Carbon Stripper Foils Research Articles

Development of a highly reproducible mixed ion beam sputtering method for long-lived carbon stripper foils

Heavy ion beam sputtering may be used to prepare carbon stripper foils with long lifetimes, but the breakage rate during foil preparation is very high. Carbon stripper foils have hence been prepared by a heavy ion beam sputtering method with mixed noble gas ions and tested with 3.2 MeV Ne + ions. The mechanical stress and shrinkage under high intensity beam irradiation has been partially overcome by this method, and the lifetime was extended by a factor of about 60 compared with commercially available foils. The average lifetime was 174 mC and the longest lifetime was 252 mC. These foils further showed a low breakage rate during preparation, and were very stable and reproducible.

Thickness measurements of carbon stripper foils using optical transmittance

A very simple system was built to measure the thickness of carbon stripper foils. The optical transmittance of a foil is uniquely related to its thickness. Absolute thicknesses were obtained by yield measurements in a Rutherford scattering experiment, using a sub-barrier 16O ion beam. Comparison of thicknesses obtained by differing methods is performed.

Laser plasma ablation of carbon

A new plant for fabricating carbon stripper foils by laser plasma ablation-deposition has been installed. The adaptation of the preparation process to the ultrahigh vacuum system and the pulsed (≈ 10 ns pulse width) Nd:YAG laser with a repetition rate of 50 Hz is described. Carbon deposition rates were measured as a function of laser power density, polar angle ϑ and azimuth angle ϕ, where the central laser beam defines the polar axis. The crystal structure of the ≈ 4 μg/cm 2 thick carbon foils was analyzed with respect to laser power density and polar angle ϑ. In addition, the specific gravity and resistivity of such carbon foils were measured in relation to the laser power density for carbon films mounted during deposition at ϑ = 14°.

New plant for fabricating carbon stripper foils by laser plasma ablation deposition

Our theory on the optimum strength of carbon stripper foils with respect to heavy ion induced irradiation damage at tandem energies was confirmed when newly developed carbon foils with isotropically distributed nanocrystals were tested. The new preparation method is based on a hot carbon plasma induced by 10 ns light pulses with a power density of up to 30 GW/cm 2 from a Nd:YAG laser. In order to prepare the so-called lpa-foils (carbon stripper foils prepared by laser plasma ablation deposition) in series production a new ultrahigh vacuum box coater was installed. This system offers a working pressure of about 10 −6 Pa and a substrate area of about 1000 cm 2, which means 100–200 stripper foils per charge depending on the size of the stripper frame. A new pulsed Nd: YAG laser with a repetition rate of 50 Hz was installed at the box coater in order to shorten the deposition time. A status report of the adaptation of the lpa-process to the new setup is presented in detail.

Development of heavy ion beam sputtering method for long-lived carbon stripper foils

A heavy noble gas ion beam sputtering (HIBS) technique was developed to prepare carbon stripper foils with a characteristic of long lifetime. The dependence of lifetimes on the mass of noble gas was also investigated. Compared with foils made by lighter ions such as Ne and Ar, the foils made by Kr and Xe noble gases were not so much stronger mechanically, but were long-lived under bombardment with a 3.2 MeV Ne + ion beam 3 μA in intensity and 3.5 mm in diameter. The mean lifetime in the case of Kr sputtering gas was around 51 mC, 20 times longer than that of commercially available foils. The key point in producing long-lived foils with Kr or Xe noble gas ions was found to be to decrease the amount of oxygen contaminants as much as possible.

Long-life carbon-fiber-supported carbon stripper foils

Significantly increased stripper foil lifetimes have resulted from the use of carbon fibers to suspend a carbon stripper foil in an 800 MeV proton beam. Two carbon foils, each 16 mm × 16 mm and 100 μg/cm 2, were superimposed on each other to produce an equivalent 200 μg/cm 2 “postage stamp” foil which was then sandwiched between two fine grids composed of 4–5 μm diameter carbon fibers. The carbon foils were made by electron-beam evaporation-condensation techniques. The “postage stamp” foil survived irradiation with 800 MeV protons at a flux of 6.6 × 10 16 cm −2s −1 to a fluence of 1.1 × 10 23 protons/cm 2. The effective lifetime of the foil was determined by reduced stripping efficiency due to foil shrinkage. Compared to previously used carbon foils, the new foil extended stripper lifetimes by up to 300% and reduced beam losses by 30%. This allowed an increase of average stored beam current by 30% and decreased radiation exposure to operations personnel by one third, for foil changes.

Development of laser plasma ablation-deposition techniques for carbon stripper foils

The aim to develop irradiation resistant carbon stripper foils for swift heavy ions led to the new technique of laser plasma ablation-deposition of carbon, in which a pulsed high power Nd:YAG laser induces a hot carbon plasma for deposition on suitable substrates in high vacuum. The essential physical property of the new technique is the ablation of monoatomic carbon with an average charge state of 4+ and a broad spectrum of energies of up to 1 keV of the monomers. These conditions influence the nucleation and growth of a carbon film in such a way that a nearly isotropic orientation of the nanocrystals in the condensed film is achieved. This results, as postulated, in a much better strength against irradiation damage caused by heavy ions, compared to all other types of stripper foils.

Nitrided carbon foils as long-lived charge strippers

Nitrided carbon stripper foils with excellent lifetimes and mechanical properties have been made by a new method based on reactive nitrogen-ion-beam sputtering. The foils showed no shrinkage and maintained mechanical flexibility during long periods of irradiation by ion beams. The average integrated current stripped by such foils before breakage was 75 mC using a 3.2 MeV Ne + beam flux of 4 μA, 3.5 mm in diameter. This capability is about 30 times greater than commercially available carbon stripper foils. Details are given for the method of preparation and the compositions of the foils produced.

