This paper deals with wave propagation and power coupling in blue-core helicon plasma driven by various antennas and frequencies.It is found that compared to non-blue-core mode,for blue-core mode,the wave can propagat...This paper deals with wave propagation and power coupling in blue-core helicon plasma driven by various antennas and frequencies.It is found that compared to non-blue-core mode,for blue-core mode,the wave can propagate in the core region,and it decays sharply outside the core.The power absorption is lower and steeper in radius for blue-core mode.Regarding the effects of antenna geometry for blue-core mode,it shows that half helix antenna yields the strongest wave field and power absorption,while loop antenna yields the lowest.Moreover,near axis,for antennas with m=+1,the wave field increases with axial distance.In the core region,the wave number approaches to a saturation value at much lower frequency for non-blue-core mode compared to blue-core mode.The total loading resistance is much lower for blue-core mode.These findings are valuable to understanding the physics of blue-core helicon discharge and optimizing the experimental performance of blue-core helicon plasma sources for applications such as space propulsion and material treatment.展开更多
The effect of the radial density configuration in terms of width, edge gradient and volume gradient on the wave field and energy flow in an axially uniform helicon plasma is studied in detail. A three-parameter functi...The effect of the radial density configuration in terms of width, edge gradient and volume gradient on the wave field and energy flow in an axially uniform helicon plasma is studied in detail. A three-parameter function is employed to describe the density, covering uniform,parabolic, linear and Gaussian profiles. It finds that the fraction of power deposition near the plasma edge increases with density width and edge gradient, and decays in exponential and "bumpon-tail" profiles, respectively, away from the surface. The existence of a positive second-order derivative in the volume density configuration promotes the power deposition near the plasma core, which to our best knowledge has not been pointed out before. The transverse structures of wave field and current density remain almost the same during the variation of density width and gradient, confirming the robustness of the m=1 mode observed previously. However, the structure of the electric wave field changes significantly from a uniform density configuration, for which the coupling between the Trivelpiece-Gould(TG) mode and the helicon mode is very strong, to non-uniform ones. The energy flow in the cross section of helicon plasma is presented for the first time, and behaves sensitive to the density width and edge gradient but insensitive to the volume gradient. Interestingly, the radial distribution of power deposition resembles the radial profile of the axial component of current density, suggesting the control of the power deposition profile in the experiment by particularly designing the antenna geometry to excite a required axial current distribution.展开更多
螺旋波等离子体源以其高电离效率与高密度优势受到多个领域的青睐。螺旋波放电高电离效率的机理或者功率耦合模式,一直是困扰该领域学者的难点之一,对于放电过程与特性的诊断则是揭示其物理机制的重要途径。光谱诊断能够克服介入式诊断...螺旋波等离子体源以其高电离效率与高密度优势受到多个领域的青睐。螺旋波放电高电离效率的机理或者功率耦合模式,一直是困扰该领域学者的难点之一,对于放电过程与特性的诊断则是揭示其物理机制的重要途径。光谱诊断能够克服介入式诊断手段对等离子体的干扰同时受等离子体烧蚀等弊端,且响应速度快、操作灵活。为研究螺旋波等离子体的放电特性以及气体压力的影响,开展了以氩气为工质气体的光谱实验研究,并针对实验开展了Helic程序数值模拟。通过改变光纤探头焦距调整径向诊断位置,得到谱线强度的径向分布。由氩原子4p-4s能级跃迁产生的谱线主要集中在740~920 nm区间,谱线相对强度较离子激发谱线较强。实验研究发现,在较低氩气压力范围(0.2 Pa< P Ar <1.0 Pa),随着压力增加,放电光强迅速增加,但是当压力增加到大于1.0 Pa之后,光强增长的趋势变缓,甚至部分谱线的相对强度不再增长,达到类饱和状态,朗缪尔探针测量得到离子密度变化趋势与其相似。光强分布在靠近径向边界处( r ≈4 cm)存在凸起,且随压力增加,该凸起分布更为明显。通过对电子温度的计算发现,压力增加到一定程度将影响放电均匀性。仿真结果显示,增大压力,功率沉积密度的径向分布逐渐向径向边界处积累,与实验观察到的谱线强度径向凸起相一致,螺旋波与TG波的耦合效率增加。随着气体压力的增加,Er的径向边界峰值降低,原因是波所受阻尼增强, TG波被有效地局限于径向较窄的边界处。电流密度轴向分量Jz在等离子体内部和边界处的峰值呈显著的减小趋势,可见,虽然压力增加一定程度上提高了等离子体密度,但却相应的减小了电离率,导致轴向电流密度受限。但是径向电流密度Jr却呈现先减小后增大的趋势,且增长幅度明显,综合来看,放电效率有所提高。可见适当增加气体压力,有助于提高放电的功率耦合效率和强度,增加等离子体密度。光强比值法是针对线性谱线参数计算的典型方法, Helic程序亦是专业领域内认可度很高的计算工具,结果可靠,分析方法具有可借鉴性。实验及仿真结果对于提高氩气工质下的螺旋波放电强度提供了一定的参考价值。展开更多
