High voltage measurements
The goal of our new experiment is the measurement of high voltages in the range of 10 to 100 kV using precise laser spectroscopy of ions with a well-known transition frequency in the ion’s rest-frame . We want to reach a precision of at least 1 ppm, which is of interest for many applications.
High voltage measurements are currently realized using high voltage dividers that convert a high voltage over a chain of resistors to a lower voltage with a precisely known dividing ratio. Commercial systems using this technique achieve a typical accuracy of 100 ppm (10kV ±1V). With a huge effort, a relative accuracy of up to 1 ppm (10kV +- 10mV) can be reached. Due to aging effects of the resistors, voltage dividers have to be recalibrated regularly.
Our approach is based on collinear laser spectroscopy. A laser beam is superimposed on a beam of fast ions. The resonance frequency f0 in the ions rest frame is shifted to
fL = f0 (1 – β) γ
in the laboratory frame, due to the relativistic Doppler effect. Here, β=v/c is the ion velocity as a fraction of the speed of light and γ is the time dilatation factor γ=1/(1-β2)1/2. If the laser is tuned to fL, the ions are resonantly excited and fluorescence light can be detected. With the known rest-frame frequency, the ion velocity can be determined with the formula given above. To suppress systematic errors as far as possible, we will work with two laser beams in a so-called pump-and probe technique as it is shown schematically in Fig. 1.
Hence, it is possible to determine high voltages by measuring optical frequencies and directly relate them to a natural constant, the frequency of the ionic transition. The experiment is installed in the basement of the Institute for Nuclear Physics. A Photo of the beamline is shown in Fig. 2. The laser systems are also under development. “Miniforschung”, Bachelor- and Master-Theses are offered. Some examples are listed here.