Possibility of Fiber-Laser Inertial Fusion Energy

Isao Matsushima

National Institute of Advanced Industrial Science and Technology (AIST), C2, 1-1-1, Umezono, Tsukuba, 3058568,

Japan

*Some of figures in this presentation are cited from internet web pages and published literatures. Their citation sources are indicated under the figures. They may have their own copyrights or intellectual property rights.

ファイバーレーザー核融合の可能性

IFE Ignition comming soon!

But, ....How about the laser driver?

http://www-lmj.cea.fr/

LMJNIFhttps://lasers.llnl.gov/

1 GW IFE Power Plant1 GW IFE Power Plant

Laser Efficiency is Crucial!

Laser Efficiency5%

Target Gain100

Thermo-Electric

40%

40 MJ40 MJ40 MJ40 MJ

1 GW25 Hz2 MJ 200 MJ

Laser Efficiency10%

Target Gain100

Thermo-Electric

40%

60 MJ60 MJ20 MJ20 MJ

1 GW

17 Hz2 MJ 200 MJ

ASHURA Project successfully finished

2005.3.31

High-Power KrF LaserSuper-ASHURA

3.2 kJElectro-Optical Efficiency 2.3%

DPSSL

Mercury (LLNL, Yb:S-FAP)5~10 Hz, 65 J, 6.5% efficiency65 J / 800 kW × 1 ms / 73% LD ==>5.9%C. Bibeau, et. al, J. Phys. IV France, 133, 797-803 (2006).

HALNA (Osaka, Nd:glass)10 Hz, 25.6 J/ 800 kW × 2 × 0.15 ms / 50% LD ==> 5.3%T. Kawashima, et. al, J. Phys. IV France, 133, 615-620 (2006).

LUCIA (LULI, Yb:YAG) 4 J/1 Hz, 1.5 J/10 Hz,

Polaris (Jena, Yb:glass)0.1 Hz, 20 J

J. Kawanaka, http://www.ile.osaka-u.ac.jp/

産業用高効率超短パルス Yb:YAGレーザーの開発(NEDO プロジェクト　産総研 + メガオプト社 )

詳細は 12aVII4 にて発表

最大出力１０Ｗ以上、パルスエネルギーｍＪクラス、繰返し１０ｋＨｚ～、パルス幅サブピコ秒、電気―光効率１０％を常温にて動作する産業用レーザー

目標

Fiber Laser

http://www.ipgphotonics.com/

Up to 10mJ energy per pulse400 ns pulse durationUp to 200 W average output powerMax Power consumption 1200W

An example as a commercial product

16.7% Wall-Plug Efficiency

Fiber Laser IFE (G.A. Mourou, C. Labaune, D. Hulin, A. Galvanauskas in IFSA2007)

Short-pulse Broad-Bandwidth

Fig. 2. Spectrum of the pulses with grating distances of 28 mm (solid curve) and 30 mm (dashed curve)

Xiangyu Zhou,Dai Yoshitomi, Yohei Kobayashi, and Kenji Torizuka, “Generation of 28-fs pulses from a mode-locked ytterbium fiber oscillator”, Opt. Express, 16, 7055-7059 (2008).

CPA Amp (80 MHz)75 W Pump 41.5 W before Compression

(20 ps, 0.52 μJ)41.5 W/75 W = 52%

30 W after Compression 100 fs @ 10 W* 　周、他、応物予稿　 2008 秋

Limitation of Fiber Laser

Fig. 2. Damage limits and exper imental measurements. Solid lines, bulk-damage thresholds (50 J/cm2 for 1-ns pulses) for 200- and 50-μm core fibers. Dashed line, self-focusing threshold of 3.7 MW in fused silica.

Ming-Yuan Cheng, Yu-Chung Chang, Almantas Galvanauskas, Pri Mamidipudi, Rupak Changkakoti, and Peter Gatchell, “High-energy and high-peak-power nanosecond pulse generation with beam quality control in 200-mm core highly multimode Yb-doped fiber amplifiers” Opt. Lett. 30, 358 (2005).

