Pulse to pulse modulation of the CERN PS complex

The CERN PS complex (CPS) comprises three accelerators in series: the 50 MeV Linac, the 800 MeV Booster (PSB) and the 28 GeV main synchrotron (PS). Since the beginning of May 1976 this complex has delivered beams to three main users: the 400 GeV SPS, the 30 GeV ISR and the 25 GeV PS experimental areas

A Low Emittance Lattice for the CLIC Damping Ring

Damping rings with very small normalized equilibrium emittance and short damping times are required to deliver trains of bunches with a high repetition rate for the high-luminosity linear colliders. Using analytic expressions for the equilibrium emittance as a function of deflection angle per dipole, as well as the expression for the Twiss parameters providing the minimum emittance, a strategy to stay close to this mini-mum is described. In order to get as close as possible to the optimum Twiss parameters values, a quadruplet lattice with high horizontal phase advance is introduced. Finally, this approach is illustrated for the particular case of the CLIC damping ring and the resulting performance is described

Fundamental Design Principles of Linear Collider Damping Rings, with an Application to CLIC

Damping Rings for Linear Colliders have to produce very small normalised emittances at a high repetition rate. A previous paper presented analytical expressions for the equilibrium emittance of an arc cell as a function of the deflection angle per dipole. In addition, an expression for the lattice parameters providing the minimum emittance, and a strategy to stay close to this, were proposed. This analytical approach is extended to the detailed design of Damping Rings, taking into account the straight sections and the damping wigglers. Complete rings, including wiggler and injection insections, were modelled with the MAD [1] program, and their performance was found to be in good agreement with the analytical calculation. With such an approach it is shown that a Damping Ring corresponding to the Compact Linear Collider (CLIC) parameters at 0.5 and 1 TeV centre-of-mass energy, and tunable for two different sets of emittance and injection repetition rate, can be designed using the same ring layout

The LEP Pre-Injector as a Multipurpose Facility

The LEP Pre-Injector (LPI) provides electron and positron beams at 500 MeV. In 1988, it was used for the first time to produce single electrons at 180 MeV in order to calibrate the L3 detector. Since this first experiment a dedicated irradiation area has been built downstream of the linac. This facility uses electron beams with an energy range adjustable from 180 MeV to 700 MeV with intensity, pul se duration and repetition rate, which can be varied within wide limits. Some LEP detectors, and almost all future LHC (Large Hadron Collider) detectors, have already used this facility intensively. W hen the LPI accumulator works at 308 MeV, the critical energy of the synchrotron light radiated in the bending magnets is 45 eV. It corresponds to the synchrotron radiation which will be produced by 7 TeV protons in the LHC. To study the crucial issue of desorption in the LHC vacuum chamber a first synchrotron light line, at room temperature, has been installed followed by a second one for cryogeni c temperatures. This paper reviews the experiments that have been done, the beam characteristics for these facilities and the possible evolutions in the near future

Isochronous Optics and Related Measurements in EPA

The time structure of the CLIC (Compact Linear Collider) drive beam is obtained by the combination of electron bunch trains in rings using RF deflectors [1]. The rings must be isochronous, in order to preserve the bunch length and separation during the combination process (4-5 turns). A first isochronicity test has been performed in the CERN EPA (Electron Positron Accumulator) ring. The calculated isochronous lattice can be obtained by changing the strength of existing quadrupole families without hardware modifications. Measurements of the synchrotron frequency and of the beam's time structure have been made for both the normal and the isochronous lattices. Streak camera measurements of the bunch length have been used to tune the lattice around the isochronous point. The bunch length increases rapidly over a few turns in the normal case, while no appreciable bunch lengthening is observed over 50 turns in the isochronous case. A quantitative evaluation of the momentum compaction is obtained by measuring the bunch separation in a train when close to, and far from, the isochronous condition. Plans for future tests in the EPA ring are also outline

Hodge polynomials of some moduli spaces of Coherent Systems

When $k<n$, we study the coherent systems that come from a BGN extension in which the quotient bundle is strictly semistable. In this case we describe a stratification of the moduli space of coherent systems. We also describe the strata as complements of determinantal varieties and we prove that these are irreducible and smooth. These descriptions allow us to compute the Hodge polynomials of this moduli space in some cases. In particular, we give explicit computations for the cases in which $(n,d,k)=(3,d,1)$ and $d$ is even, obtaining from them the usual Poincar\'e polynomials.Comment: Formerly entitled: "A stratification of some moduli spaces of coherent systems on algebraic curves and their Hodge--Poincar\'e polynomials". The paper has been substantially shorten. Theorem 8.20 has been revised and corrected. Final version accepted for publication in International Journal of Mathematics. arXiv admin note: text overlap with arXiv:math/0407523 by other author

Curve counting via stable pairs in the derived category

For a nonsingular projective 3-fold $X$, we define integer invariants virtually enumerating pairs $(C,D)$ where $C\subset X$ is an embedded curve and $D\subset C$ is a divisor. A virtual class is constructed on the associated moduli space by viewing a pair as an object in the derived category of $X$. The resulting invariants are conjecturally equivalent, after universal transformations, to both the Gromov-Witten and DT theories of $X$. For Calabi-Yau 3-folds, the latter equivalence should be viewed as a wall-crossing formula in the derived category. Several calculations of the new invariants are carried out. In the Fano case, the local contributions of nonsingular embedded curves are found. In the local toric Calabi-Yau case, a completely new form of the topological vertex is described. The virtual enumeration of pairs is closely related to the geometry underlying the BPS state counts of Gopakumar and Vafa. We prove that our integrality predictions for Gromov-Witten invariants agree with the BPS integrality. Conversely, the BPS geometry imposes strong conditions on the enumeration of pairs.Comment: Corrected typos and duality error in Proposition 4.6. 47 page

A Low Charge Demonstration of Electron Pulse Compression for the CLIC RF Power Source

The CLIC (Compact Linear Collider) RF power source is based on a new scheme of electron pulse compression and bunch frequency multiplication using injection by transverse RF deflectors into an isochronous ring. In this paper, we describe the modifications needed in the present LEP Pre-Injector (LPI) complex at CERN in order to perform a low-charge test of the scheme. The design of the injector (including the new thermionic gun), of the modified linac, of the matched injection line, and of the isochronous ring lattice, are presented. The results of preliminary isochronicity measurements made on the present installation are also discussed.Comment: 3 pages, 5 figures, submitted to the LINAC 2000 Conferenc