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ICRF System

IonCyclotron Range of Frequencies (ICRF) heating is a method that can directlyheat the ions to the high temperature needed for the fusion reaction. It isforeseen to couple as much as 30 MW of ICRF power at frequencies between40-80MHz for CFETR. A CRAFT ICRF system has been constructed to meet with theseobjectives and specifications:

Scientific objectives

•   Toprovide a testing facility with 2MW RF power for finding a solution to use ICRFin CFETR

•   Solvingtechnical challenges and developing required technologies.

•    Manufacture,testing and validating of the key components for the CFETR ICRF system

Specifications

•    Frequency:  40-80MHz

•    Combinationpower:  2.5MW

•    Pulselength:  1000 s

System Composition and main parameters

TheCRAFT ICRF system is composed of RF transmitters, high voltage power supplies,coaxial transmission line, feedthrough, and antennas. The system of theschematic layout is shown in Fig

1)   RF transmitters

The transmittersinclude an amplitude and frequency control and monitor unit, an RF poweramplifier chain, a direct current (DC) high voltage power supply (HVPS), and acooling system(see figure 2.). The RF power amplifier chain consists of three stages,i.e., 5 kW-stage broadband solid state amplifier (SSA), 100 kW-stage tetrodedrive power amplifier (DPA), and 1.5 MW-stage tetrode final power amplifier(FPA), tunable from 40 MHz to 80 MHz As there are the limitations of the singletube power and port size, a 3dB hybrid coupler takes the output from twogenerators (phased 90°) and combines them into one output (shown in Fig.2),which is expected to combine 2 × 1.5MW power to 2.5MW output power. 

1)      Transmission line

The transmission line is composedby (a) a pressurized 12 in 50Ω coaxial transmission line, (b) impedancematching systems with a triple liquid stub tuner and (c) a vacuum transmissionline called an interface. The vacuum interface links the transmission line toan antenna.

2)      Antenna

A Travelling Wave Antenna (TWA)is proposed for CFETR, which comprises an array of mutually coupled resonantstraps connected in parallel, and where the power is fed in at the first andout at the last strap of the array. Compared with the traditional loop antenna,it has a lot of advantages:

• Allow maximizing power coupling

• Reduce the power density

• Reduce associated electric fields and voltage

• Increase the reliability of the system usingindependent sections

Key Technologies

The ICRF systemconstruction is expected to solve the following key technologies:

Ÿ  Highpower long pulse combination technology.

Ÿ  DevelopmentICRF antenna reliability technology

Ÿ  ICRFantenna Remote Handing (RH)compatibility and maintainability