Micrometeoroid simulation studies on metal targets

Abstract

Experiments on impact craters and impact ionization of dust particles have been performed using iron microparticles from a 2‐Mv Van de Graaff accelerator. The particle velocity υ ranged from 0.2 to 40 km/sec and the mass m ranged from 1 × 10−15 g to 5 × 10−10 g. The analysis and mass determination of iron microspheres on smooth targets and of iron layers of the projectile in the middle of impact craters have been done with an electron microprobe. The Kα radiation emitted by the iron layer in the crater has been measured as a function of mass and velocity of the projectile. The radiation measurement gives, in combination with the crater diameter D, a means for the determination of the projectile parameters m and υ. The targets used were Ag, Al, Cu, Cd, and W. Within an error of approximately 20% the total mass of the iron projectile has been found inside the craters in W, Cu, and Al targets at velocities of ≤13 km/sec. The impact ionization has been studied for impact velocities of up to 40 km/sec and projectile masses of down to 10−15g. The yield of either ions or electrons, normalized to the incident mass m, can be described by an empirical relation of the form Q = const ƒ(θ, υ) · mα · υβ, where θ is the angle of incidence. Analysis of impact ionization has been applied to extremely sensitive detectors of cosmic dust particles. The impact cratering and ionization are discussed in terms of shock effects by applying the Rankine‐Hugoniot theory. The energy partition in the form of kinetic energy and internal energy (e.g., elastic compression and irreversible heating) is discussed as a function of the velocity of iron particles impacting the targets Al, Cu, W, and Au. As a result, W and Au are targets that transform a greater fraction of the primary energy into heating and ionization of projectile material.

Cometary impact effects at the Moon: Implications for lunar swirl formation

“…5). While this may be a slight over-estimation, ionized fractions exceeding 0.1 are consistent with laboratory studies of the plasma generated by 40 km/s impactors (Dietzel et al, 1972). .…”

“…The most important distinction between cometary and asteroidal impacts are the differing impact velocities: asteroids are described by an approximate median velocity of v $ 16 km=s (Yue et al, 2013), in contrast to the much higher velocities typical of comets (v rms $ 52 km=s) (Hartmann et al, 1981). As target vaporization efficiency scales approximately as (Dietzel et al, 1972). Hence, the dusty plasma environment in the inner comae of comets, which contain significant ionized species prior to impact, will likely experience a large amplification in electron density during impact.…”

Electromagnetic properties of impact-generated plasma, vapor and debris

“…It is reasonable to suppose that at very high velocities the level of ionization and the amount of neutral vapor asymptotically approach a linear dependence on energy (v2) and the fractional ionization will approach a constant value ( 4 ) which is only dependent on impact geometry, projectile and target materials. Little evidence of this asymptotic behavior, however, is seen in the Dietzal et al [7] data. With a reasonably conservative extrapolation of Equation (1) to Leonid encounter velocities (72 M s ) , 10-20% of the plasma produced by Leonid impacts on spacecraft will be ionized and highly conductive.…”

“…At modest impact velocities (5 Ms), the level of ionization is low (typically M s , however, the ionization level can be as much as 0.1 [7]. It is reasonable to suppose that at very high velocities the level of ionization and the amount of neutral vapor asymptotically approach a linear dependence on energy (v2) and the fractional ionization will approach a constant value ( 4 ) which is only dependent on impact geometry, projectile and target materials.…”

“…Images are produced from the best available original document. Dietzel et al [7], studied the production of plasma from small particles in the hypervelocity impact regime. They used a parallel plate capacitor with 40 V/cm electric field to separate and measure the positive and negative constituents of the plasma for to 5x10-" g iron projectiles striking a tunsten target atl-40 km/s.…”