The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Pulsed Septum Magnet with a Wide Flat-top
Kiyoshi KITAGAWA, Yoshir() IR1E, Tadarnichi KAWAKUBOKEK Accelerator Laboratory, High Energy Accelerator Research Organization, Tsukuba, lbaraki, 305 JAPAN
Abstract

At the cyclic particle accelerators, we usually use theseptum magnets when the beam is injected and extracted.
When the magnetize current is an impulse wave but not aD.C. wave we need level the highest point of the pulse.
At the KEK PS accelerators, till today duration of theflat-top has been 100 p.Sec(4-msec base and 8000 A peak).
Because we made the new power supply which is
expected to 350 p.Sec (At the same base and peak current).
we want to report the circuit and principle, and conclusion.

current and the voltage ofthe load.
But, when a center of theshaking time moves wemust adjust every time.
Also when the difference of
Fig-2 ( b )the frequency is less than
10-kHz the beam is injected a way :from the closed orbit
occasionally.
Therefore, we have to increase the flat top time of thepulse, twice or more.
2 Requirement of the Pulse Format
at a Rating or the Load

1 Introduction

In KEK, proton accelerator consists of many sections,
pre-injector, linac, booster,and main-ring. (Fig-1)
When the beam isextracted from the booster,
the frequency of acceleration is 6.027-MHz, andwhen the beam is injectedto the main ring, it is6.017-MHz.
Because there is difference of 10-kHz between
the two frequencies, theperfect transport timing
comes every 100 p.Sec.
So we have needed thepulsed septum magnet.
where the duration of theflat-top is 100 p.Sec, but
recently, we need thelonger flat top time, toanswer to the sift of thecenter of the shaking time,
and the difference of thefrequency. Structure of thecircuit is shown in Fig-2(a).
Resonance circuit consistsof the condenser-(Co) andthe reactive load-(Lo).
Fig-2(b) is sinusoidal..

There are several methods to increase duration of theflat-top of the pulse. But we must usc the existing load andtransformer.
The specifications on the load magnet arc in thefollowing:
1) Peak current must be about 8000-A.

(Output of the power supply is 1600-A.)
2) Peak of the voltage (maximum ofLo•dlldt) is less than200-V.
(OUtput of the power supply is 1000-V.)
3) Product Ilflt of the load is less than 270-Ascc/pulsc.
(OUtput of the power supply is 55-Ascc/pulse.)
These requirements are derived :from view point of heat,voltage, magnetic saturation of the core of the transformer
and droop in the secondary current.
In order to the requirements (1}-(3), ~c form of the pulse
must be like the trapezoid only: neither sinusoidal current
with wider base nor P.F.N. can be used.
3 Construction and Calculation,of the New 1yPe Power-supply

3.1Principle

Fig-~ shows principle of the construction of our circuit. Inthe circuit. the current of the coil (Lo) satisfies the next
differential equation.

atr ( 111)d I
2

r7+ GJL,. + CiLo + CiL,. c4 2 + GJCi.fvL1 =O• • • • •(1)

The general solution lo(t) of this equation appearsl 0 (t) =Ac.ostDtt+ BsintDtt+C~t+Dsin~t••••••• •( 2)·~ Fig-2 (a)-47-The I I th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

between the two coils.
4 Adjusting Co,Cl and L1

4.1 CoWe adjust the Co under the suitable Ct.Lt ( Ct •• Co/10,Lt •• Lo /10).
Consequently we obtain Co= 2700 )Lf, but this value islarger than old one (Co=2200 J.Lf) .
• • • .. • • ( 4)By changing the Ct. we adjusted a flat-top to lie on astraight line; not-curving on the top.
.
.
The width of flat-top, having 0.1% flatness, IS shghtly
increased by making a concave shape at the top ; this isdone by using smaller Ct value.

Further we take the values of Co, c~. Lo. L1..s_= ..!:...L.=C 0

L0n((n - 1) 2=P1)

We obtain

4.3 L1and equation ( 4 ) isJ 0 (t)=(n - l)aJ 0 L 0

E 0 sin--aJ 0 t
n1+

By changing the Lt. we leveled the highest point (straightline). Firstly, we adjust roughly for exchanging taps andbring the straight line to near the top. Secondly, we adjust
the details for changing M (moving the coil Ltt)
A pulse motor is mounted to adjust L1 from the remotecentral control room, too.

n -1n22(n 2 - l)aJo Lo[~ > £11 >0, and(5)E 0 sin(n-l)aJ 0 t
1%=t/Jc;ro]When we choose n to 4m-l (m is integer), equation ( 5)appears on Fig-4 (a) , (b) , (c) and (d) for m=l,2,3 and 4,respectively.
For n (=4m-l), most desirable one is 3, but we adopt 11
because of too high inductance(Lt). longer base-line andringing. (CdCo=LtiLo=O.ll ). .
.
...
It can be confirmed easily that tf a capactty and mttial
voltage of the condenser-(Co) are same at the circuit of theFig-2. 111e peak current and maximum volta?e of the ~oad­(Lo) are same also but a skirt of the pulse ts expandmg alittle( n/(n-l)time ).
This is one of the reason which we could not adapt 3 or 7forn.
3. 2 Construction

For the circuit of the new power supply is shown in Fig-5.
The equation of this circuit is given like the equation(!).
(For dldt=>D){(CoD+go)(CtD+gt)CLoD+ro)(LtD+rt)+(CoD+g)(L1D+r t)+(CoD+go)(LoD+ro)+(C1D+gt)(LoD+ro)+ 1} Io=O • • • • • • • •( 6 )Where L1=Lil+L 12+2M+L2, go,g1.ro and r1 are conductance and resistance of Co,CJ.Lo and Lt. respectively.
Since it is very difficult to solve this equation, and also
we don't find out the correct value of Lo and ro. we haveprovided many corrective condensers in. order t~ fineadjust the C1-value, and varied M by changmg the dtstance5 Driving the Power-supply with Load

We take 210 ).IF and 175 )Lf for Ct. and 2700 )Lf for Co.
The current wave form by the current transformer (CT) is
shown in Fig-6; (a) is the case for an old power supply, (b)is new one. And expanded top shapes of these curves areshown in fig-7; (a) is for conventional resonant network, (b)and (c) for C1=210 )Lf and 175 )Lf, respectively.
It can be seen that time of flat top is expanding from 2.5
to3.5 times rather than that of the old one.
6 Test by the Beam

Then we studied magnetic field wave of load magnet bypassing 500MeV proton beam through it. Kicked angle ofbeam was studied using profile monitor. ;Result of the test
is shown in Fig-8.
It appears that (a) : real positions at a profile monitor ~d(b) : variation of a kick angle by the septum magnet whtch
is calculated from(a). (0:Ct=200 )Lf, •:Ct=175 J.Lf)
7 Conclusion

Because there is no large difference between Fig-7 andFio-8
it is adequate to adiustusing C1 and L~.which. haveb)~
the parameter near the calculated value, only by seetng thecurrent wave form from the CT.

-48-The 11th Symposium on Accelerator Science and Technology,Harima Science· Garden City, 1997

Acknowledgment
The authors thank Mr.Y.Arakida who helped taking dataand exchanging condenser and tap of coil, and Mr.T.
Tanigaki (I. D.X.) who made the power supply accepting
our difficult orders.

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