ABSTRACT
The collective Thomson scattering of high-power millimeter-wave radiation on plasma density fluctuations (CTS) is widely used for diagnosing the velocity distribution function of energetic ions in fusion plasma. In this paper, we discuss a non-standard scheme of CTS measurements, which exploits strong refraction of probing and scattered microwave beams when reflecting from the cut-off layer in dense plasma. The scheme may be realized with the existing CTS diagnostic system at the Gas-Dynamic Trap (GDT) facility, a large open magnetic trap operating at Budker Institute (Novosibirsk, Russia). This requires a minor upgrade of the available hardware and essentially increases the range of plasma densities allowed for CTS measurements, as well as its sensitivity and spatial resolution. A detailed study of CTS efficiency for different geometries and plasma conditions at GDT is performed by means of an advanced numerical model that allows for an accurate description of non-Gaussian beam scattering in inhomogeneous plasma. To perform this task, we develop a quasi-optical theory of scattering, which itself may be of general interest.
ABSTRACT
This Letter describes plasma discharges with a high temperature of bulk electrons in the axially symmetric high-mirror-ratio (R=35) open magnetic system gas dynamic trap (GDT) in the Budker Institute (Novosibirsk). According to Thomson scattering measurements, the on-axis electron temperature averaged over a number of sequential shots is 660±50 eV with the plasma density being 0.7×10^{19} m^{-3}; in few shots, electron temperature exceeds 900 eV. This corresponds to at least a threefold increase with respect to previous experiments both at GDT and at other comparable machines, thus, demonstrating the highest quasistationary (about 1 ms) electron temperature achieved in open traps. The breakthrough is made possible by application of a new 0.7 MW/54.5 GHz electron cyclotron resonance heating system in addition to standard 5 MW heating by neutral beams, and application of a radial electric field to mitigate the flute instability.
ABSTRACT
The Budker Institute of Nuclear Physics in worldwide collaboration has developed a project of a 14 MeV neutron source for fusion material studies and other applications. The projected neutron source of the plasma type is based on the gas dynamic trap (GDT), which is a special magnetic mirror system for plasma confinement. Essential progress in plasma parameters has been achieved in recent experiments at the GDT facility in the Budker Institute, which is a hydrogen (deuterium) prototype of the source. Stable confinement of hot-ion plasmas with the relative pressure exceeding 0.5 was demonstrated. The electron temperature was increased up to 0.9 keV in the regime with additional electron cyclotron resonance heating (ECRH) of a moderate power. These parameters are the record for axisymmetric open mirror traps. These achievements elevate the projects of a GDT-based neutron source on a higher level of competitive ability and make it possible to construct a source with parameters suitable for materials testing today. The paper presents the progress in experimental studies and numerical simulations of the mirror-based fusion neutron source and its possible applications including a fusion material test facility and a fusion-fission hybrid system.
