Radio frequency group at IPR started their activities in late eighties. Now we have developed and regularly operate systems at hundreds of kilowatt level. During a short period, the group has also diversified in frequency ranges of operation. Today, we at IPR have three operating high power (hundreds of Kilowatts) RF and Microwave systems at different frequencies besides many small systems at few tens of kilowatt level.

Additional heating and current drive is essential to raise and sustain an ohmically produced tokamak plasma. To satisfy these requirements for tokamak ADITYA and Superconducting Steady state Tokamak (SST-1) programmes, it was decided to build three systems around three frequency ranges. Ion Cyclotron Resonance Heating (ICRH) system is the first indigenous system developed in our laboratory. It is modular hence the system prepared for ADITYA is being used as the driver stage for ICRH system on SST-1. Non-inductive current drive is almost mandatory for our upcoming SST-1 tokamak programme. Considerable success has been achieved in the Lower Hybrid frequency range in this concept. A megawatt level Klystron based CW system has been developed to use in the SST-1 experiment. Experiments with this system on current drive in ADITYA plasma by asymmetric lower hybrid waves would boost our confidence by end of this year. For easy breakdown of the plasma in tokamaks electron cyclotron frequency based systems are often used. They are also used for electron heating experiments. Two such systems are being made ready for use on our Tokamaks. One of these systems on ADITYA has been commissioned.

ICRH CW system has been developed in our laboratory. The system operates between 20-45 MHz range and at discrete frequencies 70, 91.2 MHz. It is modular in out put power. Most significant work accomplished by this group has been the development of various components of the complete system along with integration of it to tokamak ADITYA. It is a chain of amplifiers with final output of 200KW capable of operating between 20 – 45 MHz.

A final stage of 1.5 MW is added to the system to prepare the ICRH system for SST–1. Another amplifier stages for 70 and 91.2 MHz have also been added to the system. High power transmission line has been indigenously fabricated and commissioned to deliver the power to the antenna, positioned inside the tokamak vacuum vessel, through a sophisticated UHV compatible interface (vacuum transmission line). Slow stub matching (in secs and 20-30 msec) technique has been developed and implemented in the system. Fast frequency (~2 ms) matching technique is also being developed to optimise matching during 1000 second discharge in SST-1. It has been a great experience in developing these systems.

The second system we have at present is a 1 MW Klystron based CW (1000 sec) system at 3.7 GHz. This system will finally evolve into the much required current drive system to have steady state operation of SST-1 Tokamak. Successful commissioning of the two 500 KW each CW Klystrons at 3.7 GHz with the available DC power alongwith all required subsystems has been the highlight of the activities of the group in this frequency .

We have built a test system around one of these klystrons. Indigenously designed and fabricated high power components are being tested before being integrated for SST-1. In the event of a fault we remove the high voltage of the order of 70,000 V in 5-10 microseconds.