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

Abstract

Neutron emission in EAST was investigated by a time-resolved monitor system which consists of four 3 He proportional counters and a 235 U fission chamber. The D-D neutron flux increased approximately an order of magnitude during the 27 MHz ion-cyclotron radio frequency (ICRF) heating, demonstrating that the ICRF wave heated the plasma effectively. In addition in lower hybrid wave (LHW) experiment with higher plasma parameters D-D neutrons were also detected. However, masses of photoneutrons were generated in Ohmic discharges with low plasma density. Effect of plasma density on the production of photoneutrons was studied, and it is found that LHW can suppress the generation of the runaway electrons and reduce the share of the photoneutrons effectively.

Velocity-space sensitivity of neutron spectrometry measurements

“…where the γ values are given by equation (21). Thus, the probability function is the fraction of the gyro-orbit that leads to neutrons with energies within the given neutron energy range.…”

“…γ (E n ) is found by inserting v n = 2En mn in equation (21). In energy-pitch coordinates, the probability becomes…”

“…The limiting edges separating the observable region in velocity space from the unobservable region, i.e. the edges of the weight functions, can be found by inserting cos(γ ) = ±1 in equation (21), as in this case the projected velocities and therefore the neutron energies are at their extreme values. In this case, equation ( 21) can be rewritten in the form…”

“…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].…”

Development of a wide-range neutron flux monitoring system in EAST

“…Thus, the development of a wide dynamic range NFM system that covers low Y n s in a radio-frequency (RF) wave-heating scenario, and high Y n s under NBI conditions is necessary for EAST fusion-neutron measurement. However, in the early operation stage of EAST, with only the activation of RF heating, the NFM system mainly relies on high-sensitivity 3 He counters; these counters are ill suited to high Y n conditions after NBI system operation [11]. Thus to upgrade the NFM detector, a 235 U fission chamber (FC) and a signal-processing digitizer were added relatively recently.…”