A. "Sanpei

A. Ejiri

C." Suzuki

H. Himura

S. Masamune

T. Akiyama

National Institute for Fusion Science (NIFS-Repository)

Measurement of electron density proﬁ le of the edgeand divertor plasma is very important issue for studyof fusion plasma physics. In 2009, we had developeda cross detector which simultaneously detects referenceand transmitted waves from two ports. The use of crossdetector has lead to improved accuracy in the phase shiftmeasurement. One of the important issues of this studyis the development of multi channel measurement sys-tem, which will be applied for low density regime suchas diverter plasma of LHD. Developed an interferometersystem was applied for a low aspect ratio (A) reversedﬁ eld pinch (RFP) plasma, then obtained a preliminaryexperimental result1). However, an analysis from theobtained experimental result is less-accurate because at-tenuation of transmitted wave is more likely to occurwith electron density closed to cutoﬁ density. In orderto accurize our system, in this study, we have adoptedan up-converter system. All data are obtained from thelow-A RFP device, REversed ﬁ eld pinch of Low AspecteXperiment (RELAX)2, 3), which has low electron den-sity � 1018−19.Fig. 1: Schematic of the developed up-converter inter-ferometer system.The schematic of developed up-convertor systemis shown in Fig.1. In this study, we choose 60 GHzmicrowave oscillator. The microwave oscillator is IM-PATT diode (HUGES, 47174H-1280), which has max-imum power 25.4 dBm. In order to protect the oscil-lator from reﬁ ected wave, an isolator is inserted on cir-cuit. A directional coupler (HUGES, 45324H-1210) splitsthe microwave to probe and reference signals. Some fre-quency synthesizers have been used to accurize the pick-up waves. By comparison the Lissajous ﬁ gure from thedeveloping up-converter system with that from the ex-isting cross detector systems, we may expect that thedeveloping up-converter system has more accuracy withelectron density closed to cutoﬁ density. Experimentalveriﬁ cation is in progress.Another issue of this collaborative work is measure-ment of the electron density of RELAX with an inter-ferometer, which is a 104 GHz heterodyne system onloan from the TST group at the University of Tokyo.The detailed density measurement has been performedusing the heterodyne system consisting of two (104.00GHz and 104.45 GHz) gun oscillators. The frequency ofboth the transmitted and reference waves are convertedto the intermediate frequency, IF (450 MHz) with mix-ers. The IF signals are then ampliﬁ ed and are mixedwith an IQ detector whose outputs are cosine and sinecomponents of the phase shift caused by the plasma. Weshould note that the cutoﬁ electron density for 104 GHzis 1.34 × 1020m−3. Figure 2 shows a sample of timeevolutions of Ip and line averaged electron density nemeasured using the 104 GHz interferometer in RELAXplasma. Comparison the developing up-converter systemwith the 104GHz heterodyne remains as future work.Fig. 2: Time evolution of plasma current and line aver-aged electron density.1) M. Sugihara et al., Plasma Fusion Res., 5, S2061(2010).2) S. Masamune et al., Trans. of Fusion Sci. Technol. 51(No. 2T) (2007) 197.3) S. Masamune et al., J. Phys. Soc. Jpn. 76 (No.12)(2007) 123501.152§32. Accuracy Enhancement of Simple System of Millimeter-wave Interferometer for Low Density PlasmasSanpei, A., Himura, H., Masamune, S. (Kyoto Inst. Tech.),  Ejiri, A. (Univ. Tokyo),  Akiyama, T., Suzuki, C.

Accuracy Enhancement of Simple System of Millimeter-wave Interferometer for Low Density Plasmas

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