117099859
Collective dynamics of duffing oscillators: Model for dipole ripple
The emittance growth due to power supply ripple in dipoles is modeled by the collective behavior of forced Duffing oscillators. The method of averaging reduces the problem to an autonomous system. A coarse grained long time limit of the phase space density and the rate of approach to this limit are discussed in terms of the autonomous system. The equilibrium density, the rate of approach to equilibrium and the equilibrium values depend crucially on the detuning parameter. We find the frequencies which lead to the largest emittance growth in three different forcing regimes and also characterize the dependence of emittance growth on forcing amplitude in these regimes.
56450130
Impedance description of coherent synchrotron radiation with account of bunch deformation
We are concerned with coherent longitudinal motion in a storage ring, especially with situations in which coherent synchrotron radiation (CSR) can in∞uence stability of the beam. The collective force from CSR is usually described by an impedance or a wake function in such a way that the force depends only on the charge distribution at the present time. This description is exact only for a rigid bunch, since causality demands that the force depend on the prior history of the bunch. We show how to treat a deforming bunch by applying the \complete impedance" Z(n;!), a function of wave number and frequency. We derive this impedance and study its analytic properties for a special model: radiation from circular orbits shielded by parallel plates representing the metallic vacuum chamber. We analyze the corresponding collective force, obtaining the usual formula as a flrst approximation, plus easily computed corrections that depend on present and prior values of the time derivative of the charge density. In related papers we have applied these results in numerical simulations of instabilities induced by CSR. PACS numbers: Valid PACS appear here
39490210
Equilibrium fluctuations in an N-particle coasting beam: Schottky noise effects
We discuss the longitudinal dynamics of an unbunched beam with a collective effect due to the vacuum chamber and with the discreteness of an N-particle beam (Schottky noise) included. We start with the 2N equations of motion (in angle and energy) with random initial conditions. The 2D phase space density (Klimontovich density) for the N particles is a sum of delta functions and satisfies the Klimontovich equation and the Vlasov equation. An arbitrary function of the energy also satisfies the Vlasov equation and we linearize about a convenient equilibrium density taking the initial conditions to be independent, identically distributed random variables with the equilibrium distribution. The linearized equations can be solved using a Laplace transform in time and a Fourier series in angle. The resultant stochastic process for the phase space density is analyzed and compared with a known result. Work is in progress to study the full nonlinear problem.
15693839
Self-consistent computation of electromagnetic fields and phase space densities for particles on curved planar orbits
We discuss our progress on the self-consistent calculation of the 4D phase space density (PSD) and electromagnetic fields in a Vlasov-Maxwell formulation. We emphasize coherent synchrotron radiation (CSR) from arbitrary curved planar orbits, with shielding from the vacuum chamber, but space charge forces are naturally included. Our focus on the Vlasov equation will provide simulations with lower numerical/statistical noise than standard PIC methods, and will allow the study of issues such as emittance degradation and microbunching due to space charge and CSR in bunch compressors. The fields excited by the bunch are computed in the lab frame from a new double integral formula. The field formula is derived from retarded potentials by changes of variables. It is singularity-free and requires no computation of retarded times. Ultimately, the Vlasov equation will be integrated in beam frame coordinates using our method of local characteristics. As an important intermediate step, we have developed a "self-consistent Monte Carlo algorithm", and a corresponding parallel code. This gives an accurate representation of the source and will help in understanding the PSD support. In addition we have (1) studied carefully a 2D phase space Vlasov analogue and (2) derived an improved expression of the field of a 1D charge/current distribution which accounts for the interference of different bends and other effects usually neglected. Bunch compressors will be emphasized.
