plasma physics and fusion energy · pdf fileplasma physics and fusion energy research paddy mc...

Plasma Physics and Fusion Energy Research

Paddy Mc Carthy,

Physics Department, UCC, 1/11/2011

Research Group: Plasma Data Analysis Group:

P. J. Mc Carthy (Group Leader)

R. Armstrong (Visiting Researcher)

PhD Students:

Diarmuid Curran

Mike Dunne (TCD graduate!)

Tom O’Gorman

MSc Students:

Brendan Cahill

Shane O’Mahony

Funders: Euratom, Max Planck Institut für Plasmaphysik, Munich

TCD Graduate Plasma Physics Module PY5012 Guest Lecture 1st Nov 2011

Lecture Outline:

Plasma Overview

Fusion Energy and Tokamaks

How the Tokamak overcomes particle drift in a closed

axisymmetric system

Research topics in UCC

Fusion in Europe and further afield


Plasmas are conductive assemblies of charged

particles, neutrals and fields that exhibit collective

effects, carry electrical currents and generate

magnetic fields.

What is a plasma?


Why are we interested in

plasmas? •! Fusion Energy

–!Potential source of safe, clean, and abundant

energy.

•! Astrophysics

–!Understanding plasmas helps us understand

stars and stellar evolution.

•! Plasma Applications

–!Plasmas can be used to build computer chips

and to clean up toxic waste.


per nucleon


!" Fission is easiest at low energies; cross-section is maximum here

!" Fusion is vanisingly unlikely at low energies; cross-section is miniscule


Puzzle: T = 1keV at centre of sun.

Proton-Proton Coloumb Barrier height:

How can 1 keV protons overcome a 1 MeV barrier?

Answer: (Gamow, 1930) Quantum Tunnelling


2He3 (0.82 MeV) + n (2.5MeV)

1D2 + 1D

2

1T3 (1 MeV) + p (3 MeV)

Relevant Fusion Reactions in the Laboratory

1D2 + 2He3

2He4 (3.6 MeV) + p (14.7MeV)

1D2 + 1T

3 2He4 (3.5 MeV) + n (14.1MeV)

3Li6 (7.4%) + n

2He4 + 1T3 + 4.8 MeV

3Li7 (92.6%) + n

2He4 + 1T3 + n – 2.8 MeV


!

" 3#1020s m

$3


It promises a large-scale energy source with basic fuels which are

abundant and available everywhere;

Very low global impact on the environment – no CO2 greenhouse gas

emissions;

Day-to-day-operation of a fusion power station would not require the

transport of radio-active materials;Power stations would be inherently

safe, with no possibility of “meltdown” or “runaway reactions”;

There is no long-lasting radioactive waste to create a burden on future

generations;

While development and capital investment costs are high, the marginal

cost of supply is expected to be negligible compared to that of energy

derived from fossil fuels.

Fusion Energy - Advantages


Fusion reaction is difficult to initiate

High temperatures (millions of degrees) in a clean, high vacuum

environment are required;

Technically complex and high capital cost reactors are needed

More research and development needed to bring concept to fruition

The physics is well advanced, but but technological and material

challenges requiring a multi-decade sustained effort must be overcome.

Fusion Energy - Disadvantages


Tokamak •! Donut shape

•! Unlike mirror, no end losses

because the field lines go

around and close on themselves

•! But major problem with

particle drift if magnetic field

lines are circular in form.

Schematic picture of the tokamak


Particle Drift Recap…

Parallel motion

Gyration

ExB drift

Pololarization drift Grad-B and curvature drifts

General expression for the drift velocity of the guiding centres of

particles of charge q in a uniform B field and sub ject to an

additional force F:


Trajectories of a 75 eV electron in a B ! field of 1 mT and

E # fields of 0 (top), 150 V/m (middle) and 1500 V/m (bottom).

Insight into drift motion

Left/right half-orbits are

symmetric, but up-

down half-orbits are

strongly asymmetric =>

particle travels more to

right than to left.


Toroidal curvature*

•! The toroidal magnetic field

follows form

•! And therefore varies with

major radius R as

Top down view of the tokamak

Toroidal magnetic field coils

Next 5 slides based on Warwick University

Physics of Fusion Power course TCD Graduate Plasma Physics Module PY5012 Guest Lecture 1st Nov 2011

Toroidal curvature

•! The toroidal magnetic field has a gradient

•! Which leads to a combined curvature

and !B drift in the vertical direction:

From we get

Note that the sign

of the drift depends

on the sign of the

charge q !

