Ion Cyclotron Range Of Frequencies Research Articles

Evolution of hydrogen isotopes retention behavior of in-situ boronization films in EAST

Effective management of hydrogen isotopes retention in plasma-facing materials (PFMs) is crucial, particularly when utilizing tritium (T) as fuel, for the success of burning plasma operations. Boronization, a widely employed technique for controlling fuel recycling and mitigating impurity influx from plasma-surface interactions into the core of burning plasma, significantly influences hydrogen isotopes retention in PFMs. In this study, boronization films were generated by ion cyclotron range of frequency (ICRF) discharge assisted boronization with C2B10H12 as boron source on tungsten substrates at Experimental Advanced Superconducting Tokamak (EAST) which employing ITER-like water-cooled W monoblock PFMs and components (PFCs), followed by in-situ glow discharge (GD) cleaning for 2 h and 20 shots (180 s) edge-plasma exposure. Employing the Material and Plasma Evaluation System (MAPES), representative samples were analyzed after each process. The resultant carbon–boron films, dense and continuous, exhibited thickness up to 120 nm and were identified as amorphous in structure. It was observed that the D2-GD cleaning resulted in a significant isotopic exchange effect, effectively reducing the hydrogen (H) retention in the carbon–boron films. This hydrogen isotope replacement efficiency was found to be influenced by the thickness of the films. Notably, after boundary plasma exposure, samples with thicker films demonstrated an enhanced capacity to capture deuterium (D), adsorbing 10 times more D than bare tungsten (W). Our findings offer transformative insights for T recycling analysis and the plasma operation of devices like International Thermonuclear Experimental Reactor (ITER), highlighting the impact of boronization and subsequent treatments on hydrogen isotope retention behavior in PFMs.

Detection of ion cyclotron emission by using an ion cyclotron range of frequency antennas-based diagnostic system in experimental advanced superconducting tokamak

In the experimental advanced superconducting tokamak (EAST), a novel ion cyclotron range of frequency (ICRF) antenna-based diagnostic system is designed to measure ion cyclotron emission (ICE) driven by high-energy ions. The diagnostic system includes ICRF antenna straps, a three-tune impedance matching system, a coaxial switching system, a direct current block, and a data acquisition and storage system. Using the coaxial switching system, the ICRF antenna can be switched from the heating mode to the coupling mode between two discharges. In the 2023 EAST experiment campaign, core ICE was observed using the ICRF antenna-based diagnostic system during neutron beam injection heating, and the obtained results agreed well with the signal detected by the previous high-frequency B-dot probe-based diagnostic system.

Iterative addition of parallel non-local effects to full wave ICRF finite element models in axisymmetric tokamak plasmas

The current response of a hot magnetized plasma to a radio-frequency wave is non-local, turning the electromagnetic wave equation into an integro-differential equation. Non-local physics gives rise to wave physics and absorption processes not observed in local media. Furthermore, non-local physics alters wave propagation and absorption properties of the plasma. In this work, an iterative method that accounts for parallel non-local effects in 2D axisymmetric tokamak plasmas is developed, implemented, and verified. The iterative method is based on the finite element method and Fourier decomposition, with the advantage that this numerical scheme can describe non-local effects while using a high-fidelity antenna and wall representation, as well as limiting memory usage. The proposed method is implemented in the existing full wave solver FEMIC and applied to a minority heating scenario in ITER to quantify how parallel non-local physics affect wave propagation and dissipation in the ion cyclotron range of frequencies (ICRF). The effects are then compared to a reduced local plane wave model, both verifying the physics implemented in the model, as well as estimating how well a local plane wave approximation performs in scenarios with high single pass damping. Finally, the new version of FEMIC is benchmarked against the ICRF code TORIC.

