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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS -1963
14a1,127
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ORNG-A-30gr
JUN 22 1965
MASTE

To be submitted for publication in the June Issue of IEEE Transactions on Nuclear Science,
Proceedings of the 1967 U.S. National Particle Accelerator Contorence, Washington, D.C.,
March 1-3, 1967.
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MAGNET SYSTEM FOR A 4-MeV EXPERIMENTAL SEPARATED ORBIT CYCLOTRON*
E. D. Hudson and F. E. McDaniel
CFSII RRICES
Oak Ridge National Laboratory
Oak Ridge, Tennessee
2H.C. : 300, MK 65
Summary
One of six sector-magnets for the 4-MeV
Separated Orbit Cyclotron Experiment (SOCE)
has been assembled and tested. The magnets for
the SOCE are quite different and much simplified
from previous SOC magnet concepts; all pole tips
are of the same radius of curvature and each set
is excited by a separate coil-pair. The pole-tip
fields vary smoothly from 3,5 kilogauss at injec
tion (1 MeV) to 6,6 kilogauss at full energy. The
field index, n, varies from 0.58 to 0.52, A
unique pole-tip design with an integral vacuum
chamber has been developed. The ampere-turn
requirements for the main poletip coils and
trimming coils have been determined. A simple
but highly precise magnetic field scanning device
has been developed for use with the SOCE
magnets,

HCUCCI
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Fig. 1. Plan view of 4-MeV Experimental SoC.
Introduction
The 4. MeV Separated Orbit Cyclotron
Experiment (SOCE) is being built to study
experimentally a variety of problems that are
theoretically complex, such as space-charge and
beam loading phenomena, and to gain practical
experience and insight into tha operation of the
· SOC as a system. The SOCE will be a multi-
particle variable energy, accelerator providing
protons in the energy range 1.7 to 4.0 MeV,
deuterons from 1.7 to 4.0 MeV, and 3He ions
from 2,7 to 8 MeV. Fig. 1 shows the plan of the
accelerator. The principal specifications of the
machine are listed in Tablo I. Variable energy
is accomplished by varying the magnetic field to
provide resonance at some chosen harmonic
(32-50 for protons). Addicional details of this
accelerator experiment will be found in compan-
ion papers in these Proceedings."
The magnet system for the 4-MeV SOC
departs radically from previous concepts. The
details of one sector magnet are shown in Figs. 2
and 3. Magnetic focusing is "constant gradient,"
as in a weak focusing synchrotron but, as a
result of the large circumference factor, the
focusing is actually quite strong. All pole tips
are of constant radius, a characteristic per-'
mitting the use of a simplified fabrication
method. The pole tip field strength varies
linearly with momentum, from 3,5 KG at injec-
tion to 6.6 KG at extraction for 4,0-MeV protons.
The field index, n, ranges from 0.58 to 0.52 in
steps through the machine; all magnets on the
first turn are n= 0,58, on the second n = 0.56,
etc.
Pole Tip Contours
The pole tips are 6.5 in, in width and have
a constant slope, except for a 0.375-in, flat
Table 1 - Specifications for the SOCE
Energy range, MeV
Protons
1.7-4.0
Deuterons
1.7-4.0
Alpha particles
3,4-8.0
SHe ions
2.7-8,0
Sectors
Turns
Turn separation, min, in,
Turn separation, max, in,
17.8
Beam radius, min, in.
62.0
Beam radius, max, in,
115.2
Aperture, in.
1.5 by 3,0
Pole-tip magnetic field (4-MeV p), G 3300-6600
Field index, n
0.58 -0.52
Magnet copper, tons
1.5
Magnet steel, tons
44
Magnet power (4-Me V p), kW
40
Harmonic number (4-MeV p)
32
Frequency, MHZ
Peak cavity volta ge (4-MeV p), kV
83.4
Cavity power 1088, kW
11.8
50
*Research sponsored by the U, S. Atomic
Energy Commission under contract with Union
Carbide Corporation,
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YOKE
MAGNETIC FIELD (KG)
DEVIATION FROM THEORETICAL (G)
(CCAISTANT SLOPE POLE FACES)


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BEAM APERTURE
TEUTTON
32ң
VIEW A-A
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INCHES
-2.5 -2.0 -45 -40 -0.
5 0 05 10 15 20 25
DISTANCE (in)
Fig. 4. Pole-tip magnetic field and gradient.
Fig. 2. Drawing of SOCE sector magnet.

CONSTANT IRON SLOPE
n0.56
FIELD DEVIATION (G)

