Ion Temperature Profiles Research Articles

Extensions to the charge exchange recombination spectroscopy diagnostic suite at ASDEX Upgrade.

A new core charge exchange recombination spectroscopy diagnostic has been installed in the ASDEX Upgrade tokamak that is capable of measuring the impurity ion temperature, toroidal rotation, and density on both the low field side (LFS) and high field side (HFS) of the plasma. The new system features 48 lines-of-sight (LOS) with a radial resolution that varies from ±2 cm on the LFS down to ±0.75 cm on the HFS and has sufficient signal to run routinely at 10 ms and for special circumstances down to 2.5 ms integration time. The LFS-HFS ion temperature profiles provide an additional constraint on the magnetic equilibrium reconstruction, and the toroidal rotation frequency profiles are of sufficiently high quality that information on the poloidal velocity can be extracted from the LFS-HFS asymmetry. The diagnostic LOS are coupled to two flexible-wavelength spectrometers such that complete LFS-HFS profiles from two separate impurities can be imaged simultaneously, albeit with reduced radial coverage. More frequently, the systems measure the same impurity providing very detailed information on the chosen species. Care has been taken to calibrate the systems as accurately as possible and to include in the data analysis any effects that could lead to spurious temperatures or rotations.

Argon impurity transport studies at Wendelstein 7-X using x-ray imaging spectrometer measurements

In the first operational phase of the stellarator Wendelstein 7-X (W7-X), the x-ray imaging crystal spectrometer (XICS) system has been commissioned for measuring radial profiles of ion and electron temperature, T i and T e, plasma rotation velocities, v P, and selected impurity densities, n Z . This paper shows the first measurements of the spectrometer and gives an initial calculation of impurity transport parameters derived from an Ar impurity transport study. Using Bayesian analysis, the temporal evolution of Ar impurity density profiles after an Ar gas puff could be observed with a time resolution of up to 5 ms, yielding a maximum value for the diffusion coefficient of D = 1.5 m2 s−1 at ρ ~ 0.5 and small pinch velocities in the inner plasma region.

Observation of internal transport barrier in ELMy H-mode plasmas on the EAST tokamak

The internal transport barrier (ITB) has been obtained in ELMy H-mode plasmas by neutron beam injection and lower hybrid wave heating on the Experimental Advanced Superconducting Tokamak (EAST). The ITB structure has been observed in profiles of ion temperature, electron temperature, and electron density within ρ < 0.5. It was also observed that the ITB formation is stepwise. Due to the ITB formation, the confinement quality H98y2 increases from 1 to 1.1 and the normalized beta, βN, increases from 1.5 to near 2. The fishbone activity observed during the ITB phase suggests the central safety factor q(0) ∼ 1. Transport coefficients are calculated by particle balance and power balance analysis, showing an obvious reduction after the ITB formation.

Recent progress of magnetic reconnection research in the MAST spherical tokamak

In the last three years, magnetic reconnection research in the MAST spherical tokamak achieved major progress by the use of new 32 chord ion Doppler tomography and 130 channel YAG and 300 channel Ruby Thomson scattering diagnostics. In addition to the previously achieved high power plasma heating during merging, detailed full temperature profile measurements including the diffusion region have been achieved for the first time. 2D imaging measurements of ion and electron temperature profiles have revealed that magnetic reconnection mostly heats ions globally in the downstream region of outflow jet and electrons locally around the X-point. The toroidal field in MAST “over 0.3T” strongly inhibits cross-field thermal transport, and the characteristic peaked electron temperature profile around the X-point is sustained on a millisecond time scale. In contrast, ions are mostly heated in the downstream region of outflow acceleration and around the stagnation point formed by reconnected flux mostly by viscosity dissipation and shock-like compressional damping of the outflow jet. Toroidal confinement also contributes to the characteristic ion temperature profile, forming a ring structure aligned with the closed flux surface. There is an effective confinement of the downstream thermal energy due to a thick layer of reconnected flux. The characteristic structure is sustained for longer than an ion-electron energy relaxation time (∼4 ms), and the energy exchange between ions and electrons contributes to the bulk electron heating in the downstream region. The toroidal guide field mostly contributes to the formation of a localized electron heating structure around the X-point but not to bulk ion heating downstream.

