Comparison of the Heating Properties of LaB6 and CeB6 Due to the Back Comparison of the Heating Properties of LaB6 and CeB6 Due to the Back

Bakr, Mahmoud; Kinjo, Ryota; Choi, Yongwoon; Omer, M.; Yoshida, Kyohei; Ueda, Shigenori; Takasaki, Masato; Ishida, Keiichi; Kimura, N.; Zen, Heishun; Sonobe, Taro; Kii, Toshiteru; Masuda, Kazuyoshi; Ohgaki, Hideaki

doi:10.3938/jkps.59.3273

Cited by 8 publications

(4 citation statements)

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“…Simulation has been performed to compare the effect of BB electrons between LaB6 and CeB6. The results revealed that CeB6 has 20% less impact by BB electrons compared to LaB6 [18]. Based on this results, single crystals of LaB6 and CeB6 with 1.8 mm diameters, prepared using the floating zone method, were purchased to compare the BB effect experimentally.…”

Section: Selection Of Cathode Materialsmentioning

confidence: 98%

“…More recently, a compensation system for the temperature change in the cathode using an external laser system has been proposed [15]. However, few papers have looked at the influence of the cathode material's properties in reducing the BB effect [16], [17], [18]. To increase the efficiency of the T-RF gun, it is preferable to reduce the BB effect from the source by minimizing the change in the cathode temperature and the current density in the cathode surface.…”

Section: Introductionmentioning

confidence: 99%

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Influence of the Cathode Material Properties in Reducing the Back-Bombardment Effect in Thermionic RF Gun

Bakr

Ohgaki

2018

IEEE Trans. Electron Devices

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Abstract-The effect of back bombardment (BB) electrons is considered one of the main obstacles for extensive use of thermionic RF guns. Ten hexaboride materials named (Ca, Sr, Ba, La, Ce, Pr, Nd, Sm, Eu, and Gd) B6 are investigated in this work to survey the effect of the cathode material on reducing BB electrons and compare them with LaB6 (which is widely used as a thermionic cathode). A numerical model was used to conduct this study. Besides the numerical calculations; an experiment has been performed to determine the work functions of CeB6 and LaB6. The results from the numerical calculations revealed that (Ba, Ca, and Nd) B6 are less affected by BB electrons: 42, 50, and 59 % respectively, compared with LaB6, for low beam current applications. In contrast, for high beam current duties, (Nd, Ce, and Sm) B6 have minimum influence by BB electrons compared with other hexaborides. The study concluded that BB electrons are strongly affected by the properties of the cathode material, especially thermionic emission and material density. Moreover, the study suggests that it is worthwhile to prepare BaB6, CaB6, NdB6, and SmB6 as cathode materials, then to subject them to a real experimental test using thermionic RF gun to compare their performance and BB effect against LaB6.

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Section: Selection Of Cathode Materialsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Influence of the Cathode Material Properties in Reducing the Back-Bombardment Effect in Thermionic RF Gun

Bakr

Ohgaki

2018

IEEE Trans. Electron Devices

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“…It has been reported that CeB 6 is more resistive to carbon contamination and has a lower evaporation rate than LaB 6 [17,19] and hence there is a possibility that CeB 6 will have longer lifetime than LaB 6 as LHEP tip. Until recently LaB 6 and graphite were more common candidates to be chosen as LHEP tip [14,15,18,[20][21][22] and CeB 6 is emerging now as popular candidate for LHEP [16]. A high density small diameter (1.0 mm) high power laser light (in this case, coherent-make, CW CO 2 laser @10.6 µm wavelength having maximum output power 55 W) is used to heat the probe tip.…”

Section: Introductionmentioning

confidence: 99%

Temperature response of laser heated emissive probe materials under vacuum and free atmospheric conditions

Kanik¹,

Sarma²,

Ghosh³

et al. 2020

Laser Phys.

