Measurement of wakefield intensity

Abstract

We report on the measurement of the wakefield of an ion moving through a beam–foil plasma using an indirect experimental method. The standard beam–foil time-of-flight technique is used to measure the lifetime of the perturbed H-like V 2s2S1/2 state due to its passage through the wakefield. This measured lifetime along with the theoretical lifetimes of pure H-like V 2s2S1/2 and 2p2P1/2 states has been used to determine the Stark mixing parameter of H-like 2s2S1/2 and 2p2P1/2 states, which is further exploited to determine the wakefield at the surface of the exit foil. The wakefield intensity during the passage of 160 MeV 5123V ion through thin C-foil as well as Au-foil is found to be as high as 3.2 ± 0.07 × 107 V cm−1.

Fast Ion Surface Energy Loss and Straggling in the Surface Wake Fields

“…Since the exit wakefield for the metal part is predicted to be larger than that for polypropylene or PET (a nonconductor), we propose that the differential energy loss as well as the differential straggling is due to this exit wake field. These measurements reveal wake-field-induced Stark mixing of the substates in a solid [9,10]. Hence, we tentatively ascribe this extra differential energy loss to the stronger metal exit wake field.…”

“…Segregating the contributions of the two surfaces from the bulk has not yet been possible. However, many years ago, bulk wake-field-induced Stark mixing of the sub states in H-like Kr ions [9] and recently the surface wake field intensity [10] in carbon foils have been measured. The latter showed that small surface wake field can be distinguished from the large bulk energy loss field in an atomic level lifetime measurement [10].…”

Role of Ion-Surface Interaction at the Entry Surface on the Energy Loss of Highly Charged Slow Ions in Solids

“…Therefore, no target ionization is possible by electron capture processes, however, target ionization by direct ionization process will take place equally by all the charge species. The contribution of energy loss from direct ionization can be obtained from As mentioned already that surface wakefield gave rise to energy loss at the surface [3] and the energy loss due to surface wakefield varies with charge state. Further, we discussed above that nearly neutral atoms emerge out from the exit surface irrespective of the difference in charge state at the incidence.…”

“…Long ago Ritchie [2] suggested with the basis of surface plasmon theory that a fast electron moving through a foil would lose its energy to both bulk as well as surface. Nevertheless only recently, our experiment [3] showed that stopping power of swift ions through solids can also distinguish these two contributions clearly. Surface stopping power is determined to be only a two order of magnitude smaller than that of the bulk stopping power of the 3.1 MeV/u vanadium ion beam passing through a carbon foil.…”

“…However, it has been experimentally shown that such effects do not exist [13,14]. On the contrary, it has recently been shown that the surface wakefield at the exit surface rather plays an important role on the ions [3]. Such a field is not possible to exist for highly charged slow ions as it originates from surface plasmons at the exit side due to passage of swift ions with velocity greater than the Fermi velocity.…”