On the bootstrap current in the TJ-II stellarator

ABSTRACTBootstrap current in stellarators is usually very small since they operate solely with the magnetic confinement provided by the external currents. Since plasma pressure gradients are always present, the bootstrap current is always finite, but the magnetic design can be optimized to minimize it. In the heliac configuration, there is no optimization and therefore it is important to estimate the actual bootstrap current generated by given pressure profiles. Here, we use the configuration of the TJ-II heliac to calculate the bootstrap current for various density regimes using the kinetic code DKES. We compute the mono-energetic transport coefficients and to find first the thermal ambipolar diffusion coefficients and the corresponding radial electric field and then the respective bootstrap current. This is made taking experimental density and electron and ion temperature profiles. In spite of the convergence problems of DKES at low collisionality, we can obtain bootstrap current values with acceptable uncertainties, without using Monte Carlo methods. The resulting rotational transform is used to obtain the rational surfaces' location and predict the transport barriers observed in the experiments.

Ion density and temperature profiles along (XGSM) and across (ZGSM) the magnetotail as observed by THEMIS, Geotail, and ARTEMIS

AbstractCharacteristics of the two‐dimensional configuration of the magnetotail current sheet are important for modeling magnetotail motion/evolution and charged particle energization. Because of the magnetotail current sheet's dynamical nature, however, simultaneous plasma and magnetic field measurements at different radial distances are required to reveal this configuration. Simultaneous observations of the magnetotail current sheet from Time History of Events and Macroscale Interactions during Substorms (THEMIS) D (around 10RE downtail), Geotail (around 30RE downtail), and Acceleration, Reconnection, Turbulence and Electrodynamics of the Moons Interaction with the Sun (ARTEMIS) P1 (around 55RE downtail) are used to study distributions of plasma (ion) density and temperature along (Earth‐Sun direction) and across (north‐south direction) the magnetotail. Fourteen events (each including several current sheet crossings at different downtail distances) are studied. We demonstrate that the plasma temperature along and across the magnetotail varies more significantly than plasma density does. The temperature decrease from equatorial plane to current sheet boundaries is a major contributor to the cross‐tail pressure balance. The Alfven velocity VA,B calculated at the current sheet boundaries increases significantly toward the Earth from 700 km/s at lunar orbit ∼55RE to 2200 km/s around ∼10RE downtail. The corresponding energy (mp is the proton mass) is 4 times larger than the plasma temperature T0 in the magnetotail's equatorial plane, whereas the ratio EA/T0 is constant along the magnetotail. The plasma temperature T0 measured around lunar orbit in the magnetotail agrees well with the simultaneously measured energy of solar wind protons (VSW is the solar wind speed).

Investigation of energy transport in DIII-D High-βP EAST-demonstration discharges with the TGLF turbulent and NEO neoclassical transport models

Energy transport analyses of the DIII-D high- EAST-demonstration discharges have been performed using the TGYRO transport package with the TGLF turbulent and NEO neoclassical transport models under the OMFIT integrated modeling framework. Ion energy transport is shown to be dominated by neoclassical transport and ion temperature profiles predicted by TGYRO agree closely with the experimental measured profiles for these high- discharges. Ion energy transport is largely insensitive to reductions in the flow shear stabilization. The Shafranov shift is shown to play a role in the suppression of the ion turbulent energy transport below the neoclassical level. Electron turbulent energy transport is under-predicted by TGLF and a significant shortfall in the electron energy transport over the whole core plasma is found with TGLF predictions for these high- discharges. TGYRO can successfully predict the experimental ion and electron temperature profiles by artificially increasing the saturated turbulence level for ETG driven modes used in TGLF.

Development of Multichannel Ion Doppler Spectroscopic System by Using Fast Camera

SUMMARYThe multichannel ion Doppler spectroscopic (M‐IDS) system using a fast camera as detectors has been newly developed to measure the spatial profiles of impurity spectral line emissions from plasmas. The M‐IDS system developed with eight viewing chords is characterized by the simplest optical systems, a fast sampling frequency, high number of shooting, and a low crosstalk of 3.5% on each chord. In order to verify the usefulness and reliability of the M‐IDS system, we have applied it for the start‐up plasma produced in the helicity injected spherical torus device. Resultantly, we have successfully measured the radial profiles of Doppler ion temperature Ti.D and Doppler ion velocity vi.D of the plasma with a good Gaussian fitting. However, we have found that the sampling frequency is upper limited by 25 kHz because the signal detected with a faster frequency from the CIII impurity line emission is too weak to be analyzed, and thus the sensitivity of the total system needs to be improved.

