Abstract
CERN currently delivers antiprotons for trapping experiments with the antiproton decelerator (AD), which slows the antiprotons down to about 5 MeV. This energy is currently too high for direct trapping, and thick foils are used to slow down the beam to energies which can be trapped. To allow further deceleration to $\ensuremath{\sim}100\text{ }\text{ }\mathrm{keV}$, CERN is initiating the construction of ELENA, consisting of a ring which will combine rf deceleration and electron cooling capabilities. We describe a simple frictional cooling scheme that can serve to provide significantly improved trapping efficiency, either directly from the AD or first using a standard deceleration mechanism (induction linac or rf quadrupole). This scheme could be implemented in a short time. The device itself is short in length, uses accessible voltages, and at reasonable cost could serve in the interim before ELENA becomes operational, or possibly in lieu of ELENA for some experiments. Simple theory and simulations provide a preliminary assessment of the concept and its strengths and limitations, and highlight important areas for experimental studies, in particular to pin down the level of multiple scattering for low-energy antiprotons. We show that the frictional cooling scheme can provide a similar energy spectrum to that of ELENA, but with higher transverse emittances.
Highlights
Scientific demand for low-energy antiprotons continues to grow for various experimental initiatives, including direct measurements of charge-to-mass ratios and production and trapping of antihydrogen, and eventually may lead to measurements of trapped neutral antimatter to test directly the weak equivalence principle and CPT invariance [1,2,3].The primary source of low-energy antiprotons remains the antiproton decelerator (AD) at CERN, but experiments typically suffer from low capture efficiency, because the antiprotons still exit the AD at average energies far above achievable electrostatic trap depths
The extra low-energy antiproton (ELENA) upgrade [4,5] to the AD is under development, which will use a postdecelerator and
In order to further increase the proportion of trappable antiprotons, between the AD and the frictional cooling section, we consider various ideas for deceleration, including the ELENA proposal, an induction linac, and a radiofrequency quadrupole (RFQ) system, and compare them to the use of only a foil
Summary
Scientific demand for low-energy antiprotons continues to grow for various experimental initiatives, including direct measurements of charge-to-mass ratios and production and trapping of antihydrogen, and eventually may lead to measurements of trapped neutral antimatter to test directly the weak equivalence principle and CPT invariance [1,2,3]. In order to trap the antiprotons, the beam is first sent through a degrading foil which slows the particles on average but leads to large particle losses and energy spread due to straggling effects, so only a small fraction of the antiproton source can typically be trapped. We propose a simple scheme for longitudinal slowing and cooling of the antiproton beam delivered by the AD, utilizing an optional deceleration section, based on either an induction linac or rf quadrupole (RFQ), followed by a degrading foil and a frictional cooling section. The frictional cooling stage consists of a series of thin carbon foils separated by reaccelerating electrostatic gradients Such a scheme would not be quite as effective as ELENA would be, but is an adequate and available option for antiproton experiments, at lower costs and with a smaller footprint. Advantages and limitations of the scheme, and of future directions for study
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