A present status of the diagnostics in EAST is presented.As a very importantstep of the EAST project,tens of diagnostics were employed for operation and protection of themachine,plasma control and physics analysis to accommodate requirement for the study on plasmaperformance in EAST with upgraded radio frequency (RF)injection power up to 4 MW (bothLHCD and ICRF)in the forthcoming years.Recently,new diagnostics are set up to provide severalprofiles of key plasma parameters for the further evaluation and better understanding of the plasmaperformance and physics in EAST,including a 25-channel Thomson scattering system for densityand electron temperature,a metal bolometry for radiated power,an X-ray crystal spectroscopyfor both ion and electron temperatures and plasma rotation velocity,etc.It is expected thatthese diagnostics would play an important role in data analysis and interpretation combined withintegrated modeling.
During the current flat-top phase of electron cyclotron resonance heating discharges in the HL-2A Tokamak,the behaviour of runaway electrons has been studied by means of hard x-ray detectors and neutron diagnostics.During electron cyclotron resonance heating,it can be found that both hard x-ray radiation intensity and neutron emission flux fall rapidly to a very low level,which suggests that runaway electrons have been suppressed by electron cyclotron resonance heating.From the set of discharges studied in the present experiments,it has also been observed that the efficiency of runaway suppression by electron cyclotron resonance heating was apparently affected by two factors:electron cyclotron resonance heating power and duration.These results have been analysed by using a test particle model.The decrease of the toroidal electric field due to electron cyclotron resonance heating results in a rapid fall in the runaway electron energy that may lead to a suppression of runaway electrons.During electron cyclotron resonance heating with different powers and durations,the runaway electrons will experience different slowing down processes.These different decay processes are the major cause for influencing the efficiency of runaway suppression.This result is related to the safe operation of the Tokamak and may bring an effective control of runaway electrons.
Neutron emission in EAST was investigated by a time-resolved monitor systemwhich consists of four 3He proportional counters and a 235U fission chamber. The D-D neutron fluxincreased approximately an order of magnitude during the 27 MHz ion-cyclotron radio frequency（ICRF） heating, demonstrating that the ICRF wave heated the plasma effectively. In additionin lower hybrid wave （LHW） experiment with higher plasma parameters D-D neutrons were alsodetected. However, masses of photoneutrons were generated in Ohmic discharges with low plasmadensity. Effect of plasma density on the production of photoneutrons was studied, and it is foundthat LHW can suppress the generation of the runaway electrons and reduce the share of thephotoneutrons effectively.
Operation of HT-7 tokamak in a multicycle alternating square wave plasma current regime is reported.A set of AC operation experiments,including LHW heating to enhance plasma ionization during the current transition and current sustainment,is described.The behaviour of runaway electrons is analysed by four HXR detectors tangentially viewing the plasma in the equatorial plane,within energy ranges 0.3-1.2 MeV and 0.3-7 MeV,separately.High energy runaway electrons (～MeV) are found to circulate predominantly in the opposite direction to the plasma current,while the number of low energy runaway electrons (～tens to hundreds of keV) circulating along the plasma current is comparable to that in the direction opposite to the plasma current.AC operation with lower hybrid current drive (LHCD) is observed to have an additional benefit of suppressing the runaway electrons if the drop of the loop voltage is large enough.
This paper reports that an experimental investigation of fast pitch angle scattering(FPAS) of runaway electrons in the EAST tokamak has been performed.From the newly developed infrared detector(HgCdTe) diagnostic system,the infrared synchrotron radiation emitted by relativistic electrons can be obtained as a function of time.The FPAS is analysed by means of the infrared detector diagnostic system and the other correlative diagnostic systems(including electron-cyclotron emission,hard x-ray,neutrons).It is found that the intensity of infrared synchrotron radiation and the electron-cyclotron emission signal increase rapidly at the time of FPAS because of the fast increase of pitch angle and the perpendicular velocity of the energetic runaway electrons.The Parail and Pogutse instability is a possible mechanism for the FPAS.
