The production and properties of high energy X-radiation from a 30 MeV. electron synchrotron

311 Pages·042.413 MB·English

by  Layne, D. A

THE PRODUCTION AND PROPERTIES OF
HIGH ENERGY X-RADIATION FROM
A 30 MEV. ELECTRON SYNCHROTRON
by D.A. LAYNE
'I
being a thesis for the degree of
m Doctor of Philosophy in the University of London
Royal Cancer Hospital,
London, S.W.3.
JUNE,“1951.
ProQuest Number: 10096569
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THfc PRODUCTION AND PROPERTIES OF HIGH hWhRGY X-RADIATION
FROM A 50 MEV. ELECTRON SYNCHROTRON.
Abstract of Thesis^
The thesis can be divided roughly into two parts.
The first part deals with the design, construction end
operation of the accelerator, whilst the second is devoted
mainly to a theoretical study of the process of betatron
injection.
The section on design is concerned with problems
associated with synchrotron magnets end a critical survey
of the Important design criteria and techniques is presented.
The 30 MeV. magnet is given as a particular example and some
original work on the application of relaxation methods is
described. The ways in which power can be supplied to the
magnet are considered end also some experiments on the use
of an on-load tap changer. Experimental results of magnet
excitation cnaracteristlcs are compared with calculated
values and a detailed account is given of magnetic field
measurements involving the use of new techniques.
In the operation of the machine, original experiments
are described and discussed on the effect of varying a number
of operating parameters. An attempt is made to determine
the relative importance of these and compare the working
efficiency of American betatrons with the 30 MeV. synchrotron.
The theoretical study of the injection process
can again be sub-divided into two main parts. The first is
an original investigation of the Influence of charge and
current images on the maximum theoretical circulating current.
In the second part an attempt is made to develop a quantitative
expression for Kerst Self-contraction and to compare
theoretical calculations with experimental results. Whilst
the comparison is favourable and, for the first time, a
number of observed phenomena can be explained by the use of
the theory, the validity of Kerst Self-contraction la
questioned.
AGMOWLEDGMENTS
_
The author wishes to acknowledge the continuous encourage­
ment and generous interest given by Professor W*V. Mayneord
He would also like to express his gratitude to Mr. V.A.
Hughes of the English Electric Company, without whose
invaluable help and advice much of the magnetic work could
never have been accomplished; also to Mr. W. Gilbert-
Purssey for the preparation of diagrams and Miss J. Adams
for the typescript. He is particularly indebted to the
Medical Research Council and the Royal Cancer Hospital for
providing facilities for the research.
D.A. LAYNE.
TABLE OF SYMBOLS
Except where otherwise stated, the symbols to be found in the
text have the following meanings.
A - vector potential.
A(>- cross-sectional area of betatron cores.
Aj- area of gap in series with betatron cores,
electron radial oscillation amplitude,
electron axial oscillation amplitude.
6 - magnetic induction.
C- - capacitance.
6 - velocity of light.
£ - particle energy.
E^ - maximum particle energy.
e - electronic charge.
f - mains supply form factor.
f - magnet mains supply frequency.
- magnetic orbital field strength,
maximum orbital field strength.
- field strength at any radius.
- radial component of magnetic field.
- vertical component of magnetic field.
^ - axial height of magnet air gap at the equilibrium orbit
A, - axial height of magnet air gap at any radius.
X - magnet R.M.S. excitation current or total electron
beam circulating current (distinction made clear
in the text}.
magnet peak excitation current.
^ - injector filament current.
L - injector peak emission.
L - mean magnet inductance or self-inductance at orbit
(distinction made clear in text).
guide field inductance.
^5
- betatron flux inductance.
Lj, - magnet parallel tuning inductance.
- maximum number of revolutions of particles before
being in danger of striking the injector.
nrv - magnetic field law index.
- reactive power in magnet circuit.
Q - total circulating charge in vacuum chamber.
