G. Fuchs

Goeler, S. von

K." Toi

S. "Ohdachi

National Institute for Fusion Science (NIFS-Repository)

§19. Development of Tangential Soft X-ray Camera Ohdachi, S., Fuchs, G. (Institut fiir Plasmaphysik, Forschungszentrum Jiilich GmbH), von Goeler, S. (Princeton Plasma Physics Laboratory), Toi, K. A tangential soft X-ray(SX) camera has many advantages over the conventional SX diode array system. 1) It can provide 2-D image directly with-out uncertain assumptions in reconstruction, e.g. the solid rotation of the plasma. 2) Perturbed struc-tures in fluctuations are usually parallel to the mag-netic field. Since the sightlines of the tangential camera are nearly parallel to the magnetic field lines, the spatial resolution for the fluctuations with higher m number is much better than that in tomo-graphic reconstruction where the sightlines are al-most perpendicular to the magnetic field. We have been developing a tangential SX camera since 1997 and had installed on TEXTOR-94 Tokamak!) last year. A block diagram of this system is shown in Fig. I. Soft X-ray radiation from the plasma is converted to visible light by a fast phosphor (P-47) screen. The light is guided by a plastic bundled fiber (2 m in length) to a image in-tensifier (Hamamatsu V4440 V-mod), which is sur-rounded by an iron box to eliminate the stray mag-netic field from TEXTOR. The output image is am-plified and recorded by an ICCD camera equipped with a fast shutter (Hamamatsu C4077). The video signal from the camera is digitized by CAMAC ADC (LeCroy 6810) and the data are acquired by a windows NT workstation. ICCD with Fast Shutter HAMAMATSU C4077 [I----Jlvideo Signal Large Diameter (NTSC) P47(Fast Phosphor) SX Image Intensifier ! + Fiber Optic Plate HAMAMATSU V4440U·Mod j I i Shutter Control , .. -- .. --- -- _J I S~ECE~gn~ I 'rawtoot~Detecio~I=: JJri~g~r; j' SCSI NTSC-> Time Series data:CPS312 : .: ... ' ,: Waveform Memory: LeCroy 6801 ! iW6n:JJcc'l ; Crate Controller: Kinetics KS3929[ J ~.:~~~~I I l§o~YI~~(ffIFS) : Fig. I. The conceptual diagram of our tangential SX camera. 158 The cOIuplexity of this system is caused by the need for photons. In order to study a fast phe-nomena, e.g. the sawtooth crash, the exposure time for one frame should be very short. We need a large diameter (100 mm) phosphor screen to obtain a good SIN ratio. Photons collected by this system are enough for a fast shutter ( ~t = 1 rv 10j.ls ) without loosing the spatial resolution ( 3cm in plasma typically) in auxiliary heated plasmas. Series, of the images obtained in the initial experiments are shown in Fig. 2. An NB is injected between two frames. Increase in the SX intensity and the outward shift of the plasma can be seen. Fig. 2. SX radiation profile from a tangential port. Magnetic axes are estimated and plotted as a reference. Vertical lines in the images are shadows from a stainless wire in front of the camera. There are several points to be improved. One is a trigger system. We take only eight sequential frames at every 30ms now. A new controller ( saw-tooth detector in Fig.I. ) will make the exposure time synchronized with the sawtooth; we will be able to study the process of sawtooth crashes in de-tail with new controller. Another important issue is the interpretation of the measured data. Softwares to reconstruct the 2-D image of the SX emission are under development2) . After the experiments on TEXTOR-94 in this fiscal year, this system will be transferred and will be installed on LHD in the 4th ( or later) experi-mental campaign. References 1) S. von Goeler, et al. , Rev. Sci. Instrum., 70, 599 (1999) 2) G. Fuchs, et al. , in Proc. 26th EPS Conference on Controlled Fusion and Plasma Physics, Maastricht, to be published 

Development of Tangential Soft X-ray Camera

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