Characteristics of the Extracted Negative-Ion Beam in a ...
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Single-Aperture Grid with SMP SMP was positioned near the PG aperture on the source plasma side (thickness: 0.3 mm; width: 30 mm; and length: 10 mm) The electron current can be effectively reduced bending the magnetic field lines and by trapping electrons with the SMP at the extraction region. Multi-Aperture Grid wit SMP Characteristics of the Extracted Negative-Ion Beam in a Cesium-Free Negative-Ion Source using TPDSheet-U A.TONEGAWA , H.KAMINAGA, K.HANAIN, T.TAKIMOTO, K.N.Sato*, K. KAWAMURA Department of Physics, School of Science, Tokai University, *Tokyo University of Science [email protected] •This study reports a progress toward realizing a high-performance Cs-free negative ion source, that produces negative ions by volume production in a magnetized-sheet plasma device (TPDsheet-U). • Negative hydrogen ions are successfully extracted from the sheet plasma by single/multi-aperture grids, and the ratio of the extracted electron current J EG (e) and hydrogen negative-ion current J c (H − ), J EG /J c decreases from 10 to 0.2 with a soft magnetic material plate (SMP), which is a physical filter that prevents electron diffusion from the extraction region. •The J c is approximately 5-8 mA/cm2 at Vex of 10 kV, Id of 80 A, the gas pressure of 0.3 Pa, and the magnetic field strength of 40 mT. ABSTRACT Basic Characteristics of Sheet Plasma A magnetized sheet plasma is suitable for generating negative hydrogen ions through dissociative attachment because the distance between the region containing high-energy electrons (10–15 eV) and low-energy electrons, which is the region just in front of the grid (y = 10 - 25 mm). Effects of the SMP on Extracted Ion Beam of Single The SMP is effective in reducing the electron co-extraction. The ratio of the extracted electron current J EG (e) and hydrogen negative-ion current J c (H − ), J EG /J c decreases from 2 to 0.2 with SMP, which is a physical filter that prevents electron diffusion from the extraction region. Extracted Ion Beam of Multi-aperture Grids with SMP Negative hydrogen ions have been successfully extracted from the sheet plasma on the multi-aperture grids. The negative ion current density Jc was about 5-8 mA/cm 2 under the following conditions: extraction voltage V ex of 10 kV, discharge current I d of 80 A, gas pressure of 0.3 Pa, and magnetic field strength of 40 mT. The electron current JEG(e) with the SMP is reduced by about 85% compared to that without the SMP. OUTCOME •Most negative-ion sources use Cs to comply with the strict requirements. However, a careful control of the amount of Cs vapor is required, and regular maintenance becomes difficult for long-time operations. Thus, the Cs consumption must be reduced, or alternative method for a Cs-free ion source is highly necessary. •The reduction of electron co-extraction is also a common and essential issue for all negative-ion sources. A co-extracted electron causes power wastage and a high heat load of the extraction grid. •This study presents a design of Cs-free negative ion source using volume production in TPDsheet-U with a single- and multi-aperture grid and the characteristic of the developed extraction system on it. We have applied a soft magnetic material plate (SMP) in this study. to reduce the electron co- extraction. BACKGROUND •In this work, the characteristics of extracted beam current by single and multi-aperture grids with SMP are investigated in a magnetized sheet plasma system without Cs seeding (TPDsheet-U). •The SMP is effective to reduce the JEG/JC as a physical filter to prevent the diffusion of electrons from the extraction region. •The performance of the current density of the negative hydrogen ion beam Jc without Cs on TPDsheet-U is approximately half of that of the negative ion source on ITER-NBI with Cs. CONCLUSION (a) J C (H − ) and J EG (e), (b) J EG /J C ratioversus I d on the Multi-Aperture Grids ID: 845 [1] K. Hanai, et.al., Fusion Eng. and Des. 146 (2019)2721. [2] H. Kaminaga, et.al., Rev. Sci. Instrum. 91 (2020) 113302. ACKNOWLEDGEMENTS Cs-Free Negative-Ion Source TPDsheet-U REFERENCES •This work is performed with the support and under the auspices of the NIFS Collaboration Research program (NIFS20KOAR025). (a) J C (H − ) and J EG (e), (b) J EG /J C ratio versus I d on the Single-Aperture Grids Cs-Free Negative-Ion Source TPDsheet-U
Transcript of Characteristics of the Extracted Negative-Ion Beam in a ...