Characterization of SOL profiles and turbulence in ICRF-heated plasmas in EAST

Scrape-off layer (SOL) profiles and turbulence in ion cyclotron range of frequency (ICRF)-heated plasmas are investigated by the reciprocating probe diagnostic system (FRPs) and gas puff imaging (GPI) diagnostic in EAST. A radio-frequency (RF) sheath potential reaching up to 100 V is identified proximate to the ICRF antennas. Notably, the amplitude of this RF sheath potential escalates in response to rising ICRF power and inversely with plasma density. When a RF sheath is present in the far SOL, a pronounced density ‘shoulder’ forms in front of the ICRF antennas, while the ‘shoulder’ fade away as the antenna and associated RF sheath shift outwards. A strong E r shear is revealed by measurements from both FRPs and GPI. Analysis of the poloidal wave number-frequency spectrum reveals suppression of high-frequency turbulence in the far SOL due to the RF sheath. This effect is manifested in the reduced autocorrelation time τ c and reduced average blob size δ blob of the SOL plasma. Intriguingly, the poloidal propagation direction of the low-frequency turbulence reverses from the electron to the ion diamagnetic drift direction at the RF sheath location. A surge of tungsten impurity is potentially attributed to the heightened interaction between the SOL plasmas and the wall material. Shifting the ICRF antennas outward, to alleviate heat spots, results in the relocation of the RF sheath to the shaded region of the main limiter. This shift amplifies the radial velocity of blobs in the far SOL and concurrently diminishes the SOL density when compared to conditions without ICRF injection. The properties of ion saturation current fluctuations are consistent with the stochastic model predictions.

Simulation of ion cyclotron wave heating in the EXL-50U spherical tokamak based on dispersion relations

This study investigates the single-pass absorption (SPA) of ion cyclotron range of frequency (ICRF) heating in hydrogen plasma of the EXL-50U spherical tokamak, which is an upgraded EXL-50 device with a central solenoid and a stronger magnetic field. The reliability of the kinetic dispersion equation is confirmed by the one-dimensional full-wave code, and the applicability of Porkolab's simplified theoretical SPA model is discussed based on the kinetic dispersion equation. Simulations are conducted to investigate the heating effects of the fundamental and second harmonic frequencies. The results indicate that with the design parameters of the EXL-50U device, the SPA for second harmonic heating is 63%, while the SPA for fundamental heating is 13%. Additionally, the optimal injection frequencies are 23 MHz at 0.9 T and 31 MHz at 1.2 T. The wave vector of the antenna parallel to the magnetic field, with a value of , falls within the optimal heating region. Simulations reveal that the ICRF heating system can play an important role in the ion heating of the EXL-50U.

Fast-ion orbit origin of neutron emission spectroscopy measurements in the JET DT campaign

In the JET DTE2 deuterium-tritium campaign, neutron diagnostics were employed to measure 14 MeV neutrons originating from D(T,n)4He reactions. In discharge 99965, a diamond matrix detector (KM14) and a magnetic proton recoil (MPRu) detector with a vertical and an oblique line-of-sight were used, respectively. At the timepoints of interest, a significant decrease in the expected diagnostic signals can be observed as electromagnetic wave heating in the ion cyclotron range of frequencies (ICRF) is switched off. Utilizing only TRANSP simulation data, the fast-ion distribution is found to have been likely composed mostly of trapped orbits. In contrast, analysis performed using orbit weight functions revealed that the majority of neutrons in the KM14 Ed=9.3 MeV and MPRu Xcm=33 cm measurement bins are to have originated from fast deuterium ions on co-passing orbits. This work explains the perhaps surprising results and shows that the relative signal decrease as ICRF heating is switched off is largest for counter-passing orbits. Finally, for the magnetic equilibria of interest, it is shown how stagnation orbits, corresponding to ∼1 % of the fast-ion distribution, were completely unobservable by the KM14 diagnostic.

Design and analysis of radio frequency window for the China Fusion Engineering Test Reactor ion cyclotron range of frequency heating system.

