Ion Cyclotron Resonance Heating Power Research Articles

Time resolved neutron emission spectroscopy of DT plasmas with ion cyclotron resonance heating

The energy spectrum of the DT neutron emission was measured in experiments carried out at JET for plasmas of deuterium–tritium heated with different ion cyclotron resonance heating (ICRH) schemes. The spectrum was measured with the magnetic proton recoil spectrometer. The data were analyzed in up to three spectral components, which were ascribed to the underlying reactions involving thermal, epithermal, and high-energy ions. The results include time resolved information for individual discharges. High-energy components in the fuel ion population were found in most cases and analyzed in terms of a tail temperature. Changes in the (minority) deuterium concentration in the range of 12–20% were found to affect significant the ICRH power absorption and its perturbation of the minority velocity distribution.

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

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 He3 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.Received 23 December 1997DOI:https://doi.org/10.1103/PhysRevLett.80.4681©1998 American Physical Society

Numerical analysis of helium ash removal by using ICRH-driven ripple transport

Helium ash removal across the last closed flux surfaces in a deuterium-tritium fuelled tokamak plasma is studied using an orbit-following Monte Carlo simulation. Ripple transport of helium ash ions is induced by ion cyclotron resonance heating (ICRH) of short-lived ions, which are produced by charge exchange of with incoming neutral species. It is found that the required ICRH power in an ITER grade tokamak plasma is 10-15 MW and the helium transport to the first wall is localized within an area given by 1.3 m in the toroidal direction and 0.7 m in the poloidal direction.

Production of sheared flow during ion cyclotron resonance heating in tokamak plasmas

An approach of producing the poloidal ion rotation by using ion cyclotron resonance heating (ICRH) is presented in core tokamak plasmas. The mechanism employed here is inducing a poloidal density inhomogeneity by rf cyclotron heating and then destabilizing the anomalous Stringer spin-up. A criterion for destabilization of the poloidal ion rotation in the presence of a rf wave is given, which depends on the ratio of the characteristic time of inhomogeneous density formation to the ion collision time. The numerical results have shown that the poloidal ion rotation can be destabilized in the present ICRH power level.

Effects of Nonlinear Wave Absorption on the Radiation Loss Fraction during Second Harmonic Minority Ion Cyclotron Resonance Heating Experiments in JT-60U

The ratio of an increment in radiation power to ion cyclotron resonance heating (ICRH) power (ΔP rad main/P IC) decreased from about 40% to below 10% with increasing ICRH power in JT-60U. The most plausible mechanism for the anomalous behavior of ΔP rad main/P IC is inferred to be nonlinear wave absorption, which was experimentally estimated from the time derivative of the diamagnetic stored energy at the turn-off timing of the ICRH pulse. Nonlinear wave absorption observed during the experiments supported the theoretical estimation using a full wave code incorporating the 1-D Fokker-Planck code.

Modeling of sawtooth destabilization during radio-frequency heating experiments in tokamak plasmas

Sawtooth oscillations in tokamaks have been stabilized using ion cyclotron resonance heating (ICRH), but often reappear while ICRH continues. It is shown that the reappearance of sawteeth during one particular ICRH discharge in the Joint European Torus (JET) [Campbell et al., Phys. Rev. Lett. 60, 2148 (1988)] was correlated with a change of sign in the energy δW associated with m=1 internal kink displacements. To compute δW, a new analytical model is used for the distribution function of heated minority ions, which is consistent with Fokker–Planck simulations of ICRH. Minority ions have a stabilizing influence, arising from third adiabatic invariant conservation, but also contribute to a destabilizing shift of magnetic flux surfaces. As the minor radius of the q=1 surface rises, the stabilizing influence of minority ions diminishes, and the shape of the plasma cross section becomes increasingly important. It is shown that an increase in ICRH power can destabilize the kink mode: this is consistent with observations of sawteeth in JET discharges with varying levels of ICRH. It is suggested that the sawtooth-free period could be prolonged by minimizing the vertical extent of the ICRH power deposition profile.1996 American Institute of Physics

The effect of different ICRH heating scenarios on the jet scrape-off layer

Investigation of the scrape-off layer (SOL) at different toroidal and poloidal positions has been carried out in JET for limiter discharges with and without ion cyclotron resonance heating (ICRH). A wide range of plasma conditions ( I p ≈1−5 (rmMA), B T ≈1.8−3.5 T, 〈 n e 〉 ≈ (1−5) × 10 19 m −3 ), ICRH heating scenarios (H and He 3 minority, quadrupole, monopole, dipole antenna phasing) and different machine configurations were investigated. The total ICRH power coupled to the JET plasma was ≤ 7.2 MW, when three antennae were used, and ≤ 13 MW using eight antennae operation. Limiter discharges were produced with either eight discrete graphite limiters or two full toroidal belt limiters. Density profiles in the SOL were found to decay exponentially with an e-folding length, λ n e , which changes with total input power, wall conditioning and plasma species. The modification of the plasma edge depends on the antenna phasing. The scaling of edge temperature, edge density and impurity production with 〈 n e 〉 and P T for different scenarios is presented. Changes in SOL parameters are also compared with different torus wall and antenna conditioning.

Ion cyclotron wave effects on the ion velocity distribution in a tandem mirror

Experiments have been conducted in the end cells of a tandem mirror to determine the effect of ion cyclotron resonance heating (ICRH) on the ion pitch angle and velocity distribution. An ICRH power of 2-4 W·cm−3 was measured to have both a directed and a diffusive velocity space effect on the mirror trapped plasma ions, which have densities of (4-6) × 1012 cm3 and average perpendicular energies of 600-1000 eV. On low energy streaming ions (10-50 eV, v∥ > v⊥), the ICRH has a directed pitch angle effect which causes a dominant number of the eventually trapped ions to reflect or to mirror near the resonant magnetic field and to generate a sloshing ion like velocity distribution. However, a sloshing ion like axial density profile was not measured. On hotter thermal ions (600-1000 eV) the ICRH has a measurable diffusive effect, which increases with RF electric field and spreads the distribution function 15-25° around the pitch angle of the RF resonance. On hot test particles generated by 6.9 keV neutral beams injected nearly perpendicularly to the axis, Coulomb and charge exchange collisions were found to dominate over RF diffusion. These observations are discussed in the context of RF kick-per-pass and quasi-linear theory.