Characterization and Comparison of Control Units for Piezo Actuators to be used for Lorentz Force Compensation inth ILC

Superconducting accelerators, such as the International Linear Collider (ILC), rely on very high Q accelerating cavities to achieve high electric fields at low RF power. Such cavities have very narrow resonances: a few kHz with a 1.3GHz resonance frequency for the ILC. Several mechanical factors cause tune shifts much larger than this: pressure variations in the liquid helium bath; microphonics from pumps and other mechanical devices; and for a pulsed machine such as the ILC, Lorentz force detuning (pressure from the contained RF field). Simple passive stiffening is limited by many manufacturing and material considerations. Therefore, active tuning using piezo actuators is needed. Here we study a supply for their operation. Since commercial power amplifiers are expensive, we analyzed the characteristics of four power amplifiers: (iPZD) built by Istituto Nazionale di Fisica Nucleare (Sezione di Pisa); and a DC-DC converter power supply built in Fermilab (Piezo Master); and two commercial amplifiers, Piezosystem jena and Piezomechanik. This paper presents an analysis and characterization of these amplifiers to understand the cost benefit and reliability when using in a large scale, pulsed beam accelerator like the ILC

Systematic Improvements in Transmon Qubit Coherence Enabled by Niobium Surface Encapsulation

We present a novel transmon qubit fabrication technique that yields systematic improvements in T$_1$ coherence times. We fabricate devices using an encapsulation strategy that involves passivating the surface of niobium and thereby preventing the formation of its lossy surface oxide. By maintaining the same superconducting metal and only varying the surface structure, this comparative investigation examining different capping materials and film substrates across different qubit foundries definitively demonstrates the detrimental impact that niobium oxides have on the coherence times of superconducting qubits, compared to native oxides of tantalum, aluminum or titanium nitride. Our surface-encapsulated niobium qubit devices exhibit T$_1$ coherence times 2 to 5 times longer than baseline niobium qubit devices with native niobium oxides. When capping niobium with tantalum, we obtain median qubit lifetimes above 200 microseconds. Our comparative structural and chemical analysis suggests that amorphous niobium suboxides may induce higher losses. These results are in line with high-accuracy measurements of the niobium oxide loss tangent obtained with ultra-high Q superconducting radiofrequency (SRF) cavities. This new surface encapsulation strategy enables further reduction of dielectric losses via passivation with ambient-stable materials, while preserving fabrication and scalable manufacturability thanks to the compatibility with silicon processes

Fine structure of substorm and geomagnetically induced currents

The rapid changes dB/dt of the Earth’s magnetic field due to substorms can excite large geomagnetically-induced currents (GICs) that can have harmful effects on technological systems. This paper presents an analysis of the characteristics of dB/dt enhancements observed in Fennoscandia using data from the IMAGE magnetometer chain along a geomagnetic longitude of 110o. The abrupt geomagnetic field variations may be associated with the substorm onsets, isolated magnetic impulsive events (MIEs), and quasi-periodic series of MIEs, known as Ps6 pulsations (periods 5-15 min). For a detailed examination of the latitudinal structure of dB/dt enhancements and their association with the auroral oval boundaries we applied the technique of magnetic keograms. This simple technique helps to visualize and characterize the fine structure of substorm, namely the location in time and latitude of dB/dt enhancements. The location of the auroral oval boundaries has been estimated with the OVATION-prime model. Among the different types of impulsive disturbances investigated auroral substorm onset provides the largest GICs (few tens of A). Isolated nightside MIEs are also effective in the excitation of GICs (>10 A). Ps6 pulsations are effective in the excitation of GICs with magnitude about 20 A and even higher. Monochromatic Pc5 pulsations are capable to induce noticeable GICs, up to ~13 A. Large localized disturbances on short timescales are the actual drivers of GICs, and they may be imagined like geomagnetic “strokes” during magnetospheric “thunderstorms”

Formation of Oxide Fuels on Vt6 Alloy in the Conditions of Anodial Polarization in Solutions H2SO4

We report results of research into a process of electrochemical oxidation of the titanium alloy VT6 in solutions of H2SO4. It is shown that the character of forming dependences for alloy samples depends on the magnitude of current density. At j<0.5 А·dm–2, a continuous oxide film does not form at the surface of the alloy; the assigned value for voltage is not reached. At j>0.5 А·dm–2, a continuous oxide film forms at the surface of the alloy; a linear character of dependences is observed. The films obtained under these conditions relate to the interferential-colored films. A film thickness limit is defined by the assigned magnitude of U and does not depend on other parameters of the electrolysis. For the series of identical values for U, dependence of τ‒j has a linear shape. The color of the oxide film is determined by the value of voltage and does not depend on the current density and electrolyte concentration. We established a correspondence between a color of the film and the magnitude of U in the range of 10‒100 V. This effect is due to the fact that the formation of a film at anodic polarization occurs in the presence of a gradient in the potential whose quantity for titanium is a constant magnitude. Increasing the assigned magnitude of U leads to a proportional increase in the maximum thickness of the oxide, which determines its color. Results of our study on determining the effect of electrolysis parameters on the characteristics of oxide films made it possible to substantiate the mode for obtaining TiO2 films at the surface of the alloy VT6. The data obtained form the basis for the development of technology for electrochemical oxidation of titanium implants in order to render functional properties to their surface

Searches for New Particles, Dark Matter, and Gravitational Waves with SRF Cavities

International audienceThis is a Snowmass white paper on the utility of existing and future superconducting cavities to probe fundamental physics. Superconducting radio frequency (SRF) cavity technology has seen tremendous progress in the past decades, as a tool for accelerator science. With advances spear-headed by the SQMS center at Fermilab, they are now being brought to the quantum regime becoming a tool in quantum science thanks to the high degree of coherence. The same high quality factor can be leveraged in the search for new physics, including searches for new particles, dark matter, including the QCD axion, and gravitational waves. We survey some of the physics opportunities and the required directions of R&D. Given the already demonstrated integration of SRF cavities in large accelerator systems, this R&D may enable larger scale searches by dedicated experiments

The SOX experiment hunts the sterile neutrino

The SOX (Short distance neutrino Oscillations with BoreXino) experiment aims to perform a resolutive measurement for testing the longstanding hypotesis of a sterile neutrino in the eV2 mass scale. A very intense and well calibrated 144Ce−144Pr antineutrino source will be placed under the large size and very low background Borexino detector at Laboratori Nazionali del Gran Sasso in Italy. Borexino demonstrated a such energy and position resolution that the disappearance experiment can be performed and the short distance oscillations might be directly observed. In this paper an overview of the key elements of the experiment is given and the expected sensitivity to determine the sterile neutrino mass is shown