The Ion Cyclotron Range of Frequency (ICRF) heating system of the China Fusion Engineering Test Reactor (CFETR) is intended to provide plasma heating with a minimum power output of 20MW, which demands the Radio Frequency (RF) window to possess a higher performance requirement. This paper presents the design of an RF window for the CFETR ICRF heating system and focuses primarily on the design and confirmation of its electromagnetic performance. The RF window can be effectively matched in the operating frequency range and has an S11 of under -59 dB. The geometry of the cone type ceramics was optimized to reduce the surface tangential electric field distribution. An analysis of the electric field distribution of the RF window at 50kV indicates that the pressure side was below 2.3 kV/mm and the vacuum side was below 1.3 kV/mm. Furthermore, a transmission line test bench with an open-terminated setup was constructed to conduct withstand voltage tests on the mockup, and the results showed that the mockup could withstand 62kV for 2s and 47kV for 120s.

Studies of the material erosion and deposition during the wall conditioning processes using quartz crystal microbalance in EAST

To study material erosion and deposition during different wall conditioning processes in the Experimental Advanced Superconducting Tokamak (EAST), two newly developed quartz crystal microbalances (QMBs) at the mid-plane of port C (C-QMB) and port J (J-QMB) with the same radial radius were used for in-situ and real-time measurements during the 2021 autumn experimental campaign. It was found that the material deposition was mainly influenced by the location of the antenna and the power of the ion cyclotron range of frequency (ICRF), rather than the location of the gas inlet, during the wall cleaning with helium plasma and siliconization assisted with ICRF plasma. The higher energy and density of plasma could result in higher deposition rates near the antenna. While, during lithium (Li) coating, the material deposition was greatly influenced by the location of the Li oven due to the deposition of unionized Li atoms. The ICRF power influenced the material deposition behavior far away from the Li ovens. Besides, a stronger effect on impurity suppression was observed with a more uniform deposition trend of Li coating. This necessitates further study on the influence of factors such as the location of the Li oven and ICRF antenna, the temperature of ovens, and ICRF power on the homogeneity of wall conditioning.

JET D-T scenario with optimized non-thermal fusion

In JET deuterium-tritium (D-T) plasmas, the fusion power is produced through thermonuclear reactions and reactions between thermal ions and fast particles generated by neutral beam injection (NBI) heating or accelerated by electromagnetic wave heating in the ion cyclotron range of frequencies (ICRFs). To complement the experiments with 50/50 D/T mixtures maximizing thermonuclear reactivity, a scenario with dominant non-thermal reactivity has been developed and successfully demonstrated during the second JET deuterium-tritium campaign DTE2, as it was predicted to generate the highest fusion power in JET with a Be/W wall. It was performed in a 15/85 D/T mixture with pure D-NBI heating combined with ICRF heating at the fundamental deuterium resonance. In steady plasma conditions, a record 59 MJ of fusion energy has been achieved in a single pulse, of which 50.5 MJ were produced in a 5 s time window (P fus = 10.1 MW) with average Q = 0.33, confirming predictive modelling in preparation of the experiment. The highest fusion power in these experiments, P fus = 12.5 MW with average Q = 0.38, was achieved over a shorter 2 s time window, with the period of sustainment limited by high-Z impurity accumulation. This scenario provides unique data for the validation of physics-based models used to predict D-T fusion power.

Design of power and phase feedback control system for ion cyclotron resonance heating in the Experimental Advanced Superconducting Tokamak

Ion cyclotron range of frequency (ICRF) heating system is an important auxiliary heating method in the experimental Advanced Superconducting Tokamak (EAST). In EAST, several megawatts of power are transmitted with coaxial transmission lines and coupled to the plasma. For the long pulse and high power operation of the ICRF waves heating system, it is very important to effectively control the power and initial phase of the ICRF signals. In this paper, a power and phase feedback control system is described based on field programmable gate array (FPGA) devices, which can realize complicated algorithms with the advantages of fast running and high reliability. The transmitted power and antenna phase are measured by a power and phase detector and digitized. The power and phase feedback control algorithms is designed to achieve the target power and antenna phase. The power feedback control system was tested on a dummy load and during plasma experiments. Test results confirm that the feedback control system can precisely control ICRF power and antenna phase and is robust during plasma variations.

