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Вакуум для ускорителей

Пошли материалы новой ЦЕРНовской школы по ускорителям, на сей раз - техника вакуума.

Brief Introduction to Particle Accelerators: https://arxiv.org/abs/2006.02821
Pedro Fernandes Tavares
This lecture is a brief introduction to charged particle accelerators. The aim is to provide the reader with basic concepts and tools needed to describe the motion of charged particles under the action of guiding and focussing fields, with an emphasis on those aspects that are relevant to understanding and quantifying how accelerator vacuum systems affect accelerator performance. Even though the focus is on electron accelerators and, in particular, electron storage rings used as synchrotron light sources, most of the concepts described are of general application to a wider class of particle accelerators.
Comments: 21 pages, contribution to the CAS - CERN Accelerator School: Vacuum for Particle Accelerators, 6-16 June 2017, Glumslöv, Sweden


Fundamentals of Vacuum Physics and Technology: https://arxiv.org/abs/2006.01464
Eshraq Al-Dmour
A good vacuum performance in particle accelerators is vital for their successful operation. The reasons why a good vacuum is needed, together with the basics of vacuum physics and technology and the main gas sources inside the vacuum system, are presented here.
Comments: 21 pages, contribution to the CAS - CERN Accelerator School: Vacuum for Particle Accelerators, 6-16 June 2017, Glumslöv, Sweden

Vacuum Controls and Diagnostics: https://arxiv.org/abs/2006.03263
G. Pigny, A. Rocha
This paper describes the CERN's vacuum control system from the field devices to the Supervisory Control and Data Acquisition software. First, a particular attention is given to the environment present in the accelerators, like noise coupling and ionizing radiation, which can affect the quality of the measurements and the reliability of the system. Then, the main vacuum instruments and their associated conditioning circuits and controllers are presented, before to introduce the hardware interlock logic and alarms used for the vacuum system and the machine protection. Finally, the Supervisory Control and Data Acquisition software and its architecture are described, including data engineering and the main functionalities provided to the users for controls and diagnostics.
Comments: 23 pages

Vacuum for accelerators: introduction to materials and properties: https://arxiv.org/abs/2006.02212
Stefano Sgobba
In modern accelerators, stringent requirements are placed on the materials used for vacuum systems. Their physical and mechanical properties, machinability, weldability and brazeability are key parameters. Adequate strength, ductility, magnetic properties at room as well as low temperatures are important factors for vacuum systems of accelerators working at cryogenic temperatures. In addition, components undergoing baking or activation of Non-Evaporable Getters (NEG) or directly exposed to the beam impose specific choices of material grades for suitable outgassing and mechanical properties in a large temperature range. Today, stainless steels are the dominant materials of vacuum systems. The reasons for specific requirements in terms of metallurgical processes are detailed for obtaining adequate purity, inclusion cleanliness and fineness of the microstructure. In many cases these requirements are crucial to guarantee the final leak tightness of the vacuum components. Innovative manufacturing and material examination technologies are also treated.
Comments: 30 pages



Materials & Properties: Mechanical Behaviour: https://arxiv.org/abs/2006.01499
Cedric Garion
All systems are expected to be designed to fulfil their functions over their requested lifetime. Nevertheless, failure of a system may occur, and this is unfortunately, true also for vacuum systems. From a mechanical point of view, buckling, leak by fatigue crack propagation, rupture of a fixed support under unbalanced vacuum force... may happen. To well understand and anticipate the behaviour of a structure, it is mandatory to first understand the mechanical behaviour of materials as well as their failure modes. This is presented in a first part of the document. Then, the structural behaviour of a vacuum system and its relationship with the material properties is discussed. Finally, guidelines for the material selection for a given application are roughed out.
Comments: 19 pages

Materials & Properties: Thermal & Electrical Characteristics: https://arxiv.org/abs/2006.02842
Sergio Calatroni
This lecture gives an introduction to the basic physics of the electrical conductivity of metals, its temperature dependence and its limiting factors. We will then introduce the concept of surface resistance, of high relevance in accelerators for its link with beam impedance and for RF applications, including notions related to the anomalous skin effect. The surface resistance will help establishing a link to heat exchanges between bodies by radiation, and to the concept of emissivity. Thermal conductivity will then be introduced, discussing both its electron and phonon exchange components, and the relevant limiting factors.
Comments: 20 pages


Impedances and Instabilities: https://arxiv.org/abs/2006.06540
R. Wanzenberg
The concepts of wake fields and impedance are introduced to describe the electromagnetic interaction of a bunch of charged particles with its environment in an particle accelerator. The wake fields can act back on the beam and lead to instabilities, which may limit the achievable current per bunch, the total current, or even both. Some typical examples are used to illustrate the wake function and its basic properties. Then the frequency-domain view of the wake field or impedance is explained, and basic properties of the impedance are derived. The impedance of a cavity mode is illustrated using an equivalent circuit model. The relation of wake field effects to important beam parameters is treated in the rigid beam approximation. Several examples are employed to illustrate the impact of the geometry and the material properties of the vacuum chamber on the impedance. Finally, a basic introduction to beam instabilities based on a head tail model of the beam is given.
Comments: 28 pages



