Design of the Superconducting Section of the SPL LINAC at CERN

In order to set up a powerful proton source for a future Neutrino Factory, increasing at the same time the flux of protons available for new and existing facilities, CERN is studying a 2.2 GeV superconducting H- linac for 4 MW beam power, called SPL. The superconducting part of this linac covers the energy range from 120 MeV to 2.2 GeV. Three sections made of 352 MHz cavities with nominal ß of 0.52, 0.7 and 0.8 bring the beam energy up to 1 GeV. From this energy, superconducting cavities from LEP, or ß =0.8 cavities, can be used to reach the final energy of 2.2 GeV. This paper covers the optimisation for the superconducting part, the beam dynamics design principles, the matching between sections, and the results of multiparticle simulations with up to 50 million particles. To demonstrate the stability of the design matched and mismatched input beams are used

Design and Development of RF Structures for Linac4

Linac4 is a new 160 MeV Hâ linac proposed at CERN to replace the 50 MeV Linac2 as injector to the PS Booster, with the goal of doubling its brightness and intensity. The present design foresees after RFQ and chopping line a sequence of three accelerating structures: a Drift Tube Linac (DTL) from 3 to 40 MeV, a Cell-Coupled DTL (CCDTL) to 90 MeV and a Side Coupled Linac (SCL) up to the final energy. The DTL and CCDTL operate at 352 MHz, while in the SCL the frequency is doubled to 704 MHz. Although the injection in the PS Booster requires only a low duty cycle, the accelerating structures are designed to operate at the high duty cycle required by a possible future extension to a high-power linac driver for a neutrino facility. This paper presents the different accelerating structures, underlining the progress in the design of critical resonator elements, like post-couplers in the DTL, coupling slots in the CCDTL and bridge couplers for the SCL. Prototyping progress for the different structures is reported, including the RF design of a DTL tank prototype and results of low- and high-power tests on a CCDTL prototype

Comparison of Options for the Injector of PS2

In its report, the SPC Review Panel has highlighted that the construction of a 4 MW SPL has to be motivated by the needs of a well-defined and approved physics programme, and that it should be compared with a Rapid Cycling Synchrotron (RCS) when considering only the needs of LHC. This report is meant to answer these remarks by describing the version of the SPL that would be built for the needs of LHC alone (the Low Power SPL or LP-SPL) and by making a preliminary comparison with an RCS

A Search for Instantons at HERA

A search for QCD instanton (I) induced events in deep-inelastic scattering (DIS) at HERA is presented in the kinematic range of low x and low Q^2. After cutting into three characteristic variables for I-induced events yielding a maximum suppression of standard DIS background to the 0.1% level while still preserving 10% of the I-induced events, 549 data events are found while 363^{+22}_{-26} (CDM) and 435^{+36}_{-22} (MEPS) standard DIS events are expected. More events than expected by the standard DIS Monte Carlo models are found in the data. However, the systematic uncertainty between the two different models is of the order of the expected signal, so that a discovery of instantons can not be claimed. An outlook is given on the prospect to search for QCD instanton events using a discriminant based on range searching in the kinematical region Q^2\gtrsim100\GeV^2 where the I-theory makes safer predictions and the QCD Monte Carlos are expected to better describe the inclusive data.Comment: Invited talk given at the Ringberg Workshop on HERA Physics on June 19th, 2001 on behalf of the H1 collaboratio

Development of RF System Model for CERN Linac2 Tanks

An RF system model has been created for the CERN Linac2 Tanks. RF systems in this linac have both single and double feed architectures. The main elements of these systems are: RF power amplifier, main resonator, feed-line and the amplitude and phase feedback loops. The model of the composite system is derived by suitably concatenating the models of these individual sub-systems. For computational efficiency the modeling has been carried out in the base band. The signals are expressed in in-phase - quadrature domain, where the response of the resonator is expressed using two linear differential equations, making it valid for large signal conditions. MATLAB/SIMULINK has been used for creating the model. The model has been found useful in predicting the system behaviour, especially during the transients. In the paper we present the details of the model, highlighting the methodology, which could be easily extended to multiple feed RF systems

RF Structures for Linac4

Linac4 is proposed to replace the existing proton linac at CERN (Linac2). Using an increased injection energy of 160 MeV instead of 50 MeV, Linac4 is expected to double the beam intensity in the PS Booster (PSB) and will thus be the first step towards higher brightness beams in the LHC. In this paper we re-assess the choice of RF structures for Linac4. Different accelerating structures for different energy ranges are compared in terms of RF efficiency, ease of construction and alignment, and necessary infrastructure. Eventually we present the final choice for Linac4

High gradient tests of an 88 MHz RF cavity for muon cooling

The scheme for a Muon Cooling channel developed at CERN in the frame of Neutrino Factory studies foresees the use of 44 and 88 MHz cavities operating at a real-estate gradient as high as 4 MV/m. To assess the feasibility of this scheme, including high-gradient operation at relatively low frequency and the production and handling of high RF peak powers, a test stand was assembled at CERN. It included an 88 MHz resonator reconstructed from a 114 MHz cavity previously used for lepton acceleration in the PS, a 2.5 MW final amplifier made out of an old linac unit improved and down-scaled in frequency, and a PS spare amplifier used as driver stage. After only 160 hours of conditioning the cavity passed the 4 MV/m level, with local peak surface field in the gap exceeding 25 MV/m (2.4 times the Kilpatrick limit). The gradient was limited by the amplifier power, the maximum RF peak output power achieved during the tests being 2.65 MW. This paper presents the results of the tests, including an analysis of field emission from the test cavity, and compares the results with the experience in conditioning ion linac RF cavities at CERN