Characterizing the gap eigenmode of shear Alfv′en waves(SAWs) and its interaction with energetic ions is important to the success of magnetically confined fusion. Previous studies have reported an experimental observ...Characterizing the gap eigenmode of shear Alfv′en waves(SAWs) and its interaction with energetic ions is important to the success of magnetically confined fusion. Previous studies have reported an experimental observation of the spectral gap of SAW on the on Large Plasma Device(LAPD)(Zhang et al. 2008 Phys. Plasmas 15 012103), a linear large plasma device(Gekelman et al. 1991 Rev. Sci. Instrum. 62 2875) possessing easier diagnostic access and lower cost compared with traditional fusion devices, and analytical theory and numerical gap eigenmode using ideal conditions(Chang 2014 Ph.D Thesis at Australian National University). To guide experimental implementation, the present work models the gap eigenmode of SAWs using exact LAPD parameters. A full picture of the wave field for previous experiment reveals that the previously observed spectral gap is not global but an axially local result. To form a global spectral gap, the number of magnetic mirrors has to be increased and stronger static magnetic field makes it clearer. Such a spectral gap is obtained for the magnetic field of B0(z) = 1.2 + 0.6 cos[2π(z-33.68)/3.63] with 7.74-m magnetic beach. By introducing two types of local defects(corresponding to Eθ(z0) = 0 and E’θ(z0) = 0 respectively), odd-parity and even-parity discrete eigenmodes are formed clearly inside the gap. The strength of these gap eigenmodes decreases significantly with collision frequency, which is consistent with previous studies. Parameter scans show that these gap eigenmodes can be even formed successfully for the field strength of B0(z) = 0.2 + 0.1 cos[2π(z-33.68)/3.63] and with only four magnetic mirrors, which are achievable by the LAPD at its present status. This work can serve as a strong motivation and direct reference for the experimental implementation of the gap eigenmode of SAWs on the LAPD and other linear plasma devices.展开更多
Alfvnic gap eigenmode(AGE) can eject energetic particles from confinement and thereby threaten the success of magnetically controlled fusion. A low-temperature plasma cylinder is a promising candidate to study this ei...Alfvnic gap eigenmode(AGE) can eject energetic particles from confinement and thereby threaten the success of magnetically controlled fusion. A low-temperature plasma cylinder is a promising candidate to study this eigenmode, due to easy diagnostic access and simple geometry, and the idea is to arrange a periodic array of magnetic mirrors along the plasma cylinder and introduce a local defect to break the field periodicity. The present work validates this idea by reproducing a clear AGE inside a spectral gap, and more importantly details the influence of the number and depth(or modulation factor)of magnetic mirror on the characteristics of AGE. Results show that AGE is suppressed by other modes inside the spectral gap when the number of magnetic mirrors is below a certain value, which leads to a weakened Bragg’s effect. The structure and frequency of AGE remain unchanged for a decreased number of magnetic mirrors, as long as this number is enough for the AGE formation. The width of spectral gap and decay constant(inverse of decay length) of AGE are linearly proportional to the depth of magnetic mirror, implying easier observation of AGE through a bigger mirror depth. The frequency of AGE shifts to a lower range with the depth increased, possibly due to the unfrozen plasma with field line and the invalidity of small-perturbation analysis. Nevertheless, it is exciting to find that the depth of field modulation can be increased to form AGE for a very limited number of magnetic mirrors. This is of particular interest for the experimental implementation of AGE on a low-temperature plasma cylinder with limited length.展开更多
