Simulations of the microtearing instability developing in plasma of the Globus-M spherical tokamak were performed using the GENE gyrokinetic code in the flux-tube linear approximation mode. Under the ...effect of the instability, the magnetic islands form on the scale of the ion Larmor radius, and the magnetic field fluctuations occur that generate electron heat fluxes. The ion heat fluxes as well as the fluxes associated with the electrostatic fluctuations are negligible. The maximum growth rate of the microtearing instability is reached at a collision frequency within the experimental range of the collision frequency variation, within which the BT × τE ∝ ν*−0.4±0.1 scaling calculations were performed 1. In similar calculations performed at the MAST tokamak, the growth rate decreases with decreasing collisionality in the entire range of the collision frequency variation, within which the BT × τE ∝ ν*−0.82 scaling calculations were performed 2. This can explain why the dependences of energy confinement time on the collision frequency obtained for the MAST&NSTX and the Globus-M tokamaks are different.
The Globus-M2 spherical tokamak is the considerably upgraded Globus-M facility. Its technical parameters were increased as much as possible to achieve the promising range of physical parameters ...(sub-fusion temperatures and collisionality of much less than unity). These parameters will be achieved in a compact magnetic configuration similar to that of the Globus-M tokamak, the plasma current and toroidal magnetic field amounting to 0.5 MA and 1 T, respectively. The demand to increase the magnetic field and plasma current in the Globus-M2 resulted in the need for a complete redesign of the electromagnetic system because the plasma equilibrium requirements have changed and the mechanical and thermal loads have considerably increased as compared to the Globus-M. The vacuum vessel and the in-vessel components of the new Globus-M2 tokamak remain the same. Power supplies were upgraded to provide the required currents in the toroidal field coil and the central solenoid. The Globus-M2 tokamak was build up and preliminary tests were carried out. New auxiliary heating systems and diagnostics were developed and installed to be used in future experiments. Fist plasma was achieved at the Globus-M2 in April 2018.
The conventional method for determining the effective ion charge Zeff is based on measurements of the bremsstrahlung intensity in the spectral regions free from line radiation. This paper describes ...the design of the Zeff diagnostics at the Globus-M tokamak as well as the results of the first measurements. With allowance for the emission intensity estimates, the geometry of the experiment was chosen; the filter monochromators for recording bremsstrahlung were designed and manufactured. Using the Thomson scattering data on Te (R) and ne (R) profiles, time dependences Zeff (t) were obtained in several shots of the Globus-M tokamak. The results of simulations Zeff performed using the ASTRA transport code are consistent with these measurements.
Results of experimental studies of toroidal Alfvén eigenmodes (TAEs) in the Globus-M spherical tokamak (
R
= 36 cm,
a
= 24 cm) are reported. The experiments were carried out in a wide range of plasma ...parameters at a magnetic field of up to 0.5 T and plasma current of up to 250 kA. Auxiliary plasma heating was performed by tangential injection of a deuterium beam with a power of
P
b
= 0.75 MW and particle energy of
E
b
= 28 keV into deuterium plasma. The experiments have shown that the TAE-induced loss of fast particles decreases with increasing plasma current and magnetic field. Using multifrequency Doppler backscattering diagnostics, it is established that the TAEs are localized at the plasma periphery. Results of simulations of the Alfvén continuum and TAE structure by means of the modified KINX and CAXE codes agree satisfactory with the experimental data on the TAE frequencies and localization.
The results from calculations of the anisotropic fast particle distribution function in the Globus-M/M2 spherical tokamaks are presented. The calculations were performed using the NUEBAM code, the ...reasons for the anisotropy occurrence are discussed (injection geometry, low toroidal magnetic field and plasma current, presence of neutral particles). It is shown that the anisotropy decreases with increasing toroidal magnetic field and plasma current: the density of the slowed down fast ions with energies of E < 4 keV almost doubles and the averaged perpendicular velocity of fast ions increases.
