Ion Cyclotron Resonance Heating Research Articles

Interaction between the core and the edge for ion cyclotron resonance heating based on artificial absorption plasma model

Abstract In numerical simulations of the ion cyclotron range of frequencies (ICRF) wave heating scheme, core solvers usually focus on wave propagation and absorption mechanisms within the core plasma region. However, the realistic scrape-off layer (SOL) plasma is usually simplified, making it difficult to have deeper understanding of wave propagation and absorption within the SOL. In this work, we employ a cold plasma assumption and an artificial absorption mechanism based on the approach of reference (Zhang et al 2022 Nucl. Fusion 62 076032), to study wave propagation and absorption in the realistic SOL plasma of the EAST. During the exponential decay of the total coupled power with respect to the toroidal mode numbers, several fluctuations are observed in the case of low collisional frequencies. The fluctuations may be caused by the cavity modes associated with specific toroidal mode numbers. Due to the presence of cutoff densities, the edge power losses and the total coupled power exhibit different behaviors before and after the cut-off layer is “open”. Furthermore, the simulation results obtained from the kinetic model in reference (Zhang et al 2022 Nucl. Fusion 62 076032) is discussed. This suggests that both the core-edge combined model and the artificial mechanism are capable of simulating wave propagation and absorption.

Interaction between the core and the edge for ion cyclotron resonance heating based on artificial absorption plasma model

Abstract In numerical simulations of the ion cyclotron range of frequencies (ICRF) wave heating scheme, core solvers usually focus on wave propagation and absorption mechanisms within the core plasma region. However, the realistic scrape-off layer (SOL) plasma is usually simplified, making it difficult to have deeper understanding of wave propagation and absorption within the SOL. In this work, we employ a cold plasma assumption and an artificial absorption mechanism based on the approach of reference (Zhang et al 2022 Nucl. Fusion 62 076032), to study wave propagation and absorption in the realistic SOL plasma of the EAST. During the exponential decay of the total coupled power with respect to the toroidal mode numbers, several fluctuations are observed in the case of low collisional frequencies. The fluctuations may be caused by the cavity modes associated with specific toroidal mode numbers. Due to the presence of cutoff densities, the edge power losses and the total coupled power exhibit different behaviors before and after the cut-off layer is “open”. Furthermore, the simulation results obtained from the kinetic model in reference (Zhang et al 2022 Nucl. Fusion 62 076032) is discussed. This suggests that both the core-edge combined model and the artificial mechanism are capable of simulating wave propagation and absorption.

Analysis of radiation conditions in the CFETR ion cyclotron resonance heating antenna

An ion cyclotron resonance heating (ICRH) antenna will be installed in the equatorial port plug of the China Fusion Engineering Test Reactor (CFETR) for heating ions and electrons in plasma. This study reports the latest neutronic modeling and analyses of antenna for the subsequent optimization of the shielding design, with radiation damage, nuclear heating, gas generation of key components, and shutdown dose rate (SDDR) used as main indicators. Results showed that the nuclear heating of the BP was extremely high, thus posing a high risk to the structure, highlighting the necessity of further upgrading the shielding performance. In addition, the SDDR was more than 100 μSv/hr 12 days after the shutdown, rendering hands-on maintenance in the areas at a short time challenging. Meanwhile, key contributors to higher SDDR have been analyzed.

Detection of alpha heating in JET-ILW DT plasmas by a study of the electron temperature response to ICRH modulation

In the JET DTE2 campaign a new method was successfully tested to detect the heating of bulk electrons by α-particles, using the dynamic response of the electron temperature T e to the modulation of ion cyclotron resonance heating (ICRH). A fundamental deuterium (D) ICRH scheme was applied to a tritium-rich hybrid plasma with D-neutral beam injection (NBI). The modulation of the ion temperature T i and of the ICRH accelerated deuterons leads to modulated α-heating with a large delay with respect to other modulated electron heating terms. A significant phase delay of ∼40° is measured between central T e and T i, which can only be explained by α-particle heating. Integrated modelling using different models for ICRH absorption and ICRH/NBI interaction reproduces the effect qualitatively. Best agreement with experiment is obtained with the European Transport Solver/Heating and Current Drive workflow.

