The goal of the Linac4 project is to build a 160 MeV H− linear accelerator replacing Linac2 as injector to the PS Booster (PSB). The new linac is expected to increase the beam brightness out of the PSB by a factor of 2, making possible an upgrade of the LHC injectors for higher intensity and eventually an increase of the LHC luminosity.
Furthermore, Linac4 is designed for possible operation at high-duty cycle (5%), if required by future high-intensity programs (SPL).
Linac4 will be located in an underground tunnel connected to the Linac4-PSB transfer line. A surface building will house RF equipment, power supplies, electronics and other infrastructure.
The Linac4 commissioning with beam is expected to take place in 2013/14; the connection to the PSB will depend on the program for long-shut downs of the LHC.
The main Linac4 beam parameters are as follows:

Ion species H-
Output energy 160 MeV
Bunch frequency 352.2 MHz
Max. rep. rate 2 Hz
Beam pulse Length 400 microsec
Chopping scheme 222/133 transmitted bunches/empty buckets
Mean pulse current 40 mA
Beam power 5.1 kW
N. particles per pulse 1.0 ·1014
N. particles per bunch 1.14 ·109
Beam transverse emittance 0.4  pmm mrad (rms)

Linac4 is composed of an ion source, a Front-end (Radio Frequency Quadrupole and a chopper line), an Alvarez Drift Tube Linac (DTL), a Cell-Coupled Drift Tube Linac (CCDTL) and a Pi-mode structure (PIMS), for an overall length of 86 metres. A 70 m long transfer line joins the present Linac2 to the PSB line. The RF accelerating structures will operate at 352.2 MHz frequency, re-using some RF equipment from LEP (klystrons, circulators and waveguides) and taking advantage of existing RFQ technology. Charge exchange injection will be implemented in the PSB, together with the modifications required in the PSB injection line to cope with the higher injection energy.
Although the duty cycle for the PSB does not exceed 0.1%, all the accelerating structures are designed for a maximum duty cycle of 5%, to allow for future operation of Linac4 as the first part of a high-power SPL (Superconducting Proton Linac).

The Linac4 basic architecture is shown here:

The Linac4 systems layout

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