A one dimensional model is developed for defective gap mode(DGM)with two types of boundary conditions:conducting mesh and conducting sleeve.For a periodically modulated system without defect,the normalized width of...A one dimensional model is developed for defective gap mode(DGM)with two types of boundary conditions:conducting mesh and conducting sleeve.For a periodically modulated system without defect,the normalized width of spectral gaps equals to the modulation factor,which is consistent with previous studies.For a periodic system with local defects introduced by the boundary conditions,it shows that the conducting-mesh-induced DGM is always well confined by spectral gaps while the conducting-sleeve-induced DGM is not.The defect location can be a useful tool to dynamically control the frequency and spatial periodicity of DGM inside spectral gaps.This controllability can be potentially applied to the interaction between gap eigenmodes and energetic particles in fusion plasmas,and optical microcavities and waveguides in photonic crystals.展开更多
A new compact cascaded arc device for plasma-wall interaction study is developed at the Institute of Plasma Physics,Chinese Academy of Sciences.A magnetic field up to 0.8 T is achieved to confine plasmas in a 1.2 m lo...A new compact cascaded arc device for plasma-wall interaction study is developed at the Institute of Plasma Physics,Chinese Academy of Sciences.A magnetic field up to 0.8 T is achieved to confine plasmas in a 1.2 m long and 0.1 m diameter vacuum chamber.Gas fluid type analysis in this compact vacuum system was done under high particle flux condition.The gas pressure obtained by calculation was consistent with the measurement result.Continuous argon plasma discharge with ion flux of~0.5×10^(24)m^(-2)s^(-1)is successfully sustained for more than 1h.The effects of magnetic field configuration,gas flow rate,and discharge arc current on the ion flux to target were studied in detail.展开更多
The remaining challenges, confronting high-power microwave (HPM) sources and pulsed power generators, stim- ulate the developments of robust relativistic electron beam sources. This paper presents a carbon fibre cat...The remaining challenges, confronting high-power microwave (HPM) sources and pulsed power generators, stim- ulate the developments of robust relativistic electron beam sources. This paper presents a carbon fibre cathode which is tested in a single pulsed power generator. The distribution and the development of cathode plasma are observed by time-and-space resolved diagnostics, and the uniformity of electron beam density is checked by taking x-ray images. A quasistationary behaviour of cathode plasma expansion is observed. It is found that the uniformity of the extracted electron beam is satisfactory in spite of individual plasma jets on the cathode surface. These results show that carbon fibre cathodes can provide a positive prospect for developing a high-quality electron beam.展开更多
This paper mainly investigates plasma characterization on carbon fiber cathodes with and without cesium iodide (CsI) coating powered by a - 300 ns, - 200 kV accelerating pulse. It was found that the CsI layers can n...This paper mainly investigates plasma characterization on carbon fiber cathodes with and without cesium iodide (CsI) coating powered by a - 300 ns, - 200 kV accelerating pulse. It was found that the CsI layers can not only improve the diode voltage, but also maintain a stable perveance. This indicates a slowly changed diode gap or a low cathode plasma expansion velocity. By spectroscopic diagnostics, in the vicinity of the cathode surface the average plasma density and temperature were found to be -3×10^14 cm^-3 and - 5 eV, respectively, for an electron current density of - 40 A/cm^2. Furthermore, there exists a multicomponent plasma expansion toward the anode. The plasma expansion velocity, corresponding to the carbon and hydrogen ions, is estimated to be - 1.5 cm/μs. Most notably, Cs spectroscopic line was obtained only at the distance - 0.5 mm from the cathode surface. Carbon and hydrogen ions are obtained up to the distance of 2.5 mm from the cathode surface. Cs ions almost remain at the vicinity of the cathode surface. These results show that the addition of CsI enables a slow cathode plasma expansion toward the anode, providing a positive prospect for developing long-pulse electron beam sources.展开更多