Single-Aperture Grid with SMP
SMP was positioned near the PG aperture on thesource plasma side (thickness: 0.3 mm; width: 30 mm; and length: 10 mm)
The electron current can be effectively reducedbending the magnetic field lines and by trappingelectrons with the SMP at the extraction region.
Multi-Aperture Grid wit SMP
Characteristics of the Extracted Negative-Ion Beam in a Cesium-Free Negative-Ion Source using TPDSheet-U
A.TONEGAWA, H.KAMINAGA, K.HANAIN, T.TAKIMOTO, K.N.Sato*, K. KAWAMURADepartment of Physics, School of Science, Tokai University,
*Tokyo University of [email protected]
•This study reports a progress toward realizing a high-performance Cs-freenegative ion source, that produces negative ions by volume production ina magnetized-sheet plasma device (TPDsheet-U).
• Negative hydrogen ions are successfully extracted from the sheet plasmaby single/multi-aperture grids, and the ratio of the extracted electroncurrent JEG(e) and hydrogen negative-ion current Jc(H−), JEG/Jc decreasesfrom 10 to 0.2 with a soft magnetic material plate (SMP), which is aphysical filter that prevents electron diffusion from the extraction region.
•The Jc is approximately 5-8 mA/cm2 at Vex of 10 kV, Id of 80 A, the gaspressure of 0.3 Pa, and the magnetic field strength of 40 mT.
ABSTRACTBasic Characteristics of Sheet PlasmaA magnetized sheet plasma is suitable for generating negative hydrogenions through dissociative attachment because the distance between theregion containing high-energy electrons (10–15 eV) and low-energyelectrons, which is the region just in front of the grid (y = 10 - 25 mm).Effects of the SMP on Extracted Ion Beam of SingleThe SMP is effective in reducing the electron co-extraction. The ratio of theextracted electron current JEG(e) and hydrogen negative-ion current Jc(H−),JEG/Jc decreases from 2 to 0.2 with SMP, which is a physical filter thatprevents electron diffusion from the extraction region.Extracted Ion Beam of Multi-aperture Grids with SMPNegative hydrogen ions have been successfully extracted from the sheetplasma on the multi-aperture grids. The negative ion current density Jc wasabout 5-8 mA/cm2 under the following conditions: extraction voltage Vex of10 kV, discharge current Id of 80 A, gas pressure of 0.3 Pa, and magneticfield strength of 40 mT. The electron current JEG(e) with the SMP is reducedby about 85% compared to that without the SMP.
OUTCOME
•Most negative-ion sources use Cs to comply with the strict requirements.However, a careful control of the amount of Cs vapor is required, andregular maintenance becomes difficult for long-time operations. Thus, theCs consumption must be reduced, or alternative method for a Cs-free ionsource is highly necessary.
•The reduction of electron co-extraction is also a common and essentialissue for all negative-ion sources. A co-extracted electron causes powerwastage and a high heat load of the extraction grid.
•This study presents a design of Cs-free negative ion source using volumeproduction in TPDsheet-U with a single- and multi-aperture grid and thecharacteristic of the developed extraction system on it. We have applied asoft magnetic material plate (SMP) in this study. to reduce the electron co-extraction.
BACKGROUND
•In this work, the characteristics of extracted beam current by single andmulti-aperture grids with SMP are investigated in a magnetized sheetplasma system without Cs seeding (TPDsheet-U).
•The SMP is effective to reduce the JEG/JC as a physical filter to preventthe diffusion of electrons from the extraction region.
•The performance of the current density of the negative hydrogen ionbeam Jc without Cs on TPDsheet-U is approximately half of that of thenegative ion source on ITER-NBI with Cs.
CONCLUSION
(a) JC(H−) and JEG(e), (b) JEG/JC ratioversus Id on the Multi-Aperture Grids
ID: 845
[1] K. Hanai, et.al., Fusion Eng. and Des. 146 (2019)2721.[2] H. Kaminaga, et.al., Rev. Sci. Instrum. 91 (2020) 113302.
ACKNOWLEDGEMENTS
Cs-Free Negative-Ion Source TPDsheet-U
REFERENCES•This work is performed with the support and under the auspices of the
NIFS Collaboration Research program (NIFS20KOAR025).
(a) JC(H−) and JEG(e), (b) JEG/JC ratio versus Id on the Single-Aperture Grids
Cs-Free Negative-Ion Source TPDsheet-U