ˆ R ˆ " ˆ Z

0 B 0

# B

R0 0


Toroidal curvature

•! The drift

•! Leads to charge separation

•! Build up of an electric field

(calculate through the balance

with polarization)

•! And then to an ExB velocity

Poloidal cut of the tokamak.


Toroidal curvature has its price

•! The ExB velocity

•! Is directed outward and will

move the plasma on the wall in

a short timescale (µs)

Poloidal cut of the tokamak.


Remedy : a plasma current

•! A toroidal current in the plasma will generate a poloidal field (field lines short way round)

•! Combined toroidal and poloidal fields make helical field lines so that all particle orbits sample top/inside/bottom/outside regions.

•! Vertical !B drift still present, but helical field lines “short out” any tendency towards charge separation by accelerating electrons along the field line to maintain charge neutrality.

•! Charge separation no longer occurs and particles are well confined.

The field lines wind around helically .


Blick in das Plasmagefäß von ASDEX Upgrade

Cross-section of ASDEX Upgrade tokamak showing toroidal and poloidal field coils


PDAG List of Collaborative Projects & Research Topics

ASDEX Upgrade Project

CLISTE Interpretive Equilibrium Code

Function Parameterization

MHD activity analysis to improve q profile identification

Thomson Scattering analysis: ECE comparison

Wendelstein 7-X Project

Fast recovery of W7-X equilibria

Transport and spectroscopy experiments using a DP machine

ITER diagnostic design studies: Group involvement in

Integrated Tokamak Modelling Taskforce


Fluid Pressure

v. minor radius 100 kPa

-!p jxB !

R

Z

Fluid pressure gradient (outward force/V) balances inward pinch force/V: jxB = !p

Grad-Shafranov

equation: scalar,

weakly nonlinear PDE

Axisymmetry of tokamak

simplifies jxB = !p:


Interpretive Equilibria: Finding an equilibium to match data

•! Regularize source profiles: choose a functional form with a

reasonable number of free parameters

•! Flexible form very desirable. Good choice: Cubic Splines

•! Initialize to a default current distribution (centred in vessel)

•! (i) Solve Poisson-like linear PDE for trial Jtor (R,Z) by a

least squares best fit to input experimental data which must

be expressible as a linear function of the free parameters

•! (ii) Construct updated flux function and find new plasma

boundary (we are solving a free boundary problem)

•! (iii) Construct updated Jtor (R,Z) using updated flux

surface topology and free parameter values.

•! Iterate steps (i)-(iii) until a convergence criterion is met

Interpretive Tokamak Equilibrium at IPP Garching: CLISTE


Physics & Astronomy

Society, UCC

31/1/2006 TCD Graduate Plasma Physics Module PY5012 Guest Lecture 1st Nov 2011

Equilibrium Magnetics only 12-knot spline model (28 fit parameters)

E18 ROE 13kA

flux loops B probes MSE Ped.Pres. J||Bneo " ne dl I SOL

#17151, 3.850s


Magnetics & Q=1 & DCN+LID & ROE & MSE & YAR fit

E18 ROE 0.5 kA

#17151, 3.850s

flux loops B probes MSE Ped.Pres. J||Bneo " ne dl I SOL


The Wendelstein 7-X Stellarator (under construction in Greifswald) TCD Graduate Plasma Physics Module PY5012 Guest Lecture 1st Nov 2011

Physics & Astronomy

Society, UCC

31/1/2006

ne=1.1e17 m-3 Te=0.6eV PHe=9.6e-3mb

ne=1.5e17 m-3 Te=0.4eV PHe=1.2e-2mb

Physics & Astronomy

Society, UCC

31/1/2006

Four decades

of progress in

achieving

confinement

times* leading

to scientific

breakeven

*

!

" E =(3/2) p dV#Heating Power

The Future of Fusion Energy Research: ITER"

ITER, the International Tokamak

Experimental Reactor is being

constructed at Cadarache, near

Aix en Provence, on a 10 year

timeframe for c. #7.5bn and will

operate for c. 25 y at projected

running costs of #7.5bn. "

SSP


R. Aymar, Nobel Symposium Stockholm, 2005

Summary

Fusion offers one of the greatest hopes for a long-term solution to

the problem of a viable, environmentally friendly source for the

world’s future energy needs.

Fusion research is carried out within the framework of plasma

physics, a key current area of both fundamental and applied

research.

At UCC, we participate (both on and off-campus) in experiments at

major fusion labs in Germany and the U.K. as well as in ITER

design activities.


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