CERN Accelerator School Vacuum in accelerators

416 Pages·2007·19.32 MB·English

CERN–2007–003
11June2007
ORGANISATION EUROP(cid:131)ENNE POUR LA RECHERCHE NUCL(cid:131)AIRE
CERN
EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
CERN Accelerator School
Vacuum in accelerators
Platja d’Aro, Spain
16–24 May 2006
Proceedings
Editor: D. Brandt
GENEVA
2007
CERN–320copiesprinted–June2007
Abstract
Theseproceedingspresentthelecturesgivenatthetwentiethspecializedcourseorganizedbythe
CERNAcceleratorSchool(CAS),thetopicbeingVacuuminAccelerators. ThecoursewasheldinPlatja
d’Aro, Spain, from 16 to 24 May 2006. A similar course took place in Snekersten, Denmark, in 1999,
withproceedingspublishedasCERN99-05. Afteranintervalofsevenyears,theaimofthiscoursewas
topresentareviewoftheactualstateoftheartandtohighlightthelatestdevelopmentsinthefield.
The lectures start with a general overview of vacuum, accelerators and cryogenics followed by a
moredetailedreviewofthebasicprinciplesconcerningthermalandnon-thermaloutgassing. Morespe-
cializedlecturesarethenproposedongasdynamics,ontheinteractionofenergeticparticleswithmatter,
and on beam–gas collisions. The production and measurement of vacuum is addressed in subsequent
lectures on pumps and vacuum gauges which present a detailed view of the materials currently used in
accelerators. The next part of the course is dedicated to the construction and operation of vacuum sys-
tems: design rules, leak detection, sealing, cleaning, and materials. Finally, lectures of general interest
are presented on topics like industrial application of vacuum, history of vacuum, cold vacuum systems,
ITER,andfuturechallengesforextremelyhighvacuumandaccelerators.
iii
iv
Foreword
The aim of the CERN Accelerator School (CAS) to collect, preserve and disseminate the knowl-
edgeaccumulatedintheworld’sacceleratorlaboratoriesappliesnotonlytogeneralacceleratorphysics,
but also to related sub-systems, equipment, and technologies. This wider aim is achieved by means of
specializedcourses. For2006,thetopicofthecoursewasVacuuminAcceleratorsanditwasheldatthe
ParkHotelSanJorge,Platjad’Aro,Spain,from16to24May2006.
Vacuum in Accelerators had already been treated in the framework of CAS courses, namely in
1999 inSnekersten, Denmark. However, after seven yearsand considering theenormous developments
achievedinthefield,itwasunanimouslyfeltthattherewasarealneedtopresentanupdatedversionof
thepreviouscourse.
The present course was elaborated in collaboration with the ALBA Synchrotron Light Facility
(Consortium CELLS) in Barcelona. In particular, the outstanding contribution of the Programme co-
ordinators Dr N. Hilleret (CERN) and Dr L. Miralles (CELLS) and the enthusiastic contribution of the
LocalOrganizingCommitteecomposedofLluisMiralles,LauraCamposandYolandaRuiz,weremost
invaluable.
ItisalsoimportanttounderlinethattheLocalOrganizingCommitteesuccessfullycontributedto
identifyingsponsorsfromIndustrytoprovidefinancialsupportandofferscholarshipstohighlydeserving
youngstudents,whowouldotherwisenothavebeenabletoattendtheschool.
As always, the backing of the CERN management, the guidance of the CAS Advisory and Pro-
grammeCommittees,theattentiontodetailoftheLocalOrganizingCommitteeandalsothemanagement
andstaffoftheParkHotelSanJorgeensuredthattheschoolwasheldunderoptimumconditions.
Very special thanks must go to the lecturers for the enormous task of preparing, presenting, and
writinguptheirtopics.
Finally, the enthusiasm of the participants who came from 24 different countries was convincing
proofoftheusefulnessandsuccessofthecourse.
It is my pleasure and my privilege to thank most sincerely all those persons who helped in mak-
ing the course a success, including the team of the CERN Scientific Text Processing Service for their
dedicationandcommitmenttotheproductionofthisdocument.
DanielBrandt
CERNAcceleratorSchool
v
April 2006

PROGRAMME
VACUUM IN ACCELERATORS (16-24 May 2006, Platja D’Aro, Spain)

Time Wednesday Thursday Friday Saturday Sunday Monday Tuesday Wednesday
17 May 18 May 19 May 20 May 21 May 22 May 23 May 24 May
08:30 Opening Talk Thermal Non-thermal Partial Analytical & Cold/Sticky Buses
Outgassing Outgassing Pressure Numerical Systems to Airport
The ALBA Gauges Tools for
Project Vacuum Systems

