ON THE BEAM OF PHOTON FACTORY STORAGE RING
Y. Kamiya and M. Kihara
Photon Factory,
National Laboratory for High Energy Physics

Abstract
Since the comissioning of the storage ring in February, some of the orbit
parameters have been measured, so that they can be compared with the designvalues. Although preliminary, the results will be reported here.
1.

Closed Orbit Distortions

Due to the magnet imperfection and alignment errors, the actual closed
orbit should be displaced from the ideal one. The measured orbits show thepeak-to peak values of ±6 mm in the horizontal plane and ±4 mm in the verticalplane. These values are well below the expected maximum closed orbit distortions.
The closed orbit has been corrected by means of steering dipoles. Becauseof unavoidable errors in the readings of position monitors and the current
settings of the correctors, the correction should be made iteratively by themethod of the least squares. In the computer simulation, we have alreadyknown that eight correctors should be adequate in each iteration process,while there are 28 and 42 correctors in the horizontal and vertical planes,
respectively. Concludingly, three iterations are sufficient for the.correction
and the further iteration can not improve the smoothness of the closed orbit.
This shows that the correction of the orbit is ultimately limited by theaccuracy in the position monitor and the corrector. The resultant distortionof the closed orbit was within ±1 mm and ±0.5 mm in the horizontal and thevertical directions, respectively.

2.

Chromaticitie s

The variation of the betatron tune as a function of energy is called thechromaticity. The central energy of stored electrons can be varied by changing
the rf frequency, while keeping the magnetic field constant. Comparison
between theoretical and experimental values is seen in the following table.

3.

Natural chromaticity

E; = t:,vf (t:,E/E)

Experimental

Theoretical

5.0

5.4

-4.7

-6.6

Betatron Function

The focusing system of the storage ring consists of twelve families ofquadrupole magnets. Each family contains 4 to 8 magnets, and is energized byan independent power supply. The values of betatron functions Bx and By at
the position of quadrupole magnet can be obtained experimentally by measuring
the variation of betatron tunes Vx or Vy as changing the current of that
quadrupole family. The difference between theoretical and experimental values-85-

is typically 10%.
The dispersio n function nx was experime ntally obtained by measuring thevariation of closed orbit as changing the rf frequency . The discrepan cy
between theoretic al and experimen tal values is also less than 10%.
4.

Resonance s

Although the systemati c investiga tion of the resonance s has not yet been
performed , we have observed the linear coupling resonance s at Vx = Vy and thethird order resonance at Vy
4.33. At Vx = Vy the beam became round butstable, as expected. At Vy = 4.33 the beam became unstable.
5.

Current Dependent Phenomena

We have observed the tune shift and the tune spread depending on thestored current. The tunes in both direction s were shifted to higher values
with increasin g current, which suggests that positive ions are trapped in thepath of the electron beam and act as the focusing force onto electrons .
Beam blow-up phenomena have been observed in the horizonta l plane duringinjection , At a certain current value, the beam begins to blow-up suddenly
and be lost. It depends on the betatron tune and can be avoided by shifting
the horizonta l tune to higher values.

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