CERN Accelerator School Intermediate accelerator physics

538 Pages·2006·23.89 MB·English

CERN–2006–002
26January2006
ORGANISATION EUROP(cid:131)ENNE POUR LA RECHERCHE NUCL(cid:131)AIRE
CERN
EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH
CERN Accelerator School
Intermediate accelerator physics
DESY, Zeuthen, Germany
15–26 September 2003
Proceedings
Editor: D. Brandt
GENEVA
2006
CERN–360copiesprinted–January2006
Abstract
The fifth CERN Accelerator School (CAS) Intermediate course on Accelerator Physics was held at the
DESY-Zeuthen Laboratory, Zeuthen, Germany from 15 to 26 September 2003. Its syllabus was based on the
decision to definitively associate the Intermediate level course with the concept of afternoon courses. Con-
sequently, the programme was composed of lectures in the mornings (dedicated to core topics) and of three
‘specialization’ courses in the afternoons, whereby each participant selected one of the proposed subjects and
followed this course every afternoon for a detailed tuition on this specific topic. This year, the three proposed
afternoon courses were ‘Optics Design, Measurement and Correction’, ‘Instrumentation, Beam Diagnostics
and Feedback Systems’, and ‘Linac Structures’. Keeping in mind that the afternoon courses are not meant to
be lectures but rather a mixture of theory and experimental applications, it follows that it is not possible to
incorporate these courses in the proceedings. Consequently, the proceedings present the lectures given during
themorningsessions.
The lectures can be classified in three distinct categories: first, the core topics already introduced at the
Introductory level but treated at a more advanced level, such as transverse and longitudinal dynamics, linear
imperfections, vacuum, magnet design, particle sources, and beam instabilities. Secondly, the topics requir-
ing some preliminary knowledge, and thus only introduced at the Intermediate level, such as non-linear ef-
fects, sources of emittance growth, Landau damping, dynamics with damping, insertion devices, luminosity
and beam–beam effects. The third category is composed of plenary lectures directly related to the proposed
afternoon courses, i.e., lattice cells, insertions, beam instrumentation and feedback, beam diagnostics, linac
structures,andsuperconductingRFcavities. These32lectureswerecompletedbythreeseminars,sixtutorials
withsixhoursofguidedstudy,a10-hourafternooncourse,andaPostersession.
iii
iv
Foreword
The CERN Accelerator School was established in 1983 with the mission to preserve and disseminate the
knowledge accumulated at CERN and elsewhere on particle accelerators and storage rings of all kinds. Until
1993, this was carried out principally by means of a biennial programme of introductory and advanced two-
weekcoursesongeneralacceleratorphysicsaimingtobridgethegapbetweenthelevelofknowledgeattained
withauniversitydegreeandthatrequiredforstartingacceleratorresearchwork.
In1995, itwasrecognizedthattheleveloftheadvancedcoursewaspossiblytoohighandnotnecessarily
adapted anymore to the needs of the young scientists entering the field of accelerator physics. Consequently,
the advanced level course was replaced by an intermediate level course. The first Intermediate course was
organizedin1995inEger,Hungary.
Although the present proceedings are for the fifth Intermediate course on general accelerator physics held
inZeuthen, GermanyinSeptember2003,theyarethefirstproceedingstobepublishedasaCERNReportfor
acourseattheintermediatelevel.
The intermediate level, which is clearly meant to be a logical follow-up of the introductory course, is
composed of three distinct parts: first, some core topics (introduced at the introductory level) are reviewed
at a more advanced level. Secondly, essential topics, which require some preliminary basic knowledge, are
introduced(e.g.,non-lineareffects,Landaudamping,beam–beameffects). Finally,thespecificityoftheInter-
mediatecourse, namelythe‘afternooncourses’, whereeachparticipantselectsoneofthreeproposedsubjects
andfollowsthiscourseeveryafternoonforadetailedtuitiononthisspecifictopic.
Thebasicobjectiveoftheintermediatelevelisthereforenotonlythattheparticipantsfollowregularlectures
inthemornings,butthattheyalsohaveanopportunitytoacquirea‘solid’introductiontoatopicwhich,ideally,
shouldbenewtothem. Thisspecializationshouldnotbecomposedoflectures,butratherofamixtureoftheory
andexperimentalapplications.
