NON-DESTRUCTIVE EMITTANCE MEASUREMENT FOR THE KEK 20 MeV LINEK. Ebihara, M. Tejima, T. Kawakubo
S. Takano, z. Igarashi and H. Ishimaru
National Laboratory for High Energy Phy'sics
Abstract
The transverse emittance of the)linac beam is measured non-destructively
by the use of five profile monitors 1 which are the secondary emission typewith the multi-wire. This measurement usually takes such assumptions that theemittance shape of the beam is elliptical and the intrinsic beam profile is theGaussian distribution. Therefore, if the real beam is different from theseassumptions, the error of the measurement becomes very large. In order to makethis error small, we take only the former assumption, but don't use the latterone. Owing to this improvement, we can calculate the beam emittance which isvery similar to the real one, even if the beam profiles are far from the Gaussian
distributions.
Fundamentals for the percent beam in the measurement
In order to measure the beam emittance non-destructively, the five profile
monitors are installed in the 20 MeV beam transport line be.tween the linac andthe booster synchrotron. The square of the beam half width Wk' which is measured
at the k-th profile monitor, is expressed as follows;(1)

where E is the beam emittance, So, ao and Yo are the twis parameters at thefirst profile monitor and a 1 .(j = 1, 2) is the element of the transfer matrix
from the profile monitor to the k-th one. And the beam center Yk at the k-thprofile manito~ is expressed by the terms of the center Yk and its first deriva·
tive yJ at the first profile monitor as follows;
k o'k okk
(2)(k = 0, 1, ---, 4)a11Yc + a12Yc
Yc
The beam widths Wk and the centers yk are measured from the outputs of fiveprofile monitors. Putting these valfies into the equations (1) and (2), theemittance parameters Ek' ak' Sk' Yk' Yk and Yk' are calculated by the leastsquar method.
As shown in the Fig. 1-b, the profile g9o (x), in which 90% of the beam
is contained within the corresponding ellipse, can be calculated as follows;
g9o(x) = gloo(x) - (Gloo/10 S1oo) h(x)Xwheref max g 100 (x) dx, which is corresponding to the 100% beamXprofile area,•m1nXf max h(x) dx, which is corresponding to the elliptical areaof the 100% beam emittance,
xminh(x) in this equation means the height which is shown with the slant line in
the Fig. 1-b. By using the equation (3), the profiles of the 90% beam at
every five profile monitors can be obtained. The half widths and the centersof the 90 % beam are easily calculated from the obtained profiles. Puttingthese values into equations (1) and (2), E, a, S, y, Yk and Yk' at the 90%-155-beam are calulated. Using the same technique, the characteristic s of 90 %,80 %, .•••• and 10% beam emittance are obtained successively.
The measurement and the calculation of the beam profile are performed
with the minicomputer (MELCOM-70).
Results
The emittance figure calculated by this method is shown in Fig. 2. As
compared this figure with the emittance figure which is Teasured by the use of
the single slit multi-collecto rs type emittance monitor 2 • the emittance shapes
agree well each other. The difference of the emittance size has been studied
at present. Finally, the characteristic s of the percent emittances are shownin the Table.
References1)
2)

H. Ishimaru et al., Recent Progress of the Beam Profile Measurements for
KEK 12 GeV proton Synchrotron, Proceeding of the 2 1 nd Symposium on Accelerator Science and Technology, (1978) 125.
KEK Annual Report 1975, (1975) 11.
TABLE.

CHARiotCTER I STI C OF .,'• EtHTTAHCE

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80%7e·-;

e.e;~59~49%

30~:20%10!;

Et'IIT

79.(9f.5.Q957.61

42.61

37.60

28.63

·C.G .. 71

25,58

25,4B

23.99

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BETA

3.23

2 .. 74

2.67

1 .. 99

1. 82

~.52

2.%

2.66

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2.50

GAtlN

8.7i

i:l.ille.·~!6,?90.6'?

e'r.::.,,,0.73

1:),58!:),513

0.47

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o1r<:Ar1112X

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Fig.l-a %Emittance Figure-812Fig.2 %Emittance Figure

Fig.l-b Beam Profile-156-