Calculation of Longitudinal Instability Threshold Currents for Single Bunches

Based on the publication by M. Venturini, et al. [1] a computer program has been developed that solves the Vlasov Fokker Planck equation numerically on a two dimensional grid. In this code different types of longitudinal interactions and their combinations are implemented. Calculations have been performed for the 1.7 GeV storage ring BESSY II and the 600 MeV ring MLS using the wake created by the shielded coherent synchrotron radiation CSR . The results are compared with measurements on both rings which were based on the observation of the onset of time dependent fluctuations bursts of CSR [2, 3]. Fair agreement is found between theory and experiment. The theoretical results complement calculations performed by Bane, et al. [4] for this type of interaction. The new results emphasize the resistive nature of the CSR interaction, especially in regions where shielding effects are small or the resonance like features of this wake are important. It is found that in these regions the instability is weak and thresholds depend on the damping tim

Longitudinal stability of short bunches in storage rings with strong longitudinal Focusing

In the BESSY VSR project, the variable bunch length storage ring, two high gradient accelerating structures at 1.5 and 1.75 GHz will be phased such that long and short bunches can be stored simultaneously. The longitudinal stability of the short bunches is investigated taking into account the shielded CSR and a purely inductive impedance. Multi particle tracking studies and numerical solutions of the Vlasov Fokker Planck equation show that threshold currents for short bunches do not follow the simple scaling law which was found for long bunches. The inductive impedance can even lower the thresholds for the instability. With an 80 times increased accelerating gradient and reasonable assumptions on the inductive impedance for shorter bunches stable operation can be expected with bunches 1.8 ps long RMS value and 0.8 mA current. According to the calculations and operating in a dedicated low alpha mode will produce stable 40 mu A bunches with 400 fs lengt

CSR driven Longitudinal Single Bunch Instability Thresholds

The interaction of a short bunch of electrons with its own coherent synchrotron radiation, CSR, leads to low longitudinal instability thresholds. According to Bane, et al. [1] these thresholds follow a quite simple scaling law. More detailed theoretical calculations for the underlying shielded CSR impedance have been performed for BESSY II and the Metrology Light Source, MLS. It is found that there are additional parameter regions where the instability is weak and thus the thresholds depend on the longitudinal damping time, Tlong, and the synchrotron tune, 1 Tsyn. Most of the observed longitudinal instability features [2, 3] are in surprisingly good agreement with the theoretical finding

Propositional Dynamic Logic for Message-Passing Systems

We examine a bidirectional propositional dynamic logic (PDL) for finite and infinite message sequence charts (MSCs) extending LTL and TLC-. By this kind of multi-modal logic we can express properties both in the entire future and in the past of an event. Path expressions strengthen the classical until operator of temporal logic. For every formula defining an MSC language, we construct a communicating finite-state machine (CFM) accepting the same language. The CFM obtained has size exponential in the size of the formula. This synthesis problem is solved in full generality, i.e., also for MSCs with unbounded channels. The model checking problem for CFMs and HMSCs turns out to be in PSPACE for existentially bounded MSCs. Finally, we show that, for PDL with intersection, the semantics of a formula cannot be captured by a CFM anymore

Improvements of the Set Up and Procedures for Beam Energy Measurements at BESSY II

With a 7 T wiggler in operation all attempts to detect the resonant depolarization of the electron spins were unsuccessful at BESSY II. This was attributed to the severely reduced degree of spin polarization of the electrons moving in the alternating fields of the strong wiggler which on the other hand nearly doubles the radiation loss per turn. The key to a clear detection of the depolarization is the improvement of the sensitivity of the polarimeter, based on the spin dependent Touschek scattering cross section and the more effective and thus full depolarization of the beam. With these improvements the high precision beam energy determination can again be performed in parallel to the normal user operation and without any noticeable perturbations to the bea

Field evaluation of entomopathogenic nematodes against orchard pests

Survival of pest in micro-plot trials (container studies) or field plot trials was monitored after exposure to commercially used EPN strains. Experimental plots were artificially infested with pest larvae that naturally burrowed into the soil for diapause. Either larval mortality or adult emergence, was assessed to estimate the control effect of the EPN treatment. Here we present preliminary results from three ongoing projects

The Injector Layout of BERLinPro

BERLinPro is an Energy Recovery Linac Project running since 2011 at the HZB in Berlin. A conceptual design report has been published in 2012 [1]. One of the key components of the project is the 100 mA superconducting RF photocathode gun under development at the HZB since 2010. Starting in 2016 the injector will go into operation, providing 6.6 MeV electrons with an emittance well below 1mm mrad and bunches shorter than 5 ps. In 2017 the 50 MeV linac will be set up and full recirculation is planned for 2018. The injector design has been finalized and is described in detail in this paper. Emphasis is further laid on beam dynamics aspects and performance simulations of two different gun cavitie

Optics Calibration at the MLS and at BESSY II

In this paper we present the results of our studies employing LOCO and MML for optics calibration at the MLS and at the BESSY II storage rings. Both the standard user modes and dedicated low alpha modes are analyze

Properties of synchronization in the systems of non-identical coupled van der Pol and van der Pol - Duffing oscillators. Broadband synchronization

The particular properties of dynamics are discussed for the dissipatively coupled van der Pol oscillators, non-identical in values of parameters controlling the Hopf bifurcation. Possibility of a special synchronization regime in an infinitively long band between oscillation death and quasiperiodic areas is shown for such system. Features of the bifurcation picture are discussed for different values of the control parameters and for the case of additional Duffing-type nonlinearity. Analysis of the abridged equations is presented.Comment: 19 pages, 9 figure

Modifications to the Machine Optics of BESSY II Necessitated by the EMIL Project

The Helmholtz Zentrum Berlin and the Max Planck Society are going to build a new dedicated X ray beam line at the synchrotron light source BESSY II which will be used for analyzing materials for renewable energy generation. The new large scale project has been dubbed EMIL. In this document we present the modifications to the machine optics and to what extent these changes affect the performance of BESSY I