Damage threshold 50 J / cm2

MJ Fiber Laser for IFE

50 J / cm2 x 200 μφ = 16 mJ

16 mJ × 108 fibers > 1 MJ

3.5

m

600 μm × 104 = 6 m

600

μm

× 1

04 =

6 m

Active Media Volume

MJ Laser is Possible

Cooling gaps?Pump LDs?Pulse Power Supplies?

May be smaller than NIF

A Conceptual Study reported

Fig. 1. FAN (Fiber Amplificaton Network): A seed pulse, is amplified by a Large Mode Area (LMA) Yb:glass single mode amplifiers up to an energy level corresponding to the saturation fluence Fsat. It is then divided equally into many branches where each individual pulse is amplified again to the same level as previously. This division and amplification sequence is repeated until the total energy coming out from the network output reaches the desired energy level. Acousto Optic Modulators (AOM) are used to eliminate deleterious feedbacks. Fast Pockels cell (PC) equips each arm for pulse shaping purposes. For this application, incoherent addition suffices and no fiber phasing is required. Coherent addition similar to the one described in Ref. [12] is required for the ignition pulse. This FAN technique has the advantage to provide nanosecond pulses with very short coherent length, i.e. ~30 μm. A variant could start with n seed pulses each with a specific wavelength. n could be as large as 104.

C. Labaune et al. “On the feasibility of a fiber-based inertial fusion laser driver”, Optics Communications 281 (2008) 4075–4080

Breakthrough Requirement 1Cost $100 × 108 fibers= $1010

1 万円 × 1 億本 = 1 兆円Mass-production method for 108 fibers

Cost down

http://www.miraipj.jp/ http://www.fujixerox.co.jp/

Silicon Photonics VCSEL

Breakthrough Requirement 2

How to Focus on Target?

Case 1 Single Mode Gaussian Beam

d1 =

2 m

m

L = 5 m

D

ω (z) = ω0 1+λ z

π ω02

⎛

⎝⎜⎞

⎠⎟

2

Gaussian Beam

ω0 = 1mm,λ = 0.5μm, z = 5m → ω(5m) = 1.28mm, D = 5.1mm

Chamber wall area 4πL2 =108π mm2⎡⎣ ⎤⎦

D < 2 mm for 108 beams

Breakthrough Requirement 2

How to Focus on Target?

Case 2 Image relay

d1 =

2 m

m

L = 5 m

D

l = 0.25 m

d0 =0.1 mm φ

Ordinal multimode fiber: NA = 0.22 --> D = 110 mm

Ideal flat-top plane wave: NA = λ/d0, λ = 0.5 μm --> NA = 0.005, D = 2.5 mm

D < 2 mm for 108 beams

Breakthrough Requirement 2

How to Focus on Target?108 beams + 108 lenses + 2×108 actuators ?100×106 beams + 100 lenses + 2×100 actuators

Coherent or Incoherent beam

combining

R. Xiao, J. Hou, M. liu, and Z. F. Jiang, Opt. Express, 16, 2015 (2008).

Digital Micromirror Device (DMD) developed by Texas Instruments (TI)M. Douglass, Proc. SPIE Vol. 4980 (2003)

MEMS

Breakthrough Requirement 3

Laser wavelength?

Yb doped Fiber Laser : λ = 1 μmIFE implosion: λ = 0.5 μm ~ 0.3 μm

Efficient Fiber SHG, THGor

Short-wavelength Fiber Laseror

New Implosion Concept for Fiber Lasers

Conclusion

Some breakthroughs are required.

Now the time to start the fiber-laser IFE Project

Fiber lasers have the potential for IFE drivers.High efficiency, simple, robust,

Cost, focusing, wavelength,

High Efficiency Laser is Key for IFE