) (1999) 93–95. [7] P. Spaedtke, INP, Junkernstr. 99, 65205 Wiesbaden, Germany (Private Communication). [8] W.B. Kunkel, Neutral Beam Injection, Fusion 1 (1981) 103 (Part B). [9] D.J. Godden, The JET 80 kV PINI recent test-bed experience and future plans, in: Joint Development Committee (JDC) meeting, 28–29th October, Cadarache, page DG II-1, 1996. [10] R. Uhlemann, Forschungszentrum Juelich Institut fuer Energieforschung IEF-4 Plasmaphysik, D-52425 Juelich, Germany (private communication).
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Design of an ion extractor system for a prototype ion source experiment for SST-1 neutral beam injector M.R. Jana ∗ , M. Bandyopadhaya, N.P. Singh, S.K. Sharma, A.K. Chakraborty, U.K. Baruah, S.K. Mattoo Institute for Plasma Research, Nr. Indira Bridge, Bhat Village, Gandhinagar, Gujarat 382428, India
a r t i c l e
i n f o
Article history: Received 15 October 2008 Received in revised form 3 August 2009 Accepted 20 August 2009 Available online 12 September 2009 PACS: 52.75.−d 29.25.Lg.Ni Keywords: Ion source Extraction system Neutral beam injector SST-1
a b s t r a c t An ion extractor system has been designed for the steady state superconducting tokamak (SST-1) neutral beam injector (NBI) for an experiment using a prototype ion source with fully integrated regulated high voltage power supply (RHVPS) and data acquisition and control system (DACS) developed at Institute for Plasma Research (IPR) to obtain experience of NB operation. The extractor system is capable of extracting positive hydrogen ion beam of ∼10 A current at ∼20 kV. This paper presents the beam optics study for detailed design of an ion extraction system which could meet this requirement. It consists of 3 grid accel–decel system, each of the grid has 217 straight cylindrical holes of 8 mm diameter. Grids are placed on a specially designed G-10 block; a fiber reinforc plastic (FRP) isolator of outer diameter of 820 mm and 50 mm thickness. Provisions are made for supplying high voltage to the grid system through the embedded feed-throughs. Extractor system has been fabricated, mounted on the SST-1 neutral beam injector and has extracted positive hydrogen ion beam of 4 A at 20 kV till now. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Neutral beam injection (NBI) is a well established technique for heating and current drive in tokamak fusion plasma [1,2]. Major components of NBI system (Fig. 1) include ion source, extractor system, neutralizer, bending magnet, ion dump, V-target, cryo pumps, power supply, data acquisition and control system (DACS). In SST-1 machine (R = 1.2 m, a = 0.2 m, ne = 2 × 1019 m−3 , Te = 1 keV), D-shaped plasma shall be produced for 1000S [3,4]. To raise the ion temperature of ∼1 keV, a neutral hydrogen beam power of 0.5 MW at 30 kV is required. Future upgrade of the SST-1 will require 1.7 MW of H◦ at 55 kV [5,6].As a part of the SST-1 NBI program, an experiment with positive hydrogen ion beam of ∼10 A at 20 kV is planned with prototype ion source integrated with RHVPS and DACS developed at IPR. This experiment would give us the information about performance of RHVPA and DACS needed for operation of PINI ion source. To fulfill this requirement an ion extractor system has been designed based on beam optics calculation using AXCELINP [7] code which takes into account the space charge effects of the ions. The output of this beam optics calculation is used for engineering design of multi-aperture 3 grid accel–decel extractor system. Three grids are made up of stainless steel fabricated at IPR work-
∗ Corresponding author. Tel.: +91 79 23962168; fax: +91 79 23962277. E-mail address: [email protected] (M.R. Jana). 0920-3796/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2009.08.004
shop. These grids are housed on G-10 block. Single insulator block made of G-10 FRP of 50 mm thickness, 820 mm OD and 250 mm ID is chosen for grid holder (GH), where machined grooves are provided for placement of grids. The paper is organised in the following way. The ion extractor system is described in Section 2. Beam optics calculation for design of extractor grid is discussed in Section 3 and finally summary is given in Section 4.
2. Ion extractor system Extractor system contains 3 grids and a grid holder which is made up of G-10 FRP insulator. Selected parameters of the extractor system are mentioned in Table 1. The acceleration grid plate has 430 mm outer diameter, thickness 4 mm and 217 straight cylindrical apertures each of radius 4 mm as shown in Fig. 2. Both deceleration grid of thickness 8 mm and earth grid of thickness 4 mm have same number of apertures. For holding the grids with requisite inter-grid distances we have designed grid holder system made up of single block of G-10 insulator shown in Fig. 3. Grooves are machined for fixing the grids and provision has been made for electrical connection to each grid through a specially designed vacuum tight connector made up of SS304 knurled rod of 8 mm diameter bonded with G-10 insulator. The extractor system along with all grids (Fig. 4) is mounted on NBI vacuum vessel. Then prototype ion source is attached with the extractor system shown in Fig. 5.
