of the ion beam can almost meet the acceptance condition using the beam optics of the ion transportation line. The repeller Einzel lens is used to adjust the beam for cases that fall short of this condition.
After manufacturing from the electron gun to the repeller assembly, they were installed on a stand with columns as an insulator. First, after the EBIS stand is located, the ion trap section, including the superconducting magnet, is installed thereon. After that, the collector and the repeller were installed, an axial alignment was adjusted using a theodolite, and an electron gun was finally installed. Figure 3.9
(a) (b)
Figure 3.9: Installation picture of ion trap section in (a) E-Gun side view and (b) repeller side view.
shows the finished installation photograph in the electron gun direction and the repeller direction. The electron beam transmission test is performed using the ion trap, the E-Gun, the collector, and the repeller, and the details of the experiment results are discussed in Sec. 4.1.
Repeller Switchyard Line
EQT Line
Figure 3.10: 3-D drawing of ion transportation line.
TMP
Cryo-pump Switchyard
Electrode Einzel Lens &
Steerer Assembly Pepperpot
Faraday Cup
Faraday Cup
Test Ion Source
Diagnostics
EQT
15°
15°
Figure 3.11: 3-D drawing of switchyard line.
electrode sends the ion beam straight or bending ±15◦ to transmit it according to the ion source to be used and the purpose of using the charge-bred ions. The beam coming from the test ion source is transmitted to the EBIS by applying the voltage according to the energy of the ion beam and bending 15 degrees. And, the beam coming from the ISOL beam line is transmitted in a straight line without any adjustment. When extracting, the highly charged ions from the EBIS are also sent in a straight line for the ISOL beamline transmission. And, they are sent to the diagnostics line by bending 15 degrees to measure using the dipole magnet of the EBIS.
And the injecting ion beam is optically adjusted using the Einzel Lens and Steerers to meet the acceptance condition, and the extracted ion beam is adjusted to be stably transmitted after the breeding
in the EBIS. When using these optics components, the parameters required to enter and exit the ion beam are different. So, the Einzel lens’ and the steerers’ voltages are changed according to the trigger signal using high-voltage amplifiers up to +30 kV for the lens and within±2 kV for the steerers.
Pepperpot and Faraday Cup are also mounted in the left cross chamber to measure incoming ion beams. Using this Faraday cup, the current of the ion beam transmitted from the test ion source or the ISOL beam line is measured, and the transverse characteristics, such as the emittance, are checked through the pepperpot. Since the pepperpot installed here is the closest diagnostic equipment to the EBIS, the acceptance for the injected ion beam was calculated based on this position. And, the exper- imental measurement is comapred with the simulation result in Sec. 2.4. An additional Faraday cup is installed to measure the current before the switchyard bends the ion beam from the test ion source.
Figure 3.12 shows an installation picture of the switchyard line connected to the previously installed ion trap, electron gun, collector, and repeller. Since all components of the switchyard line are on the
Figure 3.12: Installation picture of switchyard line.
ground potential, a stand for fixing the chamber is installed without a separate insulator. However, since the configuration described in Secs. 3.1 and 3.2 is on the HV platform, the fence is installed to avoid an accident by the high voltage, as shown in Fig. 3.12. The fence also prevents people from entering the high magnetic field area during the experiment. Thereafter, the test ion source, the diagnostics line, and the EQT line are installed on the three-pronged road, respectively.
3.3.2 Test Ion Source Line
The design, fabrication, and testing of the test ion sources used for the charge breeding test of the EBIS were conducted [17, 18]. The test ion source line consists of an ion source assembly, an acceleration tube, and a beam optics system, as shown in Fig. 3.13a. The ion source assembly is located on a high- voltage platform to control the energy of the beam being extracted out. Figure 3.13b shows the ion source assembly. It includes an ion source pellet using various elements, a focusing electrode for focusing when emitting beams, an extractor electrode for extracting ions from the pellet, and a lens electrode for stably sending the beam. For the same reason described in the previous session, the ion source assembly and the chamber connected with the switchyard are connected using an acceleration tube. Additional Einzel lenses and steerers were installed to transmit beams to the switchyard line stably.
Acceleration Tube
Ion Source Assembly Einzel Lens
& Steerers TMP
(a) Test ion source line.
Ion Source Pellet Focusing
Electrode
Extractor Electrode Lens
Electrode
(b) Ion source assembly.
Figure 3.13: 3-D drawing of (a) test ion source line and (b) ion source assembly [17, 18].
This test ion source was manufactured to use ions of various elements, and simulations were con- ducted on Cs ions using the SIMION. It confirms that the RMS emittance was about 22π·mm·mrad for beams after being transmitted to the collector [17, 18]. In addition, the Cs ion test of the manufactured test ion source was conducted, and the RMS emittance was measured as 30π·mm·mrad for a beam with 1µA at 4.9 keV energy using a pepperpot [18]. In the later experiment using the beam energy of about 20 keV, the beam’s emittance from the test ion source is expected to satisfy the acceptance condition. It shows the transverse characteristics of the Cs ion beam with an energy of 20 keV measured in Sec. 4.3.2.
3.3.3 Diagnostics Line
The diagnostics line for analyzing the characteristics of the ionized and charge-bred ion beams trans- ported from the EBIS is connected to the switchyard line. In Fig. 3.11, it is connected in a downward direction of 15 degrees, and as shown in Fig. 3.14a, the dipole magnet for A/q scanning and the Faraday cup with a slit for measuring the separated beam are installed. In addition, in order to accurately sepa- rate each A/q in the scan measurement, the Einzel lens and steers for focusing on the Faraday cup are installed before the dipole magnet.
