Ion Beam Probe Research Articles

Obtaining frequency-time diagram from perturbation signal-time diagram

Abstract In the field of nuclear fusion energy development, magnetic confinement tokamak reactors, which use strong magnetic fields to confine high-temperature plasmas, are crucial for sustainable and clean fusion energy. Disruption caused by plasma instability can terminate the fusion reaction and even cause irreparable damage to the equipment. Therefore, a thorough understanding of the underlying physical mechanisms is essential for predicting and preventing plasma disruption. The recently proposed analytical theory of plasma disruption may predict and prevent plasma disruption, but its validation requires the frequency-time signals. The Heavy Ion Beam Probe (HIBP) can provide such signals, however, because its scarcity in the world, particularly in China, it is necessary to develop more suitable methods. Here we show a new approach that employs Fast Fourier Transform (FFT) on magnetic perturbation signals to obtain frequency-time diagrams. We successfully applied this algorithm to acquire the frequency-time diagram of the J-TEXT-1054560 discharge. This new method offers an effective tool for validating the plasma disruption theory, overcoming the limitations of traditional techniques and providing a crucial methodological basis for understanding and predicting plasma disruption. This new analytical approach will accelerate the advancement of fusion technology.

Heavy ion beam probe for Wendelstein 7-X measurement capabilities as projected through its design.

A heavy ion beam probe (HIBP) diagnostic is being developed for studies of plasma equilibrium and turbulence in the optimized Wendelstein 7-X (W7-X) stellarator. Operation of W7-X has experimentally demonstrated that its optimized magnetic field results in improved neoclassical particle confinement and, as a result, turbulence is the predominant cause of energy transport. The HIBP will have the unique ability to provide experimental data needed to complement models of both neoclassical and turbulent transport. It will acquire direct measurements in the W7-X plasma interior of the electric potential (needed for understanding ambipolar particle flux) and fluctuations of electron density and potential (needed for understanding turbulence). The HIBP for W7-X will inject singly charged ion beams with energies of up to 2MeV and is designed to access the upper cross section of the W7-X plasma. We use trajectory simulations to illustrate the plasma coverage that the diagnostic can achieve in the reference magnetic configurations of W7-X. We calculate beam signal levels, discuss anticipated measurement sensitivity of broadband fluctuations of electron density and plasma potential, and show how they depend on plasma density. We also discuss the diagnostic sensitivity to equilibrium plasma potential.

Validation of the synthetic model for the imaging heavy ion beam probe at the ASDEX Upgrade tokamak (invited).

Recent experiments at the ASDEX Upgrade tokamak have provided the first ever measurements from the imaging heavy-ion beam probe. In this work, we show that the developed simulation framework can reproduce qualitatively the measurement's observed shape and position. Quantitatively, we demonstrate that the model reproduces, within the experimental uncertainties, the observed signal levels. A detailed explanation of the synthetic model is presented, along with the calibration of the optical setup that reproduces the measurements.

First measurements of an imaging heavy ion beam probe at the ASDEX Upgrade tokamak.

The imaging heavy ion beam probe (i-HIBP) diagnostic has been successfully commissioned at ASDEX Upgrade. The i-HIBP injects a primary neutral beam into the plasma, where it is ionized, leading to a fan of secondary (charged) beams. These are deflected by the magnetic field of the tokamak and collected by a scintillator detector, generating a strike-line light pattern that encodes information on the density, electrostatic potential, and magnetic field of the plasma edge. The first measurements have been made, demonstrating the proof-of-principle of this diagnostic technique. A primary beam of 85/87Rb has been used with energies ranging between 60 and 72keV and extracted currents up to 1.5 mA. The first signals have been obtained in experiments covering a wide range of parameter spaces, with plasma currents (Ip) between 0.2 and 0.8 MA and on-axis toroidal magnetic field (Bt) between 1.9 and 2.7T. Low densities appear to be critical for the performance of the diagnostic, as signals are typically observed only when the line integrated density is below 2.0-3.0 × 1019m-2 in the central interferometer chord, depending on the plasma shape. The strike line moves as expected when Ip is ramped, indicating that current measurements are possible. Additionally, clear dynamics in the intensity of the strike line are often observed, which might be linked to changes in the edge profile structure. However, the signal-to-background ratio of the signals is hampered by stray light, and the image guide degradation is due to neutron irradiation. Finally, simulations have been carried out to investigate the sensitivity of the expected signals to plasma density and temperature. The results are in qualitative agreement with the experimental observations, suggesting that the diagnostic is almost insensitive to fluctuations in the temperature profile, while the signal level is highly determined by the density profile due to the beam attenuation.

