Chapter 3
Experimental Setup
This chapter contains a detailed experimental setup of the RAON EBIS charge breeder. The basic design and fabrication of RAON EBIS have already been done [16–18, 47, 58], and there have been some mod- ifications, complements, and sub-system changes since then. It briefly describes the previous design’s essential parts and the changes and sub-systems prepared for the experiment. As shown in Fig. 1.4, the structure of the RAON EBIS charge breeder can be divided mainly into the electron gun section, the ion trap section, the collector and the repeller section, and the ion transportation line. Figure 3.1 shows the schematic drawing of the overall system of the EBIS, including the electrode arrangement for each section along the path of the ion beam from and to the ISOL beamline. Each electrode’s color represents each HV platform and is the EBIS, the cathode, the repeller, the ion source, and the ground platform, respectively. The electron gun, the collector, and the repeller are important for the electron beam uti- lization, starting with the ion trap section where the charge breeding of the ion beam takes place. Their detailed setup is described for each section divided in this way. After that, the installation and utilization of the ion transportation line, which is essential for connecting with the ISOL beamline and the beam diagnosis, are described. Finally, the detailed setup of subsystems, including the vacuum systems, which are important for the charge breeding experiment of the EBIS, is shown.
RepellerDT #11 AP #01 AP #02DT #10DT #09DT #08DT #07DT #06DT #05DT #04DT #03DT #02DT #01Cathode Y-Steerer Gun CoilCollector CoilSC MangetSteering Coil Anode
EBIS Overall System ISOL Beamline
SteererEinzel LensSwitchyard Ground PlatformGround Platform
Ground Platform
Diag. Steerer
Dipole Magnet
Repeller Platform Ion Beam Path n+ Ion Beam
Steerer
Collector Einzel Lens n+ Ion Beam
15deg Deflector 2022. 08. 16 기준
1+ Ion Beam Ground Platform
IS Steerer
1+ Test Ion Beam
1+ Ion Beam Ion Source Platform
n+ Ion Beam IS Einzel Lens Ion Source
Extractor
Lens
EQTXY-SteererGroundGround
RepellerRepeller Diag. Einzel Lens
Cathode PlatformEBIS Platform Cathode Platform
Figure 3.1: Schematic drawing of RAON EBIS overall system.
electron beam might be unstable due to the mechanical misalignment or the misalignment between the magnetic field and the electrode. So, these steering coils are used to align the trajectory of the electron beam to the axis.
The superconducting magnet is made by Tesla Engineering Ltd. and uses the external helium com- pressor to lower the temperature inside the helium vessel to 4 K, maintaining the internal pressure around 0.25 psi. The current of 96 A flows through the internal solenoid coil in the superconducting state, and the axial magnetic field of the ion trap region becomes about 6 T, as illustrated in Fig. 3.2a. The bore length of the magnet is 1320 mm in total, and the region within±350 mm from the magnet center satis- fies 0.4% of the uniformity, as shown in Fig. 3.2b. Therefore, if the breeding region is in this 700 mm section, the behavior of the ion beam in the magnetic field can be stable, and the charge breeding can also be stably performed.
- 1 5 0 0 - 1 0 0 0 - 5 0 0 0 5 0 0 1 0 0 0 1 5 0 0
- 1
01234567
Bz [T]
P o s i t i o n f r o m C e n t e r [ m m ]
(a)
- 4 0 0 - 3 0 0 - 2 0 0 - 1 0 0 0 1 0 0 2 0 0 3 0 0 4 0 0
5 . 8 5 5 . 9 0 5 . 9 5 6 . 0 0 6 . 0 5
Bz [T]
P o s i t i o n f r o m C e n t e r [ m m ]
±0 . 4 %
(b)
Figure 3.2: Axial magnetic field by SC magnet between (a)±1500 mm and (b)±400 mm [18].
Figure 3.3 shows a drift tube and chamber assembly consisting of a long chamber with drift tubes installed in the superconducting magnet bore and two cross-chambers connected to both sides of the magnet. The blue structure on the left side of the figure is the gate valve in the direction of the electron gun, and the drift tube starts from the point between it and the cross chamber. This assembly includes DT
#01∼10 and extends the DT #10 at the right end to the front of the gate valve towards the collector. DT
#04∼07 is in the uniform region of the magnetic field in Fig. 3.2b, which is used as the breeding region, and DT #08 is used as a gate to trap incoming ion beams. As used in the simulation in Sec. 2.3, each drift tube has an inner diameter of 24 mm and a total length of 2068 mm. As illustrated in Fig. 3.3, long holes in each DT are designed for vacuum pumping, and each is fixed using ceramic structures for the electrical insulation. A baffle exists in the cross chamber on the right and is a structure for the differential pumping with the collector section. It prevents affecting the breeding area by the deterioration of the vacuum when electrons are dumped in the collector during electron beam operation.
One of the essential parts in the ion trap section for the EBIS charge breeding experiment is the steering coil. The steering coil consists of four pairs and is installed between the superconducting magnet and the DT chamber. These magnets are divided into the gun side and the collector side, creating
DT #01 ~ 10
Figure 3.3: Drawing of drift tube and chamber assembly.
a magnetic field in the horizontal and vertical directions, respectively. Each pair of coils can create a magnetic field of up to 50 G and is used to optimize the electron beam transmission if a misalignment is found during the experiment. In addition, this steering magnet is installed with the water jacket. Since the heat generated when using the coil can cause a deformation of the coil, and affect the temperature of the superconducting magnet, it can be cooled using cooling water in the water jacket.
Figure 3.4: Drawing of steering coil magnets on outside of DT chamber.
The electric potential of the breeding region must be applied up to 60 kV relative to the ground, as the condition of the ion beam extracted out from the EBIS is A/q < 6 and 10 keV/u. Therefore, the components of the ion trap section, including the drift tube, are generally mounted on the HV platform.
For this purpose, a stand to support them is installed using insulators, as shown in Fig. 1.4. Afterward, when the electron gun, collector, and repeller are installed, the electron beam is ready to be used.