Analysis of stability of the peeling-ballooning modes in the edge plasma of the Globus-M tokamak is presented. Studies were performed using the ideal 3D MHD code written in the BOUT++ framework. The ...edge localized modes which are frequently observed in the Globus-M plasma could be described using MHD theory. It was found that the parameters of the Globus-M edge plasma are in the range of stability for the peeling-ballooning modes. The instability modes with a toroidal number of n = 12 and typical distances between filaments of approximately ∼12 cm were found to be the most unstable. This statement agrees with the Doppler backscattering measurements. It was also considered whether the plasma in the Globus-M2 tokamak will be stable against the PB instability.
•ITER Divertor Thomson scattering system collecting mirrors are heated up to 95 °C.•Mirror surface deformation and rotation values were obtained.•Optical system should be explored under seismic and ...electromagnetic loads as well.
ITER is a nuclear fusion research and engineering project. It is supposed to be the first fusion device designed for testing the integrated technologies, materials, and physical aspects necessary for development of the commercially available fusion-power plant. One of the important components of the project is optical diagnostic systems with collecting mirrors. These mirrors have to provide stability of optical systems under severe loads of different types that could possibly arise in the tokamak. The collecting mirrors of several ITER diagnostics have a large scale and should be installed into diagnostic ports. Thermal stress analysis of the mirror updated design is aimed to obtain deformation and rotation values of the mirrors’ reflecting surfaces in order to conduct ray tracing analysis and to edit mirrors alignment to provide correct functioning of the optical systems. The maximum temperature values of the Divertor Thomson Scattering collecting mirrors were estimated for the normal operation mode. The FE model of the second mirror takes into account all the force boundary conditions, basic kinematic boundary conditions and constraints. Boundary conditions taken for the simulation were applied on surfaces contacting with the diagnostic rack. Thermally stressed state was calculated and corresponding displacement and rotation distributions were obtained.
The latest results are presented from NBCD experiments at the Globus-M spherical tokamak. The Globus-M2 NBI upgrade program is discussed, in particular, the analysis of the injection geometry and ...choice of the optimal experiment layout. The results from numerical simulations of plasma heating and current drive by two neutral beams in the Globus-M2 shots are also analysed.
Divertor Thomson Scattering on Globus-M2 Ermakov, N. V.; Zhiltsov, N. S.; Kurskiev, G. S. ...
Plasma physics reports,
12/2023, Volume:
49, Issue:
12
Journal Article
Peer reviewed
We present the first Thomson scattering (TS) measurements of electron temperature in the lower divertor of the Globus-M2 tokamak. The divertor TS diagnostics is designed for local measurements of the
...T
e
(
z
,
t
) in the range of 1–100 eV and
n
e
(
z
,
t
) in the range of
m
–3
. Parameters of the probing Nd:YAG laser are as follows 1064 nm/2 J/100 Hz/3 ns. The probing chord is launched vertically at
R
= 24 cm and covers areas of the inner leg, vicinity of separatrix and private flux region. Along probing chord of 110 mm, 9 spatial points were realized. Advanced filter polychromators were used to analyze Thomson scattering spectra.
Among the peripheral instabilities observed at the Globus-M2 tokamak, two types of edge localized modes (ELMs) are brought into focus: ELMs synchronized and desynchronized with the sawtooth ...oscillations. The desynchronized ELMs appear in regimes that are characterized by high values of pressure in the pedestal,
p
ped
≥ 3 kPa, and they are observed in discharges with the toroidal magnetic field
B
T
> 0.6 T and plasma current
I
P
> 0.3 MA. The desynchronized ELMs belong to the type-III/V with the dominating effect of the peeling mode. The synchronized ELMs were observed in a wider range of discharge parameters, including at
B
T
< 0.6 T and
I
P
< 0.3 MA. Calculations of the stability of the peeling-ballooning (PB) mode showed that at pedestal width ψ
norm
= 0.09 and
p
ped
> 3.5 kPa, destabilization of PB modes is possible without additional influence. Experimental data shows that the microtearing mode plays a dominant role in the pedestal. The microtearing mode does not allow the pedestal at Globus-M2 tokamak to reach the state of the unstable kinetic ballooning mode (KBM), which explains the low predictive power of the EPED model at this tokamak.
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