Measured response of bubble neutron detectors and prospects for alpha knock-on diagnostics
Measurement of the neutron energy spectrum above {approx}16 MeV will yield information on the spatial and energy distributions of confined fast alphas in deuterium--tritium (DT) tokamaks (Fisher, Nucl. Fusion; Gorini Rev. Sci. Instrum.). The energetic neutrons result from fusion reactions involving the energetic ions created by alpha-fuel ion knock-on collisions. Standard two-gas bubble neutron detectors, designed to only detect neutrons with energies above a selectable threshold determined by the gas mixture, were used in preliminary attempts to measure the knock-on neutrons from DT plasmas in the Tokamak Fusion Test Reactor and Joint European Torus (JET). Subsequent measurements at accelerator neutron sources showed an unexpected below-threshold detector response that prevented observations of the alpha-induced neutron tails. Spontaneous bubble nucleation measurements show that the majority of this below-threshold response is due to slight variations in the gas mixture, and is not present in single-gas detectors. Single-gas detectors will be tested at the University of California Berkeley to determine the neutron energy threshold as a function of detector operating temperature and to confirm their suitability for alpha knock-on tail measurements. An array of single-gas detectors operating at different temperatures should allow measurements of the alpha knock-on neutron tail during planned DT experiments on JET.
- Sponsoring Organization:
- (US)
- OSTI ID:
- 40204860
- Journal Information:
- Review of Scientific Instruments, Vol. 72, Issue 1; Other Information: Othernumber: RSINAK000072000001000796000001; 628101CON; PBD: Jan 2001; ISSN 0034-6748
- Publisher:
- The American Physical Society
- Country of Publication:
- United States
- Language:
- English
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