Feasibility study of a Heavy Ion Beam Probe for the Thailand Tokamak-1

A Heavy Ion Beam Probe (HIBP) diagnostic system can offer non-disturbing, local measurement of plasma electric potential and various plasma parameters. This paper presents results of a feasibility study for implementing a HIBP system on the Thailand Tokamak-1 (TT-1). With successful plasma discharges achieved in early 2023, TT-1, is planed for upgrades and expansion of diagnostic capabilities to conduct experiments in high confinement modes. Sector K is designated for the installation of the HIBP diagnostic system, where primary beam ions are injected through the top port and secondary beam ions emerge from the horizontal port. The HIBP system consists of two main components: (1) the primary beam injection, and (2) the detection of the secondary beam. In the injection system, the incident direction of the primary beam into the plasma is controlled by two pairs of electrostatic sweepers. For the detection of the secondary beam, the electric field produced by electrostatic sweepers, each with a length of 0.25 m and inclined at 30 degrees, ensures that the secondary beam ions enter the energy analyzer entrance at the center with normal angles. Candidate ions, such as Cs+, Rb+, and K+, with varying energies, are evaluated for their suitability based on beam attenuation and plasma density conditions. Cesium ions are suitable at lower densities (n̄e≤1×1019 m−3), while Rb+ and K+ are preferable at higher plasma densities (n̄e≥1×1019 m−3). The analysis indicates that the ratio of the attenuation current is approximately in the range of 10−3 to 10−2. This study provides valuable insights for the integration of the HIBP diagnostic system into TT-1, enabling investigations of H-mode plasma physics phenomena.

Two-Dimensional Distribution of Plasma Electric Potential in the T-10 Tokamak

Heavy ion beam probe (HIBP) is a unique plasma diagnostics that makes it possible to measure the electric potential φ of high-temperature plasma and its fluctuations y, as well as the density ne and poloidal magnetic field Bpol fluctuations. Position of the point of performing measurements in the plasma vertical cross-section depends on the beam energy and angle of its entrance into the plasma. The variation of these two parameters makes it possible to construct a two-dimensional (2D) detector grid, which covers the domain of possible measurements. The measurement results obtained in the detector grid points provide for constructing 2D distributions of plasma parameters. For the OH and ECRH stages of the T-10 tokamak shots, 2D distributions of the plasma electric potential are presented for the regime with the on-axis magnetic field of Bt = 2.2 T, plasma current of Ipl = 230 kA, line-average density of ne ≈ 1.1 × 1019 m–3 and off-axis ECRH power of PECRH = 1.7 MW.

The role of charge-exchange processes in probing hydrogen plasma with a heavy ion beam

Charge-changing processes of low-charged ions, used in hydrogen plasma probing by the heavy ion beam probe method, are considered. Along with the ionization of beam ions by plasma electrons and protons, the charge-exchange processes of ions on H atoms and protons are also studied. It is shown that charge exchange of beam ions on plasma protons and H atoms, which is rarely taken into account, plays an important role in beam–plasma interaction. New data on the cross sections and rates of ionization and charge-exchange processes are presented for Tl+ and Tl2+ ions, which are frequently used for plasma diagnostics. Calculations are performed for hydrogen plasma temperatures Te = 1 eV–10 keV and densities Ne = 1012–1014 cm−3 at relatively low and high ion-beam velocities vb = 0.2 and 1.0 a.u., respectively. Special attention is paid to the determination of the electron temperatures at which the charge-exchange processes on H atoms and protons are important. Multiple ionization of beam ions by plasma electrons and protons is briefly discussed.

PLASMA PROFILES, SELF-ORGANIZATION AND ALFVEN EIGENMODES STUDIES USING THE HIBP DIAGNOSTIC IN THE TJ-II STELLARATOR

This paper reports recent experiments in the TJ-II stellarator using a dual Heavy Ion Beam probe diagnostic. The studies were focused on characterizing plasma potential profiles, investigating self-organization mechanisms and Alfven Eigenmodes (AEs). Results showed plasma equipotential measurements consistent with vacuum magnetic surfaces and the presence of zonal flows in the plasma core region. The investigation of Alfven Eigen modes showed their radial localization and poloidal asymmetries in potential and density fluctuations driven by AEs.

