H. Matsuura

H. Okada

K. Hashimoto

K. Nagaoka

S. Kobayashi

S. Ohshima

T. Mizuuchi

T. Mutoh

National Institute for Fusion Science (NIFS-Repository)

In 2010FY experiment, a new hybrid probe was con-structed and tested with Heliotron J edge plasma for theﬁrst time. Its body is made of boron nitride (BN) andequipped with four conventional Langmuir probe tipsand a temperature gradient type thermal probe (GTP)tip made of copper (Cu). The size of Cu tip is set assmall as possible to improve time response.1) So its fab-rication was very diﬃcult task and the setting of GTPtip is possible only along the axial direction of a largeprobe head (see Fig. 1). Whole probe system was con-nected to the driving system at the port 8.5 in order tostudy the edge plasma around X-point of the last closedﬂux surface of Heliotron J. From Langmuir probes, im-portant data on long distance correlation of the ﬂoatingpotential ﬂuctuation.2)Unfortunately, thermocouple signal shows muchnoise and no temperature increase even when BN coversuﬀers heat damage. This hybrid probe is driven in theaxial direction to the last closed ﬂux surface and mag-netic ﬁeld lines inside of the last closed surface crossesthe side surface of the probe head. So plasma heat ﬂuxis expected to be hindered by BN head to reach the CuGTP and S/N ratio is not so good. For Heliotron J con-dition, electrons with small gyro radius could not reachGTP and only ion heat ﬂux can be measured. This sit-uation is similar with those of the so-called ion sensitiveprobe. In order to study the plasma behavior and toconﬁrm this hypothesis, simulation with XOOPIC codewas done. XOOPIC is PIC simulation code developed inPTSG laboratory of UCBK.Figure 2 shows its geometry model. Although theCu GTP is a axis-symmetric cylinder, simple 2D geom-etry which is homogeneous along y direction was usedfor simplicity. Magnetic ﬁeld (B⃗) is along x-directionand Cu surface is set at backside of BN cover about byion Larmor radius. This is the same as those used in He-liotron J, although the small incline to side surface of BNcover ( z-component of B⃗ ) is ignored to enhance shield-ing eﬀect of B⃗ in the simulation. After the simulationstarts, ions and electrons ﬂows from there boundary butelectrons are hindered to reach Cu sensor surface. Ac-cording to the simulation progress, ions accumulates onthe Cu surface and its electric potential becomes higherthan plasma space potential (see Fig. 3), since Cu GTPwas used in the ﬂoating condition (disconnected to theground). Finally ions are also rejected electrostaticallyThis results conﬁrms our hypothesisIn the original design of the hybrid probe, this con-ﬁguration was chosen to prevent from heat concentrationon the edge of Cu sensor. Even with this, if potentialcontrol of the sensor is applied, ion heat ﬂux might bemeasurable.Fig. 1: Photo of the combined probe with a Cu GTPtip.Fig. 2: Constructed calorimeter head.Fig. 3: Schematic drawing of the old calorimeter head(left ﬁgure) and the new one (right).1) H.Matsuura et al., Ann. Rep. NIFS, Apr.2011-Mar.2012(2012)492.2) S.Ohshima et al., 24th IAEA Fusion Energy Confer-ence, (San Diego, USA, 2012 Oct.) EX/P4-17.526§27. Experimental Study on Heat Flux of Divertor Plasma (Measurement of Fluctuation and Heat Transport in the Edge Plasma of Heliotron J Device)Matsuura, H. (Osaka Pref. Univ.), Ohshima, S.,  Hashimoto, K., Okada, H., Kobayashi, S.,  Mizuuchi, T. (Kyoto Univ.), Nagaoka, K., Mutoh, T.

Experimental Study on Heat Flux of Divertor Plasma (Measurement of Fluctuation and Heat Transport in the Edge Plasma of Heliotron J Device)

Experimental Study on Heat Flux of Divertor Plasma (Measurement of Fluctuation and Heat Transport in the Edge Plasma of Heliotron J Device)

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