Analysis of fusion alphas interaction with RF waves in D-T plasma at JET

This work studies the influence of radio frequency (RF) waves in the ion cyclotron resonance heating (ICRH) range of frequencies on fusion alphas during the recent JET D-T campaign. Fusion alphas from D-T reactions are created with energies of about 3.5 MeV and therefore have significant Doppler shifts enabling synergistic interactions between them and RF waves at a broad range of frequencies, including the ones foreseen for future fusion machines in ITER (Schneider et al 2021 Nucl. Fusion 61 126058) and SPARC (Creely et al 2020 J. Plasma Phys. 86 865860502). Resonant interactions between RF waves and alphas, also called synergistic effects, will modify the alpha distribution and ultimately will have an impact on alpha orbit losses and heating. Data from JET 3.43 T/2.3 MA pulses based on the hybrid scenario (Hobirk et al 2023 Nucl. Fusion; Hobirk et al 29th IAEA FEC23 Conf. (16–21 October 2023); Challis et al 48th EPS Conf. on Plasma Physics (27 June–1 July 2022) during the DTE2 campaign (Maggi et al 2023 Nucl. Fusion)) were used for the analysis in this study. The impact of synergistic effects on alpha orbit losses and alpha heating are assessed. The conclusions are based on the analysis of experimental data for fast alpha losses, i.e. measurements from neutral particle analyser (NPA), fast ion losses scintillator detector, Faraday cups (FCs), and TRANSP (Hawryluk et al 1980 Physics of Plasmas Close to Thermonuclear Conditions vol 1 (CEC) pp 19–46) simulations. Experimental data and TRANSP analysis indicates that there are indeed changes in the alpha distribution function (DF) due to interaction with RF waves. Data from the NPA show increased 4He flux in the range from a few hundred keV up to 800 keV for pulses with RF power, while TRANSP clearly shows modifications in the fast alpha DF for these energies. Data from the scintillator detector and the FCs were compared for pulses with and without ICRH power and versus cases with enhanced alpha losses due to MHD activity. The trends from these diagnostics consistently show no additional alpha losses due to interaction with RF waves. TRANSP predictions for the impact of ynergistic effects on alpha heating show up to a 42% increase in alpha electron heating and up to a 25% increase in alpha ion heating. These effects, however, become negligibly small, less than 1%, when alpha heating is compared to the total auxiliary heating power in the investigated JET pulses.

ICRH-related impurity source and control across experiments in H, D, T plasmas at JET-ILW

The experimental and theoretical analysis were focused on experiments conducted to assess the effect of plasma isotopes, protium (H), deuterium (D), and tritium (T) on ion cyclotron resonance heating (ICRH) related plasma wall interactions. Comparison of L-mode discharges with N = 1 3He and N = 1 H minority ICRH heating scenarios were done for different isotopes. For the selected pulses, the behaviour of high-Z, mid-Z and low-Z intrinsic impurity and radiated power behaviour was investigated based on data from VUV, visible spectroscopy, and bolometry diagnostic at Joint European Torus. It was found that for N = 1 3He scenario during radiofrequency antennas operation, core W, Ni content, Be source and the radiated power are higher for π/2 in comparison to dipole antenna phasing. Lowest core Ni, W content and radiated power is clearly observed for H plasmas in comparison to D and T, where for this ICRH scenario behaviour was similar. However, lower Be photon flux is observed for T in comparison to D plasmas. Be sputtering by He particles is responsible for such an effect. Additionally, several computer simulations were conducted using the COREDIV code. The difference in the electron temperature was due to the difference in the isotope masses. Increased temperature in the central plasma in the case of T plasmas leads to higher radiation in the central plasma in comparison to H plasmas. As a result, the power across separatrix is lower and the temperature on the divertor plate decreases with the increase of the isotope mass. At these temperatures on the divertor plate, W is not sputtered by the main plasma ions H, D and T and by He. For the N = 1 H ICRH scenario clear difference between D and T plasma was observed with higher metallic impurity content for T plasma in comparison to D. Impurity content in the plasmas is found to be sensitive to the power balance between the antenna straps. Its minimum is observed for the maximum of P cen/P tot.