Impact of β n and spectrum of n = 1 applied fields on fast ion losses in DIII-D

The effect of n = 1 magnetic perturbations (MPs) on prompt fast ion losses in DIII-D has been investigated using the light ion beam probe technique. The effect of normalized beta, β n , and the plasma response to the MPs is studied for several MP spectra. Magnetics data show a strong dependence of plasma response to β n that depends on the phase difference in perturbation coils, . For most phases, the response increases with β n , however, the response is suppressed for phases between 180∘ and 240∘. Experimental data from scintillator based fast ion loss detectors shows that relative fluctuation of lost ions (20%–30% of the steady signal) does not diminish across the L- to H-mode transition for , despite the 34% decrease in radial response field and 50% decrease in poloidal response field. Simulations of the DIII-D discharges using M3D-C1 and ASCOT5 find that prompt losses from neutral beam injection in each investigated case hit the first wall at several concentrated locations: the vessel floor, midplane diagnostic ports, vessel ceiling, and inner wall. Simulated losses from co-injection neutral beams are born outside the last closed flux surface, corresponding to radial orbit displacements of 3–6 cm due to the MPs.

Development of a heavy ion beam probe diagnostic for HL-2A tokamak

A heavy ion beam probe (HIBP) is being developed and tested on the HL-2A tokamak. To focus on the turbulence measurement in high beta scenarios with the toroidal magnetic field of 1.35 T, a 500 kV thallium beam is chosen and optimized. The locations of the injection and detection system are determined based on the probing beam trajectory calculations. The status of the accelerator, sweep system, analyzer, and control system is described. Four pairs of sweep plates are positioned in both primary and secondary beamlines to actively control the beam trajectory, where thepoloidal sweepers require a maximum of 15 kV voltages to be applied. A parallel-plate energy analyzer with multi-slits is supplied by 100 kV high voltage for the electric potential measurement.The signal intensity is also evaluated to be hundreds of nA levels, 5 × 107 V/A amplifiers are therefore designed. Software is also developed to include the data acquisition as well as the control and monitoring of HIBP subsystems.

Применение просвечивающей электронной микроскопии для исследования функционального наноэлемента

Using the focused ion beam probe method, cross-section sample of a single functional device of micron dimensions were cut out for STEM and TEM studies. The use of analytical methods of transmission electron microscopy made it possible to obtain accurate data on the geometric parameters of nanoscale functional devices, the phase and elemental composition of functional element material, as well as on the concentration of free electrons at the Fermi level in the nanoelement material.

Measurements of the Radial Distributions of the Geodesic Acoustic Mode and Quasi-Coherent Mode Using a Heavy Ion Beam Probe in the T-10 Tokamak Ohmic Plasma

Measurements of the Radial Distributions of the Geodesic Acoustic Mode and Quasi-Coherent Mode Using a Heavy Ion Beam Probe in the T-10 Tokamak Ohmic Plasma

Conceptual design of a heavy ion beam probe diagnostic for the Wendelstein 7-X Stellarator.

This article describes the current state of the design of the heavy ion beam probe (HIBP) for Wendelstein 7-X (W7-X). It will be the first HIBP diagnostic on an optimized stellarator and is designed to study electric fields and ion scale turbulence in all W7-X reference magnetic configurations. The use of an existing 2 MV accelerator, located outside of the torus hall, results in the need for a circuitous primary beamline. This increases the complexity of the ion optics design to deliver a focused beam to the plasma. To access most of the magnetic configuration space of W7-X, the secondary beamline and an energy analyzer are designed to pivot, thereby redirecting a wider range of secondary beam trajectories. Signal level estimates indicate that the equilibrium potential can be measured at all radii and that the radial coverage for potential and density fluctuations measurements depends on the plasma density.

Conceptual design of a heavy ion beam probe for the QUEST spherical tokamak.

A heavy ion beam probe (HIBP) has been designed for the QUEST spherical tokamak to measure plasma turbulence and the profiles of electric potential profiles. Using a cesium ion beam with an energy of several 10keV, the observable region covers most of the upper half of the plasma. Although the probe beam is deflected by the poloidal magnetic field produced by plasma current and poloidal coil currents, it can be detected under plasma current up to 150kA by modifying the trajectories with two electrostatic sweepers. According to the numerical estimation of the intensity of the detected beam, sufficient signal intensity for measuring plasma turbulence can be obtained over almost the measurable area when the electron density is up to 1 × 1019 m-3, which is larger than the cut-off density of electron cyclotron heating in QUEST. The performance of the designed HIBP is sufficient to explore the mechanisms of heat and particle transport in magnetically confined plasmas, including the influence of plasma wall interactions, which is a goal of the QUEST project.

