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Charge Neutralization by Foils to Study Alpha Edge Flux Produced in Magnetic Fusion Reactors

Glenn Gerdin, Donald Mueller, Bernard W. Wehring

Fusion Science and Technology

Volume 7 / Number 2 / March 1985 / Pages 180-196


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A method is proposed to measure the properties of the alphas escaping a deuterium-tritium-fueled magnetically confined fusion reactor. This method is called the charge neutralization approach; it involves the slowing down of alphas in carbon foils of known thickness so that a significant percentage of the alphas are neutralized. These alphas can be detected by methods similar to those developed for charge-exchange neutral analysis. The foils would be placed in a recessed slot in the foil holder that would, in turn, be placed in the shadow of the limiter to reduce the heat and particle flux to the foils. Considerable energy selection can be achieved by varying the foil thickness; the lower limit on detectable alpha energy is ∼200 keV. The ratio of alpha signal to nuclear noise was estimated for a ZnS scintillator 15 μm thick being operated in the current mode in a borated limestone shield. Experimental values were used for the response to neutrons, and linear absorption coefficients were used for the response to gammas. The alpha wall flux was that calculated for a Tokamak Fusion Test Reactor (TFTR) with Q = 1, a plasma current of 2.5 MA, and a minor radius of 85 cm; the radiation fluxes were scaled from the one-dimensional calculations of L-P. Kufor TFTR at Q = 1. For this example, the signal to nuclear noise ratio becomes greater than unity at ∼75 cm into the shield indicating the amount of shielding material required.

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