Einzel Lens & Steerer Assembly Faraday Cup
With Slit
TMP
Dipole Magnet
(a) Diagnostics line and optics assembly.
Slit (Width < 6 mm) Slit Adjuster
(b) Faraday cup assembly with slit.
Figure 3.14: 3-D drawing of (a) diagnostics line and (b) Faraday cup assembly.
Since the energy per charge of the ion beam measured by the diagnostic line is up to 60 keV/q, in the beam optics assembly, the Einzel lens uses a voltage of up to 30 kV, and the steer uses a voltage of
±1 kV. A slit is mounted in front of the Faraday cup used in the dipole magnet scan of the ion beam, as shown in Fig. 3.14b, and the width of this slit is adjusted up to 6 mm by a slit adjuster. The slit width of 4 mm was used in the charge breeding experiment of the ion beam. Its width is adjusted experimentally according to the focusing strength of the Einzel lens to send the ion beam from the switchyard line to the Faraday Cup. The specifications of the dipole magnets used in the diagnostics line of the EBIS are shown in the Table 3.1. The range where the A/q scanning is possible using this dipole magnet can be
Deflection Angle Bending Radius Max. B Field Power
90◦ 400 mm 0.25 T 52 A, 46.6 V
Table 3.1: Specification of dipole magnet.
calculated using the magnetic rigidity [59] represented by Eq. (3.1), Bρ= p
q =
√ 2mE
q =
√ 2
s m
q ×E
q, (3.1)
whereB, ρ, p, and qare the magnetic field, the bending radius, the momentum of the beam, and the charge of the ions, respectively. And this can be represented by the mass-to-charge ratio, A/q, and the energy per charge, E/q. So, using Eq. (3.1) with the maximum B field and the bending radius in Table 3.1, the maximum A/q that can be measured is determined according to the energy per charge.
EBIS’s HV platform can operate up to 60 keV; accordingly, the extracted beam can have maximum
energy per charge of 60 keV/q. With this dipole magnet, the A/q value of an ion beam with this energy can be measured up to about 8, and the A/q measurement range is higher if the energy of the ion beam is lowered. Therefore, the diagnostics lines were installed to enable the measurement of ion beams corresponding to A/q < 6 and energy per nucleon of 10 keV/u, the specifications of the RAON EBIS.
3.3.4 EQT Line
In order to successfully conduct the charge breeding experiment in the EBIS, the singly charged ions should be transported appropriately from the ISOL beamline, and the produced charge-bred ions should be stably sent to the post-accelerator. Thus, the beam optics systems and the beam diagnostic devices are installed between the switchyard line and the EBIS branch point of the ISOL system to form the EQT (Electrostatic Quadrupole Triplet) line, as illustrated in Fig. 3.15a.
EQT Assembly
XY Steerer Y Steerer
Faraday Cup Pepperpot Faraday Cup
Pepperpot
Switchyard
EBIS Branch Point TMP
(a) EQT line. (b) EQT assembly.
Figure 3.15: 3-D drawing of (a) EQT line and (b) EQT assembly.
The quadrupole electrode used in the EQT assembly is manufactured with a radius of 34.32 mm, a distance of 60 mm, and a length of 120 mm, and consists of three sets. A quadrupole electrode has a voltage to have a polarity like that of an electrode facing each other and a polarity opposite to that of side electrodes. So, the ion beam is focused in the direction of the electrodes with the positive voltage and defocused with the negative. In addition, two sets on both sides of the three sets apply the field of the same polarity, and one set in the center uses voltages of different polarity than the rest. For example, suppose a vertical focusing field is created by applying a positive voltage in the vertical direction in the center set. In that case, it is focused horizontally through the positive voltage in the horizontal direction on both sides. It is possible to transport the beam from the RFQ-CB to the EBIS stably and the charge- bred ion beam to the ISOL beam line using this triplet. Additionally, the XY steerer is installed in the middle of the EQT line, and the Y steerer is installed in part connected to the EBIS branch point to adjust the direction of the beam to fit the axis. Only the vertical steer is used next to the EBIS branch point because an ion beam from the RFQ-CB is bent horizontally from that point. One set of diagnostic devices consisting of the Faraday cup and the pepperpot emittance meter is installed after the EBIS branch point to check the characteristics of the beam transmitted to the EBIS. After the beam is adjusted using the EQT, the second diagnostic set is installed and measures the beam once more before
the transmission and entering the switchyard line. The charge breeding test is conducted by transmitting and injecting a beam to make it suitable for the acceptance condition of the EBIS using the beam optics of the switchyard line by the result of measurement by a diagnostic system.
Diagnostics Line
FC with Slit
EQT Line Test Ion Source
RFQ-CB
EBIS Branch
Point
Figure 3.16: Installation picture of test ion source, diagnostics and EQT line.
After the switchyard line is installed, three lines designed and manufactured as above, the test ion source, the diagnostics line, and the EQT line, are installed, as shown in Fig. 3.16. After that, in the residual gas experiment, the A/q spectrum of the residual gas ions is measured using the diagnostic line, and then the measurement of the charge-bred ions using the test ion beam is performed. In addition, in connection with the ISOL system, an ion beam entering through the EBIS branch point on the right side of Fig. 3.16 from the RFQ-CB shown in the upper right side is used. Afterward, the highly charged ions are transmitted to the A/q separator in the ISOL beamline toward the post-accelerator.