Multiple particle identification by sequential frequency-shift measurement of a micro-plate

• A resonant cantilevered micro-plate is proved to be a promising candidate that can sequentially detect multiple particles. • The identification of multiple particles is regarded as an optimization problem via genetic algorithm to replace the widely-used least squares method. • Better identification accuracy is illustrated by exquisitely updating the modal shape changes of a micro-plate after each particle adsorption. • An experimental strategy based on focused ion beam and scanning probe microscopy verifies the applicability of the theoretic framework in designing and evaluating micro/nano sensors. The detection of multiple particles has been mainly studied by examining the flexural vibration properties of a one-dimensional Euler-Bernoulli beam under the assumption that the vibration mode shapes are unchanged. In fact, with the torsional vibration of the detector, valuable pieces of information can be derived, while the detection process is facilitated. Besides, the mode shapes of the detector can be easily changed by measuring multiple adsorbates or heavy analytes, which can fundamentally affect the detecting accuracy. To the best of our knowledge, these two issues have not yet been systematically considered in the literature. Along these lines, in this work, a theoretical framework is introduced to detect both the masses and positions of multiple particles absorbed on a two-dimensional micro-plate, where the history of the mass deposition events is sequentially measured from the recorded frequency shifts. The detection of multiple particles was realized by using an optimization process via the genetic algorithm, which circumvents the initial value and the local optimum problems that the widely-used least-squares method could be confronted with. In addition, an improved detection accuracy was ensured by exquisitely updating the modal shape changes of a micro-plate after the adsorption of each particle. To validate the proposed method, the frequency shifts were obtained by running modal analysis, where 20 μ concentrated masses were added sequentially on the top surface of the micro-plate modelling. As was expected, all particles could be effectively identified with enhanced accuracy. Furthermore, experimental validation was performed on Si-based micro-plates cantilevered, which were fabricated by focused ion beam milling and sequentially loaded by carrying out Pt depositions from the measured frequency shifts of the micro-plate structure before and after each sequential Pt deposition, the loaded masses and their positions in both the length and width directions were extracted. The results obtained from the model are in good agreement with the estimation based on scanning electron microscopy. The proposed method is anticipated to be further applied to multiple particle detection applications in many fields including biology, medicine and chemistry.

Improving corrosion resistance of Zn–5Al (wt%) alloy by microalloying with samarium

The role of the rare earth element Sm in as-cast Zn–5Al alloy was studied in this work. A three times higher improvement than the control group on corrosion resistance was found with rare earth Sm adding (0.15 wt%). By using an electron prove micro analyzer (EPMA), focused ion beam (FIB) and scanning Kelvin probe force microscopy (SKPFM) techniques, two main mechanisms of the premium performance of the Sm adding were revealed. One was that the non-uniform nucleation and component undercooling induced by Sm adding, reduced the α-Al layer spacing thus improved the covering efficiency of the Al2O3 film. The other was that the dissolved Sm in the Zn/Al eutectic structure modulated the electron work function thus induced the attenuation of Volta potential discrepancy. The experimental results show that when the addition of Sm is 0.15 wt%, the minimum Volta potential difference between α-Al and η-Zn phases is achieved, and excessive or deficient Sm addition will increase the Volta potential difference.

Experimental investigation of beam-ion losses induced by magnetic perturbations using the light ion beam probe technique in the ASDEX Upgrade tokamak

The impact of externally applied magnetic perturbations (MPs) on fast-ion losses has been investigated by means of the light ion beam probe (LIBP) technique in the ASDEX Upgrade tokamak. The LIBP technique allows to experimentally infer the fast-ion orbit displacement induced by MPs via first-orbit losses using scintillator based fast-ion loss detector (FILD) measurements. The fast-ion orbit displacement against different applied MP spectra has been studied. These shots were conducted in ELM mitigated H-mode plasmas. A rigid rotation of the MP coils was applied with a frequency of 1 Hz, with an n = 2 configuration and changing the differential phase between the upper and lower set of coils (ΔΦul) on a shot-to-shot basis. Beam sources Q7 (tangential) and Q8 (radial) were used to probe different fast-ion orbits with FILD1. The measured fast-ion orbit displacement ranges from 3 to 20 mm approximately, and no qualitative difference is observed between ions from beam sources Q7 and Q8. The minimum is found for a ΔΦul ∼ 50°, which is shifted with respect to the minimum of the plasma boundary displacement, found at ΔΦul ∼ 0°. A first attempt to validate the orbit following code ASCOT—including the plasma response calculated with the MARS-F code—against these experimental measurements is performed. While the dependence of the first-orbit fast-ion displacement with ΔΦul does not match the experimental measurements, these simulations do capture other features such as the order of magnitude of the orbit displacement and the importance of the toroidal spectrum of the applied perturbation.

