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The method for measuring a material eroded from surfaces of inner elements subjected to strong plasma impact in a fusion reactor and falling down to the bottom of a vacuum chamber in the form of microparticles was suggested and approved. An open ultra high frequency (UHF) resonator fabricated of two spherical mirrors was used as a measuring tool. The working frequency of 37 GHz was sweeped linearly in the frequency range of 60 MHz. Single particles of a substance (teflon, paraffin, graphite) or fine-dispersed graphite dust falling free down through the central part of the resonator caused a decrease of the resonance amplitude and shift of its eigenfrequency. Experiments with controlled properties (specific density, size, and permittivity) of substances, such as teflon or paraffin, showed that using such a resonator these characteristics can be measured with a reasonable accuracy. The effect of external magnetic field and background plasma can be taken into account.

The results of local measurements of RF discharge plasma parameters in the process of internal transport barriers (ITB) formation in the vicinity of rational magnetic surfaces in the Uragan-3M torsatron are presented. The following phenomena were observed in the process of ITB formation: widening of the radial density distribution, formation of plateaus on radial density and electron temperature distributions, formation of regions with high shear of poloidal plasma rotation velocity and radial electric field in the vicinity of stochastic layers of magnetic field lines, decrease of density fluctuations and their radial correlation length, decorrelation of density fluctuations, and increase of the bootstrap current. After the ITB formation, the transition to the improved plasma confinement regime takes place. The transition moves to the beginning of the discharge with the increase of heating power. The possible mechanism of ITB formation near rational surfaces is discussed.

As an alternative to metal-made inner elements of MM and subMM diagnostics (antennae, reflectors, waveguides) we propose the elements fabricated of carbon–graphite materials (CGM). A comparative study of antennae and reflectors made of CGM and metal for 30–150 GHz in MM and for subMM ranges was carried out under the influence of pulsed plasma streams and heating up to 1000 °C. The effect of neutron irradiation on reflectivity at 337 μm was studied as well. The obtained data demonstrated that CGM can be used as material for fabricating the above mentioned inner diagnostic components in those large-scale fusion devices where similar materials are in use for the first wall protection. The Fabry–Perot type resonator with spherical CGM-made mirrors showed rather good characteristics, and can be used for measuring plasma properties in a divertor flow.

Carbon-graphite materials are proposed for manufacturing inner elements of mm and submm diagnostics in a fusion reactor (i.e., reflectors and antennae of different kinds). The investigations of influence of pulsed power plasma streams with a power density ⩾ 1 kJ/cm2 on radiotechnical characteristics of these elements at frequencies 37.5, 75, 105, 694, 890 and 2520 GHz and neutron irradiation with a fluence ∼ 1022 n/cm2 on plane reflectors at a frequency 890 GHz were carried out. Results of our tests point out the prospect to use these materials for making the mentioned elements, especially in the case if similar materials will be used as the first wall protection.

The comparative study of morfology change of different kinds of beryllium after being subjected to the periphery plasma (nc ≤ 1013 cm−3, Te. ≃ 15 eV) of a pulse reflex discharge is carried out. It was shown that the probability of arcing is much lower for samples made of ingot as compared to samples made of the hot pressed beryllium. The latter samples differ also by high number of blisters that can be divided in two groups: every large blister with a doubled boundary (the mean diameter size is D = 0.8 μm) has a pore, and small blisters (D -0.3 μm) have no pores at all.

URAGAN-3M (U-3M) is an l=3, m=9 torsatron with R0=1 m, ā ≈ 12 cm and (ā) ≈ 0.4. The entire magnetic system is enclosed in a large vacuum chamber and there is no material limiter, so that an open helical divertor is realized in this device. A plasma is RF produced in 100% hydrogen gas and heated in the multimode Alfven resonance regime (ω ωci) at a continuous working gas leak-in. With an RF power of ~200 kW at B = 0.45 T, a quasi-steady (up to 50 ms) state of the plasma parameters sets in with e 2 × 1018 m-3, Ti(0) 130 eV and Te(0) equivalent to 300 eV. By using microwaves and Langmuir probes, the time and space behaviours of the electron density/ion saturation current are studied in the confinement volume, near the boundary of the confinement region, and in the divertor flux region. On the basis of ion saturation current profile measurements near the boundary of the confinement region the values of local particle flux density across the boundary are estimated: Γ⊥ ≈ 7 × 1020 m-2.s-1 far from the antenna and Γ⊥ approximately=1021 m-2.s-1, Γ⊥ ≈ 2 × 1021 m-2.s-1 near the antenna. Such flux densities and the corresponding diffusion coefficients are anomalously high, exceeding the neoclassical values by 2 to 3 orders of magnitude. On the other hand, these values are comparable with the flux densities and diffusivities obtained in edge plasma with similar parameters on other stellarators under NBI and ECR heating conditions. Therefore, it is claimed that the method of plasma heating that has been chosen in U-3M does not result in any substantial deterioration of particle confinement (with the possible exception of the region close to the antenna) as against other methods. Presumably, the anomalous particle transport across the boundary in U-3M is caused by destruction of magnetic surfaces and/or electrostatic drift wave turbulence. It is found that increasing the RF power results in an increase of the diverted plasma flow and of the hydrogen consumption necessary to maintain the average plasma density at a given level. This is considered as a manifestation of a common regularity, according to which particle losses grow with heating power, this effect having been observed recently on a stellarator type device under NBI and ECR heating conditions. An effect specific to U-3M, the increase of the average electron density, being observed within 1 to 2 ms after RF pulse termination, is attributed mainly to particle transport reduction due to plasma cooling, while the intensity of neutral particle ionization still remains sufficiently high in the confinement volume at the initial phase of cooling under continuous hydrogen leak-in conditions.

