Maurizio Vretenar, CERN, PS Division, CH-1211 Genève 23

In the line of many ideas to re-use the LEP Superconducting RF system, a proposal was made for the construction of a 2 GeV Superconducting Proton Linac (SPL) to inject H- ions into the CERN Proton Synchrotron (PS) [1,2]. The purpose of this linear accelerator was to improve the beam brightness in the PS by a factor 2, as compared to the present scheme for LHC injection. The LHC could thus operate in the regime of beam-beam limit and reach the ultimate luminosity. In fact, the spectrum of applications for an intense linac is much broader than its use as an element of the LHC injector. New generation of stopping muon experiments and of radio-active beams for facilities such as ISOLDE become possible. Moreover, using intense beams at relatively low energy is the most economic way of producing pions in terms of particles per watt; a high power linac is thus an excellent candidate to drive the proton beam in a muon collider or a neutrino factory complex.

The accelerator is made-up of a conventional drift-tube linac up to an energy of 100 MeV, a superconducting section made ofwith new low-b cavities up to 1 GeV, and standard LEP SC cavities up to the energy of 2 GeV. For the LHC needs, the linac would accelerates 10 mA of H¯ pulsing at the low duty cycle required by the PS. The beam will beis chopped at low energy to minimise capture losses. The RF cavities used in the energy range between 1 and 2 GeV, other major cryogenic components and the entire RF infrastructure can be recuperated from LEP leading to a cost-effective machine. The main elements to be constructed are the 100 MeV room temperature linac, new SC cavities and cryostats from 100 MeV to 1 GeV, the focusing and diagnostic equipment and the cryoplant. New civil engineering is needed for a 900900-m long tunnel and an equipment gallery.

The pulsed operation is likely to be needed for muon colliders as well as for LHC but a CW operation may be interesting for a neutrino factory; extra cooling power has then to be installed. With an adequate 100 MeV CW injector, Thisthis linac has the inherent potentiality could deliver a continuous beam of to accelerateprotons. For a linac. Assuming 10 mA beam current at 2 GeV, the beam power is 20 MW and of 10 mA the proton flux 6 ´ 1016 p/s or more than three orders of magnitude over the present PS intensityfor a proton energy of 2 GeV. Expenditures for extra cooling power can be distributed in time to match the needs for increased flux.In an evolutive scenario,

Few modifications to the SPL basic design are required for CW operation. A second proton injector (particle source and an RFQ accelerator up to 2 MeV) has to be built and connected to the main linac by a switching magnet to operate in parallel with the H¯ low duty cycle injector. The room temperature linac cavities have to be specifically slightly re-designed for CW operation and the cryogenic power will be nearly doubled tripled by the additional RF losses. The SC cavities and the RF systems are perfectly adapted for running CW with 10 mA current, as they do now for LEP., but energy consumption increases up to 70 MW.

The mainA key concern is the radiation safety for a beam power of 20 MW. In order to allow hands-on maintenance, losses in the linac have to be kept below 0.5 nA/m, a challenging figure that requires sophisticated collimation systems and a careful control of beam halo formation. The large aperture of the LEP SC cavities is an advantage in this respect because most of the halo particles are transported to the end of the linac and dumped into the target area where radiation issues are specifically addressed. Another factor to be considered is that in CW mode the electric plug power consumption of the linac would be about 70 MW.

The Table below summarises some of the parameters of the SPL for in the CW mode of operation.

Beam Current
Beam Transverse Emittance
mm, rms, normalised
Beam Energy Spread
± 2
MeV, total (Ö 5s)
Bunch Length
psec, total (Ö 5s)
Linac Length
Overall RF Power
Number of klystrons





[1] R. Garoby, M. Vretenar, "Proposal for a 2 GeV Linac Injector for the CERN PS", PS/RF/Note 96-27.

[2] D. Boussard, R. Cappi, R. Garoby, H. Haseroth, C.E. Hill, P. Knaus, A.M. Lombardi, M. Martini, P.N. Ostroumov, J.M. Tessier, M. Vretenar, "Report of the Study Group on a Superconducting Proton Linac as a PS Injector", CERN/PS 98-063 (RF/HP).