Johann Meisner

High precision hyperfine measurements in Bismuth challenge bound-state strong-field QED

Electrons bound in highly charged heavy ions such as hydrogen-like bismuth 209Bi82+ experience electromagnetic fields that are a million times stronger than in light atoms. Measuring the wavelength of light emitted and absorbed by these ions is therefore a sensitive testing ground for quantum electrodynamical (QED) effects and especially the electron–nucleus interaction under such extreme conditions. However, insufficient knowledge of the nuclear structure has prevented a rigorous test of strong-field QED. Here we present a measurement of the so-called specific difference between the hyperfine splittings in hydrogen-like and lithium-like bismuth 209Bi82+,80+ with a precision that is improved by more than an order of magnitude. Even though this quantity is believed to be largely insensitive to nuclear structure and therefore the most decisive test of QED in the strong magnetic field regime, we find a 7-σ discrepancy compared with the theoretical prediction.

An improved value for the hyperfine splitting of hydrogen-like 209Bi82+

We report an improved measurement of the hyperfine splitting in hydrogen-like bismuth (209Bi82+) at the experimental storage ring ESR at GSI by laser spectroscopy on a coasting beam. Accuracy was improved by about an order of magnitude compared to the first observation in 1994. The most important improvement is an in situ high voltage measurement at the electron cooler (EC) platform with an accuracy at the 10 ppm level. Furthermore, the space charge effect of the EC current on the ion velocity was determined with two independent techniques that provided consistent results. The result of nm provides an important reference value for experiments testing bound-state quantum electrodynamics in the strong magnetic field regime by evaluating the specific difference between the splittings in the hydrogen-like and lithium-like ions.

A Wideband Current Transformer Bridge

The development and testing results of a new current transformer (CT) test set at Physikalisch-Technische Bundesanstalt are described. The operation range for the ratio based bridge is intended for frequencies from 16.7 Hz up to 20 kHz. Equal setups of magnetically shielded current comparators with primary windings for rated currents from 100 mA up to 5 A convert the secondary currents of the standard CT and of the transformer under test (TUT) into proportional voltages. The errors of the TUT are calculated from the subsequent measurement of the complex voltage ratio. This current bridge and the voltage-ratio-based method allow comparing CTs with nonequal ratios. At 50 Hz, the measuring system offers an extended measurement uncertainty of less than 2 ppm or μrad, respectively. The bridge is verified for use with uncertainties of below 200 ppm or 400 μrad at a frequency of 20 kHz.

A wideband current transformer bridge

The work progress on a new current transformer test set at PTB is described. The operation range for the ratio based bridge is intended for frequencies from 16.7 Hz up to 20 kHz. Equal setups of magnetically shielded current comparators with primary windings for currents from 100 mA up to 5 A convert the secondary currents of the standard current transformer and of the transformer under test (DUT) into proportional voltages. The errors of the DUT are calculated from the subsequent measurement of the complex voltage ratio. At 50 Hz, the measuring system offers a basic accuracy in the order of less than ± 2 ppm or μrad respectively.

Laser spectroscopy of the ground-state hyperfine structure in H-like and Li-like bismuth

The LIBELLE experiment performed at the experimental storage ring (ESR) at the GSI Helmholtz Center in Darmstadt aims for the determination of the ground state hyperfine (HFS) transitions and lifetimes in hydrogen-like (209Bi82+) and lithium-like (209Bi80+) bismuth. The study of HFS transitions in highly charged ions enables precision tests of QED in extreme electric and magnetic fields otherwise not attainable in laboratory experiments. While the HFS transition in H-like bismuth was already observed in earlier experiments at the ESR, the LIBELLE experiment succeeded for the first time to measure the HFS transition in Li-like bismuth in a laser spectroscopy experiment.

Enabling DC-Side Metering in HVDC Stations

HVDC power transmission is now being considered not only for point-to-point interties, but also as true grids where several operators may tie into the grid, each having its own economic sphere. In this new situation, it is important that transmitted energy be distinguished from losses incurred in the converter stations, to enable a fair distribution of costs for grid operation. To this end, a metrology infrastructure is needed where high-current and high-voltage transducers must be possible to calibrate traceably, and where dc electricity meters can be calibrated and approved. A research project is currently working with these questions in a concerted European research effort, funded by the European Commission. The present publication highlights important aspects of this work.

Fault matrix based protection coordination in low voltage DC systems

Protection coordination represents one of the main challenges in the developing process of reliable and efficient DC systems. In the current research, a new protection coordination scheme based on fault matrix concept was developed. A testbed was established at Institute of High Voltage Engineering and Electrical Power Systems (elenia) laboratory, Braunschweig University of Technology to verify the operation of the proposed protection concept. Moreover, simulations using PSCAD/EMTDC were conducted. The new protection concept was implemented on 24 V DC systems. The simulation results showed that the proposed scheme is able reliably to detect the fault and isolate only the faulty part in the system.

Operation and protection of 380V DC distribution systems

The demand of a reliable, sustainable, and resilient electrical energy grid motivates the integration of renewable energy-based resources based on different technologies. New network structures are essential in approaching these goals. Low and medium voltage DC grids could introduce a key answer in this context. In this paper, the operation of 380 V DC distribution grids for different applications is reviewed and evaluated. Furthermore, a new efficient protection scheme based on credit point concept was proposed to detect, allocate and isolate faults in such DC grids. The new technique was designed in order to be implemented in the laboratory. The proposed protection scheme was tested using PSCAD software based on radial DC distribution system. The concept for experimental implementation was established and will be presented. The new approach has been found to be robust and effective in detecting, allocating, and isolating faults in DC grids.

Traceability of measurement systems for the assessment of HVDC converter efficiency

Since HVDC transmission is considered as the most favourable solution for the interconnection of several transmission grids over long distances, e.g. in offshore wind farms, the need for traceability for converter efficiency and HVDC metering has increased. Not least the economic consideration of loss distribution in such HVDC grids leads to the necessity of a metrological background for HVDC applications. To enable a comprehensive consideration of HVDC converter losses as well as those of the transmitted DC energy, several measurement systems and calibration services has been established and are briefly presented in this paper Measurement setups for calibrating efficiency measurement systems, consisting of a multi-channel power analyser and associated AC and DC sensors are described. The loss behaviour in HVDC IGBT valves is investigated using a new high voltage test bench.

Adaptive Acquisition of Power IGBT Transients With Discrimination Circuit

The frequency spectrum of the power insulated gate bipolar transistor (IGBT) circuit originates mostly from high gradient switching and low rate conduction components. High gradient transients are captured with direct probes. Switching losses are represented with 3-D surfaces acquired with Delaunay triangulation processing. Interpolation functions are introduced, allowing the prediction of the switching loss in the entire 3-D space. A chopper circuit is introduced for the acquisition of the IGBT low rate transients in the conductive stage of operation. A Zener discriminator enhances the measurement accuracy by two orders of magnitude. The experimental results are presented for a half-bridge converter. Measurement uncertainties are acquired with dc and impulse calibration apparatuses.