DESIREE&Friends 8: MOCCA and MOCCA Quattro: Molecule cameras for the position and energy resolved detection of neutral molecule fragments

by Dr Andreas Fleischmann (Heidelberg University)

Monday 12 Jan 2026, 13:00 → 13:45 Europe/Stockholm

FB54 (AlbaNova Main Building)

The MOCCA detectors are high-resolution cameras for neutral molecule fragments with kinetic energies in the keV range. They feature several thousand pixels based on metallic magnetic calorimeters and are read out using SQUIDs. To reconstruct the kinematics of electron–ion and ion–ion reactions, MOCCA measures both the energy and the impact position of molecular fragments incident on the detector, even with multiple particles hitting the detector simultaneously. The latest fabricated version is currently being deployed at the Cryogenic Storage Ring (CSR) at the Max Planck Institute for Nuclear Physics in Heidelberg, where molecular ions are stored and prepared in their rotational and vibrational ground states, allowing detailed studies of electron–ion interactions.

A four times larger version, MOCCA-quattro with 11.5k-pixels, is planned to be implemented into the Double ElectroStatic Ion Ring ExpEriment (DESIREE) at Stockholm University, which enables mutual neutralization of ions at extremely small relative velocities. This will significantly enhance studies of neutralization processes in complex molecules prepared in their quantum ground state

In this talk we will outline the idea of micro-calorimeters, in particular of the ones based on paramagnetic sensors, where the temperature-change upon the absorption of a molecule-fragment leads to a change of the magnetization of the paramagnetic temperature sensor. After touching applications in other fields, like high resolution x-ray spectroscopy, we will describe the detection principle of the MOCCA detectors in some detail and show some first results of MOCCA and MOCCA-like detectors in action. 

A. Fleischmann, N. Fiedler, D. Kreuzberger, A. Özkara, D. Hengstler, A. Reifenberger, L. Gastaldo, C. Enss, Heidelberg University

C. Jakob, L. Gamer, O. Novotný, MPIK, Heidelberg

P. Martini, S. Rosén, H. Zettergren, H. T. Schmidt, Stockholm University