Improved spatial calibration for the CXRS system on EAST.

A Charge eXchange Recombination Spectroscopy (CXRS) diagnostic system has been developed to measure profiles of ion temperature and rotation since 2014 on EAST. Several techniques have been developed to improve the spatial calibration of the CXRS diagnostic. The sightline location was obtained by measuring the coordinates of three points on each sightline using an articulated flexible coordinate measuring arm when the vessel was accessible. After vacuum pumping, the effect of pressure change in the vacuum vessel was evaluated by observing the movement of the light spot from back-illuminated sightlines on the first wall using the newly developed articulated inspection arm. In addition, the rotation of the periscope after vacuum pumping was derived by using the Doppler shift of neutral beam emission spectra without magnetic field. Combining these techniques, improved spatial calibration was implemented to provide a complete and accurate description of the EAST CXRS system. Due to the effects of the change of air pressure, a ∼0.4° periscope rotation, yielding a ∼20 mm movement of the major radius of observation positions to the lower field side, was derived. Results of Zeeman splitting of neutral beam emission spectra with magnetic field also showed good agreement with the calibration results.

Measurement of helium-like and hydrogen-like argon spectra using double-crystal X-ray spectrometers on EAST.

A two-crystal assembly was deployed on the tangential X-ray crystal spectrometer to measure both helium-like and hydrogen-like spectra on EAST. High-quality helium-like and hydrogen-like spectra were observed simultaneously for the first time on one detector for a wide range of plasma parameters. Profiles of line-integrated core ion temperatures inferred from two spectra were consistent. Since tungsten was adopted as the upper divertor material, one tungsten line (W XLIV at 4.017 Å) on the short-wavelength side of the Lyman-α line (Lα1) was identified for typical USN discharges, which was diffracted by a He-like crystal (2d = 4.913 Å). Another possible Fe XXV line (1.85 Å) was observed to be located on the long-wavelength side of resonance line (w), which was diffracted from a H-like crystal (2d = 4.5622 Å) on the second order. Be-like argon lines were also observable that fill the detector space between the He-like and H-like spectra.

Measurement of the electron and ion temperatures by the x-ray imaging crystal spectrometer on joint Texas experimental tokamak.

An x-ray imaging crystal spectrometer has been developed on joint Texas experimental tokamak for the measurement of electron and ion temperatures from the Kα spectra of helium-like argon and its satellite lines. A two-dimensional multi-wire proportional counter has been applied to detect the spectra. The electron and ion temperatures have been obtained from the Voigt fitting with the spectra of helium-like argon ions. The profiles of electron and ion temperatures show the dependence on electron density in ohmic plasmas.

Laser induced fluorescence measurements of axial velocity, velocity shear, and parallel ion temperature profiles during the route to plasma turbulence in a linear magnetized plasma device.

We report experimental measurements of the axial plasma flow and the parallel ion temperature in a magnetized linear plasma device. We used laser induced fluorescence to measure Doppler resolved ion velocity distribution functions in argon plasma to obtain spatially resolved axial velocities and parallel ion temperatures. We also show changes in the parallel velocity profiles during the transition from resistive drift wave dominated plasma to a state of weak turbulence driven by multiple plasma instabilities.

Development of core ion temperature gradients and edge sheared flows in a helicon plasma device investigated by laser induced fluorescence measurements

We report experimental observation of ion heating and subsequent development of a prominent ion temperature gradient in the core of a linear magnetized plasma device, and the controlled shear de-correlation experiment. Simultaneously, we also observe the development of strong sheared flows at the edge of the device. Both the ion temperature and the azimuthal velocity profiles are quite flat at low magnetic fields. As the magnetic field is increased, the core ion temperature increases, producing centrally peaked ion temperature profiles and therefore strong radial gradients in the ion temperature. Similarly, we observe the development of large azimuthal flows at the edge, with increasing magnetic field, leading to strong radially sheared plasma flows. The ion velocities and temperatures are derived from laser induced fluorescence measurements of Doppler resolved velocity distribution functions of argon ions. These features are consistent with the previous observations of simultaneously existing radially separated multiple plasma instabilities that exhibit complex plasma dynamics in a very simple plasma system. The ion temperature gradients in the core and the radially sheared azimuthal velocities at the edge point to mechanisms that can drive the multiple plasma instabilities, that were reported earlier.

