D-T Fusion with Ion Cyclotron Resonance Heating in the JET Tokamak

Abstract

Ion cyclotron resonance heating (ICRH) experiments have been carried out in JET D-T plasmas using scenarios applicable to reactors. Deuterium minority heating in tritium plasmas is used for the first time and produces 1.66 MW of D-T fusion power for an ICRH power of 6 MW. The Q value is 0.22, which is a record for steady state discharges. Fundamental He 3 minority ICRH, in both 50:50 D-T and tritium dominated plasmas, generates strong bulk ion heating and ion temperatures up to 13 keV. Second harmonic tritium ICRH is seen to heat mainly the electrons as expected for JET conditions. All three schemes produce H-mode plasmas. [S0031-9007(98)06143-2] PACS numbers: 52.50. Gj, 52.55.Fa, 52.55.Pi Ion cyclotron resonance heating is the only method of heating majority ions, rather than electrons, in the dense core of a tokamak reactor. Radiofrequency (rf) power is used to excite a fast magnetosonic wave, to which the high density plasma is accessible. The wave is absorbed at a cyclotron resonance which is positioned in major radius (usually the plasma center) by the choice of magnetic field and rf frequency. The ions damping the wave are often accelerated to suprathermal energies, especially if they are a minority species. This energy is then transferred to the thermal ions and electrons by Coulomb collisions. If the energy of the absorbing ions is less than a critical value, power flows mainly to the thermal ions rather than to the electrons. The critical energy at which the power to the electrons equals that to the ions is given [1] by E crit 14.8AT e ͓Sn j Z 2 j ͞n e A j ͔ 2͞3 where A is the atomic mass of the energetic ions, n e is the electron density, Z is the atomic number, the sum is over the thermal ion species, and T e is the electron temperature. For fast deuterons in a tritium plasma, E crit 14.2T e . In the JET D-minority experiments, T e is about 7 keV and E crit ഠ 100 keV, which is also the deuteron energy at which the deuterium-tritium (D-T) fusion cross section peaks. High fusion power is thus achieved at the same time as equal ion and electron heating.Several ion cyclotron resonance heating (ICRH) schemes in D-T plasmas have been included in the design of the JET system [2] which thus covers a wide frequency band, 23-57 MHz. The same schemes are being considered for the ITER reactor [3]. Three of these scenarios are minority deuterium and minority He 3 at their fundamental resonances and majority tritium at its second harmonic resonance. Recent calculations [4,5] for ITER predict that each method can produce more than 50% ion heating on the route to ignition. The present experiments have demonstrated and assessed the fundamental deuterium scheme, which has never been used previously. Also, the physics and performance of all three methods have been studied for the first time in H mode, D-T plasmas heated predominantly by ICRH. The plasmas were similar to those expected in ITER in terms of shape, safety factor ͑q͒, normalized confinement time, and the behavior of edge localized modes (ELMs), which affec...

Bulk ion heating with ICRH in JET DT plasmas

“…Neutron spectrometer measurements show a Doppler broadening [8] commensurate with T i = 13.5 ± 2.5 keV in good agreement with the charge exchange measurement. Similar results were achieved with 6.5%…”

“…Redistribution of the fast ions by sawteeth, as observed experimentally [8], is also included. The predicted fusion reactivity is in excellent agreement with the observed reactivity [13].…”

Recent progress on spherical torus research

“…A smaller FNSF, however, can produce fusion neutrons via NBI driven beam-target reactions in a similar manner to the TFTR/JET DT experiments. 71,72 To achieve the plasma parameters necessary for a FNSF, one may need plasma pressure (n T) or B Fig. 31, B T0 2 b T is plotted as a function of R 0 (as a measure of the achievable plasma pressure) for possible FNSF parameters: A ¼ 1.6, q* ¼ 3, and j ¼ 3, and a relatively modest beta of b N ¼ 3 at the two gap distances of D ¼ 0 and 10 cm.…”

Assessment of a field-aligned ICRF antenna

“…[18] However, experiments indicate that the elevated plasma potentials and poor heating efficiency is due to poor wave penetration to the plasma core. We performed a series of discharges where the heating scenario is mode conversion heating and the minority 3 He concentration is ~15%. The majority of the launched power is absorbed on electrons.…”

“…This derives, in part, from the fact that ICRF has been experimentally demonstrated to heat high performance plasmas in a number of experiments including deuterium-tritium discharges on TFTR [2] and JET [3], and has favorable scaling to burning plasmas. Unlike the previous generation of fusion experiments, the plasma facing components (PFCs) for future reactors and a growing number of experiments are high Z metals, [AUG, JET, C-Mod], due to concerns regarding material erosion and tritium retention with carbon.…”