Solar Orbiter Radio and Plasma Waves – Time Domain Sampler: In-flight performance and first results

J Souček ,Radek Lán ,M Kretzschmar ,E Lorfèvre ,Vratislav Krupař ,Dirk Plettemeier ,O Krupařová ,M Maksimović ,Jiří Baše ,Diane Bérard ,Š Štverák ,Luděk Uhlíř ,Ivana Kolmašová ,V Krasnoselskikh ,T Chust ,O Santolı́k ,A Vaivads ,Yuri V Khotyaintsev ,S D Bale ,D Píša ,A Vecchio ,M Steller ,X Bonnin

doi:10.1051/0004-6361/202140948

Abstract

Context.The Radio and Plasma Waves (RPW) instrument on board Solar Orbiter has been operating nearly continuously since the launch in February 2020. The Time Domain Sampler (TDS) receiver of the RPW instrument is dedicated to waveform measurements of plasma waves and dust impact signatures in an intermediate frequency range from 0.2 to 200 kHz.Aims.This article presents the first data from the RPW-TDS receiver and discusses the in-flight performance of the instrument and, in particular, the on-board wave and dust detection algorithm. We present the TDS data products and its scientific operation. We demonstrate the content of the dataset on several examples. In particular, we study the distribution of solar Langmuir waves in the first year of observations and one Type III burst event.Methods.The on-board detection algorithm is described in detail in this article and classifies the observed waveform snapshots, identifying plasma waves and dust impacts based on the ratio of their maximum amplitude to their median and on the spectral bandwidth. The algorithm allows TDS to downlink the most scientifically relevant waveforms and to perform an on-board statistical characterization of the processed data.Results.The detection algorithm of TDS is shown to perform very well in its detection of plasma waves and dust impacts with a high accuracy. The initial analysis of statistical data returned by TDS shows that sporadic Langmuir waves that are not associated with Type III events are routinely observed in the inner heliosphere, with a clear increase in occurrence rate closer to the Sun. We also present an example of RPW observations during an encounter of the source region of a Type III burst, which exploits the on-board calculated histograms data.

Highlights

The Radio and Plasma Waves (RPW) instrument (Maksimovic et al 2020) on Solar Orbiter includes three receivers for the digitization and on-board processing of electromagnetic field data across different frequency bands: The Low Frequency Receiver (LFR), covering the frequency range from well below 1 Hz to 10 kHz with both time series data and spectral data; the Thermal Noise and High Frequency Receiver (TNR/HFR), providing electromagnetic spectra from several kHz to 16 MHz; and the Time Domain Sampler (TDS), a medium frequency receiver dedicated to waveform measurements
The TDS wave detection algorithm has been described in detail and shows a good in-flight performance in detecting plasma waves and dust impacts
The power conversion and distribution unit (PCDU) interference prevents the detection algorithm from operating at the highest sampling rate of 524.3 ksps; we have been operating TDS at the 262.1 ksps sampling throughout the cruise phase

Summary

Introduction

The Radio and Plasma Waves (RPW) instrument (Maksimovic et al 2020) on Solar Orbiter includes three receivers for the digitization and on-board processing of electromagnetic field data across different frequency bands: The Low Frequency Receiver (LFR), covering the frequency range from well below 1 Hz to 10 kHz with both time series data and spectral data; the Thermal Noise and High Frequency Receiver (TNR/HFR), providing electromagnetic spectra from several kHz to 16 MHz; and the Time Domain Sampler (TDS), a medium frequency receiver dedicated to waveform measurements. The decimating filters are implemented in Field Programmable Gate Array (FPGA) logic, but the filter coefficients are uploaded to the FPGA by the flight software and multiple sets with slightly different characteristics can be chosen by a telecommand This decimated waveform is used as the input digital signal for waveform snapshots and TDS statistical products. A large number of input configurations is allowed by the TDS input multiplexers, but only three multiplexer settings listed in Table 1 are used routinely in scientific operations This list includes the monopole configuration SE1 suitable for dust impact measurements, but the measurements contain more noise and spurious signals of spacecraft origin. TDS supports the RPW backup mode in its LFM (low frequency mode) configuration, where nominal data is not generated, but TDS replaces LFR in the sampling of low frequency signals from SCM and BIAS This mode is presently not used in flight while LFR operates nominally

On-board wave detection

In-flight performance

TDS data products

Statistical properties of detected Langmuir waves

Conclusions