Simulating energetic ions and enhanced fusion rates from ion-cyclotron resonance heating with a full-wave/Fokker–Planck model

Reproducing fast-ion enhanced fusion rates from ion-cyclotron resonance heating (ICRH) in tokamaks requires the self-consistent coupling of a full-wave solver and a Fokker–Planck solver, which evolves multiple simultaneously resonant ion species. We introduce a new self-consistent model that iterates the TORIC full-wave solver with the CQL3D Fokker–Planck solver using the integrated plasma simulator (IPS). This model evolves the bounce-averaged ion distribution functions in both parallel and perpendicular velocity-space with a quasilinear radio frequency (RF) diffusion operator valid in the ion finite Larmor radius (FLR) limit and the RF electric fields with the resultant non-Maxwellian FLR dielectric tensor. This produces non-Maxwellian ICRH simulations that are fully self-consistent, fast, and interoperable with integrated modeling frameworks, such as TRANSP/GACODE/IPS-FASTRAN. We demonstrate our model's capabilities by validating it against experimental data in Alcator C-Mod. We then perform the first RF heating simulations of SPARC using self-consistent non-Maxwellian ion distributions to investigate the potential to enhance fusion rates using ion cyclotron resonance heating generated fast ions.

A full wave solver integrated with a Fokker–Planck code for optimizing ion heating with ICRF waves for the ITER deuterium–tritium plasma

Efficient ion heating is crucial for future fusion devices, and the only way to heat ions directly is ion cyclotron resonance heating. Reported here is a full wave solver integrated with a Fokker–Planck code for optimizing ion heating with ion cyclotron range of frequency waves for the International Thermonuclear Experimental Reactor deuterium–tritium plasma. Both the direct absorption of minority ions and the power transfer to bulk ions via collisions are considered, while also accounting for the edge effects on ion absorption near the core. The simulation results show that the appropriate scrape-off layer density profile and parallel wave number lead to enhanced edge coupling and broaden the absorption region with moderate absorption intensity of the minority ions, which is very important for ion heating. More power from the heated ions is transferred to bulk ions than to electrons through collisions in our simulation via optimization, and reducing the total RF power results in a significant increase of the absorbed fraction of bulk ions.

ICRH operations during the JET tritium and DTE2 campaigns

The JET-ILW pure tritium and deuterium–tritium (DTE2) experimental campaigns took place in 2021–2022. Tritium (T) and deuterium–tritium (D–T) operations present challenges not encountered in present day tokamaks (Horton et al 2016 Fusion Eng. Des. 109–111 925–36). This contribution focuses on ion cyclotron resonance heating (ICRH) operations in tritium and deuterium–tritium plasmas, starting with a summary of the program of improvements to the ICRH system which spanned a few years prior to these experiments. Procedures were implemented to address specific constraints from tritium and deuterium–tritium operations (tritium safety and reduced access to the RF generator area) and increase the system reliability and power availability during plasma pulses. Operation of the upgraded real time RF power control system that maximises the launched power while taking into account limitations from the system or antenna coupling is described. We also report on the result from dedicated pulses performed to assess the potential harmful impact of the 2nd harmonic tritium resonance in the plasma, close to the inner wall, when using the standard central hydrogen minority ICRH scheme. During DTE2, the ITER-like antenna was not used because water leaked from an in-vessel capacitor into the vessel on day-2 of the experimental campaign. The lessons learnt from this incident are highlighted. Finally, the ICRH plant adjustments required to safely perform ion cyclotron wall cleaning discharges are described.