55035317
COMPARISON OF 1D AND 2D CSR MODELS WITH APPLICATION TO THE FERMI @ ELETTRA BUNCH COMPRESSORS
We compare our 2D mean field (Vlasov-Maxwell) treatment of coherent synchrotron radiation (CSR) effects with 1D approximations of the CSR force which are commonly implemented in CSR codes. In our model we track particles in 4D phase space and calculate 2D forces [1]. The major cost in our calculation is the computation of the 2D force. To speed up the computation and improve 1D models we also investigate approximations to our exact 2D force. As an application, we present numerical results for the Fermi{at}Elettra first bunch compressor with the configuration described in [1].
189808711
Summary of Coherent Theory and Simulations Session
There were two types of talks which we attempt to summarize. Section 2 discusses the analytical talks and Section 3 the simulation talks. We hope that at least our summary will have the flavor of the session and serve as a reasonable pointer to papers in the proceedings and elsewhere. We take this opportunity to thank the participants of this session for making it an interesting one. The major emphasis in this session was on codes and we have tried to give an overview of basic computational strategies in Section 3 before highlighting the talks.
15193392
The D0 detector upgrade and physics program
The D0 detector at Fermilab is in the final stages of an extensive upgrade. It is designed to meet the demands imposed by high luminosity Tevatron running planned to begin March 2001. The design and performance of the detector subsystems are described and a brief outline of the physics potential is presented.
17092028
CP Violation Results from D0
We present results on CP violation from approximately 2.8 fb^{-1} of data collected by the D0 Experiment at the Fermilab Tevatron. The results presented are: (i) an improved measurement of the B_s^0 CP-violating phase from a flavor-tagged analysis of B_s^0 --> J/\psi \phi decays; (ii) a search for direct CP violation in B^{+-} --> J/\psi K^{+-} (\pi^{+-}) decays from a measurement of the charge asymmetry A_{CP}(B^{+-} --> J/\psi K^{+-}); and (iii) a search for indirect CP violation from searches for anomalous charge asymmetries in semileptonic B_s^0 decays.
110541630
Punch-through currents and floating strip potentials in silicon detectors
Punch-through currents flowing between adjacent p/sup +/ strips on the surface of silicon microstrip drift detectors have been observed. Measurements of the floating strip potential have shown that a p/sup +/ strip acquires a voltage such that the punch-through current and the leakage current are equal and opposite. The factors influencing the threshold for the punch-through effect have been compared with a simple computer model, and the predicted variation with the interstrip gap is found to be in reasonable agreement with measured values for a variety of detectors. >
126030076
Measurement of B_s Oscillations and CP Violation Results from D0
We present a measurement of the B{sub s}{sup 0} - B{sub s}{sup 0} oscillation frequency, {Delta}m{sub s}, using a combination of semi-leptonic and hadronic B{sub s} decay candidates selected from data collected by the D0 Experiment at the Fermilab Tevatron. We also present several results on CP violation, including an improved measurement of the B{sub s} CP-violating phase from a flavor-tagged analysis of B{sub s}{sup 0} {yields} J/{psi} + {phi} decays.
15585431
Measurements of the W boson mass and trilinear gauge boson couplings at the Tevatron
We present measurements of the W boson mass at the Tevatron based on $W \to \mu \nu$ events collected by CDF and $W \to e \nu$ events observed by D0 in Run Ib (1994--95). The W boson mass measured in the preliminary CDF analysis is 80.43 \pm 0.10 (stat) \pm 0.12 (syst) GeV/c^2. The D0 measured value is 80.44 \pm 0.10 (stat) \pm 0.07 (syst) GeV/c^2. We also describe measurements of the trilinear gauge boson couplings. The limits obtained on the WW\gamma and WWZ anomalous couplings from a combined D0 analysis using $W\gamma$, $WW \to \ell \nu \ell^\prime \nu^\prime$, and $WW/WZ \to e \nu jj$ production are: -0.30 < \Delta\kappa < 0.43, -0.20 < \lambda < 0.20, and -0.52 < \Delta g^Z_1 < 0.78, for a dipole form factor scale of 2 TeV. Improved limits have been obtained by combining these results with the limits derived from the LEP experiments.