Interaction Between Beams and Vacuum System Walls: https://arxiv.org/abs/2006.03277
Roberto Cimino
In modern high-intensity accelerators, the circulating beam interacts in many ways with the vacuum beam pipe, causing a variety of different phenomena. Most of them have been discussed at length in other contributions to this CAS report. I concentrate here on the effects associated with the presence of electrons in the accelerator beam pipes. Low-energy electrons in accelerators are known to interact with the circulating beam, giving raise to the formation of a so-called e− cloud. e− cloud effects can be detrimental to beam quality and stability, especially for positively charged beams. I will first describe the origin and the basic features causing e− cloud formation in accelerators, which depend not only on the beam properties but mainly on the vacuum vessel surface properties. Such material properties and the way one can study them will be here briefly presented. Finally, some of the e− cloud mitigation strategies adopted and proposed so far will be described and discussed.
Comments: 20 pages


Cleaning and Surface Properties: https://arxiv.org/abs/2006.01585
Mauro Taborelli
Principles of the precision cleaning dedicated to ultra-high vacuum applications are reviewed together with the techniques for the evaluation of surface cleanliness. Methods to verify the effectiveness of cleaning procedures are addressed. Examples are presented to illustrate the influence of packaging and storage on the recontamination of the surface after cleaning. Finally, the effect of contamination on some relevant surface properties, such as secondary electron emission and wettability, is presented. This article is an updated and shortened version of the one previously published for the CAS school on the vacuum of accelerators 2006.
Comments: 19 pages


Controlling Particulates and Dust in Vacuum Systems: https://arxiv.org/abs/2006.02820
Lutz Lilje
Particulates and dust can limit accelerator performance in various ways. In this paper the basic properties and mechanisms of contaminations due to particulates are described. With this knowledge countermeasures can be implemented to minimize degradation due to particulates inside the accelerator vacuum systems.
Comments: 16 pages

Total and Partial Pressure Measurement: https://arxiv.org/abs/2006.02707
Karl Jousten
Total pressure gauges are used to measure the level of vacuum in a system independent of the gas species. Partial pressure analysers measure the occurrence of each gas species separately. This report explains the methodology of measurement, summarizes the measurement principles of total pressure vacuum gauges, and updates the standardization work for their calibration. On the matter of partial pressure measurement, this report explains the mass filtering by the quadrupole mass spectrometers and outlines the measurement problems with these instruments.
Comments: 14 pages


Ion getter pumps: https://arxiv.org/abs/2006.02721
C. Maccarrone, P. Manassero, C. Paolini
Ion Getter Pumps (IGP) are used to create ultra-high-vacuum. The IGP operation is triggered by the Penning cell structure, which uses a combination of electrical and magnetic fields to confine electrons and start ionization and getter pumping processes. During the years, more IGP configurations have been developed to cope with different gases, such as reactive gases, hydrogen or noble gases. When the IGP is required to reach pressures lower than 10^(-8) mbar, it needs to be baked out with the whole vacuum system, in order to accelerate the release of the gas atoms trapped inside the pump materials, and the leakage current issue has to be taken into account for a reliable pressure reading.
Comments: 11 pages

Cryopumping and Vacuum Systems: https://arxiv.org/abs/2006.01574
Vincent Baglin
The understanding of complex and/or large vacuum systems operating at cryogenic temperatures requires a specific knowledge of the vacuum science at such temperatures. At room temperature, molecules with a low binding energy to a surface are not pumped. However, at cryogenic temperatures, their sojourn time is significantly increased, thanks to the temperature reduction, which allow a "cryopumping". This lecture gives an introduction to the field of cryogenic vacuum, discussing surface desorption, sticking probability, thermal transpiration, adsorption isotherms, vapour pressure of usual gases, industrial surfaces and roughness factors. These aspects are illustrated with the case of the Large Hardon Collider explaining its beam screen and its cryosorber, leaks and beam vacuum system modelling in a cryogenic environment. Finally, operation of cryogenic beam vacuum systems is discussed for LHC and other cryogenic machines.
Comments: 34 pages


NEG pumps: Sorption mechanisms and applications: https://arxiv.org/abs/2006.01537
P. Manini, E. Maccallini
This paper reports the main physical and chemical properties of NEG materials, sorption mechanisms and use of NEG pumps from high to extreme high vacuums.
Comments: 15 pages


Beam-Gas Interactions: https://arxiv.org/abs/2006.06490
M. Ferro-Luzzi
An overview of beam-gas interactions in particle accelerators is presented. The paper is focused on a few examples and tries to present basic concepts with simple formulae that should allow the reader to perform order-of-magnitude estimates of beam-gas rates.
Comments: 20 pages

Outgassing properties of vacuum materials for particle accelerators: https://arxiv.org/abs/2006.07124
Paolo Chiggiato
Gas load and pumping determine the quality of vacuum systems. In particle accelerators, once leaks are excluded, outgassing of materials is an important source of gas together with degassing induced by particle beams. Understanding, predicting, and measuring gas release from materials in vacuum are among the fundamental tasks of ultrahigh-vacuum experts. The knowledge of outgassing phenomena is essential for the choice of materials and their treatments so that the required gas density is achieved in such demanding and expensive scientific instruments. This note provides the background to understand outgassing in vacuum and gives references for further study.
Comments: 97 pages

Vacuum Acceptance Tests for Particle Accelerator Equipment: https://arxiv.org/abs/2006.10367
G.Bregliozzi
The effective and reliable operation of particle accelerator machines is strongly related to obtaining and keeping the required ultra-high vacuum level. This paper briefly presents some generic requirements to take in consideration for components that need to be installed in a particle accelerator like design constraints, materials choices, chemical cleaning process, outgassing rate, and their possible mitigation. Moreover, it will discuss vacuum acceptance tests put in place in the CERN accelerator complex for both, baked and unbaked system.
Comments: 11 pages, 8 figures

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