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As the heart of a magnetron, cathode plays an important role in the device. At present, the pure W cathode is mainly used in high-power continuous wave magnetron tube. However, the pure W cathode has low thermionic emission capability and secondary electron emission yield (1.25-1.50), which result in the cathode operating at a high temperature (2450-2700 K). The higher the operating temperature of the cathode, the faster the evaporation of its surface is, which can shorten the cathode lifetime. In order to enhance the emission current, reduce the operation temperature and prolong the lifetime of the pure W cathode, a novel refractory Y2O3-Gd2O3-HfO2 impregnated W base direct-heated cathode (Y-Gd-Hf-O impregnated cathode) is developed in this paper. The present investigation mainly focuses on the thermionic emission, work function, lifetime, emission mechanism, and anti-bombing property. The direct current (dc) emission properties of the Y-Gd-Hf-O impregnated cathode are investigated, showing that it can provide more than 0.4, 1, 4.0, 7.74, 10.5 A/cm2 current density for the space charge limitation (SCL) at 1300, 1400, 1500, 1600, 1700 ℃ respectively. Absolute zero work function for the cathode is only 1.68 eV obtained by the Richardson line method. The effective work function for the cathode is in a range of 2.6-3.1 eV obtained by the Richardson-Dushman formula. The lifetime for the cathode is more than 3600 h with an initial load of 1.5 A/cm2 at 1600 ℃. The surface microstructure, element composition and content of the Y-Gd-Hf-O impregnated cathode are analyzed by the scanning electron microscope (SEM), Auger electron spectroscopy (AES), and energy disperse spectroscopy (EDS). The analysis results show that the surface of the cathode contains the Y2O3-x semiconductor layer, which causes an improvement of the electro-conductivity during the activation. The work function of the cathode can also be reduced due to the improvement of the electro-conductivity. Besides, the addition of the transition-metal oxide HfO2 changes the internal lattice energy level, which can further reduce the work function. Therefore, the Y-Gd-Hf-O impregnated cathode has good thermionic emission capability. In addition, the anti-bombing performance of the cathode is also studied, which shows that the dc emission current density decreases linearly from the initial current density of 1.5 A/cm2 to 0.4 A/cm2 after 150-h continuous electron bombing at 10 W/cm2. In the future research, we will focus on enhancing the anti-bombing property for the Y-Gd-Hf-O impregnated cathode by using Y-Gd-Hf-O doped W base direct-heated cathode.
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Keywords:
- direct-heated cathode /
- work function /
- lifetime /
- magnetron tubes
[1] Yue S, Zhang Z C, Gao D P 2013 Acta Phys. Sin. 62 178401 (in Chinese) [岳松, 张兆传, 高东平 2013 62 178401]
[2] Yue S, Zhang Z C, Gao D P 2014 Chin. Phys. B 23 88402
