RLE Progress Report No - Research Laboratory of Electronics - MIT

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Figure 2: The SRS spectrum observed on shot number 12805. The time-resolved Thomson spectrum from the same shot is shown in Figure 3(a). A horizontal lineout of this image where the cascade separation is indicated is shown in Figure 3(b). From the SRS data we would anticipate the SRS EPW to initially occur at a Thomson wavelength of ~404.7 nm and the observed data is in close agreement with the ideal calculation. The slight discrepancy in the Thomson wavelength for the SRS EPW can be attributed to uncertainties in the absolute calibration of the wavelength scales of both the SRS and Thomson diagnostics. As indicated in Fig. 3(b), the spacing between the SRS EPW and the first cascade is ~10.6 Å. This deviates from the ideal calculation (i.e. using linear theory and resonance matching) by 0.3 Å or ~2.9%. The curvature in the Thomson spectrum follows that in the SRS spectrum. Although the time axes in Figs. 2 and 3(a) are not absolutely calibrated, there is an abrupt change in the Thomson spectrum correlated with that in the SRS spectrum. The LDI does not start immediately with the SRS most likely due to being below threshold for the interaction or due to thermal detuning as indicated by the change in the SRS wavelength with time. We believe the data definitively shows observation of the second LDI cascade step. Other data obtained from the experiment is believed to show more than two LDI cascade steps. However, the correlation between the SRS and Thomson spectra is not as easily explained as the data presented here and will be presented elsewhere.
(a) (b) Figure 3: (a) Time-resolved Thomson spectrum from shot number 12805 showing the forward propagating EPW from SRS and the second LDI cascade. (b) A horizontal lineout taken where the cascade separation is indicated in (a). The time-integrated Thomson spectrum from the same shot is shown in Figure 4. Two distinct waves are observed separated in both frequency (Thomson wavelength) and wave vector (position on the collection optic). The initial spacing in wavelength (∆λ≈10.6 Å) and wave vector Figure 4: Time-integrated Thomson spectrum from shot number 12805 showing the forward propagating EPW from SRS and the second LDI cascade. (∆k/k o ≈-0.13) is consistent with the ideal calculation using early time estimates for the electron density and temperature. The other characteristics of the spectrum can be explained as follows.
Page 1 and 2: Plasma Electrodynamics and Applicat
Page 3 and 4: 1. Results of Recent Single Hot Spo
Page 5: ps FWHM, coincident in time with th
Page 9 and 10: 2. Saturation of Stimulated Raman B
Page 11 and 12: We transformed Eqs. (1)-(5) accordi
Page 13 and 14: 3. Modes in Density Depleted Wavegu
Page 15 and 16: In Eq. (2), α = −k x , ( ) z o
Page 17 and 18: 5. Emission From Electron Bernstein
Page 19 and 20: the X-B conversion process is optim
Page 21: appear in Proceedings of the 18th I

RLE Progress Report No - Research Laboratory of Electronics - MIT

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