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Precise temporal and spatial knowledge of plasma potential has been a challenging task for decades. Gradient in values of plasma potential govern local electric fields providing insight into many other bulk plasma properties like particle drifts, confinement, transport barriers etc and plays a crucial role in determining stability of magnetically confined high temperature plasmas. In high temperature devices like tokamaks, plasma tends to develop edge bifurcations and results in edge transport barriers, which are a key tool for enhancing the plasma conﬁnement properties in magnetic fusion devices, which in turn requires knowledge of plasma potential. Conventional emissive probes (CEPs) in high temperature magnetically confined plasmas are not advisable owing to their inherent properties and tokamak parameters like high magnetic field, ultra-high vacuum pressure etc as well as tokamak geometry. A new type of emissive probe is becoming popular in recent times in such devices called the laser heated emissive probe (LHEP). Mostly, LaB6 and graphite are used as a LHEP tip owing to their inherent properties of thermal conductivity, low work function, high emissivity, higher lifetime etc. Similar with LaB6 in its mechanical and electrical properties, CeB6 is emerging as a promising candidate for LHEP. CeB6 is a better electron emitter than graphite and LaB6 at comparatively low power due to its lower work function. In this work, the heating dynamics of LaB6 and CeB6 heated by a CW CO2 laser with maximum power of 55 W have been reported. Theoretical and simulation models using Matlab and ANSYS have been developed to understand and explain the temperature gaining process of the probes. Simulation results are further validated by comparing them with experimentally measured data using an infrared camera.

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“…Thus, the metal work-function or the barrier height is an important parameter for WFD bipolar transistors. For the actual fabrication, the desirable high barrier height can be realised by a contact metal with a low work-function such as lanthanum hexaboride [12] and cerium hexaboride [13] according to the Mott-Schottky theory or special treatment of the metal/4H-SiC interface [14,15]. The output characteristic of the WFD bipolar transistor is shown in Fig.…”

mentioning

confidence: 99%

4H‐SiC work‐function‐dependent bipolar transistor with ultra‐high current gain

et al. 2014

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A new structure of a 4H-SiC bipolar transistor with ultra-high current gain is proposed and analysed by simulation. A p-type Schottky contact serving as the conventional emitter region is introduced. By proper choice of the metal work-function, the injection efficiency of the minority carrier (electron) is promoted and may be close to unity. Therefore high current gain is realised due to the high electron current density injected from the p-type Schottky contact. The simulation results show that the current gain varies with the metal work-function and could reach ∼1000, which is attractive for the base-drive circuit. Moreover, the new structure simplifies the etching process compared with the conventional bipolar junction transistor.Introduction: In past decades, bipolar junction transistors (BJTs) based on 4H-SiC have developed rapidly, owing to the superior properties of silicon carbide for high-power and high-temperature applications. As a current-driven switching and amplifying device, it is important to improve the current gain of BJTs for reducing the power losses in the drive circuit. Reducing the base thickness is a direct way, but the blocking characteristic will be significantly degraded [1]. To reduce the surface recombination between SiC and SiO 2 along the emitter-base sidewall, a suppressed surface recombination BJT structure [2] and a deep-level-reduction process [3] were proposed with special fabrication procedures. Also, the double-base structure [4] and a single base with a buried layer [5] which could accelerate the electron transport in the base region were verified by experiment and simulation.In the early years, a Schottky heterojunction bipolar transistor was proposed and demonstrated [6]. The current gain has a significant improvement, owing to the high injection efficiency of minority carriers in the Schottky heterojunction barrier emitter. It is worth noting that the high minority-to-majority carrier ratio has been demonstrated in the silicon tunnel transistor [7]. Furthermore, using this injection theory, silicon heterojunction emitter transistors with a current gain over 25 000 have been fabricated [8], and some new structures with a excellent performance have also been proposed [9,10]. In this Letter, we report a 4H-SiC work-function-dependent (WFD) bipolar transistor that replaces the conventional emitter region with the selected p-type Schottky contact. Using the theory of minority carrier injection in the Schottky contact, a large injection ratio of the minority-carrier (electron)-to-majority-carrier (hole) could be obtained due to the suppression of the majority carrier current by the large barrier height at the metal-SiC interface. Thus, the current gain is improved. Furthermore, the blocking characteristic could be maintained by the design of a floating-plate at the Schottky metal periphery.

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Comparison of the Heating Properties of LaB6 and CeB6 Due to the Back Comparison of the Heating Properties of LaB6 and CeB6 Due to the Back

Cited by 8 publications

References 0 publications

Influence of the Cathode Material Properties in Reducing the Back-Bombardment Effect in Thermionic RF Gun

Influence of the Cathode Material Properties in Reducing the Back-Bombardment Effect in Thermionic RF Gun

Temperature response of laser heated emissive probe materials under vacuum and free atmospheric conditions

4H‐SiC work‐function‐dependent bipolar transistor with ultra‐high current gain

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