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Abstract

Two neutron diagnostic systems are in use on JET for determining the ion density and temperature for deuterium plasmas. The first comprises three sets of fission counters, each mounted on a separate magnet limb on the horizontal midplane of the machine, to measure the instantaneous neutron emission from the plasma. The second is a 3-He ionization chamber spectrometer located in the well shielded Roof Laboratory about 20 m above the midplane of the machine and viewing the plasma through a collimator (set in the floor of the Roof Laboratory) aligned with a vertical diagnostic port in the vacuum vessel. The neutron emission is related to the volume integral over the plasma of the product n**2-d <sigma-nu>, where n-d is the deuterium ion density and <sigma-nu> is the plasma reactivity. For a Maxwellian plasma the reactivity varies with temperature as T**alpha-i, with alpha about 4.0 for T-i = 3 keV. Thus, assuming that the spatial profiles of density and temperature for electrons, which are measured routinely, apply also to ions with only the scale factors differing, then the neutron emission measurements provide an estimate for the product of central parameters n**2-d T**alpha-i. The 3-He chamber possesses excellent energy resolution (42 keV at 2.5 MeV) and is thus able to measure the thermal broadening of the thermonuclear neutrons, which should exhibit a nearly Gaussian energy spectrum with fwhm = 82.5 square root of T-i, with T-i in keV. The primary result from the spectrometer is therefore a value for T-i which can be used in conjunction with the neutron emission measurements to determine n-d.

Additional information

Authors: JARVIS O N, JET JOINT UNDERTAKING, ABINGDON (UK);GORINI G, JET JOINT UNDERTAKING, ABINGDON (UK);HONE M, JET JOINT UNDERTAKING, ABINGDON (UK);KAELLNE J, JET JOINT UNDERTAKING, ABINGDON (UK);MERLO V, JET JOINT UNDERTAKING, ABINGDON (UK);SADLER G, JET JOINT UNDERTAKING, ABINGDON (UK);VAN BELLE P JET JOINT UNDERTAKING, ABINGDON (UK), JET JOINT UNDERTAKING, ABINGDON (UK)
Bibliographic Reference: 12TH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS, BUDAPEST (HUNGARY), SEPT. 2-6, 1985 PP. 61-64 WRITE TO THE PUBLICATIONS OFFICER, JET JOINT UNDERTAKING, ABINGDON, OXON, OX14 3EA (UK), MENTIONING REPORT JET-P(85)10, 1985
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