High-voltage generation system for a traveling-wave Stark decelerator

TL;DR

This work presents a transformer-based high-voltage generation system for a traveling-wave Stark decelerator designed to slow heavy polar molecules like BaF and SrF. By combining eight AWG-generated waveforms with predistortion feedback, custom HV transformers, and an in-house monitoring loop, the system achieves up to $10\ \mathrm{kV}$ across a $\sim$ $151\ \mathrm{pF}$ capacitive load with precise amplitude (±$1\%$) and phase (±$2^{\circ}$) control over a sweep from $16.7\ \mathrm{kHz}$ to $2.5\ \mathrm{kHz}$ in 40 ms. The modular, SF$_6$-insulated design minimizes external dependencies while delivering high waveform fidelity (THD $<$ 0.25\% at 10 kHz) and robust stability against capacitive channel coupling. This approach enables deeper molecular traps and improved precision spectroscopy in TWSD-based experiments, with potential applicability to accelerator physics, plasma physics, and mass spectroscopy. Overall, the system demonstrates a practical, scalable solution for precise high-voltage waveform control in long, multi-channel deceleration devices.

Abstract

In this paper we describe the high-voltage generation system we have developed for a traveling-wave Stark decelerator (TWSD). The TWSD can reduce the forward velocity of a molecular beam of heavy neutral polar molecules such as strontium monofluoride (SrF) and barium monofluoride (BaF) from $\sim$ 200 m/s down to $\sim$ 6 m/s. The main motivation for the development of this device is the increased sensitivity from precision spectroscopy of the decelerated molecules to test fundamental physics. The high-voltage generation system can produce eight pulsed sinusoidal waveforms with a maximum amplitude of 10 kV and a linear frequency sweep from 16.7 kHz down to 500 Hz over the span of 40 ms at a repetition rate of 10 Hz. The eight waveforms are phase-offset to each other by 45 degrees. To slow down the heavy molecules, the decelerator is required to have a length of $\sim$ 4 m, which results in a significant capacitive coupling between adjacent channels of $\sim$ 160 pF. As a consequence, the control and stability of the waveforms is extra challenging. We designed a method that compensates for the frequency-dependent coupling between the eight channels. Allowing for amplitude and phase-offsets that do not deviate more than 1% and 2 degrees, respectively, from their design values during the frequency sweep. The system outperforms commercially available options in terms of stability, output voltage amplitude, cost and ease of maintenance. This approach is also relevant for other fields where precise control of high-voltage waveforms is required, such as particle accelerator physics, plasma physics and mass spectroscopy.

Figures (13)

• Figure 1: (a) Picture of the front view of one of the decelerator modules. (b) Isometric side view of the module showing the mounting structure used to hold and align the electrode rods.
• Figure 2: Equivalent circuit of the decelerator. The rods are labeled A through H. For a 4.5 m long decelerator, the capacitance between each pair of adjacent channels is determined to be $\sim$ 160 pF and between each channel and ground $\sim$ 57 pF Zapara.2019.
• Figure 3: Illustration of a single optimal output waveform. For clarity, the frequency is reduced by a factor of 10 and the ramp-up and ramp-down duration has been set to 10%.
• Figure 4: Schematic overview of the setup. The sequence is repeated for each channel. The dashed boxes show approximate values for the voltage and current amplitudes in that location of the setup when using a test load of 200 pF at 10 kV at the starting frequency of 16.7 kHz. For clarity, the capacitive coupling between adjacent channels and between each channel and ground is not shown.
• Figure 5: Schematic side view of a transformer. The primary and secondary coils are denoted in blue and red, respectively. Four sets of two primary coils each are connected in parallel, as indicated by the black lines, while the secondary coils are all connected in series (the connections for the secondary coils are not shown). The core material is indicated with grey, and the yellow parts are the mounting structure.