C. Carli

Matching to gantries for medical synchrotrons

Treatment of tumours by hadron-therapy is greatly improved if the patient can be irradiated from different directions. This task is performed by a gantry, i.e. a section of beam line that can be rotated around the patient. The gantry optics have to be designed in such a way that the beam at the patient is independent of the rotation angle. The various matching techniques are briefly reviewed in the light of the current development in medical synchrotrons towards active scanning, which requires a small, high-precision beam spot at the patient. In particular, beam delivery systems with rotators are discussed.

Measurement of the lifetime of Pb52+, Pb53+ and Pb54+ beams at 4.2 MeV per nucleon subject to electron cooling

Abstract By measuring the lifetime of stored beams, the recombination of the ions with cooling electrons was investigated. Rates found are larger than expected for radiative electron capture and significantly higher for Pb53+ than for Pb54+ and Pb52+. These results are important for the design of the lead ion injection system for the Large Hadron Collider and for recombination theories.

Performance potential of the injectors after LS1

The main upgrades of the injector chain in the framework of the LIU Project will only be implemented in the second long shutdown (LS2), in particular the increase of the PSB-PS transfer energy to 2GeV or the implementation of cures/solutions against instabilities/e-cloud effects etc. in the SPS. On the other hand, Linac4 will become available by the end of 2014. Until the end of 2015 it may replace Linac2 at short notice, taking 50MeV protons into the PSB via the existing injection system but with reduced performance. Afterwards, the H− injection equipment will be ready and Linac4 could be connected for 160MeV H− injection into the PSB during a prolonged winter shutdown before LS2. The anticipated beam performance of the LHC injectors after LS1 in these different cases is presented. Space charge on the PS flat-bottom will remain a limitation because the PSB-PS transfer energy will stay at 1.4GeV. As a mitigation measure new RF manipulations are presented which can improve brightness for 25 ns bunch spacing, allowing for more than nominal luminosity in the LHC.

Commissioning and first operation of the Antiproton Decelerator (AD)

The Antiproton Decelerator (AD) is a simplified source of antiprotons which provides low energy antiprotons for experiments, replacing four machines: AC (Antiproton Collector), AA (Antiproton Accumulator); PS and LEAR (Low Energy Antiproton Ring), shutdown in 1996. The former AC was modified to include deceleration and electron cooling. The AD started operation in July 2000 and has since delivered cooled beam at 100 MeV/c (kinetic energy of 5.3 MeV) to 3 experiments (ASACUSA, ATHENA and ATRAP) for 1500 h. The flux (up to 2.5 /spl times/ 10 pbar /s delivered in short pulses of 330 ns every 110 s) and the quality of the ejected beam are not far from the design specifications. A linear RF quadrupole decelerator (RFQD) was commissioned in November 2000 to post-decelerate the beam for ASACUSA from 5.3 MeV to about 15 keV. Problems encountered in converting the fixed energy AC into a decelerating machine will be outlined, and the present status of the AD, including the performance of the cooling systems and the special diagnostics to cope with beams of less than 10/sup 7/ pbars, will be reviewed. Possible future developments will be sketched.

Feasibility study for a biomedical experimental facility based on LEIR at CERN

In light of the recent European developments in ion beam therapy, there is a strong interest from the biomedical research community to have more access to clinically relevant beams. Beamtime for pre-clinical studies is currently very limited and a new dedicated facility would allow extensive research into the radiobiological mechanisms of ion beam radiation and the development of more refined techniques of dosimetry and imaging. This basic research would support the current clinical efforts of the new treatment centres in Europe (for example HIT, CNAO and MedAustron). This paper presents first investigations on the feasibility of an experimental biomedical facility based on the CERN Low Energy Ion Ring LEIR accelerator. Such a new facility could provide beams of light ions (from protons to neon ions) in a collaborative and cost-effective way, since it would rely partly on CERNs competences and infrastructure. The main technical challenges linked to the implementation of a slow extraction scheme for LEIR and to the design of the experimental beamlines are described and first solutions presented. These include introducing new extraction septa into one of the straight sections of the synchrotron, changing the power supply configuration of the magnets, and designing a new horizontal beamline suitable for clinical beam energies, and a low-energy vertical beamline for particular radiobiological experiments.

Heavy Ions in 2011 and beyond

The LHCs first heavy ion run set and tested the operational pattern for 2011 and later years: a rapid commissioning strategy intended to ensure delivery of integrated luminosity despite the risks associated with the short time-frame. It also gave us hard data to test our understanding of the beam physics that will limit performance. The 2010 experience is fed into the commissioning plan, parameter choices and projected performance for 2011. The prospects for future stages of the LHC ion program, Pb-Pb collisions at higher energy and luminosity, hybrid collisions and other species, depend critically on the scheduling of certain hardware upgrades.

Optics considerations for the PS2

CERN envisages replacing the existing proton synchrotron (PS) with a larger synchrotron (PS2) capable of injecting at higher energy into the SPS. Since it should increase the performance not only of the LHC but also CNGS and other users of beams from CERNs hadron injector complex, the new accelerator must retain much of the flexibility of the present complex. A number of candidate optics, with and without transition crossing, have been evaluated systematically and compared.

A Collimation Scheme for Ions Changing Charge State in the Leir Ring

Avalanche-like pressure rise and an associated decrease of the beam life-time, caused by (i) beam loss due to charge exchange interactions with rest gas molecules, (ii) electron capture from the electron beam of the electron cooler and (iii) ion impact induced outgassing, is a potential limitation for heavy ion accelerators. The vacuum system of the LEIR ring has to be upgraded to reach the dynamical vacuum pressure in the low 10− 12 Torr range necessary to reach design performance. A collimation system to intercept lost ions by absorber blocks made of low beam-induced out-gassing material will be installed. This paper reviews the collimation scheme and simulations of beam loss patterns around the ring.

Optics for the Antiproton Decelerator at CERN

The former Antiproton Collector (AC) at CERN has been transformed into an Antiproton Decelerator (AD) to supply high quality antiproton beams with a momentum of 100 MeV/c (kinetic energy of 5.3 MeV). As in AC, antiprotons are injected at 3.57 GeV/c and cooled by stochastic cooling system. To facilitate the deceleration and to prepare a small emittance beam for the experiments, stochastic cooling at 2 GeV/c and electron cooling at 300 MeV/c and 100 MeV/c has been incorporated. The required optics modifications are described and the results of machine commissioning are discussed.

On the optimum dispersion of a storage ring for electron cooling with high space charge

Abstract With the intense electron beams used for cooling, matching of the ion and electron velocity over the largest possible fraction of the beam profile becomes important. In this situation, a finite dispersion from the ring in the cooling section can lead to an appreciable gain in the transverse cooling speed. Based on a simple model of the cooling force, an expression for the “optimum” dispersion as a function of the electron beam intensity, the momentum spread and other properties of the ion beam will be derived. This simple theory will be compared to measurements made on the low-energy ion ring (LEIR) at CERN during 1997.