| Paper | Title | Page |
|---|---|---|
| TUPRO013 | Studies on Stochastic Cooling of Heavy Ions in the LHC | 1030 |
|
||
| Future high luminosity heavy-ion operation of the LHC will be dominated by very rapid luminosity decay due to the large collision cross-section and, to a lesser extent, emittance growth from intra-beam scattering (IBS) due to the high bunch intensities. A stochastic cooling system could reduce the emittance far below its initial value and reduce the losses from debunching during collisions, allowing more of the initial beam intensity to be converted into integrated luminosity before the beams are dumped. We review the status of this proposal, system and hardware properties and potential locations for the equipment in the tunnel. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRO013 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPME026 | TMCI Thresholds for LHC Single Bunches in the CERN-SPS and Comparison with Simulations | 1407 |
|
||
| At the beginning of 2013 an extensive measurement campaign was carried out at the SPS in order to determine the Transverse Mode Coupling Instability thresholds of LHC-type bunches in a wide range of intensities and longitudinal emittances. The measurements were performed in two different configurations of machine optics (nominal and low gamma transition) with the goal to characterize the differences in behavior and performance. The purpose of this paper is to describe in detail the measurement procedure and results, as well as the comparison of the experimental data with HEADTAIL simulations based on the latest SPS impedance model. Beside the impedances of the resistive wall, the beam position monitors (BPMs), the RF cavities, and the flanges, an advanced model of the impedance of the kicker magnets is included, which are found to play a major role in the definition of the stability region of the LHC-type bunches in the two optics configurations studied. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME026 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPME028 | Flat Bunches in the LHC | 1413 |
|
||
| A high-harmonic RF system that could serve multiple purposes was proposed for the LHC. Possible applications of the second harmonic RF system include beam stabilisation in the longitudinal plane in the absence of wide-band longitudinal feedback and reduction of bunch peak line-density. Apart from other useful features, flat bunches are expected to produce less beam-induced heating at frequencies below 1 GHz, the frequency region critical for some LHC equipment. The latter, however, can also be achieved by de-populating the bunch centre. This was demonstrated during the dedicated machine development session in the LHC using RF phase modulation. In this paper the results of tests with single bunches and nominal LHC beams are presented and the possible use of this technique in LHC operation is discussed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME028 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPME029 | Identification of High-frequency Resonant Impedance in the CERN SPS | 1416 |
|
||
| The spectrum of long bunches injected into the ring with RF switched off has been used in the SPS in the past to probe the longitudinal coupling impedance. After a large campaign of shielding of 800 inter-magnet vacuum ports in 1999 - 2001, the microwave instability threshold was significantly increased and the high-frequency spectrum of the beam became practically flat, apart from a prominent peak at around 1.4 GHz. As corresponding high-frequency impedance could potentially lead to microwave instability of high intensity bunches observed now at high energies in the SPS, a search of the source of this impedance was launched. Using a combination of impedance simulations and measurements, vacuum flanges that are present in a large quantity in the machine have been identified as a main source of impedance at this frequency. Particle simulations based on the SPS impedance model, which includes this previously unknown impedance, are able to reproduce the characteristics of the bunch spectrum and amplitude growth rates and hence, confirm that the impedance of the vacuum flanges is responsible for the observed spectral peak. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME029 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI030 | Beam Coupling Impedance of the New Beam Screen of the LHC Injection Kicker Magnets | 1627 |
|
||
| The LHC injection kicker magnets experienced significant beam induced heating of the ferrite yoke, with high intensity beam circulating for many hours, during operation of the LHC in 2011 and 2012. The causes of this beam coupling impedance were studied in depth and an improved beam screen implemented to reduce the impedance. Results of measurements and simulations of the new beam screen design are presented in this paper: these are used to predict power loss and temperature of the ferrite yoke for operation after long shutdown 1 and for proposed HL-LHC operational parameters. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI030 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI049 | Geometric Beam Coupling Impedance of LHC Secondary Collimators | 1677 |
| SUSPSNE059 | use link to see paper's listing under its alternate paper code | |
|
||
|
Funding: Work supported by European Commission within the Framework Programme 7 Capacities Specific Programme, Grant Agreement 284404 The High Luminosity LHC project is aimed at increasing the LHC luminosity by an order of magnitude. One of the key ingredients to achieve the luminosity goal is the beam intensity increase. In order to keep under control beam instabilities and to avoid excessive power losses a careful design of new vacuum chamber components and an improvement of the present LHC impedance model are required. Collimators are the main impedance contributors. Measurements with beam have revealed that the betatron coherent tune shifts were by about a factor of 2 higher with respect to the theoretical predictions based on the current model. Up to now the resistive wall impedance has been considered as the major impedance contribution for collimators. By carefully simulating their geometric impedance we show that for the graphite collimators with half-gaps higher than 10 mm the geometric impedance exceeds the resistive wall one. In turn, for the tungsten collimators the geometric impedance dominates for all used gap values. Hence, including the geometric collimator impedance into the LHC impedance model enabled us to reach a better agreement between the measured and simulated collimator tune shifts. |
||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI049 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI054 | FEM Analysis of Beam-coupling Impedance and RF Contacts Criticality on the LHC UA9 Piezo Goniometer | 1692 |
