Generation of short electromagnetic wave via laser plasma interaction experiments
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Generation of Short Electromagnetic Wave via Laser Plasma Interaction Experiments N. Yugami, Utsunomiya University, Japan US-Japan Workshop on Heavy Ion Fusion and High Energy Density Physics Sep. 28-30,2005 Department of Energy and Environmental Science, Graduate School of Engineering,

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Generation of short electromagnetic wave via laser plasma interaction experiments l.jpg
Generation of Short Electromagnetic Wave via Laser Plasma Interaction Experiments

N. Yugami,

Utsunomiya University, Japan

US-Japan Workshop on Heavy Ion Fusion and High Energy Density Physics

Sep. 28-30,2005

Department of Energy and Environmental Science,

Graduate School of Engineering,

Utsunomiya University

7-1-2 Yoto, Utsunomiya, Tochigi 321-8585, JAPAN, TEL: +81-28-689-6083, FAX: +81-28-689-7030


Outline l.jpg
Outline

A proof-of-principle experiment demonstrates the generation of the radiation from the Cerenkov wake excited by a ultra short and ultra high power pulse laser in a perpendicularly magnetized plasma. The frequency of the radiation is in the millimeter range(up to 200 GHz). The intensity of the radiation is proportional to the magnetic field intensity as the theory expected. Polarization of the emitted radiation is also detected. The difference in the frequency of the emitted radiation between the experiments and previous theory can be explained by the electrons' oscillation in the electric field of a narrow column of ions in the focal region.


Oscillating current in plasma wave l.jpg
Oscillating Current in Plasma Wave

Electron Current

Skin depth ;d c/wp

n=1.0x1016 cm-3 f=0.9 THz

Frequency ; w wp (plasma freq.)

n0 = 1016 cm3

lp = 300 mm

d  50 mm

[1] J. Yoshii et al., Phys. Rev. Lett. 79, 4194 (1997).



Slide5 l.jpg

Typical Example of Emitted Radiation

Expected Pulse Width

Experimental condition

Laser Power: 0.5 TW

B0: 8.5 kG, He 375 mTorr


Radiation intensity was proportional to the strength of b field l.jpg
Radiation intensity was proportional to the strength of B field

Laser Power ; 0.5 TW

N2 750 mTorr


Slide7 l.jpg

Plasma cavity for radiation field

Wavelength of the radiation is satisfied the matching condtion,

Strong radiation is expected to observe.

The data suggests the wavelength(frequency) depends on the strength of B field.

plasma

boundary

boundary

Plasma column works as “cavity” for radiation



Typical waveform of radiation 2 peaks were observed l.jpg
Typical Waveform of Radiation field--- 2 peaks were observed ---

Cut-off freq. of waveguide

fc = 31.4 GHz

Pulse width

200-250 ps




Freq spectrum measured by tof method each peak has different freq l.jpg
Freq. Spectrum measured by TOF field method--- Each peak has different freq. ---

Flight length L = 1.2 m

1st peak ~74 GHz

2nd peak ~40 GHz


Freq of 1st peak does not depend on b field freq of 2nd peak depends on b field l.jpg
Freq. of 1st peak does NOT depend on B field. fieldFreq. of 2nd peak depends on B field.


1st peak of radiation l.jpg
1st peak of Radiation field

  • Freq. : 74 GHz.

  • Polarization of radiation // B field

  • Frequency of radiation dose not depend on the strength of B field

Electrons' oscillation in the electric field of a narrow column of ions in the focal region.

Electron

B

x

E

+ + + + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + + + +

+ + + + + + + + + + + + + + + + +

w

z

ion column


2nd peak pulse l.jpg
2nd peak pulse field

  • Freq. : ~40 GHz.

  • Polarization of radiation B field

  • Frequency of radiation depends on the strength of B field

Bernstein mode

4

3

2

1

0

1

2

3

4


Conclusion l.jpg
Conclusion field

  • The radiation from the interaction between laser and magnetized plasma was observed.

  • Higher freq. andlower freq.components were observed.

  • Higher Freq. Component

    • Freq : 74 GHz

    • Polarization …. Parallel to B field

    • Frequency does not depend on the strength of B field.

    • Due to the electron motion parallel to the B field.

  • Lower Freq. Component

    • Polarization …. Perpendicular to B field

    • Frequency does depends on the strength of B field.

    • Bernstein mode?


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