STUDIES OF THE INTERNAL AND EXTERNAL BEAM PROPERTIES OF THE INS SF CYCLOTRON
To Honma, Mo Sekiguchi, Ko Sato, Yo Sakurada, To Yamazaki, M. Fujita,No Yamazaki, Yo Ohshiro and T. Tanabe
Institute for Nuclear Study, University of Tokyo, Tanashi, Tokyo
1.

Attempts to understand the beam properties have been continued since thefirst beam was obtained from the cyclotrono A few recent results of the study
are given in this report just to show the present status of our understandingof the internal and external beam propertieso The beam data shown in the fowllowing were taken under the conditions of operation for acceleration of 22o5-MeV
protons in a "250-turn mode", which is usually adopted in this cyclotron in thecases of light ion accelerationo
It is known that a narrow exit slit of the ion source yields accelerated
ions of better quality than a wide slit[l]• We applied this principle to the ion
2osource of our cyclotrono The exit slit of the ion source which we normally use
is a tantalum plate with a slit of 1 mm width and 10 mm heighto Instead of thistype of slit, we tried a narrow slit of Oo2 mm width with an opening angle of60°, As a result, the turn pattern of the beam observed with the differential
beam probe became cleanero This improvement enabled us to observe the wholeacceleration process from the second turn to extraction,
An example of the beam data is shown in Fig. 1, whe:~:e the observed radii ofeach turn, the difference of raddi between the successive turns and the frequencyof the radial betatron oscillation are plotted as a function of number ofrevolution. From the period of oscillation we obtained the frequencies (shown as
the open squares in the Figo), which were found to be in good agreement withcalculated one based upon the measured magnetic field data[ 2 ](shown with dots).
By adjusting the valley coil, we obtained another datum which showed asmaller amplitude of betatron oscillation, In Fig, 2 the differences xK between
the mean radii rK observed and the radii reK of the equilibrium orbit are plottednumber of revolution. The radii reK were assumed to beas a function of3]
calculated from[2A(K+C) - BK 2reKwhere the parameters A, B and C were obtained by fitting the observed r~ witha quadrutic function of K in the middle turns where this formula was supposedly
applicableo The large deviation from zero in the early turns and extraction
region may be attributed to the phase slip. The parameters obtained from thefit were found to be consistent with those used for tuningo In particular thedee voltage calculated from the parameter A was found to be 42o6 kV while thesetting was 44 kV. The number of revolution up to extraction was found to be--293-

263, while the setting was intended to be 250.
3.
A beam profile monitor has been installe d just before the exit slit
ofthe beam analyzin g magnet in order to measure quickly the momentum
distribu tionof the extracte d beam. Our efforts have been directed mainly to understa
nding
the relation between the properti es of the internal beam and the energy
spreadof the extracte d beam. While so far we have not succeede d in getting

a clearsolution of this problem, a good example is shown in Fig. 3. The momentum
distribu tions were measured under the same conditio ns of tuning exceptthat theusual exit slit of the ion source was used in the case of (a) while
the narrowslit was used in the case of (b). The improvem ent in the energy, resolutio
n isevident.
Ep= 22.5 MeV~15BOOt =14.132 MHzEE

Vd=44kV

7,00~

Ez

600~

0~10(f)

0::

sbo2

w

4000::

0~

<(.

(f)

z0:::::Jz'

300 C)

Fig. 1.

~0.05

r-200

Mean radius, turnseparati on andfrequenc y of thebetatron oscillat ionI~050100+15150200
NUMBER OF REVOLUTION

f = 14.132 MHz
Vd= 44 kV+10A=2083
B=OA4C•0.61

100

250mm2mm2LEFT

RIGI-If"'·"-r----.-+-,,-i,+-.-'.--"n-.5lomm

Numberof(a)Revolutions(b)Fig, 2,Fig. 3.

Deviatio n vs. number of revoluti onMomentum distribu tion

1.
2.
3.

I Chavet and R. Bernas, Nucl. Instrum. & Methods 47(1967) 77
T. Tanabe et al., INS-J 154(1975 )-M. E. Losel et al., IEEE Trans. Nucl. Sci. NS-14(19 79)1087-294-