The SPS as injector for LHC: Conceptual design

The LHC will be supplied with protons from the injector chain Linac2 - PS Booster - PS - SPS. These accelerators are being upgraded so as to meet the very demanding needs of the LHC: many high intensity bunches (25 ns spacing) with small emittances (transverse and longitudinal). The injector scheme which will satisfy these requirements is presented and the main challenges and problems for the machines are outlined. Some of the open issues which need further elaboration, such as tolerances on bunch intensity, are touched upon. The conversion of the PS complex enters its final phase and the first LHC-type beams have been delivered to the SPS. Finally, the Pb ion injector scheme is sketched and the promising outcome of a test campaign in LEAR is highlighted.

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The injector chain for the lhc

A 40 MHz cavity has been designed and built at CERN as part of the preparation of the PS as injector for LHC. The cavity will provide the necessary bunch spacing of 25 ns prior to injection into SPS and subsequently LHC. The mechanical design of the copper coated steel cavity was dominated by space constraints in the PS tunnel and by vacuum requirements. The salient design features described are (i) tight, multipactor-free, capacitive coupling from the power amplifier, (ii) fast RF feedback, (iii) inductively coupled tuners, (iv) an efficient, pneumatically operated gap short-circuit. The operation cycle consists of an adiabatic capture up to 100 kV gap voltage, a non-adiabatic jump to 300 kV, and subsequent bunch rotation. The multipactor voltage level at the gap lies below the operating voltage range and is easily passed through. A fast RF feedback system with a total group delay of 220 ns copes with heavy beam loading (10/sup 11/ protons/bunch) and prevents unwanted interaction with other beams in the PS. The cavity has recently been installed, the nominal gap voltage of 300 kV has been attained, and bunch lengths below 8 ns have been achieved in first tests at nominal intensity. Experimental results are reported.

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The PS 40 MHz bunching cavity

M. Benedikt, A. Blas, J. Borburgh, R. Cappi, M. Chanel, V. Chohan, G. Daems, A. Fowler, R. Garoby, J. Gonzalez, D. Grier, J. Gruber, S. Hancock, C.E. Hill, A. Jansson, E. Jensen, A. Krusche, P. Maesen, K.D. Metzmacher, R. Losito, J. Olsfors, M. Paoluzzi, J. Pedersen, U. Raich, J.P. Riunaud, J.P. Royer, M. Sassowsky, K. Schindl, H. Schönauer, L. Sermeus, M. Thivent, H. Ullrich, W. Van Cauter, F. Völker, M. Vretenar.

The PS Complex as Proton Pre-Injector for the LHC - Design and Implementation Report

A technique for splitting bunches into three has recently been proposed as an alternative to debunchingrebunching in a synchrotron[1]. The preservation of longitudinal emittance and the possibility of maintaining a gap in the bunch train are key features expected from this new process. A proof of principle has been established experimentally at the CERN PS in 1999. This showed that the nominal longitudinal characteristics of the proton beam for the LHC could be achieved at the exit of the PS with the help of triple splitting. The method is described and experimental results presented. Other possible applications are sketched.

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Demonstration of bunch triple splitting in the cern ps

CERN's Large Hadron Collider (LHC) will be supplied with protons from the injector chain Linac2-PS Booster (PSB)-PS-SPS. The required transverse beam brilliance (intensity/emittance) is almost twice that of current PS beams and the LHC bunch spacing of 25 ns must be impressed on the beam before its transfer to the SPS. The scheme involves new RF harmonics in the PSB and the PS, an increase of the PSB energy, and two-batch filling of the PS. After a successful test of the main ingredients, a project for converting the PS complex was launched in 1994. Major additions are: (i) h=1 RF systems in the PSB, (ii) upgrading of the PSB main magnet supply from 1 to 1.4 GeV operation, (iii) new magnets, septa, power supplies, kicker pulsers for the PSB-PS beam transfer, (iv) 40 and 80 MHz systems in the PS, (v) beam profile measurement devices with improved resolution. A significant part of the effort is being provided by TRIUMF under the Canada-CERN co-operation agreement on the LHC.

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Conversion of the PS complex as LHC proton pre-injector

The LHC [1] will be supplied, via the SPS, with protons from the pre-injector chain comprising Linac2, PS Booster (PSB) and PS. These accelerators have undergone a major upgrading programme [2] during the last five years so as to meet the stringent requirements of the LHC. These imply that many high-intensity bunches of small emittance and tight spacing (25 ns) be available at the PS extraction energy (25 GeV). The upgrading project involved an increase of Linac2 current, new RF systems in the PSB and the PS, raising the PSB energy from 1 to 1.4 GeV, two-batch filling of the PS and the installation of high-resolution beam profile measurement devices. With the project entering its final phase and most of the newly installed hardware now being operational, the emphasis switches to producing the nominal LHC beam and tackling the associated beam physics problems. While a beam with transverse characteristics better than nominal has been obtained, the longitudinal density still needs to be increased. An alternative scheme to produce the 25 ns bunch spacing is outlined, together with other promising developments.

The ps complex produces the nominal lhc beam

This report summarises the feasibility study of a neutron time-of-flight facility at the CERN-PS as described in Refs. [1] and [2]. The idea is to extract at 24 GeV/cproton bunches (r.m.s. length ~7 ns) on to a target. The neutrons produced by spallation are directed to an experimental area located 230 m downstream throughout a vacuum pipe (diameter ~80 cm) making use of the existing TT2A tunnel about 7 m below the ISR tunnel.

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U. Raich

Papers

The PS Complex as Proton Pre-Injector for the LHC - Design and Implementation Report

Conversion of the PS complex as LHC proton pre-injector

The ps complex produces the nominal lhc beam

Feasibility Study of a Neutron Time Of Flight Facility at the CERN-PS