Design and operation of a load-tolerant ICRH system in Experimental Advanced Superconducting Tokamak

Ion Cyclotron Resonance Heating (ICRH) has been a dependable tool for sturdy plasma heating with high RF power of several megawatts. However, a sudden increase in the reflected power during ICRH heating experiments is a problem that should be solved for future fusion experimental devices. To solve this issue, a load tolerant matching network has been designed for the ICRH system in EAST. The matching network includes a 3-stub tuner impedance matching system with conjugate-T structure, 30 Ω to 50 Ω transmission line and center grounded antenna strap. By maintaining a low reflection ratio in the network for a wide range of resistance, this matching network can allow sturdy high-power operations without fast impedance matching in EAST. In our matching network, the two arms of a conjugate-T are designed to have a λ/2 length difference which could mitigate current imbalance and antenna poloidal phasing outside of the control problem. The T-point corresponds to the maximum point of the standing wave voltage, which could greatly improve the input impedance of the antenna.

Modeling Ion Conic Formation in Io's Auroral Footprint

AbstractEnergetic ions outflowing from Jupiter's atmosphere was observed during Juno's 12th perijove crossing (PJ12) in the vicinity of Io's auroral footprint and reported by prior studies. It was hypothesized that Wave‐Particle Interactions (WPI) with ion cyclotron waves observed coincident with the ion outflow may be responsible for the heating and subsequent outflow. This study uses numerical simulation and data model comparison to test whether ion cyclotron resonant heating is indeed a plausible mechanism to explain the intense ion outflow observed. Our simulations assume that the wave heating is of limited duration due to Io's footprint motion. The simulations are moreover compared to the previously published Jupiter Energetic Particle Detector Instruments (JEDI) observations at high energies, and the lower energy Jovian Auroral Distributions Experiment (JADE) observations that were not previously reported. We find that the ion cyclotron resonant heating mechanism can indeed lead to ion conic formation and strong vertical transport under certain assumptions about the distribution of wave power with altitude. We also find that the ion outflow is energized quickly with very rapid formation of the ion conic distribution. The implications of the intense ion outflow are also examined and it is found that such strong wave heating can lead to a depletion of the topside ionosphere.

Neutronics analysis of the ion cyclotron resonance heating antenna of the China Fusion Engineering Test Reactor

Ion cyclotron resonance heating (ICRH) is an important auxiliary heating method applied to the China Fusion Engineering Test Reactor, which can effectively heat the ions and electrons in plasma. Owing to the harsh nuclear environment, neutronic analyses are required to verify tritium self-sufficiency and neutron-shielding requirements. In this study, a neutronics analysis of the ICRH antenna was conducted using the COre and System integrated engine for Reactor Monte Carlo (cosRMC) code to estimate the neutron flux, radiation damage, nuclear heating, gas generation rate of key components, and tritium breeding ratio (TBR), providing data support for the subsequent optimization of the shielding design. In addition, the neutron flux of the coils around the antenna was calculated to prevent the entry of neutrons that damage the magnetic field coils through the gaps between the port plugs and antenna, and the shielding effects of the port-plug antenna on the surrounding components were analyzed. Finally, the results obtained using the cosRMC and MCNP codes were compared, which and presented good agreement, thus verifying the reliability of the neutronic analysis using the cosRMC code.

Numerical study of minority ion heating scenarios in a spherical tokamak plasma

In this study, D(H) minority ion cyclotron resonance heating (ICRH) scenarios in Nan Chang spherical tokamak (NCST) were simulated using the full-wave code TORIC. NCST is a low-aspect-ratio (R/a = 1.67) spherical tokamak, with its core plasma parameters characterized by a magnetic field intensity of 0.36 T and a density of 1018 m−3. Our simulation results demonstrate that the ion cyclotron wave can penetrate the core plasma of the NCST more effectively with a lower toroidal mode number, indicating that resonant ions can absorb the wave energy efficiently. Furthermore, it is found that as the minority ion H concentration is increased, a noticeable decline in the left-handed electric field adjacent to the ion cyclotron resonance layer is observed. Optimal heating efficiency is attained when maintaining a minority ion H concentration within the range 5%–10%. The minority ion velocity distribution was simulated to estimate the tail temperature of minority-ICRH, which is expected to exceed 10 keV. The difference in the power efficiency with different plasma compositions [Ar(H) and D(H)] was also simulated. When the H-ion cyclotron resonance layer is located at the core plasma, the power-absorption fraction of H in Ar(H) plasma surpasses that of D and H combined in D(H) plasma under identical conditions. These simulations provide a crucial foundation and theoretical reference not only for NCST but also for other spherical tokamaks conducting ICRH experiments.