To study the heating mechanism of electron cyclotron resonance thruster(ECRT)immersed in a non-uniform magnetic field,experiments and simulations are performed based on an electron cyclotron resonance plasma source at...To study the heating mechanism of electron cyclotron resonance thruster(ECRT)immersed in a non-uniform magnetic field,experiments and simulations are performed based on an electron cyclotron resonance plasma source at ASIPP.It is found that the first harmonic of electron cyclotron resonance is essential for plasma ignition at high magnetic field(0.0875 T),while the plasma can sustain without the first and second harmonics of electron cyclotron resonance at low magnetic field(till 0.0170 T).Evidence of radial hollow density profile indicates that upper hybrid resonance,which has strong edge heating effect,is the heating mechanism of low-field ECRT.The heating mode transition from electron cyclotron resonance to upper hybrid resonance is also revealed.Interestingly,the evolutions of electron temperature and electron density with input power experience a‘delayed’jump,which may be correlated with the different power levels required for cyclotron and ionization.Moreover,when the field strength decreased,the variation of electron density behaves in an opposite trend with that of electron temperature,implying a possible competition of power deposition between them.The present work is of great interest for understanding the plasma discharge in ECRT especially immersed in a non-uniform magnetic field,and designing efficient ECRT using low magnetic field for economic space applications.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.92271113)the Fundamental Research Funds for the Central Universities(Grant No.2022CDJQY-003)+1 种基金Chongqing Entrepreneurship and Innovation Support Program for Overseas Returnees(Grant No.CX2022004)the Fund from Shanghai Engineering Research Center of Space Engine(Grant No.17DZ2280800).
文摘This paper deals with wave propagation and power coupling in blue-core helicon plasma driven by various antennas and frequencies.It is found that compared to non-blue-core mode,for blue-core mode,the wave can propagate in the core region,and it decays sharply outside the core.The power absorption is lower and steeper in radius for blue-core mode.Regarding the effects of antenna geometry for blue-core mode,it shows that half helix antenna yields the strongest wave field and power absorption,while loop antenna yields the lowest.Moreover,near axis,for antennas with m=+1,the wave field increases with axial distance.In the core region,the wave number approaches to a saturation value at much lower frequency for non-blue-core mode compared to blue-core mode.The total loading resistance is much lower for blue-core mode.These findings are valuable to understanding the physics of blue-core helicon discharge and optimizing the experimental performance of blue-core helicon plasma sources for applications such as space propulsion and material treatment.
基金supported by National Natural Science Foundation of China(No.11405271)
文摘The effect of the radial density configuration in terms of width, edge gradient and volume gradient on the wave field and energy flow in an axially uniform helicon plasma is studied in detail. A three-parameter function is employed to describe the density, covering uniform,parabolic, linear and Gaussian profiles. It finds that the fraction of power deposition near the plasma edge increases with density width and edge gradient, and decays in exponential and "bumpon-tail" profiles, respectively, away from the surface. The existence of a positive second-order derivative in the volume density configuration promotes the power deposition near the plasma core, which to our best knowledge has not been pointed out before. The transverse structures of wave field and current density remain almost the same during the variation of density width and gradient, confirming the robustness of the m=1 mode observed previously. However, the structure of the electric wave field changes significantly from a uniform density configuration, for which the coupling between the Trivelpiece-Gould(TG) mode and the helicon mode is very strong, to non-uniform ones. The energy flow in the cross section of helicon plasma is presented for the first time, and behaves sensitive to the density width and edge gradient but insensitive to the volume gradient. Interestingly, the radial distribution of power deposition resembles the radial profile of the axial component of current density, suggesting the control of the power deposition profile in the experiment by particularly designing the antenna geometry to excite a required axial current distribution.
