A new gas puff imaging (GPI) diagnostic has been developed on the HL-2A tokamak to study two-dimensional plasma edge turbulence in poloidal vs. radial plane. During a discharge, neutral helium or deuterium gas is puffed at the edge of the plasma thro
ugh a rectangular multi-capillary nozzle to generate a gas cloud on the observing plane. Then a specially designed telescope and a high-speed camera are used to observe and photograph the emission from the neutral gas cloud. The brightness and contrast in the 2-D poloidal vs. radial frames reveal the structures and movements of the turbulence. The diagnostic was put into the first experiment during the latest campaign and successfully captured blob structures of different shapes and sizes in scrape-off layer (SOL).
Understanding the interplay between charge order (CO) and other phenomena (e.g. pseudogap, antiferromagnetism, and superconductivity) is one of the central questions in the cuprate high-temperature superconductors. The discovery that similar forms of
CO exist in both hole- and electron-doped cuprates opened a path to determine what subset of the CO phenomenology is universal to all the cuprates. Here, we use resonant x-ray scattering to measure the charge order correlations in electron-doped cuprates (La2-xCexCuO4 and Nd2-xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and superconductivity. Detailed measurements of Nd2-xCexCuO4 show that CO is present in the x = 0.059 to 0.166 range, and that its doping dependent wavevector is consistent with the separation between straight segments of the Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166, but decreases at lower doping levels, indicating that it is not tied to the appearance of antiferromagnetic correlations or the pseudogap. Near optimal doping, where the CO wavevector is also consistent with a previously observed phonon anomaly, measurements of the CO below and above the superconducting transition temperature, or in a magnetic field, show that the CO is insensitive to superconductivity. Overall these findings indicate that, while verified in the electron-doped cuprates, material-dependent details determine whether the CO correlations acquire sufficient strength to compete for the ground state of the cuprates.
It is known, that at high energies of ions (more than 10 MeV for light ions) the focusing by magnetic quadrupole fields is most effective, whereas at small energies (less than 1 MeV) - the focusing by electrical quadrupole fields. At intermediate ene
rgies of ions (from 1 to 10 MeV) the efficiency of each of these types of a focusing is reduced. The authors offer to utilize for this purpose the hybrid type of focusing systems consisting of sequence of electrical and magnetic quadrupole lenses, which are localized in the same space. For making fields of electrical quadrupole lenses it is offered to utilize RF quadrupoles. The RF electrical quadrupoles are created due to the relevant configuration of drift tubes in the vicinity of an accelerating gap. As a result of the general theoretical analysis and calculation of concret
