L. Emery

Advances in orbit drift correction in the Advanced Photon Source storage ring

The Advanced Photon Source storage ring is required to provide X-ray beams of high positional stability, specified as 17 /spl mu/m rms in the horizontal plane and 4.4 /spl mu/m rms in the vertical plane. We report on the difficult task of stabilizing the slow drift component of the orbit motion down to a few microns rms using workstation-based orbit correction. There are two aspects to consider separately-the correction algorithm and the configuration of the beam position monitors (BPMs) and correctors. Three notable features of the correction algorithm are: low-pass digital filtering of BPM readbacks; despiking of the filtered orbit to desensitize the orbit correction to spurious BPM readbacks without having to change the correction matrix; and BPM intensity-dependent offset compensation. The BPM/corrector configuration includes all of the working BPMs but only a small set of correctors distributed around the ring. Thus only those orbit modes that are most likely to be representative of real beam drift are handled by the correction algorithm.

Coupled-bunch instabilities in the APS ring

A study of coupled bunch instabilities for the APS storage ring is presented. The instabilities are driven by the higher-order modes of the fifteen 352-MHz single-cell RF cavities. These modes are modeled using the 2-D cavity program URMEL. The program ZAP is then used to estimate the growth time of the instabilities for an equally spaced bunch pattern. The cavity modes most responsible for the instabilities is singled out for damping.<<ETX>>

Commissioning software tools at the Advanced Photon Source

A software tool-oriented approach has been adopted in the commissioning of the Advanced Photon Source (APS) at Argonne National Laboratory, particularly in the commissioning of the Positron Accumulator Ring (PAR). The general philosophy is to decompose a complicated procedure involving measurement, data processing, and control into a series of simpler steps, each accomplished by a generic toolkit program. The implementation is greatly facilitated by adopting the SDDS (self-describing data set) protocol, which comes with its own toolkit. The combined toolkit has made accelerator physics measurements easier. For instance, the measurement of the optical functions of the PAR and the beamlines connected to it have been largely automated. Complicated measurements are feasible with a combination of tools running independently.

Initial diagnostics commissioning results for the Advanced Photon Source (APS)

Principal diagnostics systems have been installed and nearly all have been commissioned on the subsystems of the Advanced Photon Source (APS) facility. Data have been obtained on beam position, beam profile, current, beam loss rate, and synchrotron radiation monitors on both injector rings and most recently the main 7-GeV storage ring. Results for the 150- to 450-MeV electron beams in the accumulator ring, up to 7 GeV in the injector synchrotron, and 4.5 to 7 GeV in the SR will be presented.

Beam simulation and radiation dose calculation at the Advanced Photon Source with shower, an interface program to the EGS4 code system

The interface program shower to the EGS Monte Carlo electromagnetic cascade shower simulation code system was written to facilitate the definition of complicated target and shielding geometries and to simplify the handling of input and output of data. The geometry is defined by a series of namelist commands in an input file. The input and output beam data files follow the SDDS (self-describing data set) protocol, which makes the files compatible with other physics codes that follow the same protocol. For instance, one can use the results of the cascade shower simulation as the input data for an accelerator tracking code. The shower code has also been used to calculate the bremsstrahlung component of radiation doses for possible beam loss scenarios at the Advanced Photon Source (APS) at Argonne National Laboratory.

Coupled-bunch instability study of multi-cell deflecting mode cavities for the Advanced Photon Source

The short-pulse X-ray project at the Advanced Photon Source (APS) uses four room-temperature, three-cell, 2.815-GHz, deflecting-mode cavities in two consecutive straight sections. Undamped, these cavities higher-order and lower-order resonator modes will cause multi-bunch instabilities in longitudinal and transverse planes for any bunch pattern of a 100-mA store. Damping of these modes must be part of the design of the cavities. We report calculations of instability growth rates that were essential in specifying and checking the rf design of the damping structures. We used various operating bunch patterns and scanned levels of damping of the cavities. Because one of the operating bunch patterns is not symmetric, we used a normal mode analysis implemented in the APS code clinchor. Our calculation included random sampling of resonator frequencies in a reasonable range.

Beam dynamics, performance, and tolerances for pulsed crab cavities at the Advanced Photon Source for short x-ray pulse generation

The Advanced Photon Source (APS) has decided to implement a system using pulsed crab cavities to produce short X-ray pulses using Zholents scheme. This paper describes beam dynamics issues related to implementation of this scheme with one-sector separation between the cavities. Modeling of the cavity is used to demonstrate that the deflection will be independent of transverse position in the cavity but that there is a position offset for undeflected particles. Configuration and parameter choices to optimize performance are discussed. Finally, tolerances are discussed and determined based on tracking simulations.

Direct space-charge calculation in elegant and its application to the ilc damping ring

A direct space-charge force model has been implemented in the tracking code elegant [1]. The user can simulate transverse space-charge effects by inserting space- charge elements in the beamline at any desired position. Application to the international linear collider damping ring is presented in this paper. We simulated beam under equilibrium conditions, as well as the entire damping cycle from injection to extraction. Results show that beam halo is generated due to space-charge effects. This would be a significant concern for the ILC damping ring and a detailed follow-up study is needed.

Open loop compensation for the eddy current effect in the APS storage ring vacuum chamber

Results of the effort to counter the effect due to the finite inductance of the magnet and the eddy current in the 1/2-in-thick aluminum storage ring vacuum chamber are presented. The amplitude attenuation and the phase shift of the correction magnet field inside the APS storage ring vacuum chamber were measured. A circuit to compensate for this effect was then inserted between the signal source and the magnet power supply. The amplitude was restored with an error of less than 20% of the source signal amplitude and the phase shift was reduced from 80 degrees to 12 degrees at 10 Hz. Incorporation of this circuit in the closed-loop feedback scheme and the resulting beneficial effect in the closed-orbit stabilization is discussed. >

International Linear Collider damping ring lattice design

We present a lattice design based on the theoretical- minimum-emittance (TME) cell for the international linear collider (ILC) 6.6-km 5-GeV damping ring. Several areas are discussed: momentum compaction, lattice layout, injection and extraction, circumference adjusters, phase adjuster, and dynamic aperture calculation with multipole errors.