SPARC laser cooling
Introduction
This working group prepares for "laser cooling of intense bunched beams of relativistic ions" at the FAIR heavy-ion synchrotron SIS100. These experiments require continuous technical advancement of the laser and detection systems used, together with improved analysis methods, in order to master the upcoming challenges. This endeavour requires the construction of a dedicated world-wide unique laser cooling facility at the SIS100. The active members of the working group can be found under "participants". We are working closely together with the „SPARC laser spectroscopy“ group. We are supported by the BMBF and by POF MT ARD.
Experiments
Important developments for laser cooling of bunched relativistic ion beams at GSI take place at the Experimental Storage Ring (ESR). Here, the fundamentals for applications of this method to very intense highly relativistic heavy-ion beams at the SIS100 are being made. Laser cooling will also be the only cooling method available at the SIS100. Thus far, successful laser cooling experiments have been conducted at the ESR of GSI in Darmstadt (Germany) in 2004, 2006, 2012, 2016 and 2021, using 12C3+ ion beams, and at the Cooler Storage Ring for experiments (CSRe) of the IMP in Lanzhou (China) in 2016 and in 2019, using 12C3+ and 16O5+ ion beams.
Optical diagnostics
Measuring the fluorescence from the laser-excited ions, using "optical diagnostics", is absolutely necessary, since it was shown that the evaluation of Schottky spectra ("standard" diagnostics) offers only limited access to the dynamics of very cold ion beams. Therefore, the group in Münster (Prof. Weinheimer and Dr. Hannen) started the development of a dedicated optical detection system at the ESR.
Continuous and pulsed laser systems
This development takes place in the group of Prof. Walther at the TU Darmstadt and in the group of Prof. Schramm & Dr. Bussmann at the TU Dresden (HZDR). These groups have great experience in the realisation of widely tunable cw diode-based laser systems and pulsed, bandwidth-limited, picosecond high power laser systems. Further important requirements on the pulsed laser systems are: a very high repetition rate (~MHz), variable pulse duration (ps to ns), synchronisation between the laser systems and the bunched ion beam, and high power (W!) in the UV and VIS spectral range. Finally, overlap in space, time and energy of the laser beams and the ion beam must be assured. The truly unique combination of these systems will then allow to spectrally cover the complete initial longitudinal momentum distribution of the stored ion beam. This will make it possible to simultaneously cool all the „hot“ ions in the beam, and - in general - reduce heating by intra-beam scattering (IBS) and space charge (SC) effects. This will bring laser cooling at accelerators to the next level.