The role of RF-induced E×B flows in the mitigation of scrape-off-layer convective transport during ion cyclotron resonance heating

While multiple experiments have reported a decrease in intermittent fluctuations in the far Scrape-Off-Layer (SOL) during ion cyclotron resonance heating (Antar et al 2010 Phys. Rev. Lett. 105 165001, Li et al 2022 Nucl. Eng. Technol. 54 207–19, Antar et al 2012 Nucl. Fusion 52 103005), the physical mechanism behind this observation has not been fully established yet. In this work, we demonstrate, for the first time, a direct correlation between the amplitude of RF-induced E×B flows and turbulence suppression in the far SOL. Using the Gas Puff Imaging (GPI) diagnostic on Alcator C-Mod, we show again that Ion Cyclotron Range of Frequencies can significantly alter the flow in the SOL and introduce a shear layer in regions magnetically connected close to the antenna (Cziegler et al 2012 Plasma Phys. Control. Fusion 54 105019). With the 4-strap field-aligned antenna operated in dipole phasing, the ratio of the power coupled by the central two straps to the power coupled by the outer two straps was varied. The resulting RF-induced radial electric field magnitude thus varied, and we show that the impact on the far SOL turbulence correlates with the modified E×B velocity. We then apply a newly-developed blob tracking algorithm (Han et al 2022 Sci. Rep. 12 18142) to higher-resolution GPI videos in order to directly observe the process of blob shearing by RF-induced E×B flows. We show that the radially sheared poloidal flows act as a transport barrier by stretching, stopping, and destroying filaments, which is consistent with the observed difference in turbulence statistics.

Development of a real-time impedance matching system for ion cyclotron resonance heating in experimental advanced superconducting tokamak

To achieve stable operation of an ion cyclotron resonance heating (ICRH) system in the Experimental Advanced Superconducting Tokamak (EAST), a real-time impedance matching system needs to be established to respond to antenna load variation during long pulse discharges. A new impedance matching method based on capacitors was proposed in this study. By considering the reflected voltage of the transmission line as the feedback parameter, the real-time impedance-matching system can quickly control the motors based on a programmable logic controller to determine the minimum reflection voltage. A real-time impedance matching system was successfully used on the test platform in the laboratory and on the ICRH system in EAST. A significant result is that we can match the variable impedance within 1 s by suitably adjusting the motor controller to ensure high-power and long-pulse operation of the ICRH system to satisfy the requirements of the EAST experiment.

Commissioning of the imaging neutral particle analyser for the ASDEX Upgrade tokamak

An imaging neutral particle analyser (INPA) diagnostic has been installed and commissioned at the ASDEX Upgrade (AUG) tokamak. The AUG INPA diagnostic provides energy and radially resolved measurements of the fast-ion (FI) distribution, complementing the existing set of diagnostic which measure the confined FI population. To this end, it analyses charge exchange (CX) neutrals produced in reactions between FI and neutrals injected by a neutral beam injector. These CX neutrals are ionised by a 20 nm carbon foil and deflected towards a scintillator by the machine magnetic field. The use of a scintillator as active component allows us to cover the whole plasma radial range with an energy resolution of 9 keV and a spatial of 3 cm for 93 keV deuterons. First measurements demonstrate the high sensitivity of the INPA diagnostic to different AUG fast-ion distribution functions, from NBI and ion-cyclotron resonance heating origin, and show good agreement with the synthetic diagnostic.