Identification of core ion cyclotron instabilities on HL-2A tokamak

Instabilities in multiplies of ion cyclotron frequency range are identified and termed as core ion cyclotron emission (ICE) in recent HL-2A neutral beam injection heated experiments. Characteristics of the core ICE are presented, including frequency dependence and harmonics features. The detected frequencies are found to agree well with the multiplies of the deuterium cyclotron frequency around the magnetic axis. Additionally, the core ICE exhibits a predominantly compressional property. Observations of distinct spectrum features and individual excitation of each harmonic have demonstrated that the core ICE harmonics are independent multiple modes. Notably, the variation of plasma current is a necessary condition for exciting the 4th harmonic ICE individually. The results suggest that the drive mechanism of core ICE varies between the different frequency ranges.

ICRF plasma production at hydrogen minority regime in LHD

Abstract This study aim is to develop further an ion cyclotron range of frequencies (ICRF) method of plasma production in stellarators based on the minority heating. The previous studies demonstrate production of low density plasma (9.5 × 1017m−3) at low power of up to 0.2 MW. The higher ICRF heating power experiments become possible after introducing a programmable ICRF power ramp up at the front of the ICRF pulse. With this trick, all the shots went with the antenna voltage within the safe range. Increase of the ICRF power predictably results in increase of the density of produced plasma. Without pre-ionization the plasma density achieved was 6 × 1018 m−3 which is 6 times higher than in previous experiments. However, the electron temperature was not high, the light impurities were hot fully stripped, and there were no recombination peaks after termination of the ICRF pulse. Plasma density is too low to provide good conditions for efficient plasma heating. For the reference, the ICRF heating of high density cold plasma prepared by electron cyclotron resonance heating is performed. Both electrons and ions were heated to high temperatures, and this plasma state is sustained. The antenna–plasma coupling was much better which result in larger heating power with the lower antenna voltage.

On equations for ion cyclotron modes in ‘warm’ bounded plasmas

An equation describing eigenmodes in the ion cyclotron frequency range in ‘warm’ bounded plasmas, i.e. eigenmodes which are absent in the two-fluid model but exist in kinetic theory due to finite Larmor radius of the ions, is derived for the first time. It is valid for electrostatic modes but the developed approach is generic. Calculations are carried out for two cases: first, for a homogeneous magnetic field; second, taking into account the effects of toroidicity in tokamaks. It is found that, in general, equations for eigenmodes in warm plasmas do not reduce to second-order differential equations (in contrast to those which are usually used to describe the radial structure of eigenmodes in fusion devices). The study of modes in warm plasmas is of interest, in particular, in connection with the recent observations of superthermal ion cyclotron emission in the NSTX-U spherical torus and DIII-D tokamak, which can be hardly explained by conventional theories employing fast magnetoacoustic modes.

Comparison of core Ar17+ and Mo32+ toroidal rotation in C-Mod plasmas

Core (r/a 0.5) toroidal rotation from argon (Ar17+, 40 AMU) and molybdenum (Mo32+, 96 AMU) ions has been compared in C-Mod tokamak plasmas over a wide range of operating conditions and confinement schemes, including Ohmic L-mode in the linear and saturated regimes, ion cyclotron range of frequencies heated I-mode and H-mode, as well as in discharges with induced locked modes and with external current and rotation drive. In all cases the velocities of the two impurities are identical within about 5%, for a range between −60 and +80 km s−1. This is in general agreement with the predictions of neo-classical theory.

