Study on Neutron Emission Characteristics in a Small Repetitive Plasma Focus Device

Abstract

Summary form only given. It was known that one of the most important characteristics of plasma focus is the abundant amount of neutrons that are produced when deuterium is used as filling gas. This paper presents the studying results on neutron emission characteristics. A 2.2 kJ small repetitive plasma focus device was developed and its pulsed current and quarter period are 210 kA and 1.5 mus. Among repetitive 100 shots under the repetitive rate of 1/60 Hz, the operating voltage of 18 kV and without purifying the gas, the jitter of neutron yield was large, with an order of magnitude difference between maximum and minimum. The maximum yield was 2.0times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> and the average neutron yield per shot was (5.14plusmn3.02)times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7 </sup> . Before the fiftieth shot, the average neutron yields of each six shots in sequence were almost the same. Then the average neutron yields decreased gradually. Using the optical fiber spectrometer observation, the intensities of nitrogen and oxygen (in the discharge chamber) spectral line enhance with shot number, which is important reason of the decreasing of neutron yield. The time resolution of neutron emission was measured by a scintillator-photomultiplier (ST-PMT) detector. The FWHM of neutron impulse of (38.8plusmn6.5) ns was obtained. There are two peaks on the output signal of ST-PMT detector. The first peak is from hard X-rays most of which are the high energy photons (hnu>60 keV ) that can penetrate 3 mm wall of the chamber made from stainless steel. The second peak is from 2.5 MeV D-D neutrons