BBC_Knowledge_2014-06_Asia_100p

Australia. Engineers there were baffled by

the impact the bolt of lightning had on their

lightning conductor, a copper tube, which they sent to

the physics department of the University of Sydney. A

section of the pipe seemed to be have been crushed by

a great force, collapsing it as if it were a straw.

The electrical current flowing through the lightning

conductor from the strike had produced the same

effect as an electric motor. The electricity, moving

through a magnetic field (in this case generated by the

electricity itself ) produced an inwards force on the

tube. The pulse was so intense that it collapsed the

tube. Named the ‘pinch effect’, this was considered

little more than an amusing oddity until work began

on fusion generators. It’s a variant on the pinch

effect that keeps the plasma away from the walls of a

tokamak. And in the Sandia Z-machine, the pinch

from a vast electrical discharge is used to create fusion

by inertial confinement.

In this monstrous electrical device, 20 mega-amps

of current are blasted through hundreds of extremely

thin tungsten wires. It’s like plugging an old-

fashioned light bulb directly into the National Grid.

Discharged in around 100 nanoseconds, the Z-pinch

produces 80 trillion watts (five times the output of

every power station in the world combined). The

wires vaporise, forming a plasma that is driven

inwards by the pinch effect. This also generates high

intensity X-rays which blast a hohlraum, producing

a variant on the NIF approach known as magnetised

liner inertial fusion. The technology is impressive

and a lot more compact than the NIF, but once again

the daunting practical difficulty of replacing both the

wires and the hohlraum over and over has to be faced

if this approach were ever used for power generation.

We have a long road to travel before fusion can

supply the National Grid. Each of the technologies

TECHNOLOGY - The only one of the

devices not built from scratch, the

1980 Particle Beam Fusion

Accelerator was upgraded to the

Z-machine in 1997 (itself later

upgraded). It uses the ‘pinch’ effect,

where a powerful electrical current

produces an inward force on charged

particles to produce intense heating

and compression.

ODDS OF WINNING RACE

4 to 1

SANDIA

Z-MACHINE

(Z-PINCH)

DATE STARTED 1997

METHOD Z-pinch inertial confinement

SIZE 30m-diameter chamber

LOCATION Albuquerque, New Mexico

COMPLETED 1997

3,700

MILLION

degrees Celsius is the

highest temperature

produced by the Sandia

Z-Machine.

Researchers study

the pattern of plasma

generated in the MAST

experiment’s tokamak

Researcher Ryan McBride inspects

a tiny central piece of beryllium

that will be imploded by the

powerful magnetic field generated

in the Z-machine

80 trillion watts

courses through the

Z-machine

FUSION DESIGN #4

pp y g

Researcher Ryan McBride inspects

a tiny central piece of beryllium

that will be imploded by the

powerful magnetic field generated

in the Z-machine

FUSION