Measurements of the current density in arc cathode spots from the Zeeman splitting of emission lines

Vogel, N.; Jüttner, B.

doi:10.1088/0022-3727/24/6/017

Cited by 38 publications

(7 citation statements)

References 17 publications

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“…It is known that plasma in vacuum arcs is generated in cathode microspots and expands in vacuum as a jet. The parameters of the plasma in a cathode spot have been measured with high temporal and spatial resolution in recent years [1,2]. The data obtained are in satisfactory agreement with predictions of the theory [3,4].…”

Section: Introductionsupporting

confidence: 62%

On the spatial structure of the cathode jet of a steady-state vacuum arc

Krasov¹,

Paperny²

1998

J. Phys. D: Appl. Phys.

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By means of the developed technique the local cross sectional size of the cathode plasma jet of a steady-state vacuum arc is measured. The measurements are carried out within a range of distances from the cathode. The found magnitude has been rather less than the measured cross sectional size of a steady-state integral plasma flow. The effect of a contraction of the profile of the plasma density and a simultaneous expansion of the profile of the electron temperature (which resulted from magnification of the value of ) on distances is found out also. It is possible to explain the observed effects by considering the compression of a cathode jet by an intrinsic magnetic field of a current, which in fact controls the form and the parameters of the plasma of a cathode jet at large distances from the cathode.

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Section: Introductionsupporting

confidence: 62%

On the spatial structure of the cathode jet of a steady-state vacuum arc

Krasov¹,

Paperny²

1998

J. Phys. D: Appl. Phys.

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“…Strong electric fields at the cathode surface can result in direct extraction of current from the metallic cathode surface, rather than from the arc plasma source. This extraction takes the form of cathode spots [18][19][20][21], which source extremely high current densities through localized hot spots and can result in significant surface damage. To prevent cathode spot breakdown, the electric field at the cathode surface must be minimized via reduction of local plasma density to maximize the local Debye length.…”

Section: Nucl Fusion 58 (2018) 096002mentioning

confidence: 99%

Initiation and sustainment of tokamak plasmas with local helicity injection as the majority current drive

et al. 2018

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Local helicity injection (LHI) is a non-solenoidal current drive capable of achieving high- tokamak startup with non-invasive current injectors in the plasma scrape-off layer. The choice of injector location within the edge region is flexible but has a profound influence on the nature of the current drive in LHI discharges. New experiments on the Pegasus ST with injection in the high-field-side, lower divertor region produce plasmas dominated by helicity injection current drive, static plasma geometry, and negligible inductive drive. Peak plasma current up to 200 kA, and a sustained plasma current of 100 kA for up to 18 ms, is demonstrated. Maximum achievable plasma current is found to scale approximately linearly with the effective loop voltage from LHI. A newly-observed MHD regime for LHI-driven plasmas in which large-amplitude fluctuations at 20–50 kHz are abruptly reduced on the outboard side results in improved current drive. A simultaneous increase in high frequency fluctuations (>400 kHz) inside the plasma edge suggests short wavelength turbulence as an important current drive mechanism during LHI.

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“…Usually the current density in the cathode spot can be obtained after the spot's size has been measured [16]. Besides this conventional method, there are other methods for measuring the current density at the cathode spot [17][18][19][20]. For 2% thoriated tungsten cathodes, the measured current density values are in the range 10 7 -10 10 A m −2 .…”

Section: Introductionmentioning

confidence: 99%

An experimental investigation of factors affecting arc-cathode erosion

Zhou

Heberlein

1998

J. Phys. D: Appl. Phys.

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A specially designed thermal plasma reactor system for the investigation of arc-cathode erosion has been set up. By using an OMA-spectrometer system, emission spectroscopic measurements of electron temperature and electron number density in the cathode region have been performed, together with single-colour and two-colour pyrometry of cathode temperature distributions. Observation of cathode spot behaviour has been carried out simultaneously by employing a telemicroscope and a high-speed vision system. Cathodes have been examined by SEM and EDX after arcing. For pure tungsten cathodes, the initial cathode geometry has almost no effect on the cathode spot's behaviour due to the molten state of the cathode spot. The major erosion mechanism is the ejection of liquid droplets from the cathode spot. However, the initial cathode geometry has a certain influence on the cathode's erosion for 2% thoriated tungsten cathodes. A highly non-uniform erosion pattern will occur if the cathode is overcooled, probably due to ion bombardment in the low-temperature regions of the arc-attachment spot.

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Measurements of the current density in arc cathode spots from the Zeeman splitting of emission lines

Cited by 38 publications

References 17 publications

On the spatial structure of the cathode jet of a steady-state vacuum arc

On the spatial structure of the cathode jet of a steady-state vacuum arc

Initiation and sustainment of tokamak plasmas with local helicity injection as the majority current drive

An experimental investigation of factors affecting arc-cathode erosion

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