Niels Hessel Andersen

Superconducting wind turbine generators

We have examined the potential of 10?MW superconducting direct drive generators to enter the European offshore wind power market and estimated that the production of about 1200 superconducting turbines until 2030 would correspond to 10% of the EU offshore market. The expected properties of future offshore turbines of 8 and 10?MW have been determined from an up-scaling of an existing 5?MW turbine and the necessary properties of the superconducting drive train are discussed. We have found that the absence of the gear box is the main benefit and the reduced weight and size is secondary. However, the main challenge of the superconducting direct drive technology is to prove that the reliability is superior to the alternative drive trains based on gearboxes or permanent magnets. A strategy of successive testing of superconducting direct drive trains in real wind turbines of 10?kW, 100?kW, 1?MW and 10?MW is suggested to secure the accumulation of reliability experience. Finally, the quantities of high temperature superconducting tape needed for a 10?kW and an extreme high field 10?MW generator are found to be 7.5?km and 1500?km, respectively. A more realistic estimate is 200?300?km of tape per 10?MW generator and it is concluded that the present production capacity of coated conductors must be increased by a factor of 36 by 2020, resulting in a ten times lower price of the tape in order to reach a realistic price level for the superconducting drive train.

A high-mobility two-dimensional electron gas at the spinel/perovskite interface of γ-Al2O3/SrTiO3.

The discovery of two-dimensional electron gases at the heterointerface between two insulating perovskite-type oxides, such as LaAlO(3) and SrTiO(3), provides opportunities for a new generation of all-oxide electronic devices. Key challenges remain for achieving interfacial electron mobilities much beyond the current value of approximately 1,000 cm(2) V(-1) s(-1) (at low temperatures). Here we create a new type of two-dimensional electron gas at the heterointerface between SrTiO(3) and a spinel γ-Al(2)O(3) epitaxial film with compatible oxygen ions sublattices. Electron mobilities more than one order of magnitude higher than those of hitherto-investigated perovskite-type interfaces are obtained. The spinel/perovskite two-dimensional electron gas, where the two-dimensional conduction character is revealed by quantum magnetoresistance oscillations, is found to result from interface-stabilized oxygen vacancies confined within a layer of 0.9 nm in proximity to the interface. Our findings pave the way for studies of mesoscopic physics with complex oxides and design of high-mobility all-oxide electronic devices.

Extreme mobility enhancement of two-dimensional electron gases at oxide interfaces by charge-transfer-induced modulation doping.

Two-dimensional electron gases (2DEGs) formed at the interface of insulating complex oxides promise the development of all-oxide electronic devices. These 2DEGs involve many-body interactions that give rise to a variety of physical phenomena such as superconductivity, magnetism, tunable metal-insulator transitions and phase separation. Increasing the mobility of the 2DEG, however, remains a major challenge. Here, we show that the electron mobility is enhanced by more than two orders of magnitude by inserting a single-unit-cell insulating layer of polar La(1-x)Sr(x)MnO3 (x = 0, 1/8, and 1/3) at the interface between disordered LaAlO3 and crystalline SrTiO3 produced at room temperature. Resonant X-ray spectroscopy and transmission electron microscopy show that the manganite layer undergoes unambiguous electronic reconstruction, leading to modulation doping of such atomically engineered complex oxide heterointerfaces. At low temperatures, the modulation-doped 2DEG exhibits Shubnikov-de Haas oscillations and fingerprints of the quantum Hall effect, demonstrating unprecedented high mobility and low electron density.

Structural studies of BSCCO/Ag-tapes by high-energy synchrotron X-ray diffraction

Abstract High-energy (100 keV) synchrotron X-ray diffraction has been identified as a powerful tool for characterizing texture and structural phases within Ag clad high T c superconducting tapes of the (Bi,Pb)–Sr–Ca–Cu–O (BSSCO) type during synthesis of (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O x (Bi-2223) from (Bi,Pb) 2 Sr 2 CaCu 2 O x (Bi-2212). Using a CCD camera, the texture and concentration of the dominant structural phases can be determined simultaneously within fractions of minutes. As an example, we report on the in situ annealing behavior in air at 835°C of an as-rolled monofilament tape. It is shown that the alignment of the superconducting grains takes place almost exclusively in the Bi-2212 phase. During heating, the texture profile narrows rapidly above 750°C, coincident with the dissolution of (Ca,Sr) 2 PbO 4 . A 98% conversion of Bi-2212 is obtained within 19 h, but furnace cooling leads to the formation of secondary phases such as Bi-2201 and (Ca,Sr) 2 PbO 4 . Room temperature data on similar tapes show that subsequent deformation and annealing results in a higher Bi-2223 phase purity while slightly deteriorating the grain alignment.

The structural phase diagram and oxygen equilibrium partial pressure of YBa2Cu3O6+x studied by neutron powder diffraction and gas volumetry

An experimental technique based on neutron powder diffraction and gas volumetry is presented and used to study the structural phase diagram of YBa2Cu3O6+x under equilibrium conditions in an extended part of (x, T)-phase (0.15<x<0.92 and 25°C<T<725°C). Our experimental observations lend strong support to a recent two-dimensional anisotropic next-nearest-neighbour Ising model calculation (the ASYNNNI model) of the basal plane oxygen ordering based of first principle interaction parameters. Simultaneous measurements of the oxygen equilibrium partial pressure show anomalies, one of which proves the thermodynamic stability of the orthorhombic OII double cell structure. Striking similarity with predictions of recent model calculations support that another anomaly may be interpreted to result from local one-dimensional fluctuations in the distribution of oxygen atoms in the basal plane of tetragonal YBCO. Our pressure data also indicate that x=0.92 is a maximum obtainable oxygen concentration for oxygen pressures below 760 Torr.

Oxygen-ordering superstructures in underdoped YBa 2 Cu 3 O 6 + x studied by hard x-ray diffraction

High-energy x-ray diffraction is used to investigate the bulk oxygen-ordering properties of

Crystal structure, magnetic susceptibility and thermopower of superconducting and non-superconducting Nd1.85Ce0.15CuO4+y

{\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}.

Dynamical scaling of oxygen ordering in YBa2Cu3O7- delta.

Four different superstructures of Cu-O chains aligned along the b axis and ordered with periodicity

Superstructure formation and the structural phase diagram of YBa2Cu3O6+x

ma,

Quantum Spin Liquid in Frustrated One-Dimensional LiCuSbO4

along the a axis have been observed. For