Bombarding insulating foils with highly energetic ions

Abstract

Insulating (MYLAR), semi-insulating (MYLAR-Au) and conducting foils have been bombarded by very energetic 64 MeV u −1 78 Kr 32+ ions. The velocity spectra of fast electrons emitted in the backward and forward directions have been measured and analyzed as a function of the elapsed time in the run. A shift of binary encounter and convoy electrons emitted in the forward direction toward lower velocities has been observed with insulating targets. No such shift occurs with metallic targets. The surface potential evolves with time (i.e. ion fluence) both at forward and backward emission angle. It is shown that strong bulk charging of insulating targets leads to a positive potential as high as 9 kV before charge breakdown.

Charging of insulators by multiply-charged-ion impact probed by slowing down of fast binary-encounter electrons

“…Also, a shift of CE energy was observed with polymer foils [22]. Both observations are due to heavy-ion nuclear track potential, a "nanoscopic" effect related to a single-ion track, in contrast to a "macroscopic" surface charging as evoked in [16,21].…”

“…6 and 7) were chosen. The same statistical method as reported in [16,19] is applied to the BEE peaks: (i) BEEs are separated from the background by choosing an appropriate window in the "deposited energy-TOF" bidimensional plot of (iii) Over each interval t, we calculate the average TOF by fitting a Gaussian distribution to the BEE peak and plot the BEE TOF as a function of irradiation time in Figs. 4 and 6.…”

“…The studies focused on binary-encounter electrons [11,14], convoy electrons [13,15], fast electrons produced by the "Fermi shuttle" mechanism [12,13], and also Auger electrons from the in-flight deexcitation of electroncarrying projectiles [15]. After a pilot experiment at Grand Accelerateur National d'Ions Lourds (Caen) [16], dedicated experiments on charging-up phenomena were conducted at the CS (Superconductor Cyclotron) of Istituto Nazionale di Fisica Nucleare-LNS (Catania) with insulating foils. The charging dynamics was measured via the slowing down of fast electrons: Their velocity was obtained by the time-of-flight method using the scintillation detectors of the multidetector ARGOS.…”