Design and application of HTS magnet for magneto-hydro-dynamic plasma shielding in radio blackout and heat flux mitigation experiments
Creators: name: Schlachter, Sonja I.
name: Drechsler, Antje
name: Gehring, Rainer
name: Smara, Anis
name: Dalban-Canassy, Matthieu
name: Lefevre, Nicolas
name: Oswald, Johannes W.
name: Nimer, Omar
name: Herdrich, Georg
name: Viladegut, Alan
name: Helber, Bernd
name: Luis, Diana
name: Sharma, Vatsalya
name: Giangaspero, Vincent
name: Lani, Andrea
Publisher: name: Karlsruher Institut für Technologie (KIT)
Year: 2024

description: Since the early days of space flight, the so-called radio-blackout phenomenon occurring during hypersonic flight or during atmospheric entry into a celestial bodies’ atmosphere is well known. The compressed and partially ionized species in the hot plasma in front of the spacecraft can block radio waves leading to a complete loss of communication with ground stations, data telemetry, and GPS for a significant period of time. For the Gemini and Apollo missions radio-blackout phases lasted around 3-4 minutes while the early space shuttle missions experienced up to 30 minutes long radio-blackout phases. In addition to the radio blackout, the hot plasma causes high heat flux on the spacecraft structure. In 2003 a launch damage of the thermal protection systems (TPS) of the space shuttle Columbia led to the destruction of the spacecraft during reentry. Different types of TPS, e.g. ablative TPS, refractory insulation, radiatively or actively cooled TPS, have been developed and used on different missions. 
In the framework of the European project MEESST (Magneto-Hydro-Dynamic Enhanced Entry System for Space Transportation) magneto-hydro-dynamic (MHD) based mitigation of both effects has been investigated by developing suitable simulation tools and ground-based plasma experiments. A high-temperature superconducting (HTS) magnet has been developed, commissioned and set in operation for radio-blackout and heat-flux-mitigation experiments in plasma wind tunnels at the Von Karman Institute for Fluid Dynamics (VKI, Belgium) and at the Institute of Space Systems (IRS, Germany), respectively. The non-insulated, conduction-cooled HTS magnet was designed to fit in a warm-bore cryostat (bore diameter 30 mm, space for enthalpy probe) with a water-cooled shell. It consists of 5 pancake coils wound with 4 mm wide REBCO (Rare-Earth Barium Copper Oxide) tapes with inner and outer winding radii of 33 and 71.5 mm, respectively. Four of the pancake coils contain soldered splices due to the short length of available tapes. Six soldered joints were necessary for the series connection of current leads and pancakes.
We present design, construction and test results of the MEESST magnet. The main focus of the presentation will be on the performance of the magnet and cryogenic system during the plasma experiments at VKI and IRS. Operation of the magnet in the plasma environment turned out to be challenging due to the harsh environment accompanied e.g. by the high heat flux and due to the ionized particles causing electronic noise in temperature and voltage signals. Melting of a water-cooled heat shield protecting cables, vacuum and cryogenic transfer lines, as well as shorts in the current circuit due to melted cable insulation were issues that had to be solved during the experimental campaigns. Despite the underestimated issues, it was possible to operate the non-insulated magnet stably in the experimental campaigns. 
Acknowledgement:
The MEESST project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 899298.