Details

IT14 · Gamma-Ray Measurements of Fast Alpha Particles

V. G. Kiptily and JET EFDA contributors*
Euratom/UKAEA Fusion Association, Culham Science Centre, Abingdon, Oxon, UK
vkip@jet.uk
*See the Appendix of J.Pamela et al., Fusion Energy 2004 (Proc. 20th Int. Conf. Vilamoura, 2004) IAEA, Vienna (2004)

Abstract: An overview of g-ray diagnostic observations of fast a-particles and He-ions in JET is presented and capabilities of this diagnostics in ITER are discussed. The talk will cover the following points: 1) An introduction to the physics of the used alpha-particle diagnosis, which based on measurements of the g-ray emission from the ⁹Be(a,ng)¹²C nuclear reaction. 2) A description of the experimental equipment used for the measurements, in particularly, g-ray spectrometers and 2-D gamma cameras. 3) First measurements of g-ray spectra from nuclear reactions between fusion-born a particles and Be impurities, which were done in JET D-majority plasmas just after short blips of T-NBI. In the performed experiments the time dependence of the measured spectra allowed the determination of the density evolution of alphas, and in this way a correlation between the g-ray emission decay and plasma parameters in different plasma scenarios was established. 4) Results of the gamma-ray measurements of fast ⁴He and D-ions accelerated with 3^rd-harmonic ion-cyclotron-resonance heating of ⁴He-beam [2]. Gamma-ray images of fast ⁴He -ions and evolution of the g-ray emission were simultaneously recorded for the first time in JET experiments [3] dedicated to the investigation of burning-like plasmas with 3.5-MeV fusion a-particles. 5) An application of this technique for ITER. Simultaneous measurements of several fast-ion species are paramount for the burning plasma in ITER. At least two types of fast ions are expected in the ITER plasma: 1-MeV deuterons from NBI heating and fusion alpha particles. A principal diagnostic problem in ITER will be discriminating the NBI deuterium from the fusion alpha particles. The similar measurements with 2-D g-cameras could be used in ITER, but the g-ray detector array should be protected against severe neutron emission with special neutron filters [4]. Simultaneous measurements of the NBI power deposition and evolution of the alpha-particle density profiles are very important for optimisation of different plasma scenarios and understanding of the a-particle confinement effects.

[1] Kiptily et al 2004 Phys. Rev. Lett. 93 115001.
[2] Mantsinen et al 2002 Phys. Rev. Lett. 88 105002.
[3] Kiptily et al 2005 Nucl. Fusion 45 L21.
[4] Kiptily et al 1998 Tech. Physics 43 471.