Anomalous Loss of DT Alpha Particles in the Tokamak Fusion Test Reactor Deuterium-Tritium

Details Anomalous Loss of DT Alpha Particles in the Tokamak Fusion Test Reactor Deuterium-Tritium Anomalous Loss of DT Alpha Particles in the Tokamak Fusion Test Reactor Deuterium-Tritium

Oct 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........9h&link_type=abstract

Thesis (PHD). PRINCETON UNIVERSITY , Source DAI-B 58/04, p. 1944, Oct 1997, 195 pages.

Physics

4

Scientific paper

Princeton's Tokamak Fusion Test Reactor (TFTR) is the first experimental fusion device to routinely use tritium to study the deuterium-tritium (DT) fusion reaction, allowing the first systematic study of DT alpha (α) particles in tokamak plasmas. A crucial aspect of α-particle physics is the fraction of alphas that escape from the plasma, particularly since these energetic particles can do severe damage to the first wall of a reactor. An escaping alpha collector probe has been developed for TFTR's DT phase. Energy distributions of escaping alphas have been determined by measuring the range of α-particles implanted into nickel foils located within the alpha collector. Results at 1.0 MA of plasma current are in good agreement with predictions for first orbit alpha loss. Results at 1.8 MA, however, show a significant anomalous loss of partially thermalized alphas (in addition to the expected first orbit loss), which is not observed with the lost alpha scintillator detectors in DT plasmas, but does resemble the anomalous 'delayed' loss seen in DD plasmas. None of the candidate explanations proposed thus far are fully consistent with the anomalous loss observations. An experiment designed to study the effect of plasma major radius shifts on α-particle loss has led to a better understanding of α-particle dynamics in tokamaks. Intuitively, one might suppose that confined marginally passing α-particles forced to move toward higher magnetic field during an inward major radius shift (i.e. compression) would mirror and become trapped particles, leading to increased alpha loss. Such an effect was looked for during the shift experiment, however, no significant changes in alpha loss to the 90o lost alpha scintillator detector were observed during the shifts. It is calculated that the energy gained by an α-particle during the inward shift is sufficient to explain this result. However, an unexpected loss of partially thermalized α-particles near the passing/trapped boundary was observed to occur between inward and outward shifts at an intermediate value of plasma current (1.4 MA). This anomalous loss feature is not yet understood.

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