Erratum: Collinear investigation of laser initiated reduced density channels [Appl. Phys. Lett. 43, 1010 (1983)]

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71132/2/APPLAB-45-7-808-1.pd

Collinear investigation of laser initiated reduced density channels

The characteristics of reduced density channels generated by laser initiated discharges have been investigated by means of collinear holographic interferometry and schlieren photography. We report the first direct measurements of the density profiles in the interior of such channels. Under unperturbed conditions these channels exhibit azimuthal asymmetries. Gas dynamics within the channel are also presented for the case of incident shock waves reflected from cylindrical and planar boundaries.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71306/2/APPLAB-43-11-1010-1.pd

Effect of x‐y coupling on the beam breakup instability

In solenoidal beam transport systems, motions in the x and y directions are coupled by the v×B force. A two‐dimensional coupled mode description of the beam breakup (BBU) instability is presented; its dispersion relation is derived and compared with the one‐dimensional BBU dispersion relation. In the two‐dimensional description, instability growth is doubled and two additional wave modes are found in the regime of strong focusing. In the weak focusing regime, the two‐dimensional description gives the same dispersion relation as the one‐dimensional model.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69723/2/APPLAB-58-7-699-1.pd

Dynamics of excimer laser‐ablated aluminum neutral atom plume measured by dye laser resonance absorption photography

We report the first dye laser resonance absorption photographs of a single species of aluminum ground‐state neutral atoms in the plume ablated from solid aluminum by KrF excimer laser radiation. Aluminum ground‐state neutral atoms were diagnosed by illuminating the ablated plume with a dye laser tuned to the 32P1/2–42S1/2 transition at 394.4 nm. Measurements have been performed in vacuum as well as in argon and air environments. Streaming velocities measured for neutral aluminum atoms in vacuum ranged from 0.5×106 cm/s at low excimer laser fluences of 1–2 J/cm2 to 3.4×106 cm/s at high fluences of 7 J/cm2. Dye laser resonance absorption photography measurements of ablated aluminum in argon and air showed slower expansion at 50 and 200 Torr, while observations at 760 Torr indicate turbulent mixing of aluminum neutrals near the surface. Differences between data in argon and air may be due to oxidation of neutral aluminum atoms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70489/2/APPLAB-58-15-1597-1.pd

Copper vapor laser drilling of copper, iron, and titanium foils in atmospheric pressure air and argon

A copper vapor laser (511 and 578 nm) is used to drill submillimeter diameter holes in 0.025–0.127 mm thick foils of copper, iron, and titanium. Foils are machined in atmospheric pressure air and argon. The laser is repetitively pulsed at 10 kHz with a per pulse energy of 0.5 mJ giving an average power of 5 W at the sample surface for a pulse width of 40 ns. A p‐i‐n photodiode and a photomultiplier tube detector are connected to a digital‐display timing circuit that records the number of incident laser pulses used to drill through the sample. The number of pulses is converted to an average drilling time and can provide an estimate for the average laser energy used to drill the hole. Typical data for all three materials with a per‐pulse fluence of 0.7 J/cm2 ranged from 0.1 to 500 s to produce holes of ∼0.3 mm diameter. Drilling times decreased in some cases by an order of magnitude when machining in air. This is attributed to the increased laser absorption of the metal‐oxide layer formed in air and was especially noticeable with titanium. A continuous wave thermal model is used to compare experimental data as well as verify the thermal machining mechanism.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69638/2/RSINAK-64-11-3308-1.pd

Thin film contact resistance with dissimilar materials

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98706/1/JApplPhys_109_124910.pd

Gyrotron‐backward‐wave‐oscillator experiments utilizing a high current, high voltage, microsecond electron accelerator

We report the first gyrotron‐backward‐wave‐oscillator experiments to produce high power (tube power of ∼1–8 MW), long‐pulse (0.3–1.2 μs) microwaves at high currents (0.1–2 kA) and high voltages (650–750 kV). Experiments were performed in the TE11 fundamental backward‐wave mode, with efficiencies of ∼1%–2%. Mode competition was observed which is believed to originate from the TE21 absolute instability.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70862/2/JAPIAU-72-4-1221-1.pd

Extraction of ions from the matrix sheath in ablation-plasma ion implantation

A simple one-dimensional theory is presented to assess the implantation of ions from the ion matrix sheath (IMS) in an ablated plasma plume that is approaching a negatively biased substrate. Under the assumption that the plume geometry, the electron and ion density distributions, and the potential distribution are frozen during the IMS extraction, the implanted ion current is calculated as a function of time for various substrate-plume separations. This model accurately recovers Lieberman’s classic results when the plume front is initially in contact with the substrate. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70969/2/APPLAB-78-6-706-1.pd

Heating of Contaminants on Diamond Windows

This paper examines the RF heating of the contaminants on a diamond window. Both heating of an isolated internal graphite impurity, and of a thin film on the window surface, are discussed. Comparison with recent experiments is given. It is found that heating of isolated internal graphite impurities is unlikely to account for diamond window failure. Upon averaging over the entire window, the thin surface film in general absorbs approximately a fraction of one percent of the total incident power. Intense local heating on the surface contaminant is possible, however. © 2003 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87504/2/234_1.pd

Low-noise microwave magnetrons by azimuthally varying axial magnetic field

A technique has been demonstrated to significantly reduce the noise in microwave oven magnetrons. The technique employs permanent magnets to generate an azimuthally varying axial magnetic field. Noise measurements are reported which show dramatic reductions in the noise of kW oven magnetrons operating near 2.45 GHz. The noise reduction near the carrier is some 30 dB. Microwave sidebands are reduced or eliminated. Noise reduction occurs at all anode currents, but is particularly significant at low current near the start-oscillation condition. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70840/2/APPLAB-83-10-1938-1.pd