Presentation On RF Heating By :- Saurabh Kumar Vij University of Delhi, India IPR, Bhat, Near Indira Bridge Gandhinagar, Gujarat 25-03-20111Presentation.

Presentation On RF Heating

By:-

Saurabh Kumar VijUniversity of Delhi, India

IPR, Bhat, Near Indira Bridge Gandhinagar, Gujarat

25-03-2011 1Presentation on RF Heating by - Saurabh Kumar Vij

Plan of the talk

• RF Heating• Why is heating required?• Methods of heating the plasma• ICRH and Requirements• ECRH• Results so far• Summary

25-03-2011 Presentation on RF Heating by - Saurabh Kumar Vij 2

RF Heating• Radio-Frequency Heating is one of the most efficient

way to heat the Tokamak plasma.• RF Range – 3KHz to 300 GHz



Why do we need to Heat the Plasma?• Lawson Criterion derived by John D. Lawson in 1955.• To achieve the stage of ignition in a Fusion reactor.• Attaining conditions to satisfy the Lawson criterion

ensures the plasma exceeds Breakeven – the point where the fusion power out exceeds the power required to heat and sustain the plasma.

• Later on, a new much improved version was found. • The “Triple Product” serves as a criterion to reach

ignition. e>= 1021 keV s/m3

• Power required is about 20 MW.


Different methods of Heating• Ohmic Heating - Q = I2R • RF Heating ICRH ECRH LHCD • Neutral Beam Injection• Adiabatic Compression


Why Not just Ohmic Heating?• For Fusion Plasma, we need Temperature around 10

KeV .• Ohmic Heating has a limit of 2KeV.• Because R = C. T-3/2 , So as temp. Increases resistance

decreases. • Auxiliary Heating like RF heating is required which

could provide the remaining 8-9KeV of power.• Additional Power Required:• P = 3V.ne ) • nAdditional rise in density and temperature.


Why RF is a better method?• Ohmic Heating cannot go beyond a limit of 2KeV.• Neutral beam injection is not fully developed and is also quite

difficult to achieve.• Difficult to inject NB at high density because of collisions, leading to

Plasma Disruption.• With NBI, particles hitting the inner wall is a problem.• Can also puncture the walls if NB particles hit normally.• ICRH and ECRH provides much more localized heating because B

varies inversely with R.• Absence of density limit and direct Ion heating in case of ICRF.• Most important, RF heating at ITER can lead to temperatures of 150

Million0 C.


RF Heating

• ICRH – Ion Cyclotron Resonance Heating

• ECRH – Electron Cyclotron Resonance Heating

• LHCD – Low Hybrid Current Drive25-03-2011 9Presentation on RF Heating by - Saurabh Kumar Vij

ICRH Ion Cyclotron Resonance Heating Mechanism


• Plasma ions are confined to rotating around the magnetic field lines in the Tokamak.

• If the waves have the correct frequency and polarization, their energy can be transferred to the charged particles in the plasma

• Cyclotron Frequency, Wci = e.B/mi

• The EM waves of a frequency matched to the ions are able to resonate – or damp its wave power into the plasma ions.

• Which in turn collide with other plasma particles and heat up the Plasma.

• Increasing the temperature of the bulk plasma.

• Localised heating of Plasma.

Fundamental and Second Harmonics

• Fast RF wave is required for ICRH an it is Left hand circularly polarized.

• Ions are right hand circularly gyrating around the magnetic field.

• So at the fundamental mode W = Wci

• There is no heat transferred to the ions by the RF wave.

• So at W = 2Wci , there is an energy transfer by RF wave to the ions.

• This is referred to as Second Harmonic heating.25-03-2011 11Presentation on RF Heating by - Saurabh Kumar Vij

Requirements for ICRH

25-03-2011 12

A.C D.C Oscillator

Control System

P.m Interface

Hybrid coupler

Antenna

Phase Shifter

Interface AntennaFarada

yShield

Phase Shifter

Faraday Shield

Stub

Stub

Matching Network

Presentation on RF Heating by - Saurabh Kumar Vij

Tokamak Region

Requirements for ICRH

• Generator sources – Tetrode tubes, Klystrons and Gyrotrons.

• Transmission Lines• Interface Window – Interface between

Transmission line and Tokamak.• Antenna • Faraday Screens/Shields.


25-03-2011 14

Antenna(JT-60)


25-03-2011 15

Antenna(JET)


Antenna


Faraday shield

• The Faraday shield forms the plasma facing component of the antenna.

• It blocks all the plasma particles from entering the Antenna.

• But allows the passage for EM waves towards Plasma.

• They are a series of parallel metal rods.

• This reduces the RF resistive losses.

• Can also improve the heating efficiency by 2.3 times.


ECRHElectron Cyclotron Resonance heating• It is similar to ICRH, the only

difference being that it specifically heats the electrons only.

• Electrons being almost 2000 lighter than the ions, have higher cyclotron frequencies.

• Wce = eB/Me

• Mi >>> Me

• Wce > Wci

• Thermalization is low as compared to ICRH.


ECRH Advantages over ICRH

• ICRH with its frequencies much lesser than ECRH cannot penetrate much in the vacuum vessel.

• ECRH waves can propagate in vacuum and can be steered with high precision.

• In ECRH beam can be transmitted through air which simplifies the design and allows the source to be far away from the plasma, simplifying maintenance.


Results so Far

• At JT-60U, a strongly peaked Te profile was observed and the central electron temperature increased up to 15KeV ∼under ECRH with power of 9 MW.

• Temperature in excess of 10KeV are a routine now in JET with central temperature of 16KeV with ICRH with power of 32 MW.


Summary

• To achieve Fusion, we require many Auxiliary heating methods.

• Only one of them is not sufficient enough.• So a combined effort of methods like ICRH, ECRH,

NBI is the best way to reach the desired goal.• With experiments like Aditya, JET, JT-60, Textor

etc. and the most ambitious ITER project, we can definitely create a star like Fusion on Earth.


Thank You


Presentation On RF Heating By :- Saurabh Kumar Vij University of Delhi, India IPR, Bhat, Near Indira Bridge Gandhinagar, Gujarat 25-03-20111Presentation.

Documents

talk rf heating

localized heating

auxiliary heating

heating efficiency

harmonic heating

localised heating of

saurabh kumar vij slide

rf range