Electrical tension-measurement in a multi-wire drift chamber for double beta decay experiments

Abstract

The method for the measurement of the tension of wires which constitute the DCBA (Drift Chamber Beta-ray Analyzer) for the double beta decay experiments has been studied. Two wires adjacent to each other were used for the measurement. The AC and DC electric fields were applied, and the weak current signal was detected at the resonance frequency with a phase cancellation technique. A formula representing the relationship between the wire tension and the resonance frequency was described, and it was discussed how the resonance frequency was detected and the detection accuracy was evaluated. This method was applied to the measurement of the wire tension for the prototype chamber of the DCBA. The radii of the anode wire of nichrome and the potential wire of aluminum were 12.5 and 40 micrometer, respectively. Two different voltages were applied to the two wires, and the phase of the canceler was tuned by changing the capacitance. The resonance signal pattern was observed when the frequency reached the resonance point. It was estimated that the error of the wire tension measurement was about one percent. It was confirmed that the distribution of the wire tension was more important than the absolute value itself. It was concluded that the present method using an electric field instead of a magnetic field is sufficiently accurate for the purpose.

2重ベータ崩壊実験用のDCBA(ドリフトチェンバ・ベータ線分析器)を構成するワイヤの張力測定法を研究した。測定実験として、互いに隣接する2本のワイヤを用い交流および直流電場を印加し、位相消去手法を使って共振周波数時の弱い電流信号を検出した。ワイヤ張力と共振周波数間の関係を表す式を記述し、共振周波数を検出する仕組みと、検出精度を評価する方法を論じた。本方法を、DCBAの試作チェンバ用のワイヤ張力測定に適用した。ニクロム製陽極ワイヤおよびアルミニウム製ポテンシャルワイヤの半径はそれぞれ2.5マイクロメートルおよび40マイクロメートルとした。2本のワイヤに異なる電圧を印加し、静電容量を変えて消去器の位相を同調させた。周波数が共鳴点に達した時、共鳴信号像を観測した。ワイヤ張力測定誤差は約1%であると推定した。ワイヤ張力の分布がワイヤ自体の張力の絶対値よりも重要であることを確認した。磁場の代わりに電場を用いる本方法が十分に目的とする精度を持っていると結論した。