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Observation of the Nonuniform Poloidal Flow of Impurity Ion on Magnetic Surfaces using Bidirectional Charge Exchange Spectroscopy in CHS
https://ir.soken.ac.jp/records/464
https://ir.soken.ac.jp/records/4646b5f4029e84949428784df48437026bc
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要旨・審査要旨 / Abstract, Screening Result (384.3 kB)


本文 (8.2 MB)

Item type  学位論文 / Thesis or Dissertation(1)  

公開日  20100222  
タイトル  
タイトル  Observation of the Nonuniform Poloidal Flow of Impurity Ion on Magnetic Surfaces using Bidirectional Charge Exchange Spectroscopy in CHS  
タイトル  
タイトル  Observation of the Nonuniform Poloidal Flow of Impurity Ion on Magnetic Surfaces using Bidirectional Charge Exchange Spectroscopy in CHS  
言語  en  
言語  
言語  eng  
資源タイプ  
資源タイプ識別子  http://purl.org/coar/resource_type/c_46ec  
資源タイプ  thesis  
著者名 
西村, 伸
× 西村, 伸 

フリガナ 
ニシムラ, シン
× ニシムラ, シン 

著者 
NISHIMURA, Shin
× NISHIMURA, Shin 

学位授与機関  
学位授与機関名  総合研究大学院大学  
学位名  
学位名  博士（理学）  
学位記番号  
内容記述タイプ  Other  
内容記述  総研大甲第322号  
研究科  
値  数物科学研究科  
専攻  
値  10 核融合科学専攻  
学位授与年月日  
学位授与年月日  19980324  
学位授与年度  
値  1997  
要旨  
内容記述タイプ  Other  
内容記述  The radial electric fields in magnetically confined toroidal plasmas are<br> considered to play an important role in plasma confinements. For<br>example, they change the neoclassical ripple loss in the low collisionality<br>regime in helical devices, and they are considered to be the important<br>parameter to determine the L/H transition and the anomalous transport<br>characteristics of L/Hmodes in tokamak plasmas. Therefore many efforts<br>to study the radial electric fields experimentally have been performed.<br>One method for this study is the spectroscopic measurements of the<br>rotations of impurity ions. However, toroidal effects on the plasma<br>rotations have never been studied experimentally. The coupling of<br>toroidal and poloidal rotations caused by the toroidal effect to satisfy the<br>poloidal flow conservation condition is the most important basis of<br> neoclassical transport theory and is also important for understanding the<br>supersonic (with M<small>p</small>～1 where M<small>p</small> is the poloidal Mach number) plasma<br>flows in tokamak Hmode plasmas. Therefore many related theoretical<br> studies have been made.<br /> To study this problem experimentally is to compare poloidal flux on<br> the inside and outside of the magnetic surfaces. In the poloidal rotation<br>measurements in many tokamaks, the poloidal rotation velocities only in<br> the outside were measured, since it is difficult to install the observation<br>chords viewing vertically the inside of the torus. Another severe<br>difficulty is the calibration of mechanical wavelength offset～0.5 Å) of <br>spectrometers with the accuracy for the plasma rotation measurements.<br> The study of the inside/outside asymmetry of poloidal rotation velocity requires<br> the accuracy of absolute wavelength of ～0.01 Å. To measure<br> the absolute value of the rotation velocity canceling this offset, it needs<br>the observation along opposite viewing directions. In past plasma rotation<br>measurements using the observation from one direction only, some<br>assumptions or approximations about the plasma rotation velocity profiles<br>were used. For example, the average of the poloidal rotation velocities in<br> the inside and the outside was used as poloidal rotation 'velocity' in<br> Heliotron E.<br /> In the present work, I have carried out the measurement of the profiles<br> of the poloidal rotation velocity, the temperature and the density of <br>impurity ions using bidirectional charge exchange spectroscopy (CXS) in<br>the Compact Helical System (CHS). For the purpose mentioned above, this<br>measurement system uses two fiber arrays to view vertically the beam<br> line from up and down sides simultaneously at one vertically elongated<br>section. In Heliotron/Torsatron devices like CHS, the strong parallel<br>viscosity reduces the parallel ion flow velocity which is necessary for<br> incompressible flow conservation when the perpendicular ion flow exists<br> in low aspect ratio tori. This damping is strong in peripheral region<br>where the helical ripple becomes large. However, the poloidal rotation of<br> impurity tons mainly driven by radial electric field determined by the<br>ambipolar condition of the electron and ion fluxes is also large in this <br>peripheral region. Therefore the compensation of the asymmetry of<br>inside and outside perpendicular flows by the parallel flows becomes<br>difficult in this region. When the electrostatic potential is the surface<br>quantity and the poloial rotation of ions is mainly the E×B drift, the<br> flow, especially of the impurity ions having low pressure, should be<br> compressible. Otherwise the electrostatic potential is not the surface<br>quantity or the poloidal rotation of impurity ions is not E × B drift. <br> Investigating this problem is easier in low aspect ratio devices. Therefore<br>this measurement in CHS with the lowest aspect ratio R<small>0</small>/a=5 in helical<br>devices will give the new information about the plasma rotations.