文摘螺旋波等离子体源以其高电离效率与高密度优势受到多个领域的青睐。螺旋波放电高电离效率的机理或者功率耦合模式,一直是困扰该领域学者的难点之一,对于放电过程与特性的诊断则是揭示其物理机制的重要途径。光谱诊断能够克服介入式诊断手段对等离子体的干扰同时受等离子体烧蚀等弊端,且响应速度快、操作灵活。为研究螺旋波等离子体的放电特性以及气体压力的影响,开展了以氩气为工质气体的光谱实验研究,并针对实验开展了Helic程序数值模拟。通过改变光纤探头焦距调整径向诊断位置,得到谱线强度的径向分布。由氩原子4p-4s能级跃迁产生的谱线主要集中在740~920 nm区间,谱线相对强度较离子激发谱线较强。实验研究发现,在较低氩气压力范围(0.2 Pa< P Ar <1.0 Pa),随着压力增加,放电光强迅速增加,但是当压力增加到大于1.0 Pa之后,光强增长的趋势变缓,甚至部分谱线的相对强度不再增长,达到类饱和状态,朗缪尔探针测量得到离子密度变化趋势与其相似。光强分布在靠近径向边界处( r ≈4 cm)存在凸起,且随压力增加,该凸起分布更为明显。通过对电子温度的计算发现,压力增加到一定程度将影响放电均匀性。仿真结果显示,增大压力,功率沉积密度的径向分布逐渐向径向边界处积累,与实验观察到的谱线强度径向凸起相一致,螺旋波与TG波的耦合效率增加。随着气体压力的增加,Er的径向边界峰值降低,原因是波所受阻尼增强, TG波被有效地局限于径向较窄的边界处。电流密度轴向分量Jz在等离子体内部和边界处的峰值呈显著的减小趋势,可见,虽然压力增加一定程度上提高了等离子体密度,但却相应的减小了电离率,导致轴向电流密度受限。但是径向电流密度Jr却呈现先减小后增大的趋势,且增长幅度明显,综合来看,放电效率有所提高。可见适当增加气体压力,有助于提高放电的功率耦合效率和强度,增加等离子体密度。光强比值法是针对线性谱线参数计算的典型方法, Helic程序亦是专业领域内认可度很高的计算工具,结果可靠,分析方法具有可借鉴性。实验及仿真结果对于提高氩气工质下的螺旋波放电强度提供了一定的参考价值。
基金Project supported by the National Natural Science Foundation of China(Grant No.11405271)the China Postdoctoral Science Foundation(Grant No.2017M612901)+4 种基金the Fund from Chongqing Science and Technology Commission(Grant No.cstc2017jcyjAX0047)Chongqing Postdoctoral Special Foundation(Grant No.Xm2017109)the Fundamental Research Funds for Central Universities,China(Grant No.YJ201796)the Pre-research Key Laboratory Fund for Equipment(Grant No.61422070306)the Fund from the Laboratory of Advanced Space Propulsion(Grant No.LabASP-2017-10)
文摘Characterizing the gap eigenmode of shear Alfv′en waves(SAWs) and its interaction with energetic ions is important to the success of magnetically confined fusion. Previous studies have reported an experimental observation of the spectral gap of SAW on the on Large Plasma Device(LAPD)(Zhang et al. 2008 Phys. Plasmas 15 012103), a linear large plasma device(Gekelman et al. 1991 Rev. Sci. Instrum. 62 2875) possessing easier diagnostic access and lower cost compared with traditional fusion devices, and analytical theory and numerical gap eigenmode using ideal conditions(Chang 2014 Ph.D Thesis at Australian National University). To guide experimental implementation, the present work models the gap eigenmode of SAWs using exact LAPD parameters. A full picture of the wave field for previous experiment reveals that the previously observed spectral gap is not global but an axially local result. To form a global spectral gap, the number of magnetic mirrors has to be increased and stronger static magnetic field makes it clearer. Such a spectral gap is obtained for the magnetic field of B0(z) = 1.2 + 0.6 cos[2π(z-33.68)/3.63] with 7.74-m magnetic beach. By introducing two types of local defects(corresponding to Eθ(z0) = 0 and E’θ(z0) = 0 respectively), odd-parity and even-parity discrete eigenmodes are formed clearly inside the gap. The strength of these gap eigenmodes decreases significantly with collision frequency, which is consistent with previous studies. Parameter scans show that these gap eigenmodes can be even formed successfully for the field strength of B0(z) = 0.2 + 0.1 cos[2π(z-33.68)/3.63] and with only four magnetic mirrors, which are achievable by the LAPD at its present status. This work can serve as a strong motivation and direct reference for the experimental implementation of the gap eigenmode of SAWs on the LAPD and other linear plasma devices.