Thiscoursewasmadepossiblebytheactivesupportofseverallaboratoriesandmanyindividuals. Inpartic-
ular, the help and collaboration of the DESY-Zeuthen Laboratory management and staff, especially Professor
U. Gensch, K. Varschen, M. Mende, A. Hagedorn, and Dr. P. Wegner were most invaluable. Their endless
enthusiasm and the provision of a first-class infrastructure for the lecture rooms definitely contributed to the
successoftheschool.
As always, the backing of the CERN management, the guidance of the CAS Advisory and Programme
Committees, and the attention to detail of the Local Organizing Committee (DESY-Zeuthen) ensured that the
schoolwasheldunderoptimumconditions.
Very special thanks must go to the lecturers for the enormous task of preparing, presenting, and writing
up their topics. Similarly, the enthusiasm and positive feedback of the participants was convincing proof that
an Intermediate level course with afternoon courses was the appropriate complement to the Introductory level
course.
Finally,wethanktheCERNScientificTextProcessingServicefortheirdedicationandcommitmenttothe
productionofthisdocument.
DanielBrandt
CERNAcceleratorSchool
v
Friday26/9/03Students’Feedback ClosingSession
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eptember 2003) MondayTuesday22/9/0323/9/03InstabilitiesLongitudinalin LinacsInstabilities M. FerrarioK. SchindlT4T5SpaceDynamicsChargewith Damping DynamicsConcept ofwithLuminosityDamping I L. RivkinW. HerrDynamicsBeam-BeamwithEffectsDamping II L. RivkinW. HerrL Course 1 Course 2 Course 3 Coffee & TeaGS5SeminarDynamicsPhysics madewithin BerlinDampingS. Brandt DINNERBERLINM E A L
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Programme for the Interme WednesdayThursdayFriday17/9/0318/9/0319/9/03LinearNonlinearSources ofImperfectionsImperfectionsEmittanceGrowth O. BruningO. BruningD. MöhlT1GS2T2LongitudinalTransverseTransverseDynamicsDynamicsDynamics Coffee & TeaSC - RFNon-LandauCavitiesLinearities forDamping ILS’s P. SchmüserA. StreunA. HofmannVacuum inLattices forLandauAcceleratorsLSsDamping II O. GröbnerA. StreunA. HofmannL U N C H Course 1V Course 2I SCourse 3 ICoffee & TeaSeminarGS3The MotherImperfectionsTof allAcceleratorsA. De Rujula E V E N I N G M E A L and Correction” ostics and Feedback Systems”
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RSION 10.09.2003 meMondayTuesday15/9/0316/9/0330Opening TalkTransverseDynamics 30U. GenschE. Wilson30Recap.LongitudinalTransverseDynamicsDynamics 30E. WilsonJ. LeDuff 50Recap.InsertionsLongitudinalDynamics 50J. LeDuffB. Holzer50Intro. BeamIntroduction toInstrumentationBeam& FeedbackDiagnostics 50R. JonesR. Jones 30Lattice CellsC1 30B. HolzerC230LinacStructures C3 30N. PichoffCoffee & Tea00SchoolGS1OrganisationLongitudinalDynamics 00D. Brandt 30COCKTAIL30 urse 1 = “Optics Design, Measuremeurse 2 = “Linac Structures”urse 3 = “Instrumentation, Beam Dia
VE Ti 08: 09:09: 10: 10: 11:11: 12: 14: 15:15: 16: 17: 18: 18:19: CoCoCo
vi
Contents
Foreword
D.Brandt ...................................................................................... v
Transversebeamdynamics
E.J.N.Wilson ................................................................................... 1
Latticedesigninhigh-energyparticleaccelerators
B.J.Holzer .................................................................................... 31
Introductiontobeaminstrumentationanddiagnostics
R.JonesandH.Schmickler ..................................................................... 75
IntroductiontoRFlinearaccelerators
N.Pichoff .................................................................................... 105
Linearimperfections
O.Bru¨ning ................................................................................... 129
BasicprinciplesofRFsuperconductivityandsuperconductingcavities
P.Schmu¨ser .................................................................................. 183
Non-linearitiesinlightsources
A.Streun ..................................................................................... 203
Latticesforlightsources
A.Streun ..................................................................................... 217
Sourcesofemittancegrowth
D.Mo¨hl ..................................................................................... 245
Landaudamping
A.Hofmann .................................................................................. 271
Spacecharge
K.Schindl .................................................................................... 305
Instabilities
K.Schindl .................................................................................... 321
Wakefieldsandinstabilitiesinlinearaccelerators
M.Ferrario,M.MiglioratiandL.Palumbo ...................................................... 343
Conceptofluminosity
W.HerrandB.Muratori ...................................................................... 361
