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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
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
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
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

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
Radiation intensity was proportional to the strength of B field

Laser Power ; 0.5 TW

N2 750 mTorr

slide7

Plasma cavity for radiation

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
Typical Waveform of Radiation--- 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
Freq. Spectrum measured by TOF method--- Each peak has different freq. ---

Flight length L = 1.2 m

1st peak ~74 GHz

2nd peak ~40 GHz

1st peak of radiation
1st peak of Radiation
  • 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
2nd peak pulse
  • 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
Conclusion
  • 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?