M.R. Jana et al. / Fusion Engineering and Design 85 (2010) 122–125
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Fig. 1. Schematic of neutral beam injection system [5]. Table 1 Parameters of the extractor system.
Fig. 3. Insulator G-10 FRP.
Parameter
Value
Beam current (A) Acceleration voltage (kV) Deceleration voltage (kV) Aperture radius of acceleration grid (mm) Aperture radius of deceleration grid (mm) Aperture radius of earth grid (mm) Acceleration gap (mm) Deceleration gap (mm) Diameter of acceleration grid (mm) Thickness of acceleration grid (mm) Diameter of deceleration grid (mm) Thickness of deceleration grid (mm) Diameter of earth grid (mm) Thickness of earth grid No. of aperture Extraction area (cm2 ) Current density (mA/cm2 )
10 20 −0.8 4 4 4 8 2 430 4 346 8 284 4 217 109 100 Fig. 4. Assembled extractor system mounted on SST-1 NBI vacuum vessel.
3. Beam optics calculation and design of grid geometry As mentioned above, the aim of this prototype ion source experiment was to test the performance of in-house made regulated high voltage power supply (RHVPS) integrated with data acquisition and
control system. So it was decided to design a simple ion extractor system with 3 grids each consisting of straight cylindrical apertures maintaining thickness and inter-grid distances same as actual ion extractor designed for SST-1 NBI [5,6]. It is to be noted that this prototype ion source shall be replaced by PINI ion source during actual SST-1 NBI operation. Ion beam optics calculation has been done using axis symmetry single aperture AXCEL-INP code for design of the above mentioned prototype ion extractor system consisting of 3 grids. The first grid in contact with plasma is called acceleration grid maintained at positive potential ∼20 kV. This grid separates
Fig. 2. Arrangement of apertures in acceleration grid.
Fig. 5. Prototype ion source mounted with SST-1 NBI vacuum vessel.
124
M.R. Jana et al. / Fusion Engineering and Design 85 (2010) 122–125
Fig. 6. Ion trajectory plot for single aperture 3 Grid accel–decel system.
ions from the plasma source and accelerates them towards earth grid at ground potential. The deceleration grid is maintained at negative potential of −800 V to prevent back-streaming electron beam leaking from the plasma neutralizer. The acceleration gap (d) length is 8 mm and deceleration gap length is 2 mm. These gaps have been chosen to keep the aspect ratio (S = r/d) of 0.5 which is same as actual design of ion extractor system [5,6]. This would also help us to test the performance of RHPVS integrated with DACS designed for actual beam operation. The other parameters are: extracted hydro-
gen ion current density ∼1000 A/m2 , electron temperature ∼5 eV, ion temperature ∼0.1 eV, species fractions H1 + :H2 + :H3 + :27:23:50%. Calculated ion beamlet trajectory from single aperture is shown in Fig. 6. This shows that at beam axis ion density of the plasma meniscus is not uniform and ion trajectories are hollow. This is due to the fact that apertures are not shaped (Pierce or Quasi-Pierce) properly to reduce aberration field near acceleration grid aperture. Presence of higher aberration field near beam axis due to straight cylindrical aperture in acceleration grid caused non-uniform ion density
Fig. 7. Radial emittance plot.
M.R. Jana et al. / Fusion Engineering and Design 85 (2010) 122–125
125
as extractor grids designed for 55 kV. During engineering design some of the outer apertures are removed, as these would give large beam divergence due to large plasma density variation of the ion source at outer apertures of the acceleration grid. After considering all these factors, 217 apertures are considered and arranged on extraction plane as shown in Fig. 8. 4. Experiment
Fig. 8. Hydrogen ion beam of 4 A, 20 kV coming out from neutralizer.
