Elastic and Inelastic Scattering of Low-Velocity He+ Ions in Helium

Cramer, W. H.; Simons, J. H.

doi:10.1063/1.1743506

Cited by 82 publications

(24 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To simulate the high-energy part, non-central as well as many-body collisions would have to be included, which falls beyond the scope of this work. When determining the initial He-He distance distribution we assume the active surface layer for the described collision process to be constrained towards the bulk of the droplet by the mean free path of He + in He droplets of 3Å, inferred from the gas-phase elastic collision cross section [27]. Since the He density distribution inside this layer only weakly varies with N , the simulated energy distribution is robust against variations of N .…”

Section: O N K I N E T I C E N E R G Y ( E V )mentioning

confidence: 99%

Interatomic Coulombic decay in helium nanodroplets

et al. 2017

View full text Add to dashboard Cite

Interatomic Coulombic decay (ICD) is induced in helium (He) nanodroplets by photoexciting the n = 2 excited state of He + using XUV synchrotron radiation. By recording multiple coincidence electron and ion images we find that ICD occurs in various locations at the droplet surface, inside the surface region, or in the droplet interior. ICD at the surface gives rise to energetic He + ions as previously observed for free He dimers. ICD deeper inside leads to the ejection of slow He + ions due to Coulomb explosion delayed by elastic collisions with neighboring He atoms, and to the formation of He + k complexes.Isolated atoms or molecules excited by energetic radiation typically decay through intramolecular processes such as the emission of an electron or photon. In contrast, in weakly bound complexes, locally generated electrons can additionally interact with neighboring atoms or molecules, leading to new interatomic or intermolecular interactions. Interatomic Coulombic decay (ICD) is a particularly interesting decay process which occurs when local electronic decay is energetically forbidden [1]. Thus, ICD offers a new, ultrafast decay path where energy is exchanged with a neighboring atom leading to its ionization. Since its discovery, ICD has been observed in a wide variety of weakly-bound systems from He dimers [2,3] and rare-gas clusters to biologically relevant systems such as water clusters; for reviews see [4,5]. Today, the focus is on condensed-phase systems where ICD is involved in complex relaxation mechanisms [6][7][8], which can generate genotoxic low-energy electrons and radical cations [9]. Recently, it was suggested to utilize this property of ICD for cancer treatment [10,11].Here we present the first study of ICD in helium (He) nanodroplets. He nanodroplets are generally considered as an ultracold, inert spectroscopic matrix for embedded, isolated molecules and clusters [12,13]. Upon ionization by intense or energetic radiation, however, He droplets turn into a highly reactive medium, inducing reactions and secondary ionization processes of the embedded species [14]. Their homogeneous quantum liquid density profile, and the simple structure of atomic constituents, make He droplets particularly beneficial as benchmark systems for elucidating correlated decay processes. Recent examples include the collective autoionization of multiply excited pure He droplets [15,16] and the creation of doubly charged species by one-photon ionization of doped He droplets [17]. In this work we fully characterize the product states generated by ICD and secondary processes in He nanodroplets using coincidence imaging techniques.The experiments were performed using a He droplet machine attached to a velocity map imaging photoelectron-photoion coincidence (VMI-PEPICO) detector at the GasPhase beamline of Elettra-Sincrotrone Trieste, Italy. The apparatus has been described in detail elsewhere [18,19]. Briefly, a beam of He nanodroplets is produced by continuously expanding pressurized He (50 bar) of high purity He out of a c...

show abstract

Section: O N K I N E T I C E N E R G Y ( E V )mentioning

confidence: 99%

Interatomic Coulombic decay in helium nanodroplets

et al. 2017

View full text Add to dashboard Cite

show abstract

“…The cross section of such a mechanism has been estimated for helium by many authors to 10 À15 cm 2 at low kinetic energy [32][33][34][35]. k IMFP , k EMFP have been evaluated and are given in Table 2.…”

