RESUMO
The spectral broadening of characteristic γ-ray emission peaks from the reaction (12)C((3)He,pγ)(14)N was measured in D((3)He) plasmas of the JET tokamak with ion cyclotron resonance heating tuned to the fundamental harmonic of (3)He. Intensities and detailed spectral shapes of γ-ray emission peaks were successfully reproduced using a physics model combining the kinetics of the reacting ions with a detailed description of the nuclear reaction differential cross sections for populating the L1-L8 (14)N excitation levels yielding the observed γ-ray emission. The results provide a paradigm, which leverages knowledge from areas of physics outside traditional plasma physics, for the development of nuclear radiation based methods for understanding and controlling fusion burning plasmas.
RESUMO
New transport experiments on JET indicate that ion stiffness mitigation in the core of a rotating plasma, as described by Mantica et al. [Phys. Rev. Lett. 102, 175002 (2009)] results from the combined effect of high rotational shear and low magnetic shear. The observations have important implications for the understanding of improved ion core confinement in advanced tokamak scenarios. Simulations using quasilinear fluid and gyrofluid models show features of stiffness mitigation, while nonlinear gyrokinetic simulations do not. The JET experiments indicate that advanced tokamak scenarios in future devices will require sufficient rotational shear and the capability of q profile manipulation.
RESUMO
Recent experiments at JET aimed at producing 4He ions in the MeV range through third harmonic ion cyclotron resonance heating (ICRH) acceleration of 4He beams in a 4He dominated plasma. MeV range D was also present through parasitic ICRH absorption on residual D. In this contribution, we analyze TOFOR neutron spectrometer data from these experiments. A consistent description of the data is obtained with d(d,n)3He and 9Be(α,n)12C neutron components calculated using Stix distributions for the fast D and 4He, taking finite Larmor radius effects into account and with a ICRH power partition of P(D)(RF) = 0.01×P(4He)(RF), in agreement with TOMCAT simulations.
RESUMO
Experiments were carried out in the JET tokamak to determine the critical ion temperature inverse gradient length (R/LTi=R|nablaTi|/Ti) for the onset of ion temperature gradient modes and the stiffness of Ti profiles with respect to deviations from the critical value. Threshold and stiffness have been compared with linear and nonlinear predictions of the gyrokinetic code GS2. Plasmas with higher values of toroidal rotation show a significant increase in R/LTi, which is found to be mainly due to a decrease of the stiffness level. This finding has implications on the extrapolation to future machines of present day results on the role of rotation on confinement.
RESUMO
The effect of ion cyclotron resonance heating (ICRH) on (3He)D plasmas at JET was studied with the time of flight optimized rate (TOFOR) spectrometer dedicated to 2.5 MeV dd neutron measurements. In internal transport barrier (ITB) plasma experiments with large 3He concentrations (X(3He)>15%) an increase in neutron yield was observed after the ITB disappeared but with the auxiliary neutral beam injection and ICRH power still applied. The analysis of the TOFOR data revealed the formation of a high energy (fast) D population in this regime. The results were compared to other mode conversion experiments with similar X(3He) but slightly different heating conditions. In this study we report on the high energy neutron tails originating from the fast D ions and their correlation with X(3He) and discuss the light it can shed on ICRH-plasma power coupling mechanisms.
RESUMO
The first electron temperature modulation experiments in plasmas characterized by strong and long-lasting electron and ion internal transport barriers (ITB) have been performed in JET using ion cyclotron resonance heating in mode conversion scheme. The ITB is shown to be a well localized narrow layer with low heat diffusivity, characterized by subcritical transport and loss of stiffness. In addition, results from cold pulse propagation experiments suggest a second order transition process for ITB formation.