at plasma meniscus. As mentioned above the aspect ratio of this geometry is not optimum for beam voltage of 20 kV. All these factors lead to higher beamlet divergence and hollow trajectories near beam axis. It is to be noted that in beam optics calculation for actual design of 55 kV extractor system these problems have been minimized and calculated ion beamlet trajectories are parallel to the beam axis [5]. The emittance of the ion trajectories is calculated at the exit plane of the earth grid shown in Fig. 7. The emittance plot indicates the angular spread (divergence) in phase space for all extracted ion species e.g., H1 + (m/q = 1), H2 + (m/q = 2) and H3 + (m/q = 3) respectively. The calculated RMS beamlet divergence is ∼60 mrad (≈3.5◦ ). The emittance plot also shows that extracted ion beamlet current from single aperture is ∼40 mA. Therefore to obtain ∼10 A ion beam current, the required number of aperture is 250. Single aperture beam optics calculation described here can be used in design grids consisting of multi-aperture. The effect of neighboring beams on the optics is small and can be neglected [8]. Based on single aperture beam optics calculation, extractor grids consisting of multi-aperture have been designed by TFTR, DII-D [8], JET [9] and TEXTOR [10] for neutral beam application. We have also followed the same path for design of prototype extractor grids. Looking into the interface issue of both prototype ion source chamber and flange of gate valve connected to NBI vacuum vessel; apertures are arranged in hexagonal structure on extraction plane of diameter 204 mm as shown in Fig. 8. The distances between the center of two adjacent apertures along horizontal and vertical direction are kept at 11.579 mm and 11.885 mm, respectively which are same
Electrical power connections were made to nine tungsten filaments connected to different locations on the cylindrical wall of the ion source and RHVPS connection is made to the grid system. The pressure inside the vacuum chamber is maintained to ∼1 × 10−4 Torr using Turbo molecular pump of pumping speed ∼3 × 103 l/s. Beam operation has been done by feeding 50 standard cubic centimeter per minute (SCCM) hydrogen gas into the ion source. The corresponding ion source pressure was about 1 × 10−3 Torr. Positive hydrogen ion beam of 20 kV, 4 A has been extracted from the prototype ion source shown in Fig. 8. The extracted beam current and extraction voltage waveform of 800 ms pulse length is shown in Fig. 9. Beam profile is measured with interceptor plate embedded with thermocouples and Dropper Spectroscopy is used for measurement of beam divergence and species fractions. Details of these measurement schemes and analysis of the beam characteristics shall be reported elsewhere. 5. Discussion An ion extractor system capable of extracting positive hydrogen ion beam of 20 kV, 10 A from a prototype ion source is designed. Beam optics is calculated for single aperture 3 grid accel–decel system using AXCEL-INP code. Doppler Spectroscopy measurement shows the beam divergence is ∼4◦ . In this experimental campaign, 20 kV, 4 A positive hydrogen beam has been extracted. This prototype ion source experiment with RHVPS integrated with DACS shall be helpful for actual PINI ion source operation for SST-1 NBI. At present prototype ion source has been removed and assembled PINI ion source is mounted to the vacuum vessel. Commissioning work for various beam line components including water and electrical connections, etc. are under progress. After completion of these commissioning works, operation of PINI ion source shall be undertaken. Acknowledgement Authors are grateful to both reviewers for their valuable comments towards improving the quality of the work. References
Fig. 9. Current and voltage waveform of 20 kV, 4 A positive hydrogen ion beam of 800 ms pulse.
[1] T. Ohkawa, Nuclear Fusion 10 (1970) 185–188. [2] M. Menon, Proceedings of the IEEE 69 (1981) 1012–1028. [3] Y.C. Saxena, Present status of the SST-1 project, Nuclear Fusion 40 (2000) 1069–1082. [4] D. Bora, Test results on systems developed for SST-1 tokamak, Nuclear Fusion 43 (2003) 1748–1758. [5] M.R. Jana, S.K. Mattoo, A.K. Chakraborty, U.K. baruah, G.B. Patel, P.K. Jayakumer, Long pulse characteristics of 5 MW ion source for SST-1 neutral beam injector, Fusion Engineering and Design 83 (2008) 729. [6] M.R. Jana, P.K. Jayakumar, N. Bisai, U. Baruah, P.J. Patel, N.P. Singh, et al., A high current ion accelerator system for neutral beam injector, Indian Journal of Physics 53S (2) (1999) 93–95. [7] P. Spaedtke, INP, Junkernstr. 99, 65205 Wiesbaden, Germany (Private Communication). [8] W.B. Kunkel, Neutral Beam Injection, Fusion 1 (1981) 103 (Part B). [9] D.J. Godden, The JET 80 kV PINI recent test-bed experience and future plans, in: Joint Development Committee (JDC) meeting, 28–29th October, Cadarache, page DG II-1, 1996. [10] R. Uhlemann, Forschungszentrum Juelich Institut fuer Energieforschung IEF-4 Plasmaphysik, D-52425 Juelich, Germany (private communication).