IHEP Beijing, Beijing
As the upgrade project of Beijing Electron Positron Collider (BEPC), BEPCII will still serve both high energy physics experiments and synchrotron radiation applications. The storage ring of BEPCII consists of electron ring (BER), positron ring (BPR) and synchrotron radiation ring (BSR). Up to now, we have completed two stages run. The first stage run started on Nov. 13, 2006 by using conventional magnets instead of superconducting (SC) magnets in the interaction region (IR). The second stage operation started on Oct. 24, 2007 by using SC magnets and without BESIII detector. In this paper, we will present the progress of the BEPCII storage ring diagnostics system along with the BEPCII commissioning, such as how Libera BPM has been used for the BPR first turn measurement and the injection residual orbit research of BER; COD measurement can satisfy the resolution requirement for the beam-beam scan in the IR and for the slow orbit feedback; BCM can help us on the different injection pattern; and the TFB system is important to suppress the strong multibunch instabilities when the higher beam current run. The tune meters and the beam-loss monitors are also described in this paper.
PSI, Villigen
DESY, Hamburg
Currently, a prototype fast intra bunch train feedback system is under development which is to be tested at FLASH. For pickups as well as kickers, stripline devices have been developed. The new pickup is based on the earlier designs used in the transfer lines of the swiss light source as well as in the proton cyclotron PROSCAN at PSI; in particular, the stripline electrode output coupling is intentionally mismatched in order to increase the shunt impedance seen by the beam. Two versions have been designed for a center frequency of 1.65 GHz and a loaded Q of 35. Prototypes have been fabricated and built into FLASH. The stripline kicker consists of four main elements (all in-vacuum): two stripline electrodes fabricated from extruded aluminum and two metallic ground planes, held in place by ceramic spacers. The latter reduce the mutual inductance between the electrodes and optimize the RF match for asymmetries in the RF feed. Prototypes have been built, measured in the lab, and are now in the process of being inserted into FLASH.
SLAC, Menlo Park, California
The growth rates of the longitudinal higher-order impedance-driven modes beam have greatly increased since the initial PEP-II design and commissioning. This increase is attributed to the addition of 8 1.2 MW RF klystrons and 12 accelerating cavities, as well as to operations at twice the design current and almost four times the luminosity. As a result, the requirement for the longitudinal feedback has greatly increased since the design, and the feedback filters and control schemes have evolved during PEP-II operations. In this paper growth and damping rate data for the high-order cavity driven beam modes are presented and compared with historical estimates and measurements. The available margins for the 4 A LER and 2.2 HER ring case at PEP-II are estimated, and suggestions for reliable operation are also presented. The effect of noise in the feedback processing channel is also studied. Data for different gain configurations of the filter from PEP and other accelerators are presented. These data show the tradeoff between instability control and higher noise levels.
LBNL, Berkeley, California
The Advanced Light Source Transverse Feedback System currently consists of a refrigerator sized analog delay line system. The new system is the 2nd generation Transverse Feedback System, derived from work done for PEP-II in 2004. It uses the latest generation Virtex-5 FPGA, and has 12-bit ADCs and DACs for bunch-bunch feedback at 500MHz. In addition, this system provides networked capability for setup and diagnostics.
I-Tech, Solkan
ESRF, Grenoble
Libera, the beam position processor, features the so-called Turn-by-Turn (TbT) data output, the data rate being exactly the revolution frequency of the accelerator. This data is essential for commissioning of the accelerator as well as for various machine physics studies. However, due to the "natural" properties of correctly structured filters (respecting the Nyquist theorem), the smearing between adjacent TbT samples is not negligible. The purpose of the modified DDC filter is to remove smearing between adjacent TbT samples, especially with partial fill patterns. The usage of Modified DDC filters gives the best results for the studies using the Turn-by-Turn measurements, with the benefit of "true & pure" Turn-by-Turn results (no smearing). The method, its implementation and first results are discussed in this paper.
LBNL, Berkeley, California
Typically storage ring light sources operate with the maximum number of bunches possible with a gap for ion clearing. The Advanced Light Source (ALS) has 2 nanoseconds between the bunches and typically operates with 276 bunches out of a possible 328. For experimenters doing timing experiment this bunch separation is too small and would prefer to see only one or two bunches in the ring. In order to provide more flexible operations and substantially increase the amount of operating time for time-of-flight experimenters, it is being proposed to kick one bunch on a different vertical closed orbit. By spatially separating the light from this bunch from the main bunch train in the beamline, one could potentially have single bunch operation all year round. By putting this bunch in the middle of the ion clearing gap the required bandwidth of the kicker magnets is reduced. Using one kicker magnet running at the ring repetition rate (1.5 MHz), this bunch could be permanently put on a different closed orbit. Using multiple kicker magnets, this bunch could be locally offset at an arbitrary frequency. This paper will show some first results using such a system.
This work was supported by U.S. Department of Energy under Contract No. DE-AC03-76SF00098
Diamond, Oxfordshire
Top up is becoming more and more a standard mode of operation for synchrotron light sources. Although it brings a very stable source in terms of position and intensity, the regular injections potentially perturb the beam. In order to investigate the perturbation of the beam from imperfections of the injection kickers (i.e. non-closure of the bump), we use an X-ray pinhole camera equipped with a fast CMOS-sensor giving a rate of up to 3200 frames per second to monitor the image of the beam. The analysis of the observed beam size as well as position allows quantifying the perturbation from the kickers that can be seen on beamlines. In addition we compare the observed motion to bunch-by-bunch position data recorded in both vertical and horizontal planes, which reveals to be very complementary.
LBNL, Berkeley, California
At the Advanced Light Source (ALS), imperfections in the injection system plus electron diffusion result in storage ring RF bucket contamination. A Virtex-4 FPGA is used to generate a Direct-Digital Synthesized (DDS) sinewave waveform at the vertical betatron tune frequency, which is synchronously gated on or off at the 1.6MHz ring orbit frequency. Any pattern on/off/invert in 328 buckets by 2ns at the ring orbit frequency can be set. An embedded Power-PC core in the FPGA provides TCP access for control and monitoring via a remote PC running LabVIEW.
LBNL, Berkeley, California
The Advanced Light Source (ALS) in Berkeley was the first third generation light source ever built, and since 1993 has been in continuous and successful operation serving a large community of users in the VUV and soft x-ray community. During these years the storage ring underwent through several important upgrades that allowed to maintain the performances of this veteran facility at the forefront. The ALS beam diagnostics and instrumentation have followed a similar path of innovation and upgrade and nowadays include most of the modern and last generation devices and technologies that are commercially available and used in the recently constructed third generation light sources. In this talk we will not focus on such already widely known systems, but we will concentrate in the description of some measurements techniques, instrumentation and diagnostic system specifically developed at the ALS and used during the last few years.