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[4] Zhang E Q 1980 IEEE Trans. Elec. Dev. 27 1280
[5] Qi S K, Wang X X, Luo J R, Zhao S K, Zhao Q L, Li Y, Zhang Q Proceedings of IVESC Saint-Petersburg, Russia, June 30-July 4, 2014 p18
[6] Zhang X, Wang Y, Fan J J, Zhu F, Zhang R 2014 Acta Phys. Sin. 63 167901 (in Chinese) [张雪, 王勇, 范俊杰, 朱芳, 张瑞 2014 63 167901]
[7] Wang J S, Zhou M L, Ma S Y, Zuo T Y 2006 J. Alloy. Compd. 419 172
[8] Wang X X, Liu Y W, Luo J R, Zhao Q L, Li Y, Zhang Q 2014 IEEE Trans. Elec. Dev. 61 605
[9] Wang X X, Liao X H, Luo J R, Zhao Q L, Zhang M, Wang Q F, Li Y 2014 IEEE Trans. Elec. Dev. 59 491
[10] Liu Y W, Tian H, Han Y, Liu P K, Lu Y X 2012 IEEE Trans. Elec. Dev. 59 3618
[11] Heißl M, Mitterer C, Granzer T 2014 Int. J.Refract. Met. Hard Mat. 43 181
[12] Electronic tube design handbook editorial Committee 1979 Magnetron Design Handbook (Beijing: National Defence Industry Press) p193, p211, p420 (in Chinese) [电子管设计手册编辑委员会 1979 磁控管设计手册 (北京: 国防工业出版社)第193, 211, 420页]
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[16] Wang J S, Liu J, Zhou M L, Li H Y, Zhang J X, Zuo T Y 2003 Trans. Nonferrous Met. Soc. Chin. 13 38
[17] Wang J S, Li H Y, Zhou M L, Yang S, Tao S W, Zhang J X 2003 J. Chin. Rare Earth. Soc. 21 295
[18] Bruining D H, MBE 1954 Physics and Application of Secondary Electron Emission (Oxford: Pergamon Press LTD) p19
[19] Chia C Y, Moon S J, Byung J C 2004 Thin Solid Films. 462 90
[20] Liu X Q 1980 Cathode Electronics (Beijing: Publ. House Sci) p95, p149, p184, p211 (in Chinese) [刘学悫1980阴极电子学 (北京: 科学出版社) 第95, 149, 184, 211页]
[21] Zhang M, Wang X X, Luo J R, Zhao Q L, Liao X H 2011 IEEE Trans. Elec. Dev. 58 2143
[22] Chang T J, Qi X 1999 Modern Analysis Methods of Materials (Harbin: Harbin Institute of Technology Press) pp124-125 [常铁军, 祁欣 1999 材料近代分析测试方法(哈尔滨: 哈尔滨工业大学出版社)第124-125页]
[23] Wang J S, Zhou M L, Zuo T Y, Zhang J X, Nie Z R, Hu Y C 2001 Chinese Journal of Rare Metals. 25 170 (in Chinese) [王金淑, 周美玲, 左铁镛, 张久兴, 聂祚仁, 胡延槽2001 稀有金属 25 170]
[24] Zhang E Q 1976 Acta Phys. Sin. 25 23 (in Chinese) [张恩虬 1976 25 23]
[25] Liu H Q 1987 Function of Rare Earth in Catalytic (Beijing: Publ. House Sci) p13 (in Chinese) [刘恒潜1987稀土在催化中的应用 (北京: 科学出版社) 第13页]
[26] Liao X H, Wang X X, Zhao Q L, Li Y 2010 Journal of Microwaves S1 534 (in Chinese) [廖显恒, 王小霞, 赵青兰, 李云 2010 微波学报 S1 534]
[27] Wang J S, Liu W, Ren Z Y 2010 Mater. Res. Bull. 45 324
[28] Dearnaley G 1969 Thin Solid Films. 3 161
[29] Surplice N A 1968 J. Phys. D. Ser. 1 1245
[30] Zalm P 1968 Adv. Electron. El. Phys. 25 211
[31] Qi S K, Wang X X, Luo J R, Hu M W, Li Y Proceedings of IRMMW-THz Hong Kong, China,23-28 August, 2015 p12
[32] Li X Q, Liao X H, Liu G Q 1965 Acta Electr. Sin. 1 48 (in Chinese) [李小琼, 廖显恒, 刘桂全 1965 电子学报 1 48]
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[1] Yue S, Zhang Z C, Gao D P 2013 Acta Phys. Sin. 62 178401 (in Chinese) [岳松, 张兆传, 高东平 2013 62 178401]
[2] Yue S, Zhang Z C, Gao D P 2014 Chin. Phys. B 23 88402
[3] Bisello D, Candelori A, Giubilato P, Kaminsky A, Mattiazzo S, Nigro M, Pantano D, Rando R, Silvestrin L, Tessaro M, Wyss J 2008 NuclInstrum. Meth. B 266 173
