FIP / 1-2 Rb 1 OUTCOME OF R & D PROGRAM FOR ITER ICRF POWER SOURCE SYSTEM

As per agreed procurement arrangement with IO, INDA has to supply nine (1 Prototype-unit + 8 subsequent supply) ICRF Source to IO, which is capable to deliver 2.5 MW/2000s RF power at VSWR 2:1 in the frequency band 35 – 65 MHz or 3.0 MW/3600s at VSWR 1.5:1 in the frequency band 40 – 55 MHz, accompanied by other strict requirements. As there is no such single RF active device for amplifier available to get the RF power of 2.5MW for ITER, therefore, ITER RF source consists of two parallel three-stage amplifiers chains and a combiner to achieve 2.5 MW power by each RF source for ITER. Such RF source is unique in terms of its challenging requirements. Research & Development drive is started by INDA to confirm the use of available high power vacuum tube before start of activities related to ITER deliverables, using Diacrode and Tetrode tubes. During R&D drive, only one chain experiment at 1.5MW/2000s is performed for the frequency range 3565 MHz up to VSWR 2:1, with any phase of reflection coefficient. The main objective for the R&D test is to confirm the system performance for the power, duration and frequency range as per ITER need and to check the reliability of both the tube and the amplifier with matched as well as with mismatched load (up to VSWR 2:1), which essentially simulates the plasma load condition. To upkeep the R&D experiment, required infrastructure to test RF source is established at INDA for both the type of vacuum tubes. For Diacrode based system, high power ITER relevant tests are completed in 2016 and reported elsewhere [1]. Since 2-3 years, installation and commissioning of R&D RF chain using Tetrode tubes at INDA test facility is completed with validation of all the relevant sub-systems/systems as standalone mode. The high power RF test of Tetrode based RF amplifiers chain is also conducted at 1.7MW of power for 3600s duration at 36 MHz. For other ITER operating frequencies, the system was operated at 1.5MW/2000s successfully. This paper reports commissioning of RF amplifier using Tetrode technology with various operating scenarios, dissipation limit, safety system, challenges faced during high power operation and outcome of R&D activity at INDA test facility. 1. BRIEF INTRODUCTION ITER require up to 20 MW of ICRF power to a variety of plasmas like at low power level, assisted plasma startup & wall conditioning in between the plasma shots and at full power level, heating and driving plasma current with Ion Cyclotron (IC) frequency band [1]. There will be 2 ICRH antennas, main TX lines, matching units, RF Sources, High Voltage Power Supplies (HVPS) for anode and real time local controls in the IC system. 4 number of RF sources will feed each antenna connected via 8 TX lines and matching units. The complete system will be fabricated & supplied by 3 Domestic Agencies (DAs) and ITER Organization (IO). Under RF source package, INDA is responsible for supplying total 9 (1 Prototype + 8 series production) of ICRF sources along with auxiliary power supplies and local control units to IO. Each RF source shall capable to handle 2.5 MW, 2000s RF power at VSWR 2:1 in the frequency band 36 – 60 MHz or 3.0 MW, 3600s at VSWR 1.5:1 in the frequency band 40 – 55 MHz and with other necessities. For qualifying end stage high power tetrode-tube & cavity for ITER need, dedicated R&D program has been initiated by INDA. To establish the Tetrode technology related to ICRF amplifiers, ITER-India has signed contract with Continental Electronics (USA) in 2012. The contract is to design & develop driver and final stage amplifiers using commercially available CPI make Tetrode tubes (4CW150000E & 4CM2500KG) and to test the system at 1.5MW/2000s/35-65 MHz. Once successful, such two identical chains can be combined to meet the ITER specifications. As reported earlier, the dedicated test facility at ITER-India laboratory mainly consists of low power RF section, wideband solid state pre-driver amplifier, common high voltage power supply for anodes of driver and final stage amplifiers, high power transmission line system, local control unit for control & monitoring, key safety system, water & air cooling system and 3 MW test load for testing the RF source on match and mismatch load.