JAERI-Conf 95-021

PB28

LATTICE DESIGN OF JHP CIRCULAR .ACCELERATORS
Y. Ishi and JHP synchrotron design group
Institute for Nuclear Study, University of Tokyo (INS)
3-2-1 Midori-cho, Tanashi-shi, Tokyo, 188 JAPAN

Abstract
The preliminary lattice design for the 3 Ge V booster
and the 50 GeV main ring in the JHP synchrotron complex has been done. The 3 Ge V booster accelerates protons from 200 MeV to 3 Ge V with the repetition rate
25 Hz, and injects them to the 50 Ge V main ring. The50 GeV synchrotron has no transition energy because ofthe imaginary-It optics.

1Introduction

The JHP accelerator complex mainly consists of the injector linac, the 3 GeV booster and the 50 GeV main ring (1).
The 3 Ge V booster is a rapid cycle synchrotron with theseparated function magnets. Each magnet is excited byan independent pulse power supply which is linked eachother by multi network system (2]. Therefore we can use
regular FODO lattice, and vary the horizontal tune andvertical tune independently.
The main ring has a novel lattice structure [3]. In thislattice, we can choose the value of the transition 1 as welike. This value in the 50 GeV main ring is an imaginary
number. In this report we represent the lattice designof the 3 Ge V booster and the 50 Ge V main ring. Theoptics code SAD (Strategic Accelerator Design) is utilized
to optimize the parameters and to do the particle tracking.

2...............20m

0 5 10Figure 1: Layout of the 3 Ge V booster
at the top energy. Table 2 shows the lattice parameters ofthe 3 Ge V ring.

Table 1: Parameters of the 3 GeY ·Booster
circumference
339.36m
superperiodicity
4structure
FODO
number of cells
24maximum 14.20
It
7.1
nominal tunc
(7.3, 4.3)
natural chromaticity -8.4, -6.3

3 Ge V Booster

The 3 GeV ring is operated in a very high repetition
rate 25 Hz which needs high rf acceleration voltage of
400 kV [4]. Thus the ring needs to have enough drift space
for the rf cavities. In this ring, 24 straight sections each ofwhich length is 6.57 m gives enough space for the rf cavities and the injection and extraction systems. Magnetic
field of the bending magnets is rather weak (8=0.95 T)
so that the rapid cycle operation is possible. The requirement that the ring is fitted into the KEK-PS tunnel makes
the superperiodicity of the ring 4. The overview of the ringis shown in fig 1, and the betatron functions are shown infig 2.
The nominal tune are selected as (Vr, lly) = (7 .3, 4.3).
The -rt is 7.13 which is substantially larger than -(=4.20

350 Ge V Main Ring

Protons are accelerated from :3 GcV to 50 GcV in the main
ring. At the top energy, -r is 54.3. In a conventional way ofdesigning a lattice by using regular FODO cell, It approximately equals to the horizontal tune llx. It is difficult
to avoid transition energy in the regular FODO lattice,because llx is about 20 - 30 in a machine of this scale.

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~
...

1.5~

1.0..:::!

~"3Figure 2: Beam optics functions of the JHP 3 GeV
booster. ,B.,:solid line, ,By:dashed line, 7].,:dash-dotted line.
Therefore, a imaginary-r1 lattice is employed to eliminate
the transition energy. The momentum compaction factor
is given by7J(s) ds,cr _.!_
(1)rl C p(s)= = ]_fwhere 7J(s) is the dispersion function, p(s) is the radius at
the orbit position of s in the ring and C is the circumference of the ring. A high It i.e. a low cr can be obtained
when the dispersion at the bending magnet are small.
In order to get this optics, we use a unit cell as shown in
Fig 3. This unit cell consists of three DOFO normal cells;.
..:::!

2/

I............/·.................... .

