50keV, 30mA Electron Cyclotron resonance (ECR) proton source (Fig.1) for use as an injector to Proton Linac is designed and fabricated in RRCAT. The design parameters are presented in Table1. The testing of the source is in progress. The source is excited with 350watts of microwave power at 2450MHz frequency to produce hydrogen plasma.  The plasma view is shown in Fig.2. Two-electrode extraction geometry is designed using IGUN software for extraction of the proton beam. The beam trajectory of proton beam using IGUN software is shown in Fig.3. The extraction aperture of the plasma electrode is 8mm and ground electrode is 10mm. The proton beam current 5mA (peak) at 15keV with a pulse width of 5msec., and repetition rate 100Hz is obtained. The beam current is measured at 100mm down from the source using Faraday cup. The proton current v/s extraction voltage is shown in Fig.4 (a) and pulse shape of beam is shown in Fig. 4(b).

Fig.1: ECR proton source

Fig.2: View of plasma

Fig.3: The beam trajectory of proton beam using IGUN (10mA, 15keV)

Fig.4 (a): The proton current v/s extraction voltage

Fig.4 (b): The pulse shape of beam (2volts/div, 5ms/div)

In ECR source plasma is produced by matching the frequency of the microwave source to the cyclotron frequency of an electron, in DC applied magnetic field. The magnetic field correspond to 2450MHz frequency is 875gauss.  Three solenoid coils are used to produce desired magnetic field configuration. The solenoid coils are designed using POISSON software. The measured field profile is shown in Fig.5. The major components of the source are microwave source and its transfer line WR-284 waveguide, solenoid coils, plasma chamber, vacuum system and extraction electrodes. The magnetron is used as a source of microwave power and it can deliver maximum 2kW power at 2450MHz frequency. 5kV, 1A high voltage DC power supply is used to energize the magnetron. 5V, 20A AC power supply floating at 5kV is used to power the filament.

Fig.5: The measured field profile (Flat Field)

The microwave transfer line is designed and developed using WR-284 rectangular waveguide section.  The microwave power is coupled to the plasma chamber via ridged waveguide with window and DC break. The forward and reflected power is monitored using 50dB loop directional coupler. The plasma impedance is matched and reflected power is minimized using triple stub tuner. A high power isolator is used to protect the magnetron from load imperfections by directing the reflected power to the load. The isolation offered from reflected power is 25dB.

Turbo molecular pump of 450litre/sec. is used for the evacuation of the plasma chamber and 1x10^-6mbar base pressure is maintained. The plasma chamber is fabricated in S.S. 304.  The hydrogen gas is supplied through the side port of the source chamber flange and flow is controlled through the precision valve. The source is operated at the hydrogen pressure at 2x10^-4 mbar. The plasma parameters, plasma density and electron temperature is measured using Langmuir probe. The hydrogen plasma density in the order of 2-4x10¹¹cm^-3 and electron temperature 3-7eV is obtained. The V-I characteristics of the Langmuir probe obtained form the ECR source is shown in Fig.6. The data obtained from the V-I characteristics is processed offline to generate various plasma parameters. The program for the Langmuir probe is developed in Lab-VIEW.         

 The optimization and tuning of the source is under progress to achieve 30mA proton beam current with three-electrode (accel-decel) geometry at 50keV beam energy.

Table1: The ECR proton source design parameters

Fig.6: The V-I characteristics of the ECR source