<br /> The preliminary measurements of plasma rotations using this system<br>clarified some technical problems in multichannel CXS. The most<br>important problem was the apparent wavelength shift caused by<br> the spectral fine structure of hydrogenlike ions used in CXS. This structure<br>is the redside/blueside asymmetric splitting of the lines due to a <br>relativistic effect and thus cause the redside/blueside asymmetry of the<br>Doppler broadened spectral profile. Because of this asymmetry, the<br> wavelength given by single Gaussian least square fitting shows the<br> apparent shifts which depends on Doppler widths. The observed apparent<br> shifts of CVI lines, not due to plasma rotation, in the plasma peripheral<br> region (Ti～100eV) and in the afterglow recombining phase (Ti～<br>30eV) are always redshifts regardless the direction of plasma rotation. <br> The magnitude corresponds to the velocity error of a few km/s. This<br>direction and magnitude are consistent with the calculation using the<br>collisional lmixing model. This value is not negligible in CHS plasmas, <br>and thus should be corrected.<br /> The density profile of the fully ionized impurity ions can be measured<br>using the intensity of the charge exchange spectral lines. For this purpose, <br>the initial beam density profile without attenuation was also measured in<br>the torus using H α from the beam. The measured density profile was a<br>broad and inside shifted profile compared with the calculated one. This<br>result means the possibility to measure the parameters on inside of the<br> torus with CXS. However, the calculation of the beam attenuation<br>required that the average electron densities should be less than 2 ×<br>10<sup>13</sup> cm<sup>3</sup> to avoid the ambiguity of beam attenuation calculation and the<br> degradation of signal level on the inside.<br /> The measurements of the asymmetry of the poloidal flux of fully<br> ionized carbon tons on the inside and outside of the torus were carried<br> out for the magnetic surface configurations with different magnetic axis<br> positions. In inward shifted configurations, the gradients of surface<br> function (dψ/dR) on the inside and outside of the section are almost<br> symmetric. It becomes asymmetric in outward shifted configurations<br> and the strength of the radial electric field will become asymmetric in<br> these configuration.<br /> The asymmetry of the Doppler shifts of the CVI line(Δn=87, λ<br>=5290 Å) on the inside and outside of the torus was successfully <br>measured. In outward shifted configurations, the electrostatic potential<br> calculated from this velocity using the momentum balance equation is the<br> surface quantity. The measured density of impurity ions has a hollow<br> profile and is higher on the inside of the magnetic surfaces compared<br> with that on the outside. This inside/outside asymmetry of the density profile<br> can be explained by the poloidal flow conservation on both sides<br> under the damping of toroidal rotation.<br /> In the inward shifted configurations, the density profile is a flat or<br>peaking profile and the inside/outside asymmetry is not clear. The<br>quantitative comparison or the electrostatic potential and the poloidal flow<br> on both sides is difficult in inward shifted configurations because of<br>the intense back and radiation at the inside of the magnetic axis. It<br>causes the degradation of signal/noise ratio of spectrum after subtracting<br>background spectrum. However, this change in the density asymmetry is<br>consistent with the past measurement of the toroidal rotation damping and<br>suggests the poloidal rotation accompanying the inside/outside asymmetric<br>toroidal flow. Therefore the measurement of inside/outside asymmetry of<br> the toroidal rotation velocity is an interesting future theme.  
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