CORRECTION OF CLOSED ORTIIT DISTORTION TIY TIACKLEGWINDING OF HAIN RING MAGNET IN KEK-PS
N. Kumagai andK. EndoNational Laboratory for High Energy Physics
1. Introduction
The closed orbit distortion(COD) is induced by the error
field and misalignment of magnet along the ideal orbit. In theKEK 12 GeV PS, the COD of about 11 mm in the horizontal planearise from these errors in 48 bending magnets and 56 quadrupole
at injection field, which is playing a major role in process ofbeam loss at injection porch. About 6 mm in the COD are due tothe random fluctua tion(cr-=0. 064%) of SBdl in bending magnets.
We,then,corrected the errorfield of each magnet by using backleg
coil,and improved the beam loss.
2. Closed orbit distortion and its correction
When error dipole field(.AB(~)) is only present at the~osition(Y; ), the displacement(y(~K))
w(tp~c) is given by 1 )y(t/J~c)=*,Ai<,j·DJof the orbit at position(1)(2)
D.j=L1B("/t.j)l/(Bf)(3)
AI<• = {(ii"i; COSV(11: -14>~<-1/;·/).
..t SIN'(Jt.IJ1clnumberthe,where Dj is deflection angle due to jth error field,of betatron oscillations per revolution and f3~·and (31< is betatronfunction at position~ and at position~~· respectivery. Fromeq.1, if all of the error field are corrected to zero, the displacement can be zero at any position along the ideal orbit.
The purpose of backleg coil is to correct the error fi.eld of eachmat,Tiet.

3 •. System layout
The schematic relation of this backleg correction system isshown in fig.1. This system consists of the following threeparts:
1) Coil system in main ring2) Digital programable bipolar constant current power
supply(DFPS)
3) Interface for computer control
The coil system is made of backleg coil and its backing coilwhich are wound by 3 turns around the return yoke of bending
magnet with couper conductor of 2 mm tf> shielded by polyethylene.
In order to reduce the load of DFPS, both coil systems werecouplied by transformer out phase. The 48 backleg coil systems
are combined by 22 mm~ twisted pair cable to 48 DPPS in Mi service
house ,respecti very. The D:P.PS supplies DC current with the current
resolution of 10 rnA to backleg coil to keep the COD within 1 mm.
The maximum current of 10 A creates the maximum correction-field-187-

of 6.75 Gauss, whose field strength corresponds to 0.47% ofinjection field of 1440 Gauss. To provide the orbit correction
from control room, the DPPS is combined to satellite computer in
M2 service house. The data of correction current are transferedthrough the DMA channel of accelerator control computer(ACC) andstored in D/I me1nory of the interface. One data is composed of16 bits.
1~10th bit
are used for correction data and 11th bitfor polarity. The stored data are serially transfered to eachDPPS. ~xcitation current of the backleg coil is monitored periodically(...... 10 min) with digital voltmeter(DVM). Its scanning time
per one channel is about 1 sec. The monitored current is stored
in D/0 memory and read out to ACC through the DNA channel.
4. Results
Figure 2 shows output voltage of slow intensity monitor
before and after the correction of JBdl. After.correction, it
finds out that fast decay in beam intensity is decreased,and theaccumulation-efficiency is improved about 10-20%.
Reference1) A. Ando and K. Endo, KEK-75-4(1975)

digital programable·' vvv,.-power source- 1

digital programablepower source- 4B

Fig.1

Schematic diagram of backleg correction systeml•'ig. 2

left:before correction, right:-188-

after correction