基金supported by the National Natural Science Foundation of China(Grant Nos.11405271,11372104,75121543,11332013,11372363,and 11502037)
文摘Alfvnic gap eigenmode(AGE) can eject energetic particles from confinement and thereby threaten the success of magnetically controlled fusion. A low-temperature plasma cylinder is a promising candidate to study this eigenmode, due to easy diagnostic access and simple geometry, and the idea is to arrange a periodic array of magnetic mirrors along the plasma cylinder and introduce a local defect to break the field periodicity. The present work validates this idea by reproducing a clear AGE inside a spectral gap, and more importantly details the influence of the number and depth(or modulation factor)of magnetic mirror on the characteristics of AGE. Results show that AGE is suppressed by other modes inside the spectral gap when the number of magnetic mirrors is below a certain value, which leads to a weakened Bragg’s effect. The structure and frequency of AGE remain unchanged for a decreased number of magnetic mirrors, as long as this number is enough for the AGE formation. The width of spectral gap and decay constant(inverse of decay length) of AGE are linearly proportional to the depth of magnetic mirror, implying easier observation of AGE through a bigger mirror depth. The frequency of AGE shifts to a lower range with the depth increased, possibly due to the unfrozen plasma with field line and the invalidity of small-perturbation analysis. Nevertheless, it is exciting to find that the depth of field modulation can be increased to form AGE for a very limited number of magnetic mirrors. This is of particular interest for the experimental implementation of AGE on a low-temperature plasma cylinder with limited length.
基金supported by National Natural Science Foundation of China(No.11405271)
文摘A one dimensional model is developed for defective gap mode(DGM)with two types of boundary conditions:conducting mesh and conducting sleeve.For a periodically modulated system without defect,the normalized width of spectral gaps equals to the modulation factor,which is consistent with previous studies.For a periodic system with local defects introduced by the boundary conditions,it shows that the conducting-mesh-induced DGM is always well confined by spectral gaps while the conducting-sleeve-induced DGM is not.The defect location can be a useful tool to dynamically control the frequency and spatial periodicity of DGM inside spectral gaps.This controllability can be potentially applied to the interaction between gap eigenmodes and energetic particles in fusion plasmas,and optical microcavities and waveguides in photonic crystals.
