Conceptual design of multipole injection kicker magnets for the ILSF storage ring

The standard injection scheme of the Iranian Light Source Facility(ILSF) is composed of 2 septum and 4 kicker magnets installed in a 7-meter-long straight section. Further tuning of the 4 kicker devices to reduce perturbations has proven to be almost impossible since it requires having 4 identical magnets, electronics and Ti-coated ceramic chambers. Different from pulsed dipole kicker magnets used in a conventional local-bump injection, a single nonlinear or multipole kicker provides a nonlinear distribution of magnetic fields, which has a maximum value off the axis where the injected beam arrives and a zero or near-zero value at the center where the stored beam passes by. So, here the designs of different multipole kickers, including sextupole, octupole and a nonlinear kicker, have been investigated and compared.


Introduction
Injection by 4 dipole kicker magnets is the most common injection method, which is also used in the ILSF.A new injection method using multipole kicker magnets has been proposed to solve the problems associated with dipole kicker magnets by the ALS [1], and the BESSY [2] was investigated, which was also noticed by ILSF.The magnetic field in the center of the multipole kicker magnet is zero, and the stored beam moves in this central area.The septum magnet deflects the injected beam toward the multipole kicker magnetic field.The beam was injected with the horizontal position and angle of -17.0 mm and 0.141 degrees, respectively.The multipole kicker magnet is positioned in the same straight as the septum magnet.The phase space demonstration of beam injection into the ILSF storage ring has been shown in figure 1.
This paper examines three designs, sextupole, octupole and nonlinear kicker magnet, for injection into the ILSF stored beam.

Sextupole magnet
For sextupole simulation, first, determine the desired aperture size and pay attention to the equation for a normal sextupole with ideal poles, 3 2 y- 3 = 3 ,[3-4], we draw the simulation.Considering the beam stay clear, the aperture radius of the sextupole is chosen the same as the main storage ring sextupole magnets, R=15 mm.
According to NI= ′′  3 6 0 ⁄ , where  ′′ is the field strength, R is the aperture size, and the current is 385 At, comparable to the required current in OPERA code [5].The main parameters of the sextupole magnet for the injection are given in table 1.    ⁄ , where B (3) is the octupole field gradient, the required current is 1510 At.Table 2 lists the main parameters of the octupole simulation for the injection.   ⁄ Figure 4 shows the flux line of the octupole kicker magnet, and the vertical component of the B field is shown in Figure 5.

Nonlinear magnet
A nonlinear kicker magnet has minimal effect on the stored beam [1][2], encouraging us to test and design it.Four coils are symmetrically arranged horizontally/vertically to provide a nonlinear field to reach a required magnetic field of 81.1 mT at the injection point with a flat top and to have a zero field at the center with a larger width.As plotted in figure 6, the current in the 4 inner parts of the coils is towards the inside of the plate, and the 4 outer parts are towards the outside, which the positions of the coils are too sensitive while magnet design and for sure for fabrication.Table 3 shows the main parameters of the nonlinear kicker magnet.

Conclusion
By comparing the three performed simulations, the nonlinear kicker magnet scheme minimizes the disturbances on the stored beam due to having a zero in the center with a large width.Also, the nonlinear kick-er magnet increases injection efficiency.As a result, a nonlinear design has been chosen to replace the four dipole kicker magnets in the ILSF storage ring.

Figure 1 .
Figure 1.Beam injection layout in phase space using multipole kicker.

Figure 2
Figure 2 shows the flux line of the sextupole kicker magnet, and the vertical component of the B field is plotted in figure 3.

Figure 2 .
Figure 2. Flux line in the sextupole kicker magnet by OPERA2D.

Figure 3 .
Figure 3. Vertical magnetic field for the sextupole kicker magnet

Figure 4 .
Figure 4. Flux line in the octupole kicker magnet by OPERA2D.

Figure 5 .
Figure 5. Vertical magnetic field for the octupole kicker magnet

Figure 6
Figure6shows the flux line of the nonlinear kicker magnet by OPERA2D, and the vertical magnetic field B field is shown in figure7.

Figure 6 .
Figure 6.Flux line in the nonlinear kicker magnet by OPERA2D.

Figure 7 .
Figure 7. Vertical magnetic field for the nonlinear kicker magnet

Table 1 .
Main parameters for the sextupole kicker magnet.

Table 2 .
Main parameters for the octupole kicker magnet.

Table 3 .
Main parameters for the nonlinear kicker magnet.