Application of a vacuum arc model to the determination of cathodic microjet parameters

Krinberg, I. A.; Lukovnikova, M P

doi:10.1088/0022-3727/29/11/025

Cited by 30 publications

(26 citation statements)

References 21 publications

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“…Having established a correlation between cohesive energy and plasma temperature via the cohesive energy rule, the secondary relation between the average ion charge state and boiling temperature follows. Other relations such as a correlation between mean ion charge state and temperature, 7 and mean ion charge state and ion velocity 6,15 can be deduced in the same way. 12 The significance of the cohesive energy rule is that it is a surprisingly accurate tool for predicting arc voltage, plasma temperature and ion charge state distribution ͑see Ref.…”

Section: Energetics Of Vacuum Arc Cathode Spotsmentioning

confidence: 96%

“…For instance, a relation between the sequence of ionization energies and ion charge state distribution was used to group cathode materials in a Periodic Table, thereby clarifying the systematic features of ion charge state distributions ͑CSDs͒. 6,7 Based on the CSDs, plasma parameters such as the temperature of electrons in the transition region between the dense spot plasma and the expanded nonequilibrium plasma can be derived. 7 Cathode spot processes are essentially of non-stationary nature, and time constants can be well below the microsecond region.…”

Section: Energetics Of Vacuum Arc Cathode Spotsmentioning

confidence: 99%

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Energetics of vacuum arc cathode spots

Anders

2001

Applied Physics Letters

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Vacuum arcs need to generate the current-carrying plasma at cathode spots. The cohesive energy of the cathode material determines the energy the arc needs to provide for the phase transitions of the cathode material. As recent experiments confirm, the greater the cohesive energy the higher the burning voltage (“cohesive energy rule”). This relation is founded in the energy balance of cathode spot operation, regardless of the specific cathode mechanisms involved. A greater power input, as determined by the cohesive energy via the cohesive energy rule, leads to enhanced power output in various forms such as enhanced electron temperature, ion charge states, and ion velocity. Using the Cohesive Energy Rule, secondary relations such as the well known relation between boiling point of the cathode and average ion charge state can be explained.

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Section: Energetics Of Vacuum Arc Cathode Spotsmentioning

confidence: 96%

Section: Energetics Of Vacuum Arc Cathode Spotsmentioning

confidence: 99%

Energetics of vacuum arc cathode spots

Anders

2001

Applied Physics Letters

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“…This choice is related to the fact that the ionized plasma composition exhibits "quenching" within a distance of 10 μm from the cathode and then remains constant [12][13][14]. The angle of spherical cone expansion was determined from a comparison of the results of test calculations for k = 0 and the charge composition and average ion charge known for the arc operating on pure zirconium cathode [4].…”

Section: The Effect Of Cathode Deuteration On the Parameters Of Vacuumentioning

confidence: 99%

The effect of cathode deuteration on the parameters of vacuum-arc plasma

2014

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A source of ions based on vacuum discharge is the main element of vacuum neutron generators (neutron tubes) [1]. The electrodes of this source-cathode and anode-contain the working gas (hydrogen isotopes) in occluded state. The evolution of deuterium and for mation of its ions takes place upon the initiation of a short time (~1 μs) spark arc discharge between the cathode and anode. This discharge is accompanied by erosion of the surface of electrodes, which leads to the generation of working gas ions and is a desired process, and by evaporation of the electrode base metal, which is a harmful side effect. Optimization of the working characteristics of an ion source-i.e., the specific ion yield (the ratio of the number of working gas ions to energy consumed per pulse of discharge), working life, and stability-requires adequate description of the discharge.The present Letter proposes a model for determin ing the influence of the relative content of deuterium in a zirconium cathode on the properties of vacuum arc discharge plasma. The model is based on the ecton mechanism of the vacuum arc cathode spot operation [2]. According to this mechanism, vacuum arc plasma is formed as a result of the operation of separate cells (explosive emission centers) in a cathode spot of the vacuum arc. At present, the existence of these cells is commonly accepted [2][3][4]. The arc current buildup is accompanied by growth in the number of simulta neously operating cells of the cathode spot. For this reason, the parameters of ion flux are independent or weakly dependent on the arc current up to a kiloam pere level [5].The cell current in a cathode spot amounts to sev eral amperes, and the current density at the base of a plasma jet is on the level of 10 8 A/cm 2 [2, 3], which is characteristic of the explosive electron emission. The possibility of realization of the explosive electron emission conditions in the cathode spot of vacuum arc has been discussed for a long time. However, at present, it can be ascertained that the interaction of dense near cathode plasma with microinhomogene ities on the cathode surface unavoidably leads to the initiation of explosive electron emission [6][7][8].According to the proposed model, the cathode spot of a deuterated zirconium electrode features simulta neous erosion of deuterium and zirconium. It is assumed that the ratio of erosion rates of these compo nents is determined by the degree of electrode satura tion with deuterium and does not change with the time. Most probably, these assumptions are not gener ally valid because of an extremely complicated charac ter of sorption and desorption of hydrogen isotopes and a sharp dependence of the rates of their diffusion and desorption on the temperature. Nevertheless, these premises are quite acceptable at the initial stage of operation of the ion source, when the electrodes are not strongly heated. Thus, cathode spots directly sup ply deuterium to vacuum arc plasma. In addition, we assume that plasma expansion is spherically symmet ric and, hence, a one ...

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“…Similarly, Krinberg [30][31][32] considered a multi-component plasma and solved the equations of energy and motion leading to the simple approximate expression…”

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confidence: 99%

Ion flux from vacuum arc cathode spots in the absence and presence of a magnetic field

Anders

Yushkov

2002

Journal of Applied Physics

345

155

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Because plasma production at vacuum cathode spots is approximately proportional to the arc current, arc current modulation can be used to generate ion current modulation that can be detected far from the spot using a negatively biased ion collector. The drift time to the ion detector can used to determine kinetic ion energies. A very wide range of cathode materials have been used. It has been found that the kinetic ion energy is higher at the beginning of each discharge and approximately constant after 150 µs. The kinetic energy is correlated with the arc voltage and the cohesive energy of the cathode material. The ion erosion rate has in inverse relation to the cohesive energy, enhancing the effect that the power input per plasma particle correlates with the cohesive energy of the cathode material. The influence of three magnetic field configurations on the kinetic energy has been investigated. Generally, a magnetic field increases the plasma impedance, arc burning voltage, and kinetic ion energy. However, if the plasma is produced in a region of low field strength and streaming into a region of higher field strength, the velocity may decrease due to the mirror effect. A magnetic field can increase the plasma temperature but may reduce the density gradients by preventing free expansion into vacuum. Therefore, depending on the configuration, a magnetic field may increase or decrease the kinetic energy of ions. Additionally, the angular distribution of the ion flux and ion kinetic energy has been investigated in the absence of an external magnetic field. The result can be fitted by a superposition of an isotropic and a cosine distribution. * Corresponding Author, aanders@lbl.gov 3

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Application of a vacuum arc model to the determination of cathodic microjet parameters

Cited by 30 publications

References 21 publications

Energetics of vacuum arc cathode spots

Energetics of vacuum arc cathode spots

The effect of cathode deuteration on the parameters of vacuum-arc plasma

Ion flux from vacuum arc cathode spots in the absence and presence of a magnetic field

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