_______ ...../ /Figure 3: Beam optics functions of the imaginary--(1 latticefor the 50 Ge V main ring.
the central cell has no bending magnets. [n this configuration, the dispersion at the bending magnets are small. Ifthe integration of 17/ p is negative, -,1 becomes imaginary.
Hence the beam never encounters transition in this ring.
The benefit of using this lattice is that one can obtain
imaginary-r1 keeping the optics stable. [n the arc of themain ring there are two types of focusing quadrupole magnetsQF and QFX, and two types of defocusing quadrupolemagnets QD and QDX. The It is optimized so that its absolute value is less than 100 by using these quadrupole
magnets.
The. circumference of this ring is 1442m which corresponds to the harmonic number h=34. Since we need atleast four straight sections, we take superperiodicity of 4 .
The 90° arc consists of six unit cells mentioned above. A
bending angle of each bending magnets is 3.75°. There are
four straight sections for the injection and the extraction
systems, rf cavities and devices to prepare the polarized
beam. We are also investigating the possibility of employing superferric magnets, but here we report the feasibility of the ring using normal conducting magnets. In thisscheme, there are strong constraints in designing the lattice: magnetic field of the bending magnets should be lessthan 1.8 T, and field gradient of the quadrupole magnets
should be less than 25 T /m. Therefore length of the bending magnets is 6.2m; relatively strong quadrupole magnets
which are in the insertions and the missing bend cells havethe length of 2m; the length of the remaining quadrupolesare 1.5m. Length of the arc and the straight sections are
300m and 60.5m respectively. There are four normal cells
in each straight section. Each cell has 5.56m drift spacein which one can locate the extraction septa and kickers.
Two operating modes are considered with the same thelattice: a dispersion free mode and a high intensity mode.
In the dispersion free mode, the dispersion in the straightsections are zero for the polarized beam experiments. But
for the high intensity mode, we require minimum ,emax instead of dispersion free straight sections in order to reducebeam loss.
Since the natural chromaticities are high, the tune
spread due to the momentum spread is not negligible;
chromaticity correction is essential. The correction is
performed by two family sextupole magnets SF and SD.
SF's are placed on both side of QFX's, and SD's areplaced closed to the QD's in the missing bend straightsections. The necessary field strength of these sextupole
magnets to correct the chromaticity a.'S zero are not so high(SF:29Tfm 2 , SD:59T/m 2 ) because of the high dispersion
in the missing bend sections. With these non-linear elements, we obtain enough dynamic aperture [5]. Table 3
shows the lattice parameters of the 50 GeV main ring inboth operation modes.

3.1

Dispersion Free Mode

To provide the dispersion free straight sections, we set
the horizontal phase advance in the arc t.o integer; 1/Jarc =5 x 21r. Vertical tune is changed by using the all quadrupole
magnets in the ring. On the other hand, horizontal tune
is adjusted by varying the quadrupole magnets only inthe straight sections. Therefore, it is feared that themaximum value of the betatron functions become large
when the horizontal tune is changed widely. A tunability of this operation mode is tested on several operating points at which the tunes in the arc are (vx, vy)-327-=

JAERI-Conf 95-021

Table 2: Parameters of the 50 Ge V main ring

circumference
superperiodicity
structure
number of cells
maximum 1
Itnominal tune
natural chromaticity

dispersion free high intensity
mode
mode
1442m
4
3-cell DOFO
88
54.3
27i
51i
(24.25, 20.70)(22.73, 22.66)-32, -34-30, -31(5.0, 4.8), (5.0, 4.6)' (5.0, 4.4), (5.0, 4.2).
Fig 4 shows the betatron functions at the operating
point (vx, vy) = (24.25, 20.70).

3Figure 5: Beam optics functions of the 50 GeV main ringin the high intensity mode.
tunability of this mode is tested as well as the dispersion
free mode. We vary the tune Vx =22 - 24, Vy =21 - 24,
and find that (3's are less than 32m. Dynamic apertureis examined in several operating points and found to belarger than the acceptance.

Sum1nary4

The 3 Ge V booster has been designed with regular FODO
cell structure. It will be constructed in the KEK-PS tunnel. The 50 GeV main ring has been also designed with theimaginary-~(t lattice. We investigated feasibility of 50 Ge V
main ring with imaginary-It optics, and found that it hasenough tunability and dynamic aperture.
Figure 4: Beam optics functions of the 50 GeV main ringin the dispersion free mode.
With this optics, It = 27i, f3r;zax = 32m and f3;;'ax =37m. Even if we change the Vx and vy 23.25 - 24.75 and20.70- 23.06 respectively, f3's do not exceed 40m. Also t.he
dynamic aperture at each operating point is calculated respectively after the chromaticity correction is performed,
and is found to be larger than the acceptance. Thus substantial tunability is obtained with this operation mode.

3.2

References[1] Y. Mori, eta.!. In this proceedings[2) T. Adachi, et a!. Jn this proceedings(3) U. Wienands, eta!. "The High-~tt Lattice of the SSC
Low Energy Booster", Proc. of XV-th International
Conference on High Energy Accelerators, Hamburg,1992.
[4] C. Omori, et. a!. In this proceedings

High Intensity Mode

To keep the beam loss small in the high intensity mode,the beam size is desired to be small. Then we need to make(3 as small as possible i.e. to make (3max flat all ovet· thering. To do this, we sacrifice the benefit of the dispersion
free straight sections; but we still require the imaginaryIt. Fig 5 shows the optics of this mode. One can find thatno (3 modulations.
The dispersion function in the straight sections take nonzero values; but these values are not so high that the injection and the extraction can be done in these sections. A[5] S. Machida, ct. al. In this proceedings-328-