SCHOOL OF PHYSICS & ASTRONOMY Postgraduate Form 6 Supervisor

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15 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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SCHOOL OF PHYSICS & ASTRONOMY

Postgraduate Form 6



Request for ‘Submission Pending’




The completed form should
be signed
by the
Supervisor

and
returned to Rebecca Shaw,
Education Officer, Rm G53A, School of Physics & Astronomy, Schuster Building.



Name

of Student:

Hugo Day

ID Number:

7455896

(this field MUST be completed)

Date of Entry:

Month
-

September

Year
-

2009



Title of Thesis:

Simulations and Measurements
Impedance Reduction Techniques in
Particle Accelerators









Expected Date of Submiss
ion: ___
Dec
2012
____




I under
stand that having completed the three years full time/six years part time*
of normal
registration of my PhD programme The University of Manchester will only allow me a further
12 months in which to complete and submit my

thesis. I understand that if I fail to submit my
thesis within this 12 month ‘Submission Pending’ period I will be deemed to have failed by
default, and that ‘Submission Pending’ can only be extended in exceptional circumstances,
which are described in t
he University policy document:

http://www.campus.manchester.ac.uk/medialibrary/researchoffice/graduateeducation/p
-
change
-
to
-
prog
-
pgr.p
df


I have attached a suitable project plan (no more than 1 side of A4) for the time from now until
anticipated submission and a short description of the work that is complete and the work that
still remains to be done.




Signature of student:
_________
_________________________________________________


Print name: ____________
Hugo Day
___________ Date: _____
2012
___________







I

have read the attached plan and believe the plan and submission date to be realistic.




Signed (Supervisor):




* delete

as appropriate.

With regards to the work to be included in the thesis, the majority has thus far been
completed
. This wor
k has included the following strands:

1)

Reviewing and extending the methods of carrying out bench top beam impedance
measurements on ac
celerator devices. Primarily this has involved using the coaxial wire
method to measure the transverse beam impedance of symmetric and asymmetric
structures

2)

Using the above method to comprehensively measure the beam impedance of a number
of normal conducti
ng kicker magnets from the SPS and LHC. In particular the LHC
injection kicker magnet (LHC
-
MKI)

went through an extensive measurement campaign
using the above method. Subsequently significant work has been carried out on the
beam screen of this device due
to severe heating of the device that was observed
during high intensity fills in the LHC. This involved using computational simulation
codes (in particular CST Particle Studio) to study both the impedance of the device as it
is currently installed in the L
HC
(
to verify our simulation model
)

and also to investigate
the beam impedance of other beam screen designs. These predictions have guided the
design choice of a new kicker magnet already, to be placed in the LHC in late
August/early September.

In particul
ar this device has strict limits on its performance as
a fast firing kicker magnet, and the beam screen strongly effects the field rise time of
the magnet, which must rise in between bunch trains to inject into the LHC.

3)

Studying the use of ferrites or othe
r damping materials to reduce the expected beam
induced heating in structures exhibiting strong cavity eigenmodes, that is EM cavity
resonances that can be excited by a particle beam. This can lead to very large power
deposition in the structure. This stud
y has focused on identifying the location

of the
original power loss and the subsequent reduced power loss, in particular as the ferrite
used for damping the cavity modes has a limited operational temperature. This work
has involved significant collaborati
on with other colleagues at CERN and extensive use
of the HFSS simulation code.


What remains to be finished is a study of the transverse impedance of a number of beam
screen designs for the LHC
-
MKI as well as some final summary work for the bench top
impe
dance measurement methods, this being to analyse the data for an asymmetric structure.


Writing for the thesis has already started, with 2 sub
-
chapters having been completed. A
summary schedule is given below, with a more comprehensive timetable available
on request.


End of August


All work to be included in thesis finished.

Beginning of September


Writing full time

End of October


First draft of thesis to be completed and sent in full to supervisors for review

Mid
-
December


Final version of thesis sub
mitted to Faculty for examination

End of January/early February


Viva/oral examination of thesis

























Abstract


The phenomenon of wakefields and the corresponding frequency
-
domain property, beam
coupling impedance
,

have long been studie
d in particle accelerators. They are important as a
source of beam instabilities due
to
beam
-
eq
uipment interactions and place

restrictions on the
operating parameters of particle accelerators. As accelerators have pushed towards smaller
beam emittance and
higher beam currents the importance of controlling the beam impedance
has become more important. With the latest high power accelerators, even beam
-
induced
heating due to the beam power loss has become a serious limitation on beam operation.

To
this end th
ere has been a concerted effort in recent years to find ways of reducing the beam
impedance of accelerators, through either designing new devices to

have a low beam
impedance or by

shield
ing

existing devices in a way to reduce their impedance.


In this the
sis a short review of the existing impedance reduction techniques in use in many
particle accelerators is given. The limitations and restrictions of thes
e technique
s are

also
considered. Here the
focus
is put

on the usage of damping materials to reduce the

Q of cavity
resonances
, as even with the su
bsequent reduction in impedance

heating of the damping
material can still be a serious concern
.
A

number of methods of measuring (using bench
-
top
and beam
-
based measurements) or simulating the beam impedance of d
evices

are introduced
and summarised
. In particular the use of the coaxial wire
technique,

a bench top
method for
measuring
the beam impedance of a device, and how it may be used
to measure the
longitudinal and transverse (dipolar, quadr
upolar and constant
) impedances

of symmetric and
asymmetric structures

is studied in depth
. These techniques are subsequently applied to two
significant sources of beam impedance within the LHC
-

the injection kicker magnets (LHC
-
MKIs) and elements of the collimation upgrade
s for the LHC. A comparison between
simulations and measurements of the impedance of the MKI is presented in addition to an
evaluation of alternative beam screen designs in regards to the possible beam
-
induced heating
of the structure. Two facets of the LH
C collimation upgrade are investigated
-

the choice of the
jaw material of the phase 2 secondary collimators, expected to be a significant contributor to
the LHC transverse impedance budget, and the TCTP collimator for which a full structure
simulation is
carried out to determine the effectiveness of the impedance reduction system in
place.