[4] Zhang E Q 1980 IEEE Trans. Elec. Dev. 27 1280
[5] Qi S K, Wang X X, Luo J R, Zhao S K, Zhao Q L, Li Y, Zhang Q Proceedings of IVESC Saint-Petersburg, Russia, June 30-July 4, 2014 p18
[6] Zhang X, Wang Y, Fan J J, Zhu F, Zhang R 2014 Acta Phys. Sin. 63 167901 (in Chinese) [张雪, 王勇, 范俊杰, 朱芳, 张瑞 2014 63 167901]
[7] Wang J S, Zhou M L, Ma S Y, Zuo T Y 2006 J. Alloy. Compd. 419 172
[8] Wang X X, Liu Y W, Luo J R, Zhao Q L, Li Y, Zhang Q 2014 IEEE Trans. Elec. Dev. 61 605
[9] Wang X X, Liao X H, Luo J R, Zhao Q L, Zhang M, Wang Q F, Li Y 2014 IEEE Trans. Elec. Dev. 59 491
[10] Liu Y W, Tian H, Han Y, Liu P K, Lu Y X 2012 IEEE Trans. Elec. Dev. 59 3618
[11] Heißl M, Mitterer C, Granzer T 2014 Int. J.Refract. Met. Hard Mat. 43 181
[12] Electronic tube design handbook editorial Committee 1979 Magnetron Design Handbook (Beijing: National Defence Industry Press) p193, p211, p420 (in Chinese) [电子管设计手册编辑委员会 1979 磁控管设计手册 (北京: 国防工业出版社)第193, 211, 420页]
[13] Djubua B C, Polivnikova O V Proceedings of IVESC Beijing, China, 6-10 September, 2004 p177
[14] Djubua B C, Polivnikova O V 2003 Appl. Surf. Sci. 215 242
[15] Nie Z R, Zuo T Y, Zhou M L, Wang Y M, Wang J S, Zhang J X 2000 J. Rare Earth. 18 110
[16] Wang J S, Liu J, Zhou M L, Li H Y, Zhang J X, Zuo T Y 2003 Trans. Nonferrous Met. Soc. Chin. 13 38
[17] Wang J S, Li H Y, Zhou M L, Yang S, Tao S W, Zhang J X 2003 J. Chin. Rare Earth. Soc. 21 295
[18] Bruining D H, MBE 1954 Physics and Application of Secondary Electron Emission (Oxford: Pergamon Press LTD) p19
[19] Chia C Y, Moon S J, Byung J C 2004 Thin Solid Films. 462 90
[20] Liu X Q 1980 Cathode Electronics (Beijing: Publ. House Sci) p95, p149, p184, p211 (in Chinese) [刘学悫1980阴极电子学 (北京: 科学出版社) 第95, 149, 184, 211页]
[21] Zhang M, Wang X X, Luo J R, Zhao Q L, Liao X H 2011 IEEE Trans. Elec. Dev. 58 2143
[22] Chang T J, Qi X 1999 Modern Analysis Methods of Materials (Harbin: Harbin Institute of Technology Press) pp124-125 [常铁军, 祁欣 1999 材料近代分析测试方法(哈尔滨: 哈尔滨工业大学出版社)第124-125页]
[23] Wang J S, Zhou M L, Zuo T Y, Zhang J X, Nie Z R, Hu Y C 2001 Chinese Journal of Rare Metals. 25 170 (in Chinese) [王金淑, 周美玲, 左铁镛, 张久兴, 聂祚仁, 胡延槽2001 稀有金属 25 170]
[24] Zhang E Q 1976 Acta Phys. Sin. 25 23 (in Chinese) [张恩虬 1976 25 23]
[25] Liu H Q 1987 Function of Rare Earth in Catalytic (Beijing: Publ. House Sci) p13 (in Chinese) [刘恒潜1987稀土在催化中的应用 (北京: 科学出版社) 第13页]
[26] Liao X H, Wang X X, Zhao Q L, Li Y 2010 Journal of Microwaves S1 534 (in Chinese) [廖显恒, 王小霞, 赵青兰, 李云 2010 微波学报 S1 534]
[27] Wang J S, Liu W, Ren Z Y 2010 Mater. Res. Bull. 45 324
[28] Dearnaley G 1969 Thin Solid Films. 3 161
[29] Surplice N A 1968 J. Phys. D. Ser. 1 1245
[30] Zalm P 1968 Adv. Electron. El. Phys. 25 211
[31] Qi S K, Wang X X, Luo J R, Hu M W, Li Y Proceedings of IRMMW-THz Hong Kong, China,23-28 August, 2015 p12
[32] Li X Q, Liao X H, Liu G Q 1965 Acta Electr. Sin. 1 48 (in Chinese) [李小琼, 廖显恒, 刘桂全 1965 电子学报 1 48]
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