基金supported by Comprehensive Research Facility for Fusion Technology Program of China (No. 2018000052-73-01001228)the Youth Innovation Promotion Association CAS (No. 2018484)
文摘A new compact cascaded arc device for plasma-wall interaction study is developed at the Institute of Plasma Physics,Chinese Academy of Sciences.A magnetic field up to 0.8 T is achieved to confine plasmas in a 1.2 m long and 0.1 m diameter vacuum chamber.Gas fluid type analysis in this compact vacuum system was done under high particle flux condition.The gas pressure obtained by calculation was consistent with the measurement result.Continuous argon plasma discharge with ion flux of~0.5×10^(24)m^(-2)s^(-1)is successfully sustained for more than 1h.The effects of magnetic field configuration,gas flow rate,and discharge arc current on the ion flux to target were studied in detail.
基金Project supported by the National High Technology Research and Development Program of China
文摘The remaining challenges, confronting high-power microwave (HPM) sources and pulsed power generators, stim- ulate the developments of robust relativistic electron beam sources. This paper presents a carbon fibre cathode which is tested in a single pulsed power generator. The distribution and the development of cathode plasma are observed by time-and-space resolved diagnostics, and the uniformity of electron beam density is checked by taking x-ray images. A quasistationary behaviour of cathode plasma expansion is observed. It is found that the uniformity of the extracted electron beam is satisfactory in spite of individual plasma jets on the cathode surface. These results show that carbon fibre cathodes can provide a positive prospect for developing a high-quality electron beam.
基金supported by the National High Technology Research and Development Program of China
文摘This paper mainly investigates plasma characterization on carbon fiber cathodes with and without cesium iodide (CsI) coating powered by a - 300 ns, - 200 kV accelerating pulse. It was found that the CsI layers can not only improve the diode voltage, but also maintain a stable perveance. This indicates a slowly changed diode gap or a low cathode plasma expansion velocity. By spectroscopic diagnostics, in the vicinity of the cathode surface the average plasma density and temperature were found to be -3×10^14 cm^-3 and - 5 eV, respectively, for an electron current density of - 40 A/cm^2. Furthermore, there exists a multicomponent plasma expansion toward the anode. The plasma expansion velocity, corresponding to the carbon and hydrogen ions, is estimated to be - 1.5 cm/μs. Most notably, Cs spectroscopic line was obtained only at the distance - 0.5 mm from the cathode surface. Carbon and hydrogen ions are obtained up to the distance of 2.5 mm from the cathode surface. Cs ions almost remain at the vicinity of the cathode surface. These results show that the addition of CsI enables a slow cathode plasma expansion toward the anode, providing a positive prospect for developing long-pulse electron beam sources.
基金Chinese Academy of Sciences‘100 Talent’Program(B),Pre-research of Key Laboratory Fund for Equipment(No.61422070306)Shanghai Engineering Research Center of Space Engine(No.17DZ2280800)+1 种基金National Postdoctoral Program for Innovative Talents(No.BX201700248)China Postdoctoral Science Foundation(No.2017M622035)。
文摘To study the heating mechanism of electron cyclotron resonance thruster(ECRT)immersed in a non-uniform magnetic field,experiments and simulations are performed based on an electron cyclotron resonance plasma source at ASIPP.It is found that the first harmonic of electron cyclotron resonance is essential for plasma ignition at high magnetic field(0.0875 T),while the plasma can sustain without the first and second harmonics of electron cyclotron resonance at low magnetic field(till 0.0170 T).Evidence of radial hollow density profile indicates that upper hybrid resonance,which has strong edge heating effect,is the heating mechanism of low-field ECRT.The heating mode transition from electron cyclotron resonance to upper hybrid resonance is also revealed.Interestingly,the evolutions of electron temperature and electron density with input power experience a‘delayed’jump,which may be correlated with the different power levels required for cyclotron and ionization.Moreover,when the field strength decreased,the variation of electron density behaves in an opposite trend with that of electron temperature,implying a possible competition of power deposition between them.The present work is of great interest for understanding the plasma discharge in ECRT especially immersed in a non-uniform magnetic field,and designing efficient ECRT using low magnetic field for economic space applications.