BNL, Upton, Long Island, New York
A new 3rd generation light source (NSLS-II project) is in the early stage of construction at Brookhaven National Laboratory. The NSLS-II facility will provide ultra high brightness and flux with exceptional beam stability. It presents several challenges in the diagnostics and instrumentation, related to the extremely small emittance. In this paper, we present an overview of all planned instrumentation systems, results from research & development activities; and then focus on other challenging aspects.
BNL, Upton, Long Island, New York
Three-dimensional electromagnetic simulations have suggested a variety of measures to mitigate the problem of button BPM trapped mode heating. A test fixture, using a combination of commercial-off-the-shelf and custom machined components, was assembled to validate the simulations. We present details of the fixture design, measurement results, and a comparison of the results with the simulations.
BNL, Upton, Long Island, New York
The thermal distortion resulting from BPM button trapped mode heating is potentially problematic for achieving the high precision beam position measurement needed to provide the sub-micron beam position stability required by light source users. We present a button design that has been thermo-mechanically optimized via material selection and component geometry to minimize this thermal distortion. Detailed electromagnetic analysis of the button geometry is presented elsewhere in these proceedings.
BNL, Upton, Long Island, New York
Funding: Work supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-AC02-98CH10886.
With growth of circulating current in the storage rings the heating of the beam position monitor (BPM) buttons due to the induced trapped modes is drastically increasing. Excessive heating can lead to the errors in the measuring of beam position or even catastrophic failures of pick-up assembly. In this paper we present calculations of heat generated in the button for different geometries and materials. The obtained results are used for the optimization of the BPM design for the NSLS-II project.
BNL, Upton, Long Island, New York
Impedance of two vacuum chamber components, Bellows and BPM, is considered in some detail. In order to avoid generation of Higher-Order Modes (HOM’s) in the NSLS-II bellows, we designed a new low-impedance RF shielding consisting of 6 wide and 2 narrow metal plates without opening slots between them. The short-range wakepotential has been optimized taking into account vertical offset of RF fingers from their nominal position. The results were compared with data of bellows designed at other laboratories. Narrow-band impedance of the BPM Button has been studied. TE-modes in the BPM button were suppressed by a factor of 8 by modification of existing housings. Two new types of housings are shown. The total impedance of the NSLS-II storage ring is discussed in terms of the loss factor and the vertical kick factor for a 3mm-Gaussian bunch.
BNL, Upton, Long Island, New York
The short- and long-range wakepotentials have been studied for the design of the infrared (IR) extraction chamber with large full aperture: 67mm vertical and 134mm horizontal. The IR-chamber will be installed within a 2.6m long wide-gap bending magnet with 25m bend radius. Due to the large bend radius it is difficult to separate the light from the electron trajectory. The required parameters of the collected IR radiation in location of the extraction mirror are ~50mrad horizontal and ~25mrad vertical (full radiation opening angles). If the extraction mirror is seen by the beam, resonant modes are generated in the chamber. In this paper, we present the detailed calculated impedance for the design of the far-IR chamber, and show that placing the extraction mirror in the proper position eliminates the resonances. In this case, the impedance reduces to that of a simple tapered structure, which is acceptable in regard to its impact on the electron beam.
BNL, Upton, Long Island, New York
For the NSLS-II storage ring with damping wigglers but without a Landau cavity, the low-current bunch length is 4.5mm. We have studied bunch lengthening and estimated the microwave instability threshold using the multi-particle tracking code TRANFT. An estimate of the pseudo-Green’s function for a 0.5mm driving bunch was obtained for most components of the vacuum system by using the 3D code GdfidL. With our present computer resources, certain components were too large and had too complex geometry to allow the wake for such a short bunch to be computed using GdFidL. In these cases, the actual 3D geometry was approximated by a structure having circular cross-section, and the pseudo-Green’s function was computed using the 2D code ABCI. It was found that the dominant geometric wake is due to the tapers for the in-vacuum undulators. The resistive wall wake is also important. The effect of pseudo-Green’s functions corresponding to an even shorter driving bunch (0.05mm) was investigated using the program ECHO to compute the wake of tapers with circular cross-section. Our results suggest that the microwave threshold will occur at an average single-bunch current greater than 5mA.