Data processing in the data acquisition system of the vertical neutron camera plasma diagnostics at the ITER tokamak

Abstract

The vertical neutron camera (VNC) diagnostic system’s role is the study of the plasma physics and plasma pulse control at the ITER tokamak. The VNC provides neutron flux measurements and the neutron and alpha source profile across the plasma. The VNC is composed of two neutron cameras: an upper one and a lower one. The upper VNC is located in upper port plug 18 and contains 6 fan-shaped collimators to observe the inner part of the plasma. The lower VNC is located in lower port plug 14 behind the diverter cassette and contains 5 fan-shaped collimators with the line of sight (LoS) focused on the outer part of the plasma. Each collimator has a detector unit composed of two diamond detectors and two fission chambers. The electrical signal is transmitted from the neutron detectors to the data acquisition system by a triaxial cable with mineral isolation. The signal from the neutron detectors is preliminarily amplified by current pre-amplifiers, digitized with a sampling rate of 250 MHz and transmitted from the port cell zone to the diagnostic building under normal environmental conditions by digital optical lines. In the diagnostic building, signal is preliminarily processed and transmitted to the ITER central control system. The data acquisition system was designed according to the following ITER guidelines: the Radiation Hardness Policy (RHA), the Electrical Design Handbook (EDH), the Plant Control Design Handbook (PCDH), and the Annex B for VNC Procurement Arrangement (specifies the special requirements for measurement procedures and results).