Observation of Sawtooth Redistribution of Nonthermal, Confined Alpha Particles in TFTR D-T Discharges PDF Download
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Author: B. C. Stratton
Publisher:
ISBN:
Category : Alpha rays
Languages : en
Pages : 7
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Book Description
Author: B. C. Stratton
Publisher:
ISBN:
Category : Alpha rays
Languages : en
Pages : 7
Get Book Here
Book Description
Author: B. C. Stratton
Publisher:
ISBN:
Category : Alpha rays
Languages : en
Pages : 7
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Book Description
Author:
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ISBN:
Category :
Languages : en
Pages : 10
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Radially resolved confined alpha particle energy and density distributions are routinely measured on TFTR using two diagnostics: PCX and [alpha]-CHERS. The Pellet Charge-eXchange (PCX) diagnostic uses the ablation cloud formed by an impurity pellet (Li or B) for neutralization of the alphas followed by analysis of the escaping helium neutrals. PCX detects deeply trapped alpha particles in the energy range 0.5 - 3.8 MeV. The [alpha]-CHERS technique, were the alpha signal is excited by charge-exchange between alphas and the deuterium atoms of one of the heating beams and appears as a wing on the He 468.6 nm line, detects mainly passing alphas in the range of 0.15 - 0.7 MeV. Studies of alpha losses during DT experiments on TFTR have also been conducted using lost alpha detectors located on the walls of the plasma chamber. All of these diagnostics were used for investigating the influence of sawtooth crashes on alphas in high power D-T discharges in TFTR. Both PCX and [alpha]-CHERS measurements show a strong depletion of the alpha core density and transport of trapped alphas radially outwards well beyond q = 1 surface after a sawtooth crash. Lost alpha detectors measure bursts of alpha loss of the previously confined alphas (
Author: George R. McKee
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Category : Alpha rays
Languages : en
Pages : 296
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Category : Electronic journals
Languages : en
Pages : 786
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Author: Mikhail Petrovich Petrov
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Category : Alpha rays
Languages : en
Pages : 10
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Category :
Languages : en
Pages :
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Book Description
Results from recent DT experiments on TFTR to measure the radial density profiles of fast confined well trapped[alpha]-particles using the Pellet Charge eXchange (PCX) diagnostic[PETROV M.P., et. al. Nucl. Fusion, 35 (1995) 1437] indicate that sawtooth oscillations produce a significant broadening of the trapped alpha radial density profiles.' Conventional models consistent with measured sawtooth effects on passing particles do not provide satisfactory simulations of the trapped particle mixing measured by PCX diagnostic. We propose a different mechanism for fast particle mixing during the sawtooth crash to explain the trapped[alpha]-particle density profile broadening after the crash. The model is based on the fast particle orbit averaged toroidal drift in a perturbed helical electric field with an adjustable absolute value. Such a drift of the fast particles results in a change of their energy and a redistribution in phase space. The energy redistribution is shown to obey the diffusion equation, while the redistribution in toroidal momentum P[var-phi] (or in minor radius) is assumed stochastic with large diffusion coefficient and was taken flat. The distribution function in a pre- sawtooth plasma and its evolution in a post-sawtooth crash plasma is simulated using the Fokker-Planck Post-TRANSP (FPPT) processor code. It is shown that FPPT calculated[alpha]-particle distributions are consistent with TRANSP Monte-Carlo calculations. Comparison of FPPT results with Pellet Char eXchange (PCX) measurements shows good agreement for 9 both sawtooth free and sawtoothing plasmas.
Author: S. S. Medley
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Category : Alpha rays
Languages : en
Pages : 4
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Author:
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Category :
Languages : en
Pages : 8
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The energy distributions and radial density profiles of the fast-confined trapped alpha particles in DT experiments on TFTR are being measured in the energy range 0.5 to 3.5 MeV using the Pellet Charge Exchange diagnostic developed in a collaboration involving General Atomics, the A.F. Ioffe Physical-Technical Institute, and the Princeton Plasma Physics Laboratory. A brief description of the measurement technique which involves active neutral particle analysis using the ablation cloud surrounding an injected lithium or pellet as the neutralizer is presented. In the core of quiescent TFTR discharges, measured alpha spectra are consistent with classical slowing down. Measured Doppler broadening of alphas near the birth energy is consistent with the effective temperature of interacting deuterium and tritium ions. Outside the core alpha energy spectra and density profiles are influenced by the magnetic field ripple and appear to be consistent with stochastic ripple diffusion. Sawtooth oscillations lead to the significant broadening of alpha density profiles. The experimental data are modeled using a Fokker-Planck Post TRANSP (FTTP) code which includes the effects of the classical slowing down, magnetic field ripple losses, and the sawtooth mixing of alpha particles. The comparison of the experimental data with the FPPT calculations shows that broadening of trapped alpha density profiles after the sawtooth crashes can be explained by the influence of poloidal electric field generated during the crashes.
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Languages : en
Pages : 26
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In recent Deuterium-Tritium experiments on the Tokamak Fusion Test Reactor (TFTR), both the Pellet Charge Exchange (PCX) and the alpha Charge Exchange Recombination Spectroscopy ([alpha]-CHERS) diagnostics indicate that sawtooth oscillations can cause significant broadening of the fusion alpha radial density profile. The authors investigate this sawtooth mixing phenomenon by applying a Hamiltonian guiding center approach. A model of time evolution of the Kadomtsev-type sawtooth is constructed. The presence of more than one mode in the nonlinear stage of the sawtooth crash is necessary to cause significant broadening of the alpha density profile. Use of numerical equilibria allows us to perform detailed comparisons with TFTR experimental data. The results are in reasonable agreement with [alpha]-CHERS and show a broadening of alpha particles similar to that seen in PCX measurements.
