First measurement of time-resolved neutron yield on JT-60U using a microfission chamber

Abstract

Microfission chambers, which are pencil sized ionization chamber containing fissile material inside, will be installed in the vacuum vessel as neutron monitors for International Thermonuclear Experimental Reactor (ITER). We have performed first measurements of the detector installed between the vacuum vessel and toroidal coils on JT-60U. The technical validity as a neutron monitor, such as magnetic field effect and electromagnetic noises from the plasma and heating devices, has been investigated. The detector had an excellent linearity with a 235 U fission chamber as a neutron monitor on JT-60U with the standard deviation of 3% except for some noise signals. The electromagnetic noises were caused by neutral beam injection (NBI) breakdowns, probably due to long wiring between the detector and the preamplifier. In case of plasma disruption, improper signals have not been observed. The magnetic field effect also has not been observed up to 2 T. In JT-60U, we confirmed availability of the micro fission chamber as a neutron monitor over three decades of neutron source strength up to 1.3ϫ 10 16 neutrons/ s with 1 ms temporal resolution. The biggest weakness in the detector was its noise sensitivity to NBI breakdowns. Therefore, by suppressing the electromagnetic noise, microfission chambers can be available as neutron monitors for ITER.

Velocity-space sensitivity of neutron spectrometry measurements

“…Neutron spectrometers are installed or planned on a number of machines: time-of-flight spectrometers at EAST [12] and LHD [13], and compact spectrometers at EAST [14], ASDEX Upgrade [15], JET [16] and FTU [17]. Neutron yield detectors are installed at NSTX [18], DIII-D [19], Alcator C-Mod [20], EAST [21], LHD [22], JT-60U [23], MAST [18], JET [24] and planned for Wendelstein 7-X [25] . Furthermore, both neutron spectrometers and yield detectors are planned for ITER [26].…”

Status of ITER neutron diagnostic development

“…On the basis of an MFC test at a 60 Co γ -ray facility it was estimated that the γ -ray influence will be less than 0.1% of the neutron signal in the current mode. The MFC linearity in a neutron flux dynamic range of 10 7 was demonstrated on a fission reactor [9] and during tests on JT-60U [31]. The MFC linearity was also confirmed in the temperature range of 20-250 • C in DT neutron fluxes of the Fusion Neutronic Source [10].…”

Measurement of Neutron Flux at the Initial Phase of Discharge in EAST

“…Neutron diagnostic system implemented in EAST includes a five-channel time-resolved flux monitor and a spectrometer. The detector group of flux monitor system consists of four 3 He proportion counters and one 235 U fission chamber. The 3 He counters were divided into two types according to their thermal neutron sensitivity, namely 133 cps/nv and 15 cps/nv.…”

“…The 3 He counters were divided into two types according to their thermal neutron sensitivity, namely 133 cps/nv and 15 cps/nv. The 235 U fission chamber contains highly enriched uranium of 1.4 g, with a thermal neutron sensitivity of 1.16 cps/nv [3] . The detector group is with a wide dynamic range of counting rate, about 5 orders of magnitude, and was adapted for the D-D fusion neutron yield measurement from 10 9 s −1 to 10 13 s −1 .…”