09:30 L. Miralles P. Chiggiato N. .Hilleret G. Peter R. Kersevan V. Baglin
09:30 Introduction General Design Materials Beam-Vacuum Beam-Vacuum Iter
toVacuum Rules Interaction I Interaction II Vacuum System
Lifetime, Lifetime,
E Cross-sections, Ion-Electron,
Activation Trapping, Dust,
X E-Cloud
10 :30 F. Dylla C. Hauviller S. Sgobba P. Grafström O. Gröbner M. Wykes
COFFEE COFFEE COFFEE C COFFEE COFFEE COFFEE
11:00 Introduction Mechanical Ion Pumps Leak Getter Pumps Control
to Pumps U Detection Systems
Accelerators
R

12:00 D. Brandt A. Chew M. Audi S K. Zapfe C. Benvenuti P. Strubin
LUNCH LUNCH LUNCH LUNCH LUNCH LUNCH
15:00 Physics of Gauges for Fine UHV I Cryo Pumps Surface Vacuum Aspects
Outgassing and High Gauges Properties and in
Vacuum O Cleaning Synchrotron
Light
N Sources
16:00 P. Chiggiato K. Jousten K. Jousten C. Day M. Taborelli R. Reid
16:00 Gas Dynamics Water Interaction with Sealing Use of NEG Misconceptions
Outgassing Matter Technology Pumps and and other
Coatings in Large Sources of
Vacuum Systems Problems

17:00 F. Sharipov F. Dylla J. Schou K. Sonderegger F. Mazzolini N. Hilleret
T E A T E A T E A T E A T E A T E A
17:30 Introduction to Industrial History of Large Systems Challenges for Vacuum
Cryogenics Applications Vacuum Commissioning XHV Challenges for
of Vacuum Technology for Future
Physics Research Machines

18:30 P. Lebrun D. Mueller F. Dylla K. Zapfe F. Dylla R. Reid
Welcome Special
DINNER DINNER DINNER DINNER DINNER
Drink Dinner