|
||
| The UA9 piezo-goniometer has been designed to guarantee micro-radians-accuracy angular positioning of a silicon crystal for a crystal collimation experiment in the LHC, and to minimize the impact on the LHC beam-coupling impedance. This paper presents a Finite Element Method (FEM) study of the device, in both parking and operational positions, to evaluate its impact on the LHC impedance budget. The study has been a progressive simulation work, started from the simplification of the original detailed design, and aimed at highlighting the effect of single details (e.g. objects in confining chambers) on the longitudinal and transverse components of beam-coupling impedance. In addition, the shielding contribution of the RF gaskets has been carefully evaluated, with the objective to assess the consequences for operation in case of their failure. Sensitivity analyses to simulation parameters are also performed, in order to test the FEM model robustness. A final word is drawn on the overall device impedance criticality. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI054 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI055 | Theoretical Analysis of Metamaterial Insertions for Resistive-wall Beam-coupling Impedance Reduction | 1695 |
|
||
| Resistive-wall impedance usually constitutes a significant percentage of the total beam-coupling impedance budget of many accelerator structures (e.g. for LHC, it can be more than 50%). Reduction techniques for resistive-wall components entail high electrical-conductivity coatings. This paper proposes the use of metamaterials, having negative values of magnetic permeability or dielectric permittivity (or both), for sensibly reducing or theoretically nearly cancelling the resistive-wall component of beam-coupling impedance. The proposed approach is developed by means of an equivalent transmission-line model, whose results show the potential reduction of both longitudinal and transverse impedance when using metamaterial insertions. The effects on the real and imaginary part have been singled out. The effectiveness of such materials is discussed both for negative-permittivity and for negative-permeability cases, which actually show different impacts and can be then target of proper engineering. This first-stage study opens the possibility of considering metamaterials for impedance mitigation or for setting up proper experimental setups. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI055 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI058 | Impedance Studies of the Dummy Septum for CERN PS Multi-turn Extraction | 1704 |
|
||
| A protection septum has been installed in the CERN PS section 15 in order to mitigate irradiation of the magnetic septum 16 for fast extractions towards the SPS. Impedance studies have been performed, showing that beams circulating in the septum during extraction generate sharp resonances in the coupling impedance. Impedance measurements with the wire technique have been performed, showing a good agreement with simulations. Instability rise times of trapped modes have been evaluated and compared to extraction duration. Solutions for reducing the impact on the stability of the beam have been considered. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI058 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI059 | The Proton Synchrotron Transverse impedance model | 4096 |
| SUSPSNE060 | use link to see paper's listing under its alternate paper code | |
|
||
| The current knowledge of the transverse impedance of the CERN Proton Synchrotron (PS) has been established by theoretical computations, electromagnetic simulations and beam-based measurements at different energies. The transverse coherent tune and phase advance shifts as a function of intensity have been measured in order to evaluate the total effective transverse impedance and its distribution in the accelerator. In order to understand the beam dynamics, the frequency dependence of the impedance budget has also been evaluated considering the individual contribution of several machine devices. 3D models of many PS elements have been realized to perform accurate impedance simulations, while resistive wall and indirect space charge impedances have been evaluated with theoretical and numerical computations. Finally comparisons between the total budget and the measurement results are presented. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI059 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI060 | Impedance Studies for the PS Finemet® Loaded Longitudinal Damper | 1708 |
|
||
| The impedance of the Finemet® loaded longitudinal damper cavity, installed in the CERN Proton Synchrotron straight section 02 during the Long Shutdown 2013-2014, has been evaluated. Time domain simulations with CST Particle Studio have been performed in order to get the longitudinal and transverse impedance of the device and make a comparison with the longitudinal impedance that was measured for a single cell prototype. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI060 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| TUPRI062 | The Mode Matching Technique Applied to the Transverse Beam Coupling Impedance Calculation of Azimuthally Symmetric Devices of Finite Length | 1714 |
|
||
| The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be a less accurate approximation for segmented devices. In this contribution we present the extension of the study of the beam coupling impedance of a finite length device to the transverse plane. In order to take into account the finite length, we decompose the fields in the cavity and in the beam pipe into a set of orthonormal modes and apply the Mode Matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPRI062 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |
| THPME175 | A Beam Gas Vertex Detector for Beam Size Measurement in the LHC | 3680 |
|
||
| The Beam Gas Vertex (BGV) detector is foreseen as a possible non-invasive beam size measurement instrument for the LHC and its luminosity upgrade. This technique is based on the reconstruction of beam gas interaction vertices, where the charged particles produced in inelastic beam gas interactions are measured with high-precision tracking detectors. The design studies and expected performance of the currently developed BGV prototype will be presented with an overview given of the associated vacuum, detector, and readout systems. A brief description will be given of the BGV Monte Carlo simulation application, which is based on the LHCb computing framework (Gaudi) and allows simulation studies to be performed and online event reconstruction algorithms to be developed. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPME175 | |
| Export • | reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml) | |