In the l=3, m=9 URAGAN-3M torsatron an open helical divertor is realized. Plasmas are RF produced and heated. The time and space characteristics of the plasma in the space between two coils of the helical winding and on the outward side of the helical winding are studied by microwave and probe techniques. The experimental measurements are preceded by numerical divertor field line tracing. As a result of the calculations and measurements, it is shown that the diverted plasma is formed due to (i) plasma transportation from the confinement volume; and (ii) neutral gas ionization by the near-antenna field. The flow of diverted plasma transported from the confinement volume increases with RF power. This is considered as direct evidence of an increase in particle loss with an increase in heating power, the effect having been deduced recently for a stellarator-type device under NBI and ECR heating conditions. An intense RF discharge along open field lines crossing the operating antenna results in a greatly increased diverted plasma density, in the appearance of a static positive plasma potential up to 150 V near the antenna, and possibly in significant additional RF power loss outside the confinement region.

Numerical and experimental results of Alfven wave heating of plasmas in the frequency range below the ion cyclotron frequency ( ω ω ci ) are presented. Two different types of antenna were used for plasma production and heating: a frame type antenna (FTA) conventionally used in the URAGAN-3M device and a three-half-turn antenna (THTA) proposed recently to avoid the deleterious effects of conversion of fast wave to slow wave in the plasma periphery and to perform plasma core heating more effectively. Numerical modeling of electromagnetic field excitation in the URAGAN-3M plasma by the FTA and THTA was performed using a one-dimensional code. The results of calculations showed better performance of the compact THTA compared with the FTA for the case of a high density plasma (approximately 10 13 cm −3 ). When using the THTA, the experiments performed showed the possibility of dense plasma production (more than 2 × 10 13 cm −3 ) and heating, which had not been obtained earlier in the URAGAN-3M. Shifting the power deposition profile deeper inside the plasma body with the THTA resulted in modification of the plasma density profile and an improvement in plasma confinement.

The comparative study of working characteristics of some graphite and metallic components of SHF diagnostics, such as several kinds of antennae, plane reflectors and cylindrical waveguides are presented. To simulate the consequence of a plasma disruption in large tokamaks on graphite-made antenna, we tested two antennae (MPG and ARV kinds of graphite) on the influence of power plasma flow: W ≥ 1.10 MJ/m2 with the time duration Δt ≈ 0.1 ms. All results show that the prospects to use graphite elements in a reactor-scale fusion device are rather promising.

A new approach to plasma rotation observation is microwave reflectometry. Poloidal correlation reflectometry uses cross-correlation analysis of microwaves reflected by 2 poloidally shifted parts of surface of toroidal fluctuating plasma. The reflected microwave signal is being modulated on amplitude and phase; this modulation contains information about time/space properties of perturbed reflecting surface. These perturbations are the result of plasma density perturbations in unstable plasmas. Poloidal plasma rotation will change temporal behavior of reflected signals. This change will be reflected in change of cross-correlation function of microwave detector signals. Doppler microwave reflectometry is another method of poloidal rotation velocity measurement. In this method the Doppler shift of microwaves reflected by fluctuating plasma is measured if probing antenna is tilted to the reflecting surface normal. This work is devoted to comparison of data coming from poloidal correlation and Doppler reflectometry for rotating plasma.

Plasma density fluctuations, n/spl tilde//sub e/, play an important role in the energy balance, particle and heat transport, and, in the long run, in the confinement of a thermonuclear plasma. In this paper we present the experimental results on study of the spatial structure of n/spl tilde//sub e/, in the plasma confinement region of the l=3 torsatron Uragan-3M. These data were obtained by means of a multi-channel UHF reflectometry with the homodyne detection.

In the correlation reflectometry method, two microwave signals (usually of the same polarization) are launched into plasma, reflected by a cut-off layer, received and analyzed. The spatial coherence of fluctuations is studied by changing the frequency of the second microwave signal against the first one. There is a problem of separation of these two signals as their frequencies are near to each other. This problem can be removed if one uses probing signals with different frequencies but reflected from the same plasma layer. This could be done if one uses the magnetized plasma probing via microwaves with different polarization - O- and X-mode probing. In this paper we describe the results of study of plasma fluctuation properties by using dual polarization single line microwave plasma probing in the reflex discharge. Experiments were done on the pulsed reflex discharge performed in the SS-vacuum chamber (length 150 cm, diameter 20 cm) that was put inside of magnetic solenoid producing a nearly homogeneous magnetic field up to 1.2 T.

A modified method of dual polarization single line microwave backscattering is proposed for correlation and spectral studies of density fluctuations in plasma with known geometry of magnetic field (stellarator with low β plasma, reflex discharge). Simultaneous launching of microwaves of both ordinary (O) and extraordinary (X) polarization via the same antenna has an advantage for correlation measurements of fluctuations in adjacent plasma layers because a procedure of separation of reflected waves is simplified.

Possible mechanisms responsible for metal impurity release during ICRF production and heating of the plasma are studied with the URAGAN-3 torsatron. It is shown that the edge plasma potential oscillations at the pumping frequency and its harmonics produce an impurity influx from the surface of the helical winding casings (Fe, Cr). The impurity release from the antenna surface (Ti) is caused by a quasisteady ~ 100 eV ion flux arising in the divertor magnetic flux region during the RF pulse.