121538444
Transformation of phase space densities under the coordinate changes of accelerator physics
In self-consistent modeling of many-particle systems it is convenient to solve the Maxwell equations for self-fields in coordinates based in the laboratory with time as the evolution variable, but conventional and also convenient to follow particle motion in Frenet-Serret coordinates referred to a reference orbit, with arclength along that orbit as the evolution variable. We refer to these two pictures as the laboratory system and beam system descriptions, while emphasizing that a Lorentz transformation is not involved; it is only a matter of two alternative descriptions of motion in one inertial frame. The problem then arises of how to express the laboratory system charge/current density for the Maxwell equations in terms of the phase space density described in the beam system. We find the exact expression, then make justified approximations to put the formula in a simple and practical form. Incidentally, we derive exact and approximate equations of motion in the different coordinates, without the use of the canonical formalism. The results have been applied in a study of coherent synchrotron radiation in bunch compressors.
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].
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.
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.
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. >
120475830
Physics capabilities of the DO upgrade detector
The D0 detector at Fermilab is being upgraded to meet the demands imposed by high luminosity Tevatron running planned to begin in 1998. The central tracking detectors will be replaced with silicon and scintillating fiber tracking systems inside a solenoidal magnetic field and a preshower detector will be added to aid in electron identification. The design and performance of these systems are described and detailed simulations of the physics capabilities of the upgraded detector are presented. In particular the authors focus on the study of electroweak boson properties and top quark physics and briefly describe the b-physics capabilities.
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.
16901067
W Boson Physics at the Fermilab Tevatron
We present electroweak physics results from the D0 and CDF experiments using data from p \bar p collisions at \sqrt s = 1.8 TeV. Measurements of the cross sections times branching ratios for W and Z production, the inclusive width of the W boson and the W boson mass are presented. Direct tests of the WW\gamma and WWZ trilinear gauge boson couplings are also presented based on studies of diboson production.
114249657
Development and evaluation of silicon drift chambers