Modeling of Heat Fluxes in Edge Plasma of Small Size Divertor Tokamak

The heat flows out from the tokamak core region are collected on the divertor plates and external wall. Control of heat flux exhaust in the SOL and divertor plates regions is one of the important issues in tokamak physics. There are important phenomena affecting heat flows were simulated. The simulation is based on the B2SOLPS5.0 2D multifluid code. It is demonstrated that, the following results: (1) The simulation shows that, the operation of small size divertor tokamak, the divertor plate with/without impurities influence on profiles of electron, ion temperatures, and heat loads significantly. (2) Under normal direction of parallel (toroidal) magnetic field and different values of edge plasma density, strong “SOL” heat flow exists directed towards the LFS (outer) plate. (3) The simulation results show that, the increasing of the plasma density strong influence on the ion and electron poloidal heat fluxes profile significantly. The ion and electron polodial heat flux increase by factor “~8” and “2.4” times. (4) The simulation results show that the in–out asymmetry of heat fluxes was reversed when switching on/off E × B drifts in the edge plasma of this tokamak. (5) The simulation results show correlation between the in–out asymmetry divertor heat fluxes and E × B drift velocity. (6) The observed heat loads asymmetry between HFS and LFS plates can be explained with the radial electric field in SOL. (7) Also the simulation results performed result in, the in–out asymmetry strong influence on the characteristic length of ion poloidal heat flux.

Ion temperature profiles in front of a negative planar electrode studied by a one-dimensional two-fluid model

Plasma-wall transition is studied by a one-dimensional steady state two-fluid model. Continuity and momentum exchange equations are used for the electrons, while the continuity, momentum exchange, and energy transport equation are used for the ions. Electrons are assumed to be isothermal. The closure of ion equations is made by the assumption that the heat flux is zero. The model equations are solved for potential, ion and electron density, and velocity and ion temperature as independent variables. The model includes coulomb collisions between ions and electrons and charge exchange collisions between ions and neutral atoms of the same species and same mass. The neutral atoms are assumed to be essentially at rest. The model is solved for finite ratio ε=λDL between the Debye length and λD and ionization length L in the pre-sheath and in the sheath at the same time. Charge exchange collisions heat the ions in the sheath and the pre-sheath. Even a small increase of the frequency of charge exchange collisions causes a substantial increase of ion temperature. Coulomb collisions have negligible effect on ion temperature in the pre-sheath, while in the sheath they cause a small cooling of ions. The increase of ε causes the increase of ion temperature. From the ion density and temperature profiles, the polytropic function κ is calculated according to its definition given by Kuhn et al. [Phys. Plasmas 13, 013503 (2006)]. The obtained profiles of κ indicate that the ion flow is isothermal only in a relatively narrow region in the pre-sheath, while close to the sheath edge and in the sheath it is closer to adiabatic. The ion sound velocity is space dependent and exhibits a maximum. This maximum indicates the location of the sheath edge only in the limit ε→0.

Characteristics of toroidal rotation and ion temperature pedestals between ELM bursts in KSTAR H-mode plasmas

Steep pedestal profiles of ion temperature (Ti) and toroidal rotation (Vϕ) are routinely observed in neutral beam injection (NBI)-heated KSTAR H-mode plasmas [W. H. Ko et al., Nucl. Fusion 55, 083013 (2015)]. In this work, we report a result of detailed analysis of pedestal characteristics. By analyzing a set of data with different experimental conditions, we show that Ti and Vϕ pedestals are coupled to each other and correlation between them becomes stronger when NBI-torque is lower. This suggests the existence of intrinsic toroidal torque in the pedestal. Based on a 1D transport analysis, we find that the prevalence of residual micro-turbulences is necessary to explain momentum transport in the pedestal. The estimated strength of intrinsic torque is shown to be comparable to that from a 2.7 MW NBI source. Finally, we show that non-diffusive momentum flux is indispensable to explain momentum transport in the pedestal, and a residual stress model fits the observed momentum flux reasonably.