Beam–beaminteractions
W.Herr ...................................................................................... 379
Electromagneticdesignofacceleratormagnets
R.Russenschuck .............................................................................. 411
Insertiondevices
J.Bahrdt ..................................................................................... 441
Free-electronlasers
P.Schmu¨ser .................................................................................. 477
Electronandionsourcesforparticleaccelerators
R.Scrivens ................................................................................... 495
AMAD-Xprimer
W.Herr ...................................................................................... 505
ListofParticipants .............................................................................. 529
vii

TRANSVERSE BEAM DYNAMICS
E. Wilson
CERN, Geneva, Switzerland
Abstract
This contribution describes the transverse dynamics of particles in a
synchrotron. It builds on other contributions to the General
Accelerator School for definitions of transport matrices and lattice
functions. After a discussion of the conservation laws which govern
emittance, the effects of closed orbit distortion and other field errors
are treated. A number of practical methods of measuring the
transverse behaviour of particles are outlined.
1. INTRODUCTION
During the design phase of an accelerator project a considerable amount of calculation
and discussion centres around the choice of the transverse focusing system. The lattice,
formed by the pattern of bending and focusing magnets, has a strong influence on the aperture
of these magnets which are usually the most expensive single system in the accelerator.
Figure 1 shows the lattice design for the SPS at CERN. The ring consists of a chain of
108 such cells. The principles of designing such a lattice have been treated elsewhere in this
school by Rossbach and Schmüser [1] and the methods of modifying the regular pattern of
cells to make matched insertions where space is needed for accelerating structures, extraction
systems and for experiments where colliding beams interact, will be the subject of another talk
[2].
Fig. 1 One cell of the CERN 400 GeV Super Proton Synchrotron representing 1/108 of the
circumference. The pattern of dipole and quadrupole magnets (F and D) is shown
above. Beam particles make betatron oscillations within the shaded envelopes.
1
E.J.N. WILSON
In this series of lectures I shall concentrate on those aspects of transverse dynamics
which frustrate the designer or plague the person whose job it is to make the machine perform
as well as theory predicts. I shall start with Liouville's theorem because this is an inescapable
limitation to the beam size. Next I shall explain the distortion of the central orbit of the
machine due to errors in the bending field. I shall then move on to explain how errors in
quadrupole gradients may lead to instability of the betatron motion at certain Q values known
as stopbands. Finally I shall explain why it is necessary to correct the variation of Q with
momentum with sextupoles in order to avoid these stopbands.
The more advanced topics of the influence of fields which couple the two transverse
phase planes together and fields whose non-linear nature can excite resonances which extract
particles are given in two separate talks in this school [3,4]. In those talks we shall move
away from the predictable linear behaviour to glimpse the fascinating jungle of effects which
stretch our minds at the boundaries of accelerator theory and which will be fully developed in
the Advanced Course of this school.
Since the effects I shall mention are annoying and best eliminated I shall try to indicate
how measurements may be made on a circulating beam and its transverse behaviour corrected.
Many of the effects I shall describe need only to be estimated rather than accurately predicted
but it is very important to understand their mechanism. I shall therefore prefer to introduce
concepts with approximate but physically revealing theory.
I make no apologies for building the theory from elementary definitions. These have to
be restated to give those not fortunate enough to have eaten and slept in phase space a firm
basic understanding. I hope that others who become impatient with the redefinition of basic
quantities will be eventually gratified by the later stages in the exposition of the theory and the
references I have given for further study.
2. LIOUVILLE'S THEOREM
Fig. 2 Liouville's theorem applies to this ellipse
Particle dynamics obey a conservation law of phase space called Liouville's theorem. A
beam of particles may be represented in a phase space diagram as a cloud of points within a
closed contour, usually an ellipse (Fig. 2).
2