exhaus ng energy and ash from small, aneutronic, magne c fusion

Exhaus'ng energy and ash from small, aneutronic, magne'c fusion reactors

S.A. Cohen, M. Chu-‐Cheong, A. Creely, A. Glasser, M. Khodak, E. Meier, C. Myers, T. Rognlien, A. Se<ow and D. Welch

ICC/EPR Workshop, February 2013

D-‐T burning: one neutral fusion product, n, exhausts 80% of power uniformly in 10-‐7 s.

D-‐3He burning: H and α fusion products are charged and confined.

Will the power and parTcle control (PPC)problems – ash accumulaTon and divertor power load -‐ worsen with aneutronic fuels?

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FRC recipe for solving PPC problems in aneutronic fusion

In a small (30-‐cm radius) ceramic magneTc pot

Add •  10-‐5 Mole D/s •  10-‐5 Mole 3He/s Bake at high temperature (80 keV). Vigorously sTr mixture (MHz). While cooking, frost with 0.01 Mole/s hydrogen/helium. Enjoy 1-‐20 MW fusion power

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1.  The SOL of a small FRC will be cold because of open-‐field-‐line losses.

2.  Make the SOL broad and dense by supplying gas at one end and exhausTng it at the other.

3.  Because the FRC is small, the orbits of fusion products (FPs) will pass through the SOL. FPs will slow down there, by modified classical processes, and stop there. This is non-‐local heat and parTcle transport.

4.  Power losses from the plasma core include radiaTon to the walls and heat deposited in the SOL, the lacer transported to divertor chambers.

5.  Maintain the core plasma temperature by RF heaTng.

The logic: Use the FRC’s SOL*

3 *Scrape-‐off layer

1-‐20 MW D-‐3He FRC reactor

Embodiment of logic

Benefits of being small •  Surface-‐to-‐volume raTo ~ 1/r – Maximum P/A ~ 2 MW/m2

•  FPs pass through SOL •  Stability is easier

Myers

Variable aperture size

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SOL parameters: 1D UEDGE simulaTons

1. The SOL of a small FRC will be cold

Chu-‐Cheong, Meier, Rognlien

Gas box and gas feed Electron heaTng region

2 m

Absorbing boundary

For Pfusion = 20 MW, Prad = 0, and BNozzle = 2 BFRC Maximum Pz/A = 100 MW/m2

Plasma 0.2 m

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1. The SOL of a small FRC will be cold

Chu-‐Cheong, Meier, Rognlien 6

1. Power flow in a cold SOL (10 MW case)

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1.  Oumlow through the absorbing boundary must be consistent with the gas input LSP simulaTons of oumlow from open end of FRC SOL

Se<ow, Khodak, Welch

Higher density simulaTons in progress.

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2. Make the SOL broad and dense by supplying gas at one end

At high gas-‐box neutral pressure, the plasma demagneTzes and spreads radially. RadiaTon and charge exchange hit its walls. The gas-‐box aperture can be opened to create a broader SOL. Mass augmentaTon is essenTal for spacecran propulsion applicaTons and heats exhaust heat from the FRC’s core.

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3a. Because the FRC is small, the FP orbits will pass through the SOL.

Fusion ! products! s !

3He ! 7.48!T! 3.39!p! 3.38!

4He! 3.14!

Glasser

Where we want to be

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3b. FPs will slow down & stop in the SOL

Classical slowing down (STx)

In FRC SOL Wcrit ~ 1 keV ts ~ 4 x 10-‐4 s τ  ~ 3.2 ts ~ 1.3 ms

BUT 11


CondiTons in the FRC SOL differ from those ordinarily used to calculate dW/dx

vFP ⊥ B ρe < λD

(Ωce/ωpe >1 ) vFP > vth,e

These are expected to reduce the slowing-‐down rate, thus the non-‐local heaTng of the SOL plasma.

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LSP simulaTons in 2-‐ and 3-‐D 14.7 MeV H+

Background protons

Electron cloud trails H+

PotenTal gradient slows down H+

SimulaTon Technique: Explicit EM (2D) Implicit EM (3D) Periodic box 3λD each side, External B field

Creely: 2-‐D 13

–  ArTficial ion, p+8 –  v = 0.01c (47 keV) –  V (θ =26°) to B –  np=1014 cm-‐3 –  Te = 100 eV –  Bx = 0, 10 T –  λD = 7.4 µm –  re = 2.4 µm –  24 eV/ns (Li/

Petrasso: standard)

3b. FPs will slow down in the SOL

24 eV/ns

Welch: 3D

4 days/ns with 32 processors Longer simulaTons in progress

Creely: 2-‐D, 14.7 MeV p+10 Slowing down Tme (ms) Energy conserv (%) Run Tme (ms)

3 eV/ns

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Chu-‐Cheong

150 keV

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3b. Net effect on τ

τ*FP ~ 8 x 10 x τ ~ 100 ms

Decreased Slowing-‐down rate

FracTon of orbit in SOL

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B on separatrix

Ripple

Will the 150 keV FPs thermalize before escaping?

Myers

The PFRC SOL has a mirror-‐machine-‐like geometry

Full, end-‐to-‐end, kineTc simulaTons of the SOL are necessary.

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4. SOL heat is eventually transported to divertor chambers

Field expansion in a divertor can readily lower the peak heat flux in a 20 MW reactor to < 2 MW/m2.

!145-‐ms duraTon PFRC-‐2 discharge, made possible by Hi-‐T superconducTng flux conservers, gas puffing and odd parity RMF.

Line-‐averaged electron density

15-‐ms gas puff

Current PFRC-‐2 device OperaTng at 15 kW

20 ms/div

Density from pre-‐fill

RMFo heaTng off

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Summary: Using the SOL well •  Aneutronic reacTons can greatly alleviate materials problems but then special methods are needed to avoid PPC problems.

•  Small FRCs can reduce PPC problems. •  There is NEW PHYSICS in small FRCs and their SOLs.

 Non-‐local FRC SOL heaTng by FPs  Mass augmentaTon for effecTve SOL cooling and control   Rapid loss of fusion products to the SOL avoids ash build up.

•  Control of the SOL can provide plasma parameters suitable for Spacecran propulsion Materials tesTng Power plant

Acknowledgements: This work was supported, in part, by US DOE Contract Number DE-‐AC02-‐09CH11466. We thank E. Feibush, C. Brunkhorst and B. Berlinger for technical support. 19

exhaus ng energy and ash from small, aneutronic, magne c fusion

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