# History of probe measurements on GOLEM

GOLEM has a long history of probe measurements, since its low-temperature plasmas are ideal for testing and using all kinds of probes. These are fragmented records of the past, present and future probe experiments.

# Current experimentalists

The people who have performed probe measurements on GOLEM include:

• Jiří Adámek (researcher at the Institute of Plasma Physics, Czech Academy of Sciences). The inventor of the ball-pen probe, Jirka performs mainly experiments with the combined BPP+LP probe head. His special interest is the $$I-V$$ characteristic of the ball-pen probe.

• Jan Stöckel (senior researcher at the Institute of Plasma Physics, Czech Academy of Sciences). The godfather of probe measurements on GOLEM, CASTOR and COMPASS alike, Honza supports younger researchers and supervises their experiments. His love is the (double) tunnel probe, which he helped construct back in the day with Jamie Gunn.

• Petr Mácha (PhD student at FNSPE, CTU). Petr wrote his Bachelor’s thesis, Research project and Master’s thesis on GOLEM, which is an impressive feat. He focuses on the measurements of the electron temperature using a swept Langmuir probe and using the BPP+LP method.

• Filip Papoušek (Master’s student at FNSPE, CTU). Filip’s Bachelor’s thesis and Research project concerned the electric fields in the edge plasma as measured on GOLEM and COMPASS.

• Daniela Kropáčková (Bachelor’s student at FNSPE, CTU). Daniela wrote a SOČ (high-school level research work) about Mach number measurements in the GOLEM edge plasma. The next year she wrote another SOČ about plasma stabilisation. Now a first-year student of FNSPE, she continues to work on the plasma column position calculation and plasma stabilisation.

• Martina Lauerová (high-school student). Martina is writing a SOČ about the measurement of electron temperature using Langmuir probe $$I$$-$$V$$ characteristics fitting.

• Aleš Socha (high-school student). Aleš is writing a SOČ about the measurement of edge plasma movement using the localisation of the blob birth zone.

# Past probe experiments

• Petiprobe experiments. The petiprobe is a combined Langmuir+ball-pen+double tunnel probe, assembled in 2019. In May 2020 it served Kurchatov Institute campaign in May 2020 [Lauerová et al 2019]; the probe was placed at $$r$$ = 7 cm and the discharge numbers are #32880-#33105.

• Ball-pen probe $$I$$-$$V$$ characteristics measurements. Aim: to quantify the $$\ln R = I_{sat}^- / I_{sat}^+$$ coefficient and to measure the ion temperature. Currently (September 2020) the data is being processed by a student of Jiří Adámek, Dario.

• Ball-pen probe $$I$$-$$V$$ characteristics measurements on shot-to-shot basis. Aim: to quantify the $$\ln R = I_{sat}^- / I_{sat}^+$$ coefficient and to measure the ion temperature. [Adámek 2017] [Adámek 2017]

• Double tunnel probe measurements of the Mach number. Aim: to measure the magnitude and profile of SOL parallel flows and to assess the effect of the forward/backward field configuration. [Kropáčková 2019]

• Reynolds stress measurements with the double rake probe. Aim: to compare the Reynolds stress profile in hydrogen and helium. [Grover 2016]

• Turbulent transport characterisation with the double rake probe. Aim: to compare the distribution function moments of $$I_{sat}$$ in hydrogen and helium. [Jiráková 2016]

• Electron temperature measurements comparison. Aim: to benchmark several experimental ways of measuring the electron temperature. [Mácha 2020] [Mácha 2019] [Mácha 2020]

• Edge plasma biasing. Aim: Localise GAMs (Geodesic Acoustic Modes) in the GOLEM edge plasma and characterise their impact on the turbulent transport. [Papoušek 2020]

• Langmuir probe $$I$$-$$V$$ characteristics measurement on shot-to-shot basis. Aim: Measure the electron temperature $$T_e$$ with high temporal resolution in a suite of identical discharges. [Stöckel & Svoboda 2014]

• Double rake probe pin cross-correlation in helium. Aim: measure the velocity of turbulent structures. [Svoboda 2018]

# Future probe experiments

• (September 2020) Jan Stöckel and Jiří Adámek are preparing a new rail probe, whose inclination toward the magnetic field will be able to change from shot to shot.