Validation of TRANSP simulations of the fast deuterium beam distribution in D– ³ He plasmas from (D)–(D _NBI )–( ³ He) three–ion scheme experiments at JET

Abstract At JET, Deuterium–Helium-3 (D– 3 He) experiments using ion cyclotron resonance heating (ICRH) with the three–ion scheme were conducted, involving thermal Deuterium (D), thermal Helium-3 ( 3 He), and a fast D beam injected via neutral beam injection (NBI) and further heated using ICRH. In these plasmas, intense neutron emission at the level of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>16</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> n s −1 was observed, and a non-thermal neutron spectrum was measured with the JET time of flight neutron spectrometer. Furthermore, the spatial profile of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> <mml:mn>16.4</mml:mn> </mml:mrow> </mml:math> MeV gamma rays originating from the 3 He(D, γ ) 5 Li reaction was observed. This is a weak branch ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>5</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> relative probability) of the more common 3 He(D,p) α reaction and it can be used to assess the production of alpha particles in these experiments. In this work we analyse a set of data from nuclear diagnostics in D–D NBI – 3 He experiments at JET and compare them with synthetic diagnostics based on TRANSP simulations of the fast deuterium distribution function, using the so-called ‘kick operator’ to model power transfer from the wave to the beam fast deuterons. The neutron rate predicted by the TRANSP simulations broadly agrees with data measured with fission chambers. The shape of the neutron emission spectrum is also well understood, once finite Larmor radius effects are introduced into calculations. Data from the gamma ray camera are used to infer the alpha birth profile through tomographic reconstructions based on the TREVISO code. These were compared with corresponding calculations starting from TRANSP results and showing an overall good agreement with the experimental tomographies. The validated TRANSP results are finally used to discuss the modifications of the fast deuterium distribution function and of the alpha birth profile in a set of discharges.