Section: Tablementioning

confidence: 99%

Low flux and low energy helium ion implantation into tungsten using a dedicated plasma source

Pentecoste

Thomann

Melhem

et al. 2016

Nuclear Instruments and Methods in Physics Research Section B:

View full text Add to dashboard Cite

a b s t r a c tThe aim of this work is to investigate the first stages of defect formation in tungsten (W) due to the accumulation of helium (He) atoms inside the crystal lattice. To reach the required implantation conditions, i.e. low He ion fluxes (10 11 -10 14 ions.cm 2 .s À1 ) and kinetic energies below the W atom displacement threshold (about 500 eV for He + ), an ICP source has been designed and connected to a diffusion chamber. Implantation conditions have been characterized by means of complementary diagnostics modified for measurements in this very low density helium plasma. It was shown that lowest ion fluxes could only be reached for the discharge working in capacitive mode either in a or c regime. Special attention was paid to control the energy gained by the ions by acceleration through the sheath at the direct current biased substrate. At very low helium pressure, in a regime, a broad ion energy distribution function was evidenced, whereas a peak centered on the potential difference between the plasma and the biased substrate was found at higher pressures in the c mode. Polycrystalline tungsten samples were exposed to the helium plasma in both regimes of the discharge and characterized by positron annihilation spectroscopy in order to detect the formed vacancy defects. It was found that W vacancies are able to be formed just by helium accumulation and that the same final implanted state is reached, whatever the operating mode of the capacitive discharge.

show abstract

“…In references [7,8], the authors obtained the experimental data for α which is the cross-section in cm 2 of a cubic centimeter of gas at 0 • C and a pressure of 1 mmHg. Reference [7] showed the relation between α and I to be I = 10 −20 α/3.536 m 2 . Subsequently, I was calculated as indicated by the empty circles and triangles in Fig.…”

Section: Numerical Modelmentioning

confidence: 99%

“…The solid red and dashed blue lines in each panel show I(ε) for the elastic collisions and charge exchange, respectively. These crosssections are used in our calculations, and are obtained by fitting the experimental data [7,8] which are indicated in the figures by the empty circles and triangles. The "+" symbols in the bottom panel show the experimental data used in our previous paper [4].…”

Section: Numerical Modelmentioning

confidence: 99%

Numerical Modeling of Electrodeless Electric Thruster by Ion Cyclotron Resonance/Ponderomotive Acceleration

Otsuka

Hada

Shinohara

et al. 2013

Plasma and Fusion Research

View full text Add to dashboard Cite

We developed an electrodeless electric thruster that utilizes ion cyclotron resonance/ponderomotive acceleration (ICR/PA) for ion acceleration. We conducted test particle simulations to assess the thruster's performance. We compared the thrusts obtained using argon (Ar) and helium (He) gas as propellants at the same mass flow rate. On the basis of a model that includes ion wall loss and ion-neutral collisions, we estimated the exhaust velocity and thrust. We found that He ions are less influenced by both ion wall loss and ion-neutral collisions than are Ar ions because the gyroradii of He ions are generally smaller than those of Ar ions and the ratio of the gyrofrequency to the collision frequency for He ions is larger than that for Ar ions. In addition, the exhaust velocities of He ions are larger than those of Ar ions, as predicted by the quasilinear theory and ponderomotive potential. Consequently, the thrust and specific impulse for He are larger than those for Ar.

show abstract

Elastic and Inelastic Scattering of Low-Velocity He+ Ions in Helium

Cited by 82 publications

References 13 publications

Interatomic Coulombic decay in helium nanodroplets

Interatomic Coulombic decay in helium nanodroplets

Low flux and low energy helium ion implantation into tungsten using a dedicated plasma source

Numerical Modeling of Electrodeless Electric Thruster by Ion Cyclotron Resonance/Ponderomotive Acceleration

Contact Info

Product

Resources

About