Feasibility study of heavy ion beam probe in CFQS quasi-axisymmetric stellarator

The world’s first quasi-axisymmetric stellarator, CFQS, is now under construction. The CFQS will be dedicated to studies on the interaction between flow and turbulence, and confinement improvement by suppression of turbulence in connection with proof-of-principle experiment of quasi-axisymmetry. In order to conduct this experimental research, a heavy ion beam probe (HIBP) system is planned to be installed and utilized to measure the radial electric field and its fluctuation in a CFQS plasma. In this paper, an orbit calculation for a probe beam is performed to verify feasibility of the HIBP in the CFQS. The required beam energy, possible ion species, and the observable region in a CFQS plasma are investigated. The beam attenuation by a CFQS plasma is also estimated for different beam ion species. If we use 133Cs+ as a primary probe beam, the required beam energy is expected to be 30∼50 keV, which is relatively easy to handle. In this case the beam attenuation, evaluated by the ratio between the injected and detected beam currents, is 10−3∼10−2 in a CFQS plasma with a line-averaged electron density of <1.0 × 1019 m−3. For a higher density plasma, usage of 85Rb+ is better in terms of low-beam-attenuation, and a high signal-to-noise ratio. The HIBP in the CFQS will provide a great opportunity to study physics experimentally, related to the radial electric field, poloidal flow, and turbulence suppression.

2D distributions of potential and density mean-values and oscillations in the ECRH and NBI plasmas at the TJ-II stellarator

2D plasma potential ϕ distribution was measured in the electron cyclotron resonance heating (ECRH) and neutral beam injection (NBI) plasmas of the TJ-II stellarator with the heavy ion beam probe for the whole radial range and wide area of the poloidal angle, and supported by Langmuir probe data at the edge. The whole operation domain for the on-axis ECRH was explored ( = 0.45–0.8 ×1019 m−3, P EC = 220–470 kW), in addition, NBI plasmas with = 0.9–1.3 × 1019 m−3 and P NBI = 510 kW were studied. In ECRH plasmas the density ramp-up is accompanied by the evolution of the potential from the bell-like to the Mexican hat profile, while the density profiles were flat or slightly hollow. The potential has the positive peak at the centre, and LFS-HFS (low field—high field sides) and up-down symmetry. Equipotential lines are consistent with vacuum magnetic flux surfaces. In the high-density NBI scenario, the ϕ profile was fully negative with a minimum up to −300 V at the centre, while at low-density ECRH plasma, ϕ has a maximum up to +0.9 kV at the centre. Fluctuations of potential and density are stronger in low-density scenarios and not poloidally symmetric. At the mid-radius (area of the maximum density), root mean square (RMS) of fluctuations were up to ϕ ∼ 15 V at LFS vs ∼20 V at HFS; RMS n e ∼ 2% at LFS vs ∼3% at HFS. In the NBI plasmas with the density rise, the asymmetry decreases and finally vanishing at = 1.2 × 1019 m−3. 2D distribution of the NBI-induced Alfvén eigenmodes (AEs) shows asymmetric ballooning structure: contrary to broadband turbulence, AE-associated potential perturbation dominates in the LFS with a factor up to 1.7 respect to the HFS. The electrostatic mode, excited in ECRH plasmas by suprathermal electrons also shows asymmetric structures: density perturbation dominates in the top-bottom direction compared to LFS-HFS direction.

Hydrogen isotope effect on self-organized electron internal transport barrier criticality and role of radial electric field in toroidal plasmas

Self-organized structure formation in magnetically confined plasmas is one of the most attractive subjects in modern experimental physics. Nonequilibrium media are known to often exhibit phenomena that cannot be predicted by superposition of linear theories. One representative example of such phenomena is the hydrogen isotope effect in fusion plasmas, where the larger the mass of the hydrogen isotope fuel is the better the plasma confinement becomes, contrary to what simple scaling models anticipate. In this article, threshold condition of a plasma structure formation is shown to have a strong hydrogen isotope effect. To investigate the underlying mechanism of this isotope effect, the electrostatic potential is directly measured by a heavy ion beam probe. It is elucidated that the core electrostatic potential transition occurs with less input power normalized by plasma density in plasmas with larger isotope mass across the structure formation. This observation is suggestive of the isotope effect in the radial electric field structure formation.