CO2 laser heating of plasma columns in a steady solenoid field

Abstract

A 250−J CO2 laser has been used to produce plasma columns 12−20 cm in length, 2−4 mm in diameter, from initially uniform neutral hydrogen in a steady solenoidal field up to 100 kG. Interferometric and spectroscopic measurements indicate densities and temperatures on the order of 100 eV and 5×1017 cm−3, respectively. The backward−going laser−driven wave normally present in laser breakdown has been eliminated by pulsed filling of the tube.

Observation of Stimulated Brillouin Backscattering from an Underdense Plasma

“…The fact that r is negative rather than zero implied that lower fields, which yield lower temperatures as a result of higher radial thermal conductivity, 5 also gave smaller shifts as expected from SBS, rather than larger shifts which would be expected from a Doppler shift from a faster-moving front. 4 It is quite unlikely that a critical surface exists behind the breakdown front since it would prevent radiation from reaching the front, leaving nothing to drive it.…”

“…Plasma columns 20 cm long with spectroscopically measured electron temperatures T e as high as 130 ±30 eV were produced. 4 ' 5 Observations of backscattered radiation were made by placing a 5% reflecting polyethylene beam splitter in the incident beam about 5 m from the plasma. Backscattered light reflected by it was focused onto the input slit of a 1.2-m Ebert infrared grating spectrometer with an instrumental width less than 25 A full width at halfmaximum.…”

“…4 ' 5 A column of plasma was created and heated by axial C0 2 -laser irradiation of neutral hydrogen gas in solenoidal fields up to 100 kG, using a mirror of 1-m focal length. Plasma columns 20 cm long with spectroscopically measured electron temperatures T e as high as 130 ±30 eV were produced.…”

Étude expérimentale du développement et du chauffage d'une colonne de plasma par le rayonnement d'un laser CO2 de puissance

“…Le champ maximal est de 10 T et la demipériode de 160 J.1s. Des expériences analogues [2] ont montré que pour obtenir un bon couplage entre l'énergie laser et le plasma, il est nécessaire de focaliser le faisceau laser en un point où les lignes de champ magnétique commencent à diverger. Dans notre dispositif, le point focal et le diaphragme sont placés à un endroit où le champ magnétique atteint 80 % de la valeur maximale.…”

Laser heating of magnetized plasmas

“…Rutkowski, et al [157] used a 250-J CO 2 laser to generate 0.12 -0.20-m-long hydrogen plasma columns with 0.002 -0.004-m diameters in steady magnetic fields up to 10 T. The resulting plasma parameters were k T e ~ 100 eV and n e ~5X10 17 cm' 3 . The general experimental arrangement is similar to that of Offenberger,et al [131] and a similar orifice technique was used to reduce the backward travelling breakdown front.…”