vi
Contents
Foreword
D.Brandt ................................................................................ v
Rarefiedgasdynamicsanditsapplicationstovacuumtechnology
F.Sharipov ............................................................................... 1
Introductiontocryogenics
P.Lebrun ................................................................................ 15
Designrulesforvacuumchambers
C.Hauviller ............................................................................. 31
Mechanicalvacuumpumps
A.D.Chew .............................................................................. 43
Gaugesforfineandhighvacuum
K.Jousten ............................................................................... 65
Non-thermaloutgassing
N.Hilleret ............................................................................... 87
Materialsforhighvacuumtechnology: anoverview
S.Sgobba .............................................................................. 117
Ultrahighvacuumgauges
K.Jousten .............................................................................. 145
Slowing-down processes, energy deposition, sputtering and desorption in ion and electron interactions
withsolids
J.Schou ................................................................................ 169
Thedevelopmentofultrahighandextremehighvacuumtechnologyforphysicsresearch
H.F.Dylla .............................................................................. 179
Partialpressuregauges
G.J.PeterandN.Müller ................................................................. 195
Lifetime,cross-sectionsandactivation
P.Grafström ............................................................................ 213
Leakdetection
K.Zapfe ............................................................................... 227
Basicsandapplicationsofcryopumps
C.Day ................................................................................. 241
Commissioningoflargevacuumsystems
K.Zapfe ............................................................................... 275
Analyticalandnumericaltoolsforvacuumsystems
R.Kersevan ............................................................................ 285
Getterpumping
C.Benvenuti ............................................................................ 313
Cleaningandsurfaceproperties
M.Taborelli ............................................................................ 321
TheuseofNEGpumpsandcoatingsinlargevacuumsystems: experienceandlimitations
F.Mazzolini ............................................................................ 341
Cold/stickysystems
V.Baglin ............................................................................... 351
Vacuumcontrolsandinterlocks
P.Strubin .............................................................................. 369
vii
Vacuumaspectsofsynchrotronlightsources
R.J.Reid ............................................................................... 389
Vacuumchallengesforfuturemachines
R.J.Reid ............................................................................... 401
ListofParticipants ........................................................................ 407
viii
Rarefied gas dynamics and its applications to vacuum technology
F. Sharipov
Universidade Federal do Paraná, Curitiba, 81531-990, Brazil
Abstract
Basic concepts of rarefied gas dynamics are given in a concise form. Some
problems of rarefied gas flows are considered, namely, calculations of
velocity slip and temperature jump coefficients, gas flow through a tube due
to pressure and temperature gradients, and gas flow through a thin orifice.
Results on the two last problems are given over the whole range of gas
rarefaction. A methodology for modelling the Holweck pump is described.
An extensive list of publications on these topics is given.
1 Brief history of rarefied gas dynamics
Rarefied gas dynamics is based on the kinetic approach to gas flows. In 1859 Maxwell [1] abandoned
the idea that all gaseous molecules move with the same speed and introduced the statistical approach
to gaseous medium, namely, he introduced the velocity distribution function and obtained its
expression in the equilibrium state. Thus Maxwell gave the origin to the kinetic theory of gases. Then,
in 1872 Boltzmann [2] deduced the kinetic equation which determines the evolution of the distribution
function for gaseous systems being out of equilibrium.
In 1909 Knudsen [3], measuring a flow rate through a tube, detected a deviation from the
Poiseuille formula at a low pressure. Such a deviation was explained by the fact that at a certain
pressure the gas is not a continuous medium and the Poiseuille formula is not valid anymore. A
description of such a flow required the development of a new approach based on the kinetic theory of
gases. This can be considered as the beginning of rarefied gas dynamics.
Later, advances were made by Hilbert [4], Enskog [5] and Chapman [6] to solve the Boltzmann
equation analytically via an expansion of the distribution function with respect to the Knudsen
number. The main result of this solution was a relation of the transport coefficients to the
intermolecular interaction potential, but no numerical calculation of rarefied gas flows could be
realized at that time.
In 1954 the so-called model equations [7,8] were proposed to reduce the computational efforts
in calculations of rarefied gas flows. Using these models it was possible to obtain numerical results on
rarefied gas flows in the transition regime. Thus in 1960 a numerical investigation of rarefied gas
flows began in its systematic form. For a long time, it was possible to solve only the model equations.
Practically, all classical problems of gas dynamics (Poiseuille flow, Couette flow, heat transfer
between two plates, flow past a sphere, etc.) were solved over the whole range of gas rarefaction by
applying the model equations. In 1989 first results based on the exact Boltzmann equation were
reported, see, for example, Ref. [9]. However, even using the powerful computers available nowadays,
a numerical calculation based on the Boltzmann equation itself is still a very hard task, which requires
great computational efforts. Thus, the model equations continue to be a main tool in practical
calculations.
Below, the main concepts of rarefied gas dynamics and some examples of its application will be
given. In the last section, the main results of rarefied gas dynamics that could be applied to vacuum
technology are listed.
1
F. SHARIPOV
2 Basic concepts of rarefied gas dynamics
2.1 Knudsen number and rarefaction parameter
The principal parameter of rarefied gas dynamics is the Knudsen number (Kn) which characterizes the
gas rarefaction and is defined as the ratio
(cid:65)
Kn= , (1)
a
where (cid:65) is the equivalent molecular mean free path given as
μv ⎛2k T ⎞1/2
(cid:65)= m , v = B , (2)
⎜ ⎟
P m ⎝ m ⎠
v is the most probable molecular velocity, k =1.380662×10−23J/K is the Boltzmann constant, m is
m B
the molecular mass of the gas in kg, T is the temperature of gas in K, P is its pressure in Pa, and μ
is the gaseous viscosity in Pa s.
Regarding the value of the Knudsen number, we may distinguish the following three regimes of
gas flow. If the Knudsen number is small (Kn(cid:19)1), the gas can be considered as a continuous medium
and the hydrodynamic equations [10] can be applied. This regime is called hydrodynamic. If the
Knudsen number is large (Kn(cid:21)1), the intermolecular collisions can be neglected. Under this
condition we may consider that every molecule moves independently from each other and, usually, the
test particle Monte Carlo method [11,12] is employed. This regime is called free-molecular. When the
Knudsen number has some intermediate value, we can neither consider the gas as a continuous
medium nor discount the intermolecular collisions. In this case the kinetic equation should be solved
[13–21], or the DSMC method [11,12] is used. This regime is called transitional.
Usually another quantity characterizing the gas rarefaction is used instead of the Knudsen
number, viz. the rarefaction parameter defined as
a 1
δ= = . (3)
(cid:65) Kn
Large values of δ correspond to the hydrodynamic regime and the small values of δ are
appropriate to the free molecular regime. This parameter is more convenient because many solutions
are given in terms of this parameter.
2.2 Velocity distribution function
The state of a monoatomic gas is described by the one-particle velocity distribution function f(t,r,v),
where t is the time, r is a vector of spatial coordinates, and v is a velocity of molecules. The
distribution function is defined so that the quantity f(t,r,v)drdv is the number of particles in the
phase volume drdv near the point (r, v) at the time t.
All macro-characteristics of gas flow can be calculated via the distribution function:
number density
n(t,r)=∫ f(t,r,v)dv, (4)
hydrodynamic (bulk) velocity
u(t,r)= 1∫v f(t,r,v)dv, (5)
n
2