7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Measurement of heat quantity incident into a bias-type calorimeterfor divertor thermal load reduction by direct energy conversion
H. Kanno1, M. Shibuya1, S. Nakamoto1, T. Furukawa1, H. Takeno1,H. Matsuura2, Y. Nakashima3, and M. Hirata3
1
Graduate School of Engineering, Kobe University,
2
Graduate School of Engineering, Osaka Metropolitan University,
3
Plasma Research Center, University of Tsukuba
e-mail (speaker): 197t225t@stu.kobe-u.ac.jp

In a tokamak reactor, the plasma facing surface of thedivertor plates will be exposed to high heat flux, and thethermal load reduction of the plates is one of thesignificant subjects. As one of the solutions, anapplication of a Cusp-Type Direct Energy Converter(CuspDEC), which was originally designed for a D-3He
Field Reversed Configuration fusion reactor, wasproposed.[1] According to the proposal, high-energy
charged particles from core plasma are separated inpolarity in the CuspDEC. The separated ions andelectrons are guided to different divertor plates. Eachparticle is decelerated by an electric field due to theappropriately biased divertor plate.
We are planning a simulation experiment using abias-type calorimeter (CM).[2] The CM has a function tomeasure incident current (Iin) as well as temperature of
the target plate. In the previous research of an analyticalexperiment, we used the CM to find an optimum bias
voltage for thermal load reduction. To establish a reliable
scheme, we needed the relation between heat quantity
detected by the CM (Qdet) and estimated heat quantity
incident into the CM (Qin).[3] Qin was sum of the energy
given by the incident particles. The particle energy wascalculated by using a model in which particles wereaccelerated or decelerated by the potential difference
between the plasma and the CM. However, the plasma inthe experimental device was floating, so we were unsureof the exact plasma potential and had a difficulty toevaluate Qin.
We have started a similar experiment with a different
device in which an extraction electrode is equipped withthe outlet of the plasma source to estimate plasma
potential accurately by the information of the electrodevoltage.[4] This experimental device is schematicallyshown in Figure 1. Argon plasma was generated byapplying RF power inductively. The plasma was guided
to the CM to which bias voltage (Vbias) was applied. In
this device, we obtained the voltage of the extraction
electrode (Vex) as well as signals of the CM. In the lastreport,[4] the incident heat quantity was too small toevaluate precisely. In the present experiment, we appliedbias voltage to convergence electrode (Vc) and succeeded
to improve heat quantity incident into the CM.
Figure 2 shows measured Iin-Vbias characteristic of theCM. Blue filled circles and open red circles are results of
the last experiment and the present one, respectively. The
convergence electrode was floated in the last experiment,
and biased with 300V in the present one. We can find theincident current for the same bias increases significantly.
In response to Iin, Qdet also increased. The detailed results
will be shown in the conference.
This work is supported in part by the bilateralcoordinated research between PRC, Univ. Tsukuba, NIFS,
and Kobe Univ. (NIFS19KUGM147).
References[1] H. Takeno, et al., Trans. Fusion Sci. Tech. 63(1T)(2013) 131-134.
[2] K. Ichimura, et al., Fusion Eng. Des. 136 (2018)381-385.
[3] H. Kanno, et al., 31st ITC (2022) P1-5F03.
[4] M. Shibuya, et al., 39th Ann. Meeting of JSPF (2022)
24P64.
Extraction
ElectrodeRF power
Antenna (13MHz)

Convergence
Electrode

Vbias

Calorimeter

Coil U

Argon
Gas

Coil D

Coil Apump

Figure 1. Schematic image of the experimental device.

Figure 2. Measured current versus bias voltage of thecalorimeter.