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Experimental Physics

Institute of
Experimental Physics

Photo: JJ

Inst. of Experimental Physics

GravMAGA

GravMAGA: Gravitational-wave MAGnetic-field Antenna

GravMAGA employs a search for high-frequency gravitational waves (HFGWs) that exploits their coupling to electromagnetism in the presence of a strong magnetic field. A passing GW in an external field induces an effective displacement current that generates a secondary magnetic flux, similarly to the WISPLC case. GravMAGA measures this flux with a purpose-built pickup geometry inside the 14 Tesla superconducting warm-bore solenoid at the Universität Hamburg.

The detector centers on a figure-eight (“8-shape”) pickup loop that breaks the azimuthal symmetry of the induced currents and converts the GW-driven flux into a measurable voltage. A symmetric “blind” loop provides a simultaneous background/veto channel, while an injection loop enables in-situ end-to-end calibration. Signals from the measurement and blind loops are amplified, band-filtered, and digitized in parallel, enabling real-time noise rejection.

The science target is broadband and transient HFGW signals around the 100 kHz–10 MHz band, including templates for primordial black-hole mergers and other short bursts. A GPU-accelerated matched-filter pipeline (time-domain) evaluates candidate events online using a template bank, while continuous monitoring tracks the voltage noise spectral density and environmental diagnostics. With the current pickup geometry and field map, the strain reach scales favorably with frequency, and the projected sensitivity spans ≈ 10-14–≈ 10-18 across the band, opening unexplored parameter space for HFGWs.

Detector development for GravMAGA is completed, and commissioning is now ongoing, while optimisation of magnetic shielding and ground isolation for improved noise rejection is being implemented. The modular loop holder and shielded readout allow straightforward future upgrades (e.g. additional windings, refined filtering, extended bandwidth). The warm–bore access of the 14 Tesla magnet simplifies installation and calibration, making the platform well-suited for iterative improvements and extended observing campaigns.

Figure 11: Schematic overview of the GravMAGA experiment. A 14T warm-bore solenoidal magnet houses three pickup loops: the measurement loop (ML, green), the signal injection loop (SIL, purple) used for calibration, and the blind loop (BL, gray) used as an internal noise/systematics monitor. The ML and BL signals are amplified with low-noise amplifiers (LNAs), filtered with band-pass filters (BPFs) and digitized in a shielded enclosure by a synchronized two-channel analog-to-digital converter (ADC). Calibration tones are injected via the SIL using a signal generator (SG) referenced to a common 10 MHz clock.

 

Figure 12: Projected strain sensitivity of GravMAGA for continuous signals assuming a 14T magnetic field, 10 windings per loop, loop area of 914 cm2, SNR = 3 and room temperature operation. The accessible frequency range spans 10 kHz–10 MHz.

Selected Presentations and Publications

  • J. Jödicke, M. Maroudas, T.-S. Cezar, D. Horns, GravMAGA: A Gravitational-Wave Magnetic-Field Antenna (concept note, 2025).
  • M. Maroudas, “Axion, ALP, and HFGW Searches Across Complementary Experimental Frontiers”, 20th Patras Workshop on Axions, WIMPs and WISPs, Lisbon, 24–26 Sept 2025. https://agenda.infn.it/event/46273/contributions/269303/<;/a>

Interested in writing a thesis (BSc/MSc) on this topic? Take a look at our proposals.