SECTOR MAGNET FOR THE RIKEN SSC

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SECTOR MAGNET FOR THE RIKEN SSC

S. Motonaga, H. Takebe, A. Goto, Y. Yano, T. Wada, H. Kamitsubo

To cite this version:

S. Motonaga, H. Takebe, A. Goto, Y. Yano, T. Wada, et al.. SECTOR MAGNET FOR THE RIKEN SSC. Journal de Physique Colloques, 1984, 45 (C1), pp.C1-213-C1-216. �10.1051/jphyscol:1984142�.

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Colloque C1, suppl6ment au no 1, T o m e 45, janvier 1984 page C1-213

SECTOR MAGNET FOR THE R I K E N SSC

S. Motonaga, H. Takebe, A. Goto, Y. Yano, T. Wada and H. Kamitsubo The I n s t i t u t e of PhysicaZ and ChemicaZ Research IRIKENI, ~ a k o - s h i , Saitama 351, Japan

R6sumb

-

Abstract -Construction of the RIKEN separated sector cyclotron is now going well on schedule. Three among four sector magnets have been completed by now at the factory of the manufacturer. Measurement was made on the magnetic field and operational properties, as well as on the trim coil field for some trim coils at the factory in 1982. It was found that these magnets have good performance in accordance with the design.

I -LNTRODUCT I ON

The RIKEN separated sector cyclotron(SSC) is a multi-particle and variable energy machine and can accelerate ions ranging from proton to uranium in a wide range of energies/l/. The sector magnets should produce the field distribution which provides isochronism, focusing and orbit stability for an accelerated ion. In order to realize the desired field distribution in the range of 7 to 15.5kG, studies have been done /?/with the measurement of a model magnet and the calculations using the computer program TRIM/3/.

Fabrication of the sector magnets started in 1981. Three among four sector magnets have been completed up to now at the factory of the manufacturer.

Measurement on the magnetic properties, machining accuracies and operational properties was made with the first sector magnet excited. Measurement of the field distribution for the use of orbit calculation and that of the trim coil field for several trim coils were carried out with two sector magnets. These measurements were done in 1982.

I R this report we will describe mainly the results obtained from the

measurement of the completed sector magnets.

II -SECTOR MAGNET

The detailed design studies on the sector magnets are described in the previous

'Thn1.E I. hfearnred chorocferirlic> oJ the 10"; carbor report/2/. The magnet system of the RIKEN SSC

conlent d e r ! used for the PO!LI ~ l d ~ 0 i l . c consists of four sector magnets with a sector

0 f lhe srclor inagnef.r angle of 50" and a gap distance of 8 cm. Each

c si M~ P s cu sector magnet is 5.64 m in radial length, 5.24

-

i

PFlc. O , O j 0,001 0,09 0,01, O,OOS O.Oi 0.036 6 0 0 mm in height and it has the edge profile of

O.OoI 0,10 O.O1l 0.002 O , O i 0,031 approximately B-constant type. A flange for the

vacuum chamber is welded on the side of the

0.04 <0.01 0.31 0. 14

~ ~ <0,01 k0,30 0, ~ (,Vcig~,t { perccnij ~ ~pole. Twenty-nine pairs of trim colls are ~ ~

mounted on the pole face. The yoke is divided into twenty eight sheets of slabs for convenience of construction and transportation. The ratio of cross sectional area of the yoke to that of the pole base is 0.94, which is a minimum allowable value to achieve the required strength of the base field. Poles are made of homogeneously forged steel of low carbon content whereas yokes are made of rolled steel. Results of chemical analysis of pole and yoke materials are given in Table I

.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1984142

Cl-214 JOURNAL DE PHYSIQUE

The main coil of each pole consists of sixty-six turns and is formed in size of 50 mm in thickness and 465 mm in height. The sixty-six turns of each coil are divided into eleven units. The eight units of them are connected in series through four sector magnets and excited with one power supply. The other units are also connected in series but excited with another power supply equipped with bypass circuits which adjust the difference of magnetic fields among four sector magnets.

The power consumption in the main coils of each sector magnet was measured and was found to agree with the design value of 120 kW. Maximum currents of both power supplies are 1050A. Total power is 512 kW. Current stability should be better than 1 x 10-5/4/.

The trim coil is made of a copper plate 6 mm thick and has a curved shape along the equilibrium orbit. The radial width and position of each trim coil were determined by the optimization calculation based on the trim coil field calculated with TRIM/3/. A hollow conductor is welded to each trim coil to feed electric current. They are flash-coated with A1203 for electric insulation. The power consumption of all the trim coils including cables for wiring is about 216 kW/6/.

Four types of power supplies totally having 61 control units are required to optimize the field distribution./4/.

Measurement of the fabrication accuracies of two sector magnets was done by the manufacturer. The obtained accuracies of their fabrication and assembly are as follows:

Gap distance 0.04 mm Flatness of pole face 0.002 mm Sector angle 0.006 deg Misalignment between upper and lower poles 0.1 mm Profile of pole edge 0.13 mm Parallel setting of trim coil assembly 1 mm The yoke and poles are deformed mechanically due to the strong magnetic force, the gravitational force and atmospheric pressure. Structural analysis on such mechanical deformation of the sector magnet was performed using the computer program SAP-IV

.

m

For the details of the measurement of magnetic field, we refer to Refs./5,6/.