An alternative method to mimic mode conversion for ion cyclotron resonance heating

Ion cyclotron range of frequency waves in hot plasmas exhibit spatial dispersion effects and the wave equation takes the integro-differential form. Under the local plasma model assumption, the wave equation can be simplified to the differential form and adapts to the numerical scheme of the finite element method (FEM). Even though direct absorption of fast waves by ions and electrons can be described well by the local plasma model, linear mode conversion associated with non-local effects is absent. To deal with this issue, an alternative method is put forward in this paper where quasi-electrostatic fluid waves based on the multi-fluid warm plasma model are employed to take the place of ion Bernstein waves in mode conversion. On this basis, an interative fluid-kinetics (INTFLUK) code based on the FEM is developed for full-wave simulation in hot plasmas. Derivation of the wave equations as well as benchmarking of the INTFLUK code against other wave simulation codes are carried out. In both one- and two-dimensional cases, the validity of the INTFLUK code was verified by comparison of the wave field distributions and power deposition. As a useful illustration of the INTFLUK code including the scrape-off layer and a realistic antenna, the influence of the poloidal antenna phasing difference on ion cyclotron resonance heating is analyzed. Finally, it should be noted that the method in this paper has the potential to be extended to the three-dimensional case, which will be considered in the near future.

Impact of interaction between RF waves and fast NBI ions on the fusion performance in JET DTE2 campaign

This work presents a study of the interaction between radio frequency (RF) waves used for ion cyclotron resonance heating and the fast deuterium (D) and tritium (T) neutral Beam injected (NBI) ions in DT plasma. The focus is on the effects of this interaction, also referred to as synergistic effects, on the fusion performance in the recent JET DTE2 campaign. Experimental data from dedicated pulses at 3.43 T/2.3 MA heated at (i) 51.4 MHz, giving the central minority H and n = 2 D, and at (ii) 32.2 MHz for the central minority 3He and n = 2 T. Resonances are analysed and conclusions are drawn and supported by modelling of the synergistic effects. Modelling with transport code TRANSP runs with and without the RF kick operator predict a moderate increase, of about 10%, in DT rates for the case of the RF wave—fast D NBI ion interactions at the n = 2 harmonic of ion cyclotron resonance, and a negligible impact due to synergistic interaction between fast T NBI ions and RF waves. JETTO modelling gives a 29% enhancement in fusion rates due to the interction between RF waves and fast D NBI ions, and an 18% enhancement in fast T NBI ions. Analysis of experimental neutron rates compared to TRANSP predictions without synergistic effects and magnetic proton recoil neutron spectrometer indicate an enhancement of approximately 25%–28% in fusion rates due to RF interaction with fast D ions, and an enhancement of approximately 5%–8% when RF waves and fast T NBI ions are interacting. The contributions of various heating and fast ion sources are assessed and discussed.

Tungsten accumulation during ion cyclotron resonance heating operation on WEST

The observation of radiative collapses during ion cyclotron resonance heating (ICRH) operation on the full tungsten WEST tokamak constitutes a unique opportunity to get a quantitative balance of the sources and sinks in the core region of the plasma. Experimental analysis and numerical modelling evidence a significant reduction of the effective electron heat source delivered by ICRH compared with expectations on the one hand, and a complex interplay of mechanisms acting on the collisional peaking of tungsten on the other hand. Besides providing an explanation for the observed radiative collapses, this work outlines the variety of phenomenon determining the tungsten profile in ICRH operation.

Multipactor predictions for ion cyclotron resonance heating antennas of the tokamak WEST *

During the plasma experimental campaigns performed on the tokamak WEST, a performance-limiting observation has been made on the Ion Cyclotron Resonance Heating (ICRH) system composed of three identical antennas. When only one antenna is powered while the remaining two are off, an increase in the internal pressure is measured within the non-powered antennas. The internal pressure of the non-powered antennas exceeds a safety pressure interlock whose threshold is Pa, and consequently, the application of the RF power is prohibited to avoid plasma creation within these antennas. In this paper, the multipactor phenomenon caused by the inter-antennas’ coupling is shown to be responsible for the pressure increase observed in the non-powered antennas. Additionally, an analytic estimation of the pressure rise caused by the multipactor is compared to that observed experimentally.