Accuracy of 10% is demanded to the absolute fusion measurement on ITER. To achieve this accuracy, a functional combination of several types of neutron measurement subsystem, cross calibration among them, and in situ calibration are needed. Neutron transport calculation shows the suitable calibration source is a DT/DD neutron generator of source strength higher than 10 10 n/ s neutron/second for DT and 10 8 n/ s for DD. It will take eight weeks at the minimum with this source to calibrate flux monitors, profile monitors, and the activation system.
