The Antiproton Decelerator of CERN began operation in 1999 to serve experiments for studies of CPT invariance by precision laser and microwave spectroscopy of antihydrogen ($\bar{\rm H}$) and antiprotonic helium ($\bar{p}{\rm He}^+$). The first 12 years of operation saw cold $\bar{\rm H}$ synthesized by overlapping clouds of positrons ($e^+$) and antiprotons ($\bar{p}$) confined in magnetic Penning traps. Cold $\bar{\rm H}$ was also produced in collisions between Rydberg positronium atoms and $\bar{p}$. Ground-state $\bar{\rm H}$ was later trapped for up to $\sim 1000$ s in a magnetic bottle trap, and microwave transitions excited between its hyperfine levels. In the $\bar{p}{\rm He}^+$ atom, UV transitions were measured to a precision of (2.3-5) $\times$ $10^{-9}$ by sub-Doppler two-photon laser spectroscopy. From this the antiproton-to-electron mass ratio was determined as $M_{\bar{p}}/m_e=$1836.1526736(23), which agrees with the p value. Microwave spectroscopy of $\bar{p}{\rm He}^+$ yielded a measurement of the $\bar{p}$ magnetic moment with a precision of 0.3%. More recently the magnetic moment of a single $\bar{p}$ confined in a Penning trap was measured with a higher precision, as $\mu_{\bar{p}}=-2.792845(12)$$\mu_{\rm nucl}$ in nuclear magnetons. Other measurements include the energy loss of 1-100 keV $\bar{p}$ traversing conductor and insulator targets; the cross sections of <10 keV $\bar{p}$ ionizing gas targets; and the cross sections of 5-MeV $\bar{p}$ annihilating on target foils via nuclear collisions. The biological effectiveness of $\bar{p}$ beams destroying cancer cells was measured as a possible method for radiological therapy. New experiments under preparation attempt to measure the gravitational acceleration of $\bar{\rm H}$ or synthesize $\obar{\rm H}^+$.

Physics at CERN's Antiproton Decelerator

At the last LEAP conference in Vancouver 2011 the authors stated that a project ”ELENA”, as an abbreviation for Extra Low ENergy Antiproton ring and as first discussed in 1982 for LEAR by H. Herr et al., was freshly proposed with a substantial new design and revised layout and that it was under consideration to be built at CERN. ELENA is an upgrade of the Anti-proton Decelerator (AD) at CERN and is devoted to special experiments with physics using low energy anti-protons. The main topics are the anti-hydrogen production and consecutive studies of the features of this anti-matter atom as well as the anti-proton nucleon interaction by testing the QED to high precision. During the last years the project underwent several steps in presentations at different committees at CERN and was finally approved such that the construction has started. ELENA will increase the number of useful anti-protons by about two orders of magnitude and will allow to serve up to four experiments simultaneously. Very first and convincing results from the experiments at the AD have been published recently. For high precision physics, however, it appears to be cumbersome, time consuming and ineffective when collecting the needed large numbers and high densities of anti-proton clouds with the present AD. Both the effectiveness and the availability for additional experiments at this unique facility will drastically increase, when the anti-proton beam of presently 5 MeV kinetic energy is reduced by the additional decelerator ELENA to 100 keV.

ELENA: the extra low energy anti-proton facility at CERN

/pdf/summary-and-conclusions-of-the-meeting-2wokfhhl71.pdf

Summary and Conclusions of the Meeting

This report sums up in two volumes the first 50 years of operation of the CERN Proton Synchrotron. After an introduction on the genesis of the machine, and a description of its magnet and powering systems, the first volume focuses on some of the many innovations in accelerator physics and instrumentation that it has pioneered, such as transition crossing, RF gymnastics, extractions, phase space tomography, or transverse emittance measurement by wire scanners. The second volume describes the other machines in the PS complex: the proton linear accelerators, the PS Booster, the LEP pre-injector, the heavy-ion linac and accumulator, and the antiproton rings.

/pdf/fifty-years-of-the-cern-proton-synchrotron-volume-2-3de7u29zph.pdf

Fifty years of the CERN Proton Synchrotron : Volume 2

This paper gives an overview of the evolution of stochastic beam cooling from the very beginning (in 1968) until the present-day (2011). The early history, the main achievements and the growing number of the worldwide applications are outlined.

/pdf/history-of-stochastic-beam-cooling-and-its-application-in-4bbyaqcjiw.pdf

History of stochastic beam cooling and its application in many different projects

To produce dense antiproton beams at very low energies (100 keV), it has been proposed to install a small decelerator ring between the existing AD ring and the experimental area. Phase-space blowup during deceleration is compensated by electron cooling such that the final emittances are comparable to the 5MeV beam presently delivered by the AD. An immediate consequence is a significant increase in the number of trapped antiprotons at the experiments as outlined in the proposal CERN/SPSC-2009-026; SPSC-P-338. This report describes the machine parameters and layout of the proposed ELENA (Extra Low ENergy Antiproton) ring and also gives an approximate estimate of cost and manpower needs. Since the initial estimate, published in 2007 (CERN-AB-2007-079), the ELENA design has evolved considerably. This is due to a new location in the AD hall to accommodate for the possibility of another experimental zone, as suggested by the SPSC, and also due to improvements in the ring optics and layout. The cost estimate that is presented is based on the initial document and has been updated according to the improvements in the design and layout. Where applicable, inflation has also been taken into account. The SPSC has recognized the substantial potential impact of ELENA on the AD experimental program and “strongly supports the ELENA proposal” (minutes of the meeting 29.09.2009) and the RB endorsed the conclusion from the SPSC concerning the strong scientific case for ELENA (minutes of the meeting 02.12.2009).

/pdf/elena-an-updated-cost-and-feasibility-study-36nr5tcm2v.pdf

ELENA – An Updated Cost and Feasibility Study

The situation of the present pre-injection complex will be discussed with particular emphasis on the performance limitations. Mitigation measures will be discussed assuming that substantial consolidation work can be devoted to such improvements. Possible scenarios for the implementation of these measures will be outlined, together with an analysis of the impact on the performance of the LHC machine.

/pdf/possible-improvements-to-the-existing-pre-injector-complex-zcpr2wn2lj.pdf

Possible improvements to the existing pre-injector complex in the framework of continued consolidation

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ELENA – An Updated Cost and Feasibility Study

Possible improvements to the existing pre-injector complex in the framework of continued consolidation