^ - charge density in vacuum chamber.
- radius of equilibrium orbit.
R - any radius in magnet gap.
- instantaneous orbit radius.
f - displacement of instantaneous orbit from
equilibrium orbit.
^ - circulating beam radius.
A - any radius within circulating beam.
& - useful annular cross-section of magnet gap.
T
- total number of magnet exciting coil turns.
"1^ - magnet coils R.M.S. voltage or injection voltage
(distinction made clear in text).
V
- magnetic potential.
'If - velocity of particles at injection.
Wt- - total stored energy in magnet field.
Wu." useful stored energy in magnet field.
'VX - useful annular width of magnet gap.
z - axial displacement of particles from median plane.
- axial displacement of particles from median plane
at injection.
^ - ratio of electron velocity at injection to that of light
€ - dielectric constant.
6 - azimuthal angle from orbitrary datum.
- magnetic permeability.
^ - particle radial displacement from instantaneous orbit.
Pf, - particle radial displacement from instantaneous orbit
at injection.
^ - total magnetic flux inside the equilibrium orbit.
^ - general symbol for magnetic flux.
^ - electrostatic potential.
- orbital angular velocity of particles.
i»V - radial oscillation angular frequency.
<0^- axial oscillation angular frequency.
CONTENTS
INTRODUCTION....................................... Page 1
CHAPTER I
SYNCHROTRON MGNET DESIGN AND CONSTRUCTION
SUMTÆARY
SECTION
1. GENERAL DESIGN CONSIDERATIONS ....................7
2. METHODS OF DESIGN ............................... 14
3. 30 MEV. SYNCHROTRON MAGNET ...................... 15
(a) Basic Design.
(b) Construction.
(c) Relaxation method applied to pole
profile design.
(d) Some comments on the use of an
electrolytic tank.
4. CONCLUSIONS ..................................... 36
CHAPTER II
mAgNET PgfER SUPPLIES AND EXCITATION CIRCUIT
SUmiARY
SECTION
1. GENERAL..........................................
2. lÆETHODS OP CIRCUIT TUNING .......................39
3. PARALLEL INDUCTANCE TUNING......................40
4. INDUCTANCE TUNING BY TAPPED TURNS ON
THE MAGNET AND AN ON-LOAD TAP CHANGER..........42
5. 30 MEV. MAGNET EXCITATION CIRCUIT.. ............. 48
6. CONCLUSIONS ......................................
CHAPTER III
MAGNET EXCITATION CHARACTERISTICS
SUMMARY
SECTION
1. LOSSES AND INDUCTANCE................... 51
2. COMPARISON OP IŒASURED LOSSES WITH
CALCULATED LOSSES.....:........................ 52
(a) General.
(b) Magnetic losses.
(c) Copper losses in the exciting coils.
(d) Capacitor losses.
(e ) Total circuit losses.
3. STRAY LOSSES ............. .64
4# CONCLUSIONS ..................................... 67
CHAPTER IV
magnetic "Field lieasureivIEnts and characteristics
SUmiARY
SECTION
1. GENERAL......................................... 68
2. ORBIT FIELD INTENSITY AS A FUNCTION OF
MAGNET EXCITATION .............................. .
3. AZIMUTHAL VARIATION IN MAGNITUDE AND PHASE 71
(a) Available techniques for measurement.
(b) The use of peaking strips.
(c) Peaking strip construction.
(d) Experimental technique.
(e) Initial experiments.
(f) Adjustment of field phase.
4. THE VARIATION OF MAGNETIC FIELD WITH RADIUS
AND THE DETERMINATION OF "vv" ...................
5. THE BETATRON FLUX CONDITION.................... 84
6. CONCLUSIONS........ .............................
CHAPTER V
vA(?utJM.''Injection, r.f. ato display systems
SUIÆMARY
SECTION
1. VACUUM CHAMBER AND PUMPING SYSTEM...............88
2. INJECTION SYSTEM................................ 90
(a) Electron injector.
(b) Timing equipment.
(c) Injection system.
3. R.F. SYSTEM............................. '.......92
(a) Resonator.
(b) R.F. oscillator.
(c) R.F. system.
4. DISPLAY SYSTEM ............................. 94
(a) Operating cycle.
(b) Display system
CHAPTER VI
SÙME OPERITING CHARACTERISTICS OF 50 MEV. SYNCHROTRONS
SUiaiARY
SECTION
1. GENERAL .................................... .
2. INJECTOR CALIBRATION AND RADIATION
MEASURING EQUIPIiŒNT .......... 97
(a) Injector electron emission.
(b) Injection voltage.
(c) X-ray intensity measuring apparatus.
3. BETATRON OUTPUT AS A FUNCTION OP
OPERATING PARAMETERS .......................... .
(a) Betatron output as a function of
gun emission and injection voltage.
(b) Betatron output as a function of
injection voltage.
(c) Betatron output as a function of
gun radius.