Observation of ion-cyclotron-range-of-frequency wave emission in electron-cyclotron-resonance-heated tokamak plasma

Emissions of ion-cyclotron-range-of-frequency (ICRF) waves have been observed in a solely electron-cyclotron-resonance-heated plasma, namely no fast-ion plasma, on the JT-60U tokamak for the first time. The mode frequencies are around the ion cyclotron frequency at the low-field-side plasma edge. The waves are considered to be electromagnetic and standing waves from poloidal and toroidal phase differences measured with ICRF antennas. Wave characteristics of the ICRF emissions such as frequency, polarization and propagation are similar to those of edge-ion cyclotron emissions (ICEs) driven by neutral-beam-injected fast ions although driving sources are completely different. From analysis of the resonance conditions, this ICRF wave emission is considered to be driven by the electron-cyclotron-resonance-heated fast electrons via the Cherenkov resonance condition. When ICE is used for fast ion diagnostics, such fast-electron-driven ICRF wave emission may complicate its interpretation during electron cyclotron resonance heating.

Operational requirements of the ion cyclotron wall conditioning in DTT

The Divertor Tokamak Test facility (DTT), a new superconducting tokamak (B0=6T, Ip=5.5MA, R0=2.19 m, a = 0.7 m, pulse length=100 s) (Ambrosino et al., 2021) under realization at the ENEA Frascati Research centre, needs an efficient first wall conditioning technique suitable for the use in the presence of a permanent magnetic field. The Ion Cyclotron Wall Conditioning (ICWC), based on Radio-Frequency (RF) discharges (Lyssoivan et al., 2012), with waves in the ion cyclotron range of frequencies, is one of the most efficient technique available (between discharges) for routine inter–pulse and overnight conditioning. ICWC will be performed using the first Ion Cyclotron Resonance Heating (ICRH) RF module foreseen during the first phase of DTT and constituted by two Antennas, four or two External Matching Units (EMUs) and four RF solid-state transmitters, operating in the frequency range (60–90) MHz. In the paper by means of the HFSS and CST codes, an eigenvalue analysis of the electromagnetic waves (E/H modes) excited inside the vacuum DTT volume has been carried out. Then full-wave simulations have been run for the entire DTT torus injecting a RF signal with a single and a pair of three–strap antennas, currently in the design phase for DTT, evaluating the S-parameters and the parallel electric field (E//) aligned to the toroidal magnetic field, responsible of the initial gas breakdown. On this basis the most appropriate choice for the RF feeding, in monopole phasing, as well as for the frequency of ICWC discharges in order to maximize E// has been identified and presented in the paper, demonstrating for the first time the usefulness of using an H mode at the frequency of 62.5 MHz instead of the lower frequency of 60 MHz minimizing the RF power required to activate the ionization process. Finally operational parameters for DTT, extrapolated from the analysis of ICWC experiments documented in literature, will be presented.

ICRF heating schemes for the HL-2M tokamak

The HL-2M tokamak is a new medium-sized tokamak at SouthWestern Institute of Physics. Two of its key missions are to achieve 10 keV ion temperature and investigate the behavior of energetic particles relevant to burning plasmas. A 6 MW ion cyclotron range of frequencies (ICRF) heating power is embedded in the next upgrade program of HL-2M. In order to facilitate the engineering design of the ICRF system, this paper analyses the main ICRF heating schemes for HL-2M, in terms of ion heating and energetic ion generation in particular. D(H) minority heating and the 2nd harmonic D will act as the main ion heating schemes, for which the optimal RF frequency range 27–33 MHz, antenna parallel wavenumber k // ∼ 8 m−1 are proposed and strong single pass absorption is expected under typical HL-2M plasma parameters. Full wave simulations carried out via TORIC/steady-state Fokker–Planck quasilinear solver and TRANSP codes suggest that by adopting three ion scheme or synergetic heating on neutral beam injection D ions by the 2nd harmonic D, energetic ions with energy at MeV level can be produced. This study shows that ICRF heating could play significant roles in ion heating, energetic ion generation in HL-2M.

