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A COMPACT 2.45 GHz MICROWAVE ION SOURCE BASED HIGH FLUENCE FACILITY AT IUAC Narender Kumar*, P. S. Lakshmy, G. Rodrigues, Y. Mathur, R. Ahuja, R. N. Dutt and D. Kanjilal Inter University Accelerator Centre, New Delhi-110067, India when the rings were separated by a distance of 140 mm. Abstract A compact 2.45 GHz microwave ion source has been designed and developed for production of low energy, high current singly charged ions at Inter University Accelerator Centre (IUAC), New Delhi [1, 2]. The heart of this facility consists of a permanent magnet based 2.45 GHz microwave ion source. The facility is used for ion implantation, phase formation, etching and surface patterning experiments. The ion source consists of a compact cavity with two movable permanent magnetic rings and 2kW microwave generator along with water cooled magnetron-head. It is designed to generate various ion beams of singly charged ions having energy up to 30 keV. A description of the design of 2.45 GHz microwave ion source and associated LEBT and few experimental results are presented. INTRODUCTION Figure 1: View of 2.45 GHz compact microwave ion source. Microwave ion sources are well known for their stability, ruggedness and for their long lifetime due to absence of electrodes. Microwave ion sources operating at 2.45 GHz in the off-resonance mode are being utilized for various applications in many laboratories, viz., for industrial applications [3], high current ion implanters [3], and ion beam deposition [4]. Depending upon the plasma density, ion beam intensities extracted for the singly charged ions can be very intense. A microwave ion source operating at frequency 2.45 GHz has been designed and developed at IUAC, New Delhi [1, 2]. This ion source is able to deliver relatively intense beams of lower mass singly charged ions that is used for ion implantation and ion deposition experiments. DESIGN AND INSALLATION OF 2.45 GHz MICROWAVE ION SOURCE BASED HIGH FLUENCE FACILITY At IUAC, we have designed and developed a 2.45 GHz microwave ion source based, high flux facility. The ion source consists of a non-magnetic stainless steel cavity designed for operation in the TE111 mode. The ion source constitutes of two NdFeB permanent magnet rings, each of the permanent magnet ring consists of 6 wedge shaped sectors having dimensions of 45 mm × 35 mm as shown in figure 1. The pole tip field of each sector is approximately 1 T. They are arranged in a non-magnetic stainless steel jig such that their magnetization is in the radial direction. The axial magnetic field generated by these two magnetic rings can be tuned by changing the distance between the magnetic rings with respect to each other. Figure 2 shows the measured axial magnetic field * [email protected] Figure 2: Measured axial magnetic field using two permanent magnet rings separated by distance of 140 mm. The calculated ECR surface at the operational frequency of 2.45 GHz using TRAPCAD [5] is shown in figure 3.Standard 900 bend, WR340 waveguides have been used for microwave coupling between the 2.45 GHz, 2 kW water cooled magnetron and the cavity. A quartz window is used for vacuum isolation between plasma chamber and waveguides. The high voltage DC break which consists of a thin teflon sheet, is used for high voltage isolation of ion source from ground potential and at the same time allowing the propagation of microwave energy. In order to minimize the reflection of microwave power, a ‘three-stub’ tuner is coupled between the magnetron and plasma chamber. The cooling of the plasma chamber and the microwave window is maintained by using compressed air all along the length of the plasma chamber Figure 3: Calculated ECR surface at 2.45 GHz. EXPERIMENTAL RESULTS After installation of ion source, it was integrated with the low energy beam transport system as shown in figure 5. The operation of the source and LEBT parameters is controlled and monitored using LabView interface [6] with wireless control. For hydrogen plasma working with a gas pressure of 1.4 × 10-5 mbar, microwave power 250 W and extraction voltage 20 kV, the measured total beam current, was 1.8 mA. In the case of nitrogen plasma, we obtained 760 µA of beam current at a working gas pressure of 8.4 × 10-6 mbar, microwave power of 250 W, and extraction voltage 20 kV. The variation of total beam current of hydrogen and nitrogen with extraction voltage is shown in figure 6. The tendency shows that still higher intensities can be extracted at higher voltages. Figure 4: View of the microwave ion source coupled to the microwave and extraction systems. Figure 6: Measured total beam current with variation of extraction voltage for hydrogen and nitrogen plasmas. The extraction system is a standard ‘three-electrode’ system working in the ‘accel-decel’ mode and mounted inside a vacuum chamber pumped by a 1000 l/s turbomolecular pump shown in figure 4. Gas is bled inside the plasma chamber through a capillary tube and flow rate is controlled by a gas valve controller. Taking into account the experimental conditions, the maximum voltage for ion source and the ‘accel-decel’ system is 30 kV and 15 kV respectively. A schematic view of the low energy beam transport section coupled to the microwave ion source is shown in figure 5. We also observe that there are two ring marks on the inner wall of the plasma chamber pertaining to the injection ring and the extraction ring as per the simulations. FUTURE PLANS A new compact LEBT system is planned for this system. The design and development of the new compact LEBT system is in progress. A new multi-electrode extraction system is designed for extracting intense beams. It consists of four electrodes having an aperture Figure 5: Schematic view of the low beam energy transport (LEBT) section coupled to the microwave ion source. of 10 mm & total length of 60 mm. The beam optics for this system is designed using IGUN [7] and is shown in figure 7. The 3d model based on the multi-electrode design is shown in figure 8. Figure 10: View of the new 2.45 GHz Microwave ion source plasma chamber. Figure 7: Calculated optics for transporting 10 mA of protons in newly designed multi-electrode. CONCLUSIONS A 2.45 GHz microwave source together with the low energy beam transport has been successfully designed, developed and commissioned at IUAC, New Delhi. In the near future, a compact LEBT system is found to be essential to minimise beam losses. The design and development of the compact LEBT is under progress. ACKNOWLEDGEMENT One of the authors (N. Kumar) is grateful to University Grant Commission (UGC), India for financial support through Junior Research Fellowship (JRF). The Authors would like to thank the workshop personnel and other staff members for their help. Figure 8: (a) Schematic view of the new multi-electrode extraction system and (b) cross sectional view. A new compact, water cooled plasma chamber is designed and is shown in figure 9. The fabricated new compact, water cooled plasma chamber is shown in figure10. In the new designed ion source, the advantages are better plasma chamber cooling, additional ports for Langmuir probes/diagnostics, better microwave coupling through the ridge waveguide. Figure 9: Schematic view of the new 2.45 GHz Microwave ion source’s plasma chamber. REFERENCES [1] Y. Mathur, G. Rodrigues, R. Ahuja, U. K. Rao, N. Kumar, P. S. Lakshmy, D. Kanjilal & A. Roy, Indian Particle Accel. Conf. INPAC, IUAC Delhi, Feb. 1518, 3B 60 (2011). [2] Narender Kumar, G. Rodrigues, Y. Mathur, R. Ahuja and D. Kanjilal, Workshop on Highly Charged Ions and Atomic Collisions 2012 (WHCI 2012), TIFR, Mumbai, India, Mar. 28-31, pp 16 (2012). [3] N. Sakudo, Rev. Sci. Instrum. 49,940 (1978). [4] Y. Gotoh, H. Kubo, H. Tsuji and J. Ishikawa, Rev. Sci. Instrum. 71, 1160(2000). [5] S. Biri, A. Deszsi, E. Fekete and I. Ivan, 2007 High Energy Phys. Nucl. Phys. 31, 165. [6] ni.com/labview/ [7] R. Becker and W. B. Herrmannsfeldt, Rev. Sci. Instrum. 63, 2756 (1992).