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Application of a 16-channel heterodyne ECApplication of a 16-channel heterodyne ECE diagnostic on HT-7 Tokamak E diagnostic on HT-7 Tokamak

Microwave group,presented by Bili Ling

Institute of Plasma Physics, Chinese Academy of Sciences, P.O.Box 1126, Hefei, Anhui230031, P.R.China

ASIPPChina-UK/Europe Workshop on Millimetre Waves and Terahertz Technologies

20th-22th October, 2008, Chengdu, China

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Outline

• Introduction of fusion,plasma and tokamak• Application of ECE radiometer on HT-7 to

kamak• Experimental results• Future plan for EAST ECE measurement• Summary• Acknowledgement

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Nuclear fusion is the energy source that powers the Sun and stars in which light atomic nuclei fuse together by thermonuclear reactions,releasing a large amount of energy.

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Introduction

Deuterium exists in sea water at a ratio of approximately 33 grams per cubic meter. Tritium can be produced by nuclear reaction with lithium in the fusion reactor. Lithium exists plentifully as mineral resources and is included in sea water approximately 0.2 grams per cubic meter.

Fusion power can be generated on earth using the isotopes of hydrogen,deuterium and tritium at ultra high temperature.

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To utilize the fusion energy, it is necessary to heat fuels to a temperature of more than 100 million and keep them in a plasma state for the fusion reaction to ℃continuously take place.

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Light nuclei collide with each other and form a heavier nucleus. At the moment, a huge amount of energy is released.

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Plasma is the fourth state of matter in which the electrons and nuclei which form the atoms are separated and move freely.The tokamak system, which is superior in producing and sustaining a high temperature plasma, is adopted for fusion energy research.

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In a tokamak system, a nest of magnetic field lines which are produced by external magnets located around the vacuum chamber and by a large current in the plasma confines the plasma in the vacuum chamber.

Both ions and electrons, of which the plasma consists, have electrical charge and move spirally along a magnetic field line by nature.

It is necessary to keep the plasma at a high temperature, in order to initiate and sustain the fusion reaction. Therefore, measurement of electron temperature and its profile is crucial for fusion research.

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HT-7 superconducting tokamakHT-7 superconducting tokamak

R = 1.22m, a = 0.27m

Ip = 100~250 kA (250)

BT = 1~2.5T(2.5)

ne = 1~8x1013cm-3 (7.5)

Te = 1~5 KeV (4.8)

Ti = 0.2~1.5K eV (1.8)

ICRF:

f = 15~30MHz, P = 0.3MW(0.6)

LHCD:

f = 2.45GHz, P = 1.0MW(0.8)

Pellet injector

Supersonic beam injection

Main Goal: Advanced Steady-state operation and related physics

( Ip > 100kA, Ne>1.0x13cm-3, t=60s)

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Outline



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ASIPPA plasma emits radiation over a wide

range of frequencies due to the reaction of charged particles with magnetic fields and with each other. Of particular importance is the radiation associated with electrons undergoing circular motion about magnetic field lines, the electron cyclotron emission (ECE).

For electrons with a Maxwellian distribution, the emitted power is directly proportional to the electron temperature, if the emission at a particular frequency is at the blackbody level.

The one-to-one correspondence between electron cyclotron frequency and the position in a tokamak]1[

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Application of ECE radiometer on HT-7 tokamak

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ASIPPNormally three type of diagnostics can be employed to provide electron temperature

in tokamak through monitoring ECE radiation.

The heterodyne radiometer has the highest spatial and temporal resolution amongst these three type of ECE diagnostics.

From Fusion Engineering and densign 34-35 (1997) 477-481

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ASIPPOn HT-7 tokamak, a 16-channel heterodyne ECE radiometer has been developed in col

laboration with Fusion Research Center, University of Texas.

The heterodyne ECE radiometer detects 2nd harmonic X-mode plasma emission in the frequency range 98-126 GHz.

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ASIPPSpatial resolution: ~2cm

Digital sampling time: 4us

TPX lens and conical horn antenna with corrugation on the inside wall formed the front-end

Two local oscillators: 95 GHz and 108.5 GHz

Two high-pass filters and mixers employed to perform USB measurement

Oversized WG employed to reduce the transmission attenuation

Square-law detector with 16 GHz bandwidth,1800mv/mw sensitivity converts the power to a voltage

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ASIPPThe sensitivity of the ECE radiometer can be demonstrated

by using the noise tube.

Specification of the noise tube:

Frequency range:90-140 GHz

Approx.ENR:13.0 dB

Noise tube off

Noise tube on

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Outline



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ASIPPThe clear sawtooth oscillations can be observed from the 16-channel ra

diometer, which can measure sawtooth and inverse sawtooth simultaneously.

Experimental results

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ASIPPEnergy confinement is an important issue in tokamak physics. One

of the key parameters is the electron diffusivity in the confinement region.Time to peak method can be adopted to obtain electron thermal diffusivity from ECE measurement.

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ASIPPIn HT-7 tokamak LHCD plasma discharge, strong correlation between

the ECE intensity and the displacement of plasma is observed. Maybe term of “displacement of ECE intensity” can be proposed. This study is still underway.

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time:0.7439----0.9346s

time:0.9355-----1.0829s

time:1.8571-2.0046s

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Outline



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The EAST machine assembly was completed in Jan. 2006. The first plasma discharge has been achieved successfully on the EAST in September 26, 2006. Different magnetic configurations such as Single-null (SN)and double-null (DN) have been realized.

EAST

Main Parameters of the EAST

Nominal UpgradeBo 3.5 T 4.0 T

IP 1 MA 1.5 MA

Ro 1.7 m 1.7 ma 0.4 m 0.4 mR/a 4.25 4.25

Kx 1.2-1.8 1.5-2

δx 0.2-0.3 0.3-0.5Heating and Driving:ICRH 3 MW 6 MWLHCD 3.5 MW 8 MWECRH 0.5 MW 1.5 MWNBI 8 MWPulse length 1000 sConfiguration: Double-null diver

tor Single-null divertor

Future plan for EAST ECE measurement

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ASIPPAs the toroidal magnetic fi

eld of EAST will operate up to 3.5 Tesla. Employing heterodyne radiometer to cover the whole frequency range of 2nd X-mode polarization is not economical. Grating polychromator system (GPS) is being developed in collaboration with Princeton Plasma Physics Laboratory(PPPL).

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Outline



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Summary

(1) A 16-channel heterodyne ECE radiometer has been developed on HT-7 tokamak in collaboration with Fusion Research Center (FRC), University of Texas.

(2) The sensitivity of this set diagnostic has been demonstrated by using noise tube.

(3) This diagnostic can be optimized to investigate more tokamak physics, such as MHD, heat pulse propagation, etc.

(4) GPS for ECE measurement on EAST is being developed in collaboration with Princeton Plasma Physics Laboratory PPPL.

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Acknowledgements

• We would like to thank the staffs of HT-7 tokamak and Dr.H Huang, Dr.P.Phillips (FRC,UT), Dr.G.Talor (PPPL), Dr.A.Isayama (JAEA) for the intensive collaboration.

• Thank you for your attention.

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