Measurement of the excitation characteristics and fringe field around the pole edge was done at the factory immediately after the completion of the first sector magnet.

Results of the measurement were quite satisfactory. Figure 1 shows the measured

20

1 5 -

-

-

- m

-

2

o

- Sector Magnet excitation characteristics of the sector magnet

-.-.. - Calculation together with the calculation. The magnetic field

- - 9 - Calcuiation (6% locrease yoke area)

- -x- Measurement of 15.5 kG, which is the maximum base field

1 5 . 5 k ~ -

Lpi

magnetomotive force of 1.28 x 105 ampere turns.

y ^,

^{, ,, ,}

- 1.39 x lo5 ampere turns, which is the maximum

r/'

/'

-

of the pole edge was made at the fields of 7, 10,

/'

l l l . ~ l ~ l l ~ l . l l l l where the calculated value is larger than the

0 0.5 1.0 1.5

Magnetmatlve farce(X 105AT) measured one by 2 % at the maximum.

F i g . 1. Excitation curve of the sector magnet. The field map for use in the orbit

=he data ( x ) are lol lotted together with the calculation Was measured with two sector magnets

by TRIM cade (a). Open set perpendicular to each other. Description on

circles (C) give the values predicted for the the field measuring sys tem is given in Ref. 8.

case in which the cross section of the yoke is increased by 6%.

Fig. 2. Ditributions of the average field along the radius at the 7, 11, 15 and 15,7 kG. Relative values normalaized to the field at 210 cm.

,,C$+

Ee,=135MeV/u lniectim radius

-

Fig. 4. Distribution of isochronous field for the 135 ~eV/u ~ 6 + ion near the nose region of the pole.

-

magnet

--

.

I

I I , . , l , , , , l , , ,

1 0 0 200 300

Radius hm)

Fig. 3. (a) Comparison of the effective sector angles and (b) comparison of the average field distributions along the center line of the sector magnet with those of two sector magnets at the field of 15 kG.

Measurement was made at the base fields of 7, 11, 14, 15.7 kG over the region from valley center to hill(magnet) center. Typical results of the radial field distribution are shown in Fig. 2. Figure 3 shows the change of the effective sector angle with the radius and the average field distributions along the radius, for the cases of one and two sector magnets. It can be seen that there is no remarkable difference between the two cases. In the nose region the average field decreases by about 3 % or the effective angle decreases by about 1'

.

Therefore, the isochronous field strength along the hill center line should rise in this region as shown in Fig. 4. Except in the nose region, change of the effective angle with the radius is less than 1' at every base field. The effective boundary moves inwardly from the pole edge with the increase of the field strength, which results from the saturation effect of the pole. The measurement of the trim coil field along the hill center line was made for eight of the twenty-nine trim coils

Fig. 5. Field distribution for the trim coils No. 14-15 with their current 150 and 300 A at the base fields of 7 and 16 kG.

C1-216 JOURNAL DE PHYSIQUE

with their currents of 150 and 300 A at the base fields of 7, 1 1 , 14, 15, and 16 kG.

A current of three hundred amperes was the maximum of the power supply then available. Figure 5 shows an example of the field distributions for a pair of trim coils with the currents of 150 and 300 A at the base fields of 7 and 16 kG. The field distributions of eight trim coils with a current of 100 A at the same fields are shown in Fig. 6. The saturation effect can be seen in the profile and magnitude of these field distributions. Optimal sets of the trim coil currents required for the isochronization were calculated using the measured trim coil data. The magnetic fleld distributions of coils other than those of eight trim coils were obtained by interpolating the measured data. Figure 7 shows the comparison of the calculated magnetic field distribution with the isochronous field fur 135 MeV/u ~6~ ion.

Because the deviation from the ideal isochronous field can be kept below 0.05 %, the phase slip is estimated not to exceed a few degrees.

-30 L

Fig. 6. Magnetic field distributions of the seven trim coils at the base fields of (a) 7 kG and (b) 16 kG. Each trim coil current is 100 A.

Fig. 7. Comparison of the calculated magnetic field distribution formed by the YriM coils with the

isoc ronous field for acceleration of Ck' ion to 135 MeV/u.

N --SUMMARY

Three among four sector magnets have been completed by now at the factory. We made the following measurement with one and two sector magnets: the machining accuracies, the fringe field, the field map and the trim coil fields. The measurement was performed at the factory. It was found that the completed sector magnets have good performance in accordance with the design. The whole sector magnet system will be delivered to our institute in the spring of 1984. Further detailed measurement for the whole sector magnet is scheduled to start in the summer of 1984.

REFERENCES

/I/. H. Kamitsubo: Sci. Paper I.P.C.R.n, l(1982)

/2/. S. Motonaga, et al., Reports I .P.C.R(in Japanese) 57, 156(1981) /3/. J.S. Colonias and J.H. Porst., TRIM, UCRL-16382(1965)

/4/. S. Motonaga, et al., IEEE, Trans., Vol MAG-I?, No. 5, 1836(1981) /5/. S. Motonaga et al., Sci. Paper IPCR

12,

/6/. A. Goto, et al., ibid, $54 /7/. H. Saito, et al., ibid. p49 /8/. H. Takebe, et al., ibid, p20