Influence of ICRF-NBI synergy on fast ion distribution and plasma performance in second harmonic heating experiments with deuterium NBI at EAST

Ion Cyclotron Range of Frequencies (ICRF) heating and Neutral Beam Injection (NBI) can have synergy due to the acceleration of NBI beam ions by ICRF wave fields at their harmonics. To understand the influence of ICRF-NBI synergy on fast ion distribution and plasma performance, dedicated experiments and TRANSP simulations have been carried out on EAST. The simulation results are consistent with the experimental results. They show that the ICRF-NBI synergy not only accelerates the NBI beam ions with energy lower than 80 keV to energy larger than 300 keV, but also generates fusion neutrons with energy larger than 3 MeV. Moreover, ICRF-NBI synergy improves the plasma performance by increasing the poloidal beta, plasma stored energy, core ion temperature, total neutron yield and kinetic pressure. In a typical H-mode plasma with 1.0 MW NBI and 1.5 MW ICRF power, it was observed that ICRF-NBI synergy increases the poloidal beta, plasma stored energy, core ion temperature and neutron yield by ∼35%, 33%, 22% and 80%, respectively. Various parameter scans show that the ICRF-NBI synergetic effects can be enhanced by decreasing the minority ion concentration or the distance between the harmonic resonance and magnetic axis, or by increasing the ICRF heating power or NBI beam energy. Consequently, this leads to a generation of fast ions with higher energy. For instance, the maximum energy of the fast ion tail increases from 300 to 600 keV as n(H) decreases from 5% to 0.1%.

SITAR: A Code for ICRH Antenna–Plasma Coupling

We have developed an ICRF (ion cyclotron range of frequency) heating antenna code, SITAR (Simulation of ICRH anTennA Resistance), for stripline antenna to find out its impedance in the presence of plasma. The antenna is of finite poloidal and toroidal dimensions and screened from the plasma by the Faraday shield that shorts out the toroidal components of the radio frequency field. Antenna lead current as well as toroidal and poloidal current of antenna have been taken into account. A slab geometry model for coupling of antenna with tokamak plasma and a linear model of the perpendicular refractive index for the propagation of ICRF wave in the evanescent region have been considered. The plasma in the coupling region is described by a cold plasma dielectric tensor with nonuniform density and toroidal magnetic field along the radial direction.

3D simulation of orbit loss and heat load on limiters of ICRF-NBI synergy induced fast ions on EAST

Fast ions synergy induced by ion-cyclotron range of frequency (ICRF) and neutral beam injection (NBI) are of interest not only because of their advantage of heating the plasma and drive currents, but also because of their disadvantage of damaging plasma surface components and driving MHD instabilities. In this paper, we calculate the fast ion loss and the deposition distribution of the lost particles on the limiters in EAST under the synergistic effect of the ripple field and collisions with the full-orbit-following simulation program ISSDE for the first time. The previous models to study the NBI fast ion loss by the action of ICRF are relatively simple and consider fewer influencing factors. Most studies on fast ion loss have used toroidal uniform boundaries. In this work, we consider the distribution of ICRF-NBI synergy induced fast ions with different minority H concentrations. After setting the limiter boundary, we consider the prompt fast ion loss caused by the equilibrium field and the fast ion loss caused by the ripple field and collision. Under the action of minority-ion ion-cyclotron resonant heating, the NBI fast ion distribution function has spread in the high-energy part, especially for the minority H concentration of 1%, and the fast ions show each anisotropic distribution near the resonance band on the poloidal dimension. The synergistic loss caused by the ripple field and collision will first be greater than the loss caused by either factor, and then reach a final loss fraction of 3.8%. The heat load power density of the lost fast ions on different limiters is not uniform, as well as on each limiter, which is related to the distance from the limiter to the plasma, the relative position between the limiters and the parallel direction of most fast ions. Once the study of ICRF-NBI synergy induced fast ion loss caused by the action of ripple and collision has been done, we can do optimization in a targeted manner. Such as adding ferromagnetic inserts to reduce the ripple loss and optimizing the limiters’ position to reduce or control the generation of impurities.