BNL, Upton, Long Island, New York
CERN, Geneva
Lancaster University, Lancaster
KEK, Ibaraki
SLAC, Menlo Park, California
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
LBNL, Berkeley, California
Fermilab, Batavia
Funding: This work was partially performed under the auspices of the US DOE and the European Community-Research Infrastructure, FP6 programme (CARE, contract number RII3-CT-2003-506395)}
The LHC crab cavity program is advancing rapidly towards a first prototype which is anticipated to be tested during the early stages of the LHC phase I upgrade and commissioning. Some aspects related to crab optics, collimation, aperture constraints, impedances, noise effects, beam transparency and machine protection critical for a safe and robust operation of LHC beams with crab cavities are addressed here.
CERN, Geneva
BNL, Upton, Long Island, New York
KEK, Ibaraki
Funding: This work was supported by the European Community-Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (CARE, contract number RII3-CT-2003-506395).
Modern colliders bring into collision a large number of bunches per pulse or per turn to achieve a high luminosity. The long-range beam-beam effects arising from parasitic encounters at such colliders are mitigated by introducing a crossing angle. Under these conditions, crab cavities (CC) can be used to restore effective head-on collisions and thereby to increase the geometric luminosity. In this paper, we discuss the beam dynamics issues of a single global crab cavity (GCC) for both nominal LHC optics and one upgrade LHC optics.
CERN, Geneva
BNL, Upton, Long Island, New York
In early LHC commissioning, linear and "higher-order" polarity checks were performed for one octant per beam, by launching suitable free betatron oscillations and then inverting a magnet-circuit polarity or strength. Circuits tested included trim quadrupoles, skew quadrupoles, lattice sextupoles, sextupole spool-pieces, Landau octupoles, and skew sextupoles. A nonzero momentum offset was introduced to enhance the measurement quality. The low-intensity single-pass measurements proved sufficiently sensitive to verify the polarity and the amplitude of (almost) all circuits under investigation, as well as the alignment of individual trim quadrupoles. A systematic polarity inversion detected by this measurement helped to pin down the origin of observed dispersion errors. Later, the periodic "ring dispersion" was reconstructed from the full first-turn trajectory of an injected off-momentum beam, by removing, at each location, the large incoming dispersion mismatch, forward-propagated via the optics model. Various combinations of inverted trim quadrupoles were considered in this model until reaching a good agreement of reconstructed dispersion and prediction.
CERN, Geneva
Funding: This work was supported by the European Community-Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (CARE, contract number RII3-CT-2003-506395).
The use of crab cavities in the LHC may not only raise the luminosity, but it could also complicate the beam dynamics, e.g. crab cavities might not only cancel synchro-betatron resonances excited by the crossing angle but they could also excite new ones. In this paper, we use weak-strong beam-beam model to study the incoherent linear tune shift of the weak beam, for the crossing collision case and crab collision case with a finite crossing angle. The tune shift is also compared among the head-on collision, crossing collision and crab collision cases, both analytically and numerically.
TIPC, BeiJing
IHEP Beijing, Beijing
IHEP Beiing, Beijing
Technical Institute of Physics and Chemistry, Beijing
Graduate School of the Chinese Academy of Sciences, Beijing
Funding: Work supported by NSFC 10525525
In order to obtain the design, manufacture and operational experiences on the SRF cryomodule toward ILC, a test cryomodule for 1.3GHz single 9-cell SC cavity was designed by IHEP (Institute of High Energy Physics) and TIPC (Technical Institute of Physics and Chemistry) jointly. This cryomodule will be used as a 1.3GHz 9 cell SC cavity horizontal test facility. The cryogenic system for the cryomodule is designed and will be operated at 2.0K, with the saturated superfluid helium. The major requirements, design, simulation results of the cryomodule are reported in the paper. This key component of a superconducting accelerator test unit will be built in the near future at IHEP.
IHEP Beijing, Beijing
TIPC, BeiJing
Funding: NSFC 10525525
With the aim to develop 1.3 GHz superconducting radio-frequency (SCRF） technology in the frame of ILC collaboration, IHEP has started a program to build a SCRF Accelerating Unit. This unit contains a 9-cell 1.3 GHz superconducting cavity, a short cryomodule, a high power input coupler, a tuner, a low level RF system and a high power RF source, etc. This program also includes the SCRF laboratory upgrade, which will permit the unit to be built and tested at IHEP. We will use this unit as a horizontal test stand for many 9-cell cavities and other components (e.g. input couplers, tuners), as in Europe and North America. In this paper, we report the recent R&D status and the future plan of this program.
USTC/PMPI, Hefei, Anhui
USTC/NSRL, Hefei, Anhui
Funding: "Collinear Load for Accelerators and R&D on High Power Microwave Absorbed Material" No.10775128 From National Natural Science Foundation of China
Thermal deformation caused by Non-uniform temperature distribution in disk-loaded waveguide will affect the resonant frequency of LINAC deeply. Formerly, researchers evaluated it by experiments or experience and gave their conclusion roughly and linearly. A new approach of integration of multi-disciplinary is adopted to study the relationship more accurately. After loading the loss RF power on the accelerator tube wall, the thermal deformation is calculated in software I-DEAS, and a deformed finite element model is obtained. Then nodes on inner surfaces of the cavities were extracted and sort by a customized program. According to these nodes, a new solid model is reconstructed with a self developed 3D reconstruction technology in ANSYS. B-Spline interpolation technique is used to fit a group of curves first, and then to reconstruct NURBS surfaces. The final reconstructed deformed solid model, obtained by closing the surfaces, can be exported in IGES format which is used to recalculate the resonant frequency in Microwave Studio again. The error of the reconstruction can be controlled within 3 micrometers. The resonant frequency change of every cavity can be accurately calculated.
Parietti L, etc., Thermal structural analysis and frequency shift **
Zhou, Zu-Sheng,etc. Thermal structural analysis and test **