Survey of Galileo plasma observations in Jupiter's plasma sheet

AbstractThe plasma science (PLS) instrument on the Galileo spacecraft (orbiting Jupiter from December 1995 to September 2003) measured properties of the ions that were trapped in the magnetic field. The PLS data provide a survey of the plasma properties between ~5 and 30 Jupiter radii (RJ) in the equatorial region. We present plasma properties derived via two analysis methods: numerical moments and forward modeling. We find that the density decreases with radial distance by nearly 5 orders of magnitude from ~2 to 3000 cm−3 at 6 RJ to ~0.05 cm−3 at 30 RJ. The density profile did not show major changes from orbit to orbit, suggesting that the plasma production and transport remained constant within about a factor of 2. The radial profile of ion temperature increased with distance which implied that contrary to the concept of adiabatic cooling on expansion, the plasma heats up as it expands out from Io's orbit (where Ti ~ 60–80 eV) at ~6 RJ to a few keV at 30 RJ. There does not seem to be a long‐term, systematic variation in ion temperature with either local time or longitude. This latter finding differs from earlier analysis of Galileo PLS data from a selection of orbits. Further examination of all data from all Galileo orbits suggests that System III variations are transitory on timescales of weeks, consistent with the modeling of Cassini Ultraviolet Imaging Spectrograph observations. The plasma flow is dominated by azimuthal flow that is between 80% and 100% of corotation out to 25 RJ.

DPLX: Experiment to Investigate Heating and Stability in Magnetized Rotating Dusty Plasmas

An experimental setup is under construction at the Dusty Plasma Laboratory of the University of Maryland, Baltimore County to study viscous heating and stability in magnetized rotating dusty plasmas. Azimuthal rotation will be imposed on dust, electrons, and ions by having an axial magnetic field $B$ in a vacuum chamber placed inside a 16-cm bore Bitter-type magnet, and a radial electric field $E$ centered at the chamber axis. The resulting $E \times B$ rotation is expected to have sheared rotation, which leads to viscous heating from the radial velocity profile. However, heating may also lead to interchange modes that destabilize the rotation. The planned experiments are motivated by the observations of parabolic ion and electron temperature profiles in hydrogen plasmas in a supersonic rotating magnetic mirror, where ohmic and viscous heating were the only mechanisms available for heating the plasma. The goal of the experimental setup is to magnetize and rotate dust with diameter $ \sim 1~\mu \text{m}$ that can be individually captured by particle velocimetry cameras and software. The Bitter-type magnet is planned for a steady field of 10 T with a minimum duration of 10 s per experiment.

Ion temperature measurements of L-mode filaments in MAST by retarding field energy analyser

Retarding field energy analysers (RFEAs) have been used to compare the ion temperature (Ti) of large plasma filaments with the background plasma (composed of small scale filaments) at the midplane and divertor target in L mode discharges in the Mega Amp spherical tokamak (MAST). At low densities, at the midplane and divertor, at distances from 2 to 4 cm from the separatrix the temperature of ions in large filaments was found to be 2 to 3 times larger than the background plasma. At the midplane, the electron temperature for both large filaments and background plasma was around 3 to 7 times smaller than the ion temperature and had a flat profile across the scrape off layer (SOL). At higher densities, at the midplane and divertor, both the filament and background ion temperatures were smaller than at low density. At the midplane, the filament and background ion and electron temperature profiles across the SOL were relatively flat and of comparable magnitude, ranging in temperature from 5 to 25 eV.

Vortex motion of dust particles due to non-conservative ion drag force in a plasma

Vortex motion of the dust in a dusty plasma is shown to result because non-parallelism of the ion density gradient and the gradient of the magnitude of the ion ambipolar velocity cause the ion drag force on dust grains to be non-conservative. Dust grain poloidal vortices consistent with the model predictions are experimentally observed, and the vortices change character with imposed changes in the ion temperature profile as predicted. For a certain ion temperature profile, two adjacent co-rotating poloidal vortices have a well-defined X-point analogous to the X-point in magnetic reconnection.