Electrical Engineering Department, SGSITS, Indore, INDIA Modeling and simulation of 2 MHz EXTERNAL ANTENNA FOR RF DRIVEN H¯ ION SOURCE Nayan Kumar Gunele, Sandeep Bhongade, D V Ghodke*, R M Vadjikar*, V K Senecha*, S C Joshi* Electrical Engineering Department, SGSITS, Indore, INDIA *Proton Linac & Superconducting Cavity Division, Raja Ramanna Centre for Advanced Technology ,Indore, INDIA ABSTRACT: The modeling and simulation of external antenna is important for the study of RF driven hydrogen plasma sources. The external antenna will be externally wrapped around plasma chamber. RF pulsed power feeding at 2 MHz frequency to antenna for plasma generation (ionisation) and heat up through inductive coupling. This antenna has been modeled and simulated with Opera-3D simulation platform using TOSCA module. This simulation will help to study the magnetic field behaviour and determination of electrical parameters of antenna.The analysis has been carried out by considering current of 400 Amp in antenna, the results are reported in the paper. I. Introduction The 2MHzexternal antenna is used to deliver the RF power to the plasma chamber of Hˉ Ion source [1].The antenna power will be inductively coupled with plasma source for the ionization and heating of the hydrogen gas [2,3]. Inductive coupling of plasma source reduces skin effects and provides better coupling at high power[4]. Ion source with externally wrapped RF antenna, are widely used in many applications, due to their maintenance free operation for longer lifetime as compared to ion source based on the filament type arc discharge or the internal RF antenna. RF antenna studied in this paper is solenoid in shape with two layer helical structure. The external antenna has been modeled and simulated to analyze the magnetic field behavior. The geometrical optimization was performed to enhance the performance of antenna with plasma chamber of H- ion source. This analysis helps to find the RF antenna electrical parameters and magnetic field characteristic for plasma generation and heating. RF driven hydrogen ion source operates at frequency range of 0.1 MHz to 13.56 MHz and power range is 0.1 kW to 100 kW[2, 3]. II. simulation model of external RF antenna Modeling and simulation: Modeling and simulation has been carried out inOpera-3D platform with TOSCA(magneto static analysis)module. Figure.-1 (a) shows the 3Dview of RF antenna and 1(b) shows the designed prototype antenna coil of identical size. The RF heating can be enhanced by generating high magnetic flux along Z-axis, at the center of an antenna and plasma chamber axis[4]. Hence RF antenna formed with six turns in two layers. The copper conductor has 5x5 mm square cross sectional area. The internal diameter of inner layer is 75 mm and outer diameter of outer layer is 103 mm, the spacing between the adjacent conductors is 3 mm. The simulations are carried out for measurement of magnetic field generated by the antenna. The model is solved with non-linear magnetic properties of conductor. An air region is covered to set up the boundaries of the finite element mesh in the model. The model space assumed that it consists of non-zero conductivity (σ), permeability (μ) and permittivity (ε). (a) (b) Fig. 1. (a) 3D Simulation model of external RF antenna as seen in Opera-3D. (b) Prototype RF antenna (Replica of simulation model). AC resistance and impedance calculation: The modeled and simulated RF antenna stores the energy approximately 0.25 Joule at current of 400 Amp and inductance calculated is 3.123. This value matches with the measured value of prototype antenna tested at2 MHz frequency. The RF antenna impedance was calculated as following. III. results and discussion The magnetic field values of the RF antenna at 400 Amp of current is shown in figure.2 to 4.The magnetic flux values are shown in Gauss. Figure 2 shows XZ axis Cartesian plane, the magnetic field strength is maximum on the surface of the conductor (antenna) and decreases as function of distance. The magnetic field strength (contour map) X-Y-Z axes are shown in figures 3(a) to 3(c) respectively. The peak magnetic field is ~600 Gauss near conductor and gradually decreases towards origin and generates~330 Gauss at the center of the antenna. The magnetic field pattern generated on the X and Y axis is identical because of axis symmetry. There is small difference in Y-axis magnetic field two peaks as shown in figure 3(b), this difference is due to spacing between the start and end of antenna conductor. The magnetic flux generated at the center (along the Z-axis) of the antenna is responsible for ionization and inductively coupled plasma heating, high magnetic flux generates dense plasma [4]. Fig. 2 Simulated magnetic field strength on XZ Cartesian patch Fig. 2 Simulated magnetic field strength on XZ Cartesian patch Fig. 3(c) Simulated magnetic field strength along Z- axis of a antenna. Fig. 3(b) Simulated magnetic field strength along Y-axis of antenna Figure 4 shows the magnetic field pattern generated by antenna in a histogram. The magnetic field peak is adjacent surrounding to the antenna conductor and gradually decreases outside and inside the antenna conductor. Figure 4 shows the magnetic field pattern generated by antenna in a histogram IV. Conclusion The magnetic flux generated at the center of the antenna is responsible for ionization and plasma heating. External RF antenna with 6 turns in two layers, modeled in Opera-3D. The magnetic field pattern generated by RF antenna has been simulated (solved) using TOSCA module. The RF antenna dimensions are optimized for maximum flux generation. An optimization has been done to enhance the magnetic field generated by the antenna and also to match the impedance of 50 Ω with the RF source. These optimizations are done with computer modeling and simulation by changing the geometry of the RF antenna. The magnetic field generated by antenna at current of 400 Amp is ~600Gausspeak near to the conductor and ~330Gauss at the center of the antenna. The antenna impedance parameters are calculated using energy storage and operating frequency and matches with the actual measurement on the prototype. The RF antenna design with two concentric helical coils has helped in optimization of induced magnetic field by the antenna current, leading to efficient inductive coupled plasma generation and heating needed for RF driven H- ion source. 4th IEEE APLIED ELECTROMAGNETIC CONFERENCE 2013, KIIT UNIVERSITY, BHUBANESWAR