06aB04
直流アーク陰極点に形成される溶融金属池の動的挙動と表面温度評価
Dynamic Behavior of Molten Metal Pool Formed at the Cathode Spot of DC Arc andits Surface Temperature Measurements
上杉喜彦 1、伊藤 毅 1、高田伸浩 1、田中康規 1、石島達夫 1、山口義博 2
Yoshihiko UESUGI1, Takeru ITO1, Nobuhiro TAKATA1, Yasunori TANAKA1, Tatsuo ISHIJIMA1,and Yoshihiro YAMAGUCHI2
金沢大学 1、コマツ産機 2
Kanazawa Univ.1, Komatsu Industries Corp.2
Study of the dynamic response of refractory
metals, such as tungsten to the transient andextremely high plasma heat load in type-I
ELM’s and disruptions (>100 MW/m 2) requires
experimental approaches different from those insteady state and low heat flux experiments(<10MW/m 2 ). In the present experiments, high current
stabilized arc plasmas with ~GA/m2 are used as ahigh heat flux pulse and steady state plasma source.
The plasma heat flux onto the cathode surface isseveral hundred MW/m2 in the steady state and isseveral GW/m2 in the arc ignition and quench phase.
These properties of high heat flux arc plasmas arevery useful to study the transient behavior of thedivertor materials during ELMs and disruptions infusion reactor complementally with other ELM/disruption experiments.
On the other hand, arc plasmas are used invarious devices, such as light sources, plasma arc
cutting, electric circuit breakers and ignition plugs,
etc. It is very important to understand the physicaland chemical interactions of the high heat flux
arc plasmas with the refractory metal cathode for
improvement of these industrial devices. In thepresent experiments dynamic interactions of highcurrent density arc plasmas with hot molten metal
cathode are studied using a plasma arc cutting
device, which can generate stable arc plasmas in asmall fixed volume[1].
Images of the cathode hot spot obtained from afast color camera clearly show that the rotation of
local small hot cathode spot heats the Hf cathodesurface gradually and forms the larger cathode spot
on the center of Hf electrode after ignition. Thecathode spot area spreads over gradually from thefixed local cathode spot to the whole cathode areawith increasing the arc current. The temperature
distribution estimated from the RGB and NIR
signals of the hot cathode color images shows thatthe cathode surface temperature rises up between
3,700 K and 4,300 K. This temperature is higher

than Hf melting temperature (T=2,503 K) and lower
than or close to Hf boiling temperature (T=4,547K). Thermionic electron emission current density
is calculated from the estimated cathode surface
temperature, supposing that whole cathode surface
is solid H f or solid HfO 2. Thermionic electron
emission current IHf and IHfO2 are estimated to be~160 A and 40 A, respectively when the preset arc
current is I arc=135 A. In Fig. 1 example of thecathode temperature profile is shown when RGB
color CCD camera and RGB and NIR ccd camera
are used to estimate the cathode surface temperature.
Unstable phenomena of the molten cathode pool,such as small droplet ejection accompanying wavy
motion of the molten cathode pool and large droplet
ejection from the cathode, are often observed whena new cathode with a flat cathode surface is usedat the first time. Detail phenomena of the molten
cathode pool will be shown at the meeting.
References[1]Y. Yamaguchi, et al., Journal of the Japan
Welding Society Vol. s29, No.1, pp. 010- 017(2011)
in Japanese.

Fig. 1 Cathode surface temperature profiles at thearc quenching phase estimated by two different CCD
cameras.