Fusion - Everything You Wanted to Know* * But Were Afraid to Ask - - PowerPoint PPT Presentation

Fusion - Everything You Wanted to Know* *But Were Afraid to Ask

Sam Eddinger February 7, 2013

Introduction

• Overview – What is Fusion
• Current Techniques for Scalable Fusion

– Toroidal Confinement Fusion (TOKAMAK)

• Also known as Magnetic Confinement Fusion (MCF)

– Inertial Confinement Fusion (ICF)

• Current Technical Challenges
• Future Technical Challenges
• My Role in the industry - how ICF targets are

created

Predominate Fusion Fuel

• Fusion in the sun starts with normal Hydrogen
• To maximize energy per reaction, research

uses combination of Deuterium and Tritium

What is Fusion

• Process of combining two smaller nuclei into a

larger nucleus and energy

• Energy and byproducts released are predictable

– Allows for easy detection of Fusion events

How to Cause Fusion

• Requires High Energy to overcome Coulomb

Force

How to Cause Fusion (continued)

Similarities Between Fusion and Fission

• Nuclear Reaction – Energy Released through converting

mass into energy

• Fusion/Fission fuel have high energy density

– Fusion takes ~ 5X less mass to get same energy as Fission

• Fusion/Fission events create excess neutrons

– Excess Neutrons cause surrounding material to transmutate and become radioactive

• Fusion/Fission events create radioactive material

– Tritium for fusion, many byproducts for fission

• Significant Control Systems to control both reactions
• Both technologies have the capability of breeding fuel

Relative size of Fuel for Power Plants

Differences Between Fusion and Fission

• Fission
• Breaking apart Nucleus
• Fuel Loaded into Core
• Fuel confined for years
• Performed at Low Temp.
• Neutrons needed for chain

reaction

• Removal of Poison to start

reaction

• Reactivity controlled by

poisons

• Fusion
• Putting together Nucleus
• Fuel Injected into Core
• Fuel confined for < 1 second
• Performed at High Temp.
• Temperature needed for chain

reaction

• Heating needed to start

reaction

• Poisons destroy Reactivity

(causes instability)

Differences Between Fusion and Fission (continued)

• Fission
• Each nucleus can only

fission once

• Limited fuel resource
• Radioactive waste for >

1000 years

• Decay Heat
• Many safety systems and

analyses required

• Man made technology
• Operational technology
• Fusion
• Each nucleus may be able to

fuse more than once

• Unlimited fuel resource
• Radioactive waste for ~ 100

years

• No Decay Heat
• Limited safety systems and

analyses required

• Energy source of the universe
• Always 50 years in the future

Element Selection

Fission Fusion

Three Main Design Considerations In Fusion Technologies

• Fuel Temperature

– Defined by choice of Fusion Isotopes – Higher temperature is harder to obtain and maintain

• Fuel confinement time

– Defined by technology

• MCF requires high confinement time (design challenge)
• ICF has low confinement time
• Fuel Density

– Defined by technology

• MCF has low fuel density
• ICF requires high fuel density (design challenge)

Fusion Temperature vs. Reaction Rate

• Reaction Rate is inversely proportional to confinement time

and density

• Optimizing the temperature of the fuel will minimize

the confinement time and/or density needed

Fusion Isotope Selection

Current Techniques for Scalable Fusion

Magnetic Confinement

• Two different magnetic

Fields used

– Toroidal

• Used to confine the plasma

– Poloidal

• Keeps the plasma away from

the walls

Inside the Magnetic Confinement Core

Magnetic Confinement Diagnostics

Inertial Confinement

Inertial Confinement

• Two predominate methods to

implode target

– Direct drive

• Lasers directly strike target

– Symmetrical implosion issues

– Indirect drive

• Lasers strike can called a Hohlraum

– Laser energy converted to x-rays – Requires higher laser energy output

National Ignition Facility (NIF)

NIF Internals

NIF Target Chamber

Inside the Inertial Confinement Core

NIF Target holder

NIF Target

Fusion Capsule Contained in NIF target

Current Challenges in MCF and ICF

• Neither technology can reach Breakeven (Q=1)

– Defined as Ratio of Fusion power produced / Power needed to keep the plasma in steady state

• Caused by insufficient number of fusion reactions prior to

the system becoming unstable

– Significant technical challenges to meet the requirement for both technologies

• Scientists continue to underestimate the interaction of hot

dense particles

– Q≈20 needed for commercialization – Q=∞ for the sun

Future Challenges in MCF and ICF

• Fusion creates high energy neutrons

– Expected to be 100X the flux of a fission reactor – Difficult to convert Neutron energy into power – High Neutron flux causes material embrittlement and radioactivity – Difficult to test materials at these conditions

• Fusion requires high temperatures

– Temperature cycling causes fatigue – Easy to damage system if plasma becomes instable

Future Challenges in MCF

• No easy way to convert heat into energy
• Difficult to constrain plasma for sufficient times to

generate power

– Helium and other atoms take the energy without causing additional Fusion events

• Difficult to remove these poisons without affecting plasma

– Currently external power is needed to heat plasma – Continuous injection of Fusion material for self sustaining reaction

• Reducing energy into magnets

– Superconductivity requires low temperature for magnets

Future Challenges in ICF

• Require six target implosions a second for

sufficient power

– Difficult to cool mirrors – Difficult to inject repeatably at this rate

• Impossible to have self sustaining reaction

– Need to shoot each target independently to generate Fusion energy

Schematic of a Commercial ICF plant