Fermilab, Batavia, Illinois
FNAL’s electron cooler (4.3 MV, 0.1 A DC) has been integrated to the collider operation for almost two years, improving the storage and cooling capability of the Recycler ring (8 GeV antiprotons). In parallel, efforts are carried out to characterize the cooler and its cooling performance. This paper discusses various aspects of the cooler performance and operational functionality: high voltage stability of the accelerator (Pelletron), quality of the electron beam generated, operational procedures (off-axis cooling, electron beam energy measurements and calibration) and cooling properties (in the longitudinal and transverse directions). In particular, we show measurements of the friction force and cooling rates, which we compare to a non-magnetized model and conclude that the effective electron beam radius is smaller than expected.
Fermilab, Batavia, Illinois
Presently antiprotons in Fermilab’s Recycler ring are stored between rectangular RF barriers and are cooled both by a stochastic cooling system in full duty-cycle mode and by a DC electron beam. Electron cooling creates correlation between longitudinal and transverse tails of the antiproton distribution because particles with large transverse actions are cooled much more slowly than the core ones. Introducing additional RF barriers of lower amplitude allows separating spatially (along the bunch) the core and the tail. In this scenario, stochastic cooling can be “gated” to the tail, i.e. applied with a high gain to the low-density region and turned off for the core portion of the beam. This significantly increases the cooling rate of the tail particles, while the temperature of the core is preserved by electron cooling. In this paper, we will describe the procedure and first experimental results in detail.