稀薄ガスの中のプラズマの温度を,水素以外の元素のスペクトル線の巾を観測することによって,測定する一般的方法について述べる.プラズマでは発光する原子(又はイオン)がイオンの電場の影響を強く受け,この電場の値に巾があることがスペクトル線の広がりに貢献する.この他にDoppler効果による拡がりもある.これらの全部を考慮に入れて,はじめて正しい温度が得られる.この実験では一例として,ネオンをつめたGeisler管にスパーク放電を行なって得られるプラズマの平均的温度をNe I λ5852なる線の拡がりから測定した.スパーク放電のとき得られるλ5852の波長とアーク放電(このときは各原子の受ける電場は無視できる)のとき得られる波長とをFabry-Perotのエタロンを用いて比較して,前者が長い波長の方にずれていることを確かめ,このずれの分量からプラズマの中の発光する原子の受ける電場(確率の最も大きい電場)を算出した.この電場の値をHoltsmarkの論と結びつけると,原子の受ける電場の大きさが町々であることに原因するスペクトル線の理拡がりがわかり,これを観測したスペクトル線の拡がりから差し引いたものがDoppler効果による拡がりであると仮定して,プラズマの平均的温度を算出した.Ne I λ5852の上述の波長のずれから得られた電場の値を用いてイオンの平均的密度の概略の値を計算した.

Kiyoshi MURAKAWA and Shizuyo MIZUNO, Measurement of Plasma Temperature and Ion Density. The object of this investigation is to measure the temperature of the plasma obtained by passing a condensed discharge through a Geisler tube (the inner diameter of the capillary being about 3mm) containing neon of approximately 5mm Hg pressure. The wave-length of the line Ne I λ5852 emitted from this light source was compared with that of the same line emitted from an arc discharge passing through the same Geisler tube. The comparison was made by means of a silvered Fabry-Perot etaon, and the line profile was studied by means of a microphotometer. It was found that the line Ne I λ5852 emitted from the condensed discharge was displaced to the smaller frequency side as compared with the same line emitted from an arc discharge. This is interpreted to be due to the quadratic Stark effect caused by the ionized neon atoms and electrons in the plasma, the line emitted from the arc discharge being assumed to suffer negligible Stark effect. The amount of displacement gives directly the value of the most probable electric field intensity that is given by Holtsmark's theory of line broadening. The contribution from the fluctuation of the electric field to the line breadth (neglecting the Doppler effect) can then be calculated. When this is subtracted from the observed line breadth, the remaining breadth is interpreted to be due to the Doppler effect, and the plasma temperature can be calculated by the usual formula of Doppler effect. From the most probable value of the electric field intensity Holtsmark's socalled normal field strength (Normalfeldstarke) F_n can be calculated. If we assume that there are only singly ionized atoms (in addition to the neutral atoms) present, the ion density can be approximately calculated from the value of F_n, although this assumption is not altogether correct. In the condensed discharge the discharge current is not constant but varies with time. The line profile of Ne I λ5852 (obtained in the present study) is therefore a mean profile, in which the mean is taken over the time, the intensity of λ5852 at each instant being the weight. The obtained plasma temperature is the mean temperature deduced from this "mean" profile. Even if we assume a strict validity of Holtsmark theory, the contribution of the fluctuation of the electric field intensity to the line breadth that was calculated in the present study does not have an altogether strict physical meaning. In our present example the mean plasma temperature was T=2.2×10^3 K, and the ion density N=7×10^16 per cm^3.

資料番号: SA4134967000