REFERENCE 227 G/in. CONSTANT GRADIENT
15.25
1625
17.25
RADIUS (in)
18.25
19.25
--
Fig. 5. Deviation of magnetic fields for n=0.56
and for constant iron slope on pole faces.
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Fig. 3. The completed sector magnet.
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M
region provided at the inner and outer edges to
facilitate the welding of the integral stainless
steel vacuum chamber walls, Constant-slope
pole faces were used for simplicity of fabrica - :
tion and because they give a magnetic field which
closely approximates constant-n shape, is
Measurements of magnetic field variation with
radius across the beam aperture for an n=0,56
magnet are shown in Fig. 4. The deviation of the
magnetic field from a constant-n variation is
approximately 0.1%, see Fig. 5. Beam dynam.
ics studies show this deviation to be unimportant;
neither the beam emittance or phase acceptance
are significantly affected.
Fig. 6. Pole-tip ring assembled prior to being
cut into six 60° sector magnets. .
Pole Tip Coils and Power Supply Considerations
The magnetization curves for the four gaps
of the sector magnet are shown in Fig. 7. The
Pole Tip Fabrication
The magnet design readily lends itself to
mass production techniques, A 360° ring of tips
is machined as a single operation with a vertical
turret lathe. Fig. 6. The upper and lower pole
tip rings are assembled by welding stainlc88
steel rings at the inner and outer radii. A very
shallow weld is used to minimize warpage. The
pole-tip assembly also serves as the vacuum
chamber; suitable fittings will be provided at the
ends to couple to the beam pipe.
current and number of turns in each coil has
been chosen to give approximately the correct
magnetic fields in the four gaps. The trimming
coil adjustments needed to compensate saturation
effects are quite small; the gap fields are
maintained in a constant ratio to within 1/2%
over the 75-250 ampere operating range of the
magnet. Over th is range the mean magnetic
field of the maximum-energy pole tip varies
from 3000 to 9200 gauss. Coarse adjustment of
AAT
LEGAL NOTICE
*?41
This report was prepared as an account of Govorament sponsored work. Neither the United
States, nor the Comission, nor any person acting on behalf of the Commission:
A. Makes any warranty or representation, expressed (r implied, with respect to the accu-
racy, complotene!8, or usefulness of the information contained in this report, or that the uso
of any information, apparatus, method, or prucose disclosed in this report may not Infringe
privately owned rights; or
B. Assumos any liabilitos with respect to the use of, or for damages resulting from the
Uso of any information, apparatus, method, or procede disclosed ia this report.
As used in the above, "person acting on behalf of the Commission" includes any em-
ployee or contractor of the Commission, or employee of such contractor, to the extent that
such omployos or contractor of the Commissioli, or employee of such contractor preparos,
dibaominates, or provides access to, lay information pursuant to his employment or contract
with the Commission, or ble employment with such contractor.
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1

.. l'able II - SOCE Magnet Gap Interactions
.
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W=142 TURNS 100% E
Coil No.
. 1
ine
100% EFF
Change in Magnetic Field
Igauss/100 ampere-turns
Gap 1 Gap 2 Gap 3 Gal 4
34.5 : -1.12 -0.94 -0.75
-1.15 33.2 -1.26 -1. 14
-0.94 -1.31 33,1 -1.31
-0.79 -1.02 -1.23 33,4
w N
.
A
= 420 TURNS
(N=96 TURNS 100% EFF
N=76 TURNS 100% EFE
FIELD (KG)
4 by 1. 12, 0.94, and 0.75 gauss respectively.
These interactions are small enough to be
ignored in calculating the number of turns
required for each main coil but must be taken
into account in final adjustment of the magnetic
fields with the trimming coils, : The magnitude
of the interactions depends markedly on the size
of the yoke. For these data the yoke area is.
equal to the pole tip area (100% yoke). The gap
interactions are about a factor of 10 larger for a
50% yoke as measured on a 1/4-scale modol,
O 50 100 150 200 250
CURRENT (A!
Fig. 7. Magnetization curves for the four gaps.
in the prototype magnet.
Magnet Measurement System
Comprehensive mapping of the magnetic
field of the pole tips is necessary to determine
the effective magnetic length and the contribu-
tion of the end effects to the focusing properties.
The limited access to the 1.5 in, x 5.5 wide
magnet gap, a result of integral vacuum chamber
design, has necessitated the development of a
special Hall probe positioning device, Figs. 8.
and 9. The Hall probe is mounted on a non-
magnetic plate that is restrained radially and
vertically by small grooves in the vacuum tank
side walls. The azimuthal position is deter-
mined by a precision azimuthal. indexing device
(Ultradex) located near the magnet and coupled
to the plate by a long nonmagnetic bar. The
indexing device is mounted on a milling machine
table. The table horizontal motions are used to
locate rapidly the center position of the indexing
device when transferring the field measuring
equipment to a new pair of poles. The system is
capable of positioning the Hall probe in one-
degree steps within £0.001 in. It advances
:
the magnetic field of each pole tip to within 7%
of the correct value is made by choosing the
appropriate number of turns of the pole-tip coils.
Trimming windings on each pole tip provide fine
adjustment of the magnetic field; the maximum
trimming coil power required is approximately
50 watts (20 amperes, 2.5 volts).
The coils are waind with 1/4 in, square
copper conductor with a 1/8 in. diameter water
passage. The coils for each pole-pair consist of
8 two-layer sections. These are connected in
four parallel circuits (with due attention to
symmetry) to match an existing power supply.
The power requirement at the highest field is
1000 amperes ut 150 volts. The trimming coils
consist of 24-turn double layer pancake 8 of 1/8
in. square copper bonded to the main coil
sections to provide cooling. Although their
maximum current will be only 20 amperes they
are actually capable of 100-ampare operation.
:

RO - 17.25 in. !
MOVE ABLE
ALATE
HALL PADBE
1
-
Interaction Effects
The four pole-tip sets of a sector magnet
are weakly coupled by the yoke. The effect is
small, as illustrated by Table II. For example,
a 100 ampere-turn increase in the excitation of
pole tip 1 (lowest field) produces an increase in
magnetic field in that gap of 34.5 gauss and
decreases the magnetic field in gaps 2, 3, and
PRECISION DIVIDING HEAD
Fig. 8. Schematic of Hall probe positioning
device.
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automatically after the field at each position has
been measured and recorded. The radial posi-
tion for each azimuthal scan may be changed in
0.250-in, increments by inserting the Hall probe
block dowels into the proper holes on the
positioning plate.
References
R. E. Worsham, et al, these Proceedings.
2N. F. Ziegler, these Proceedings.
3s. W. Mosko, these Proceedings.
.
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Fig. 9. Field measuring device in prototypo
magnet.
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