Stripper foil development at the NSC target laboratory

Arrangements have been made to make carbon stripper foils by electron bombardment, ethylene cracking and resistive heating. The deposition rate was found to be 0.35 μgcm −2s −1 during the glow discharge and 0.02 μgcm −2s −1 in the other two processes. An optical gauge was assembled to measure the thickness of stripper foils. An alpha thickness gauge setup was made to measure the thickness of four foils at a time without breaking the vacuum in the chamber. The thickness uniformity of 22 foils of a glow discharge batch was found to be 4%. An attempt is made to make the devices to test the strength of the foils made by these different techniques.

Variations of carbon foil lifetimes under bombardment by N+, Ne+, Ar+ and Zn+ ions

Studies of the useful lifetime of 2-5 µg cm−2 carbon stripper foils have been made using 225 keV heavy ion beam bombardment. The foils were self supporting and were mounted both in a standard and a tension-slackened manner. In determining the quality of the foil during ion bombardment several techniques were used, in particular beam-foil spectroscopy. Here the intensity of the light emitted by the foil-emergent beam was measured as a function of bombardment time. The measured lifetime before foil failure for standard foils was found to agree well with a semiempirical model proposed by Auble and Galbraith, and the slackened foils exhibited usable lifetimes 3-4 times longer than the normal foils. The properties of ordinary and slackened foils were compared under realistic conditions. It is concluded that the slackened foils are very well suited for studies of atomic spectra and meanlives of excited states using beam foil excitation methods.

Measurement of the 1s Lamb shift in hydrogenlike nickel.

The wavelength of the 2${\mathit{p}}_{3/2}$\ensuremath{\rightarrow}1${\mathit{s}}_{1/2}$ transition in hydrogenlike ${\mathrm{Ni}}^{27+}$ has been measured with an accuracy of 13 ppm. Bare ${\mathrm{Ni}}^{28+}$ ions of 11.4 MeV/amu as emerging from a carbon stripper foil were decelerated to 8.4, 6.7, 5.2, and 3.1 MeV/amu and dressed in a thin target gas by electron capture. The x rays were measured with a crystal spectrometer in Johann geometry employing a position-sensitive x-ray detector. The 1s Lamb shift in hydrogenlike nickel has been found to be 5.07\ifmmode\pm\else\textpm\fi{}0.10 eV in good agreement with theory.

Heavy-ion irradiation damage in carbon stripper foils

Slackened carbon stripper foils of about 4 μg/cm 2, produced by vacuum evaporation-condensation and used for heavy ion stripping in the terminal of the Munich MP tandem, were investigated in order to get more information about irradiation damages. Electron diffraction and electron transmission muscope investigations related with theoretical considerations revealed a clear picture of the irradiation damage mechanism in carbon stripper foils. Due to these results it can be predicted, how the crystallographic structure of a carbon foil should be constituted in order to show best stripper performance.

Hybrid-type long-lived carbon stripper foils

A new method for the preparation of hybrid-type long-lived carbon stripper foils was developed. The new procedure is based on a modification of our controlled dc arc-discharge method. The carbon foils are of the multilayer type and the layers are composed of carbon particles emitted from the electrodes in the ac arc-discharge and from the cathode in the dc arc-discharge. With this simple and powerful method long lived carbon stripper foils can be prepared with higher reliability and reproducibility than with the previous procedure.

Stripper foil requirements for optimum ion transmission at the Munich MP-tandem

The transmission of several ion beams ( 1H, 2H, 16O, 32S, 58Ni, 107Ag, 127I, and 197Au) through the Munich MP-tandem were measured as a function of stripper foil thickness, ion injection limitation, and analyzed charge state at 10 MV terminal voltage. These data offer the possibility to optimize the stripper foil thickness for the specific experimental requirements. In addition the knowledge could be broadened, how to choose the ion injection limitation conditions in order to achieve a high yield of the analyzed heavy ion charge state and a long lifetime of the carbon stripper foil.

Irradiation damage in carbon stripper foils induced by heavy ions

(1989). Irradiation damage in carbon stripper foils induced by heavy ions. Radiation Effects and Defects in Solids: Vol. 110, No. 1-2, pp. 197-199.

A simple preparation method for carbon stripper foils

A modified glow-discharge apparatus for the preparation of carbon stripper foils is described. The effects of anode size and distance between the two electrodes in the cracking chamber on the uniformity of the carbon foils are determined. The applied method to measure the thicknesses of the carbon foils and the technique to slacken stripper foils are mentioned.

Microscopic structure of flexible long-lived carbon stripper foils

We have developed flexible long-lived carbon stripper foils of about 10 μ/cm 2 in thickness by a controlled dc carbon arc-discharge method. The foils are not only mechanically strong, but also long-lived under bombardment with a 3.2 MeV Ne + ion beam of 1 μA in intensity. The mean lifetime is around 12 h. The key point in producing long-lived foils is to control the amount of carbon particles coming from the cathode by controlling the cathode spot temperature.

Development of Enhanced Long-Lived Carbon Strippr Foils for Heavy Ion Accelerators : A Challenge to Prepare Super Long Lived Carbon Stripper Foils

Development of Enhanced Long-Lived Carbon Strippr Foils for Heavy Ion Accelerators : A Challenge to Prepare Super Long Lived Carbon Stripper Foils

Characteristics of compact solid-target charge exchange analyzers for energetic ion diagnostics on tokamaks

Compact electrostatic charge exchange analyzers (18×18×13 cm) have been constructed for installation in areas of high magnetic fields and restricted access near tokamak fusion devices. The analyzers employed carbon stripping foils, and have been calibrated for proton and deuteron energies between 1 and 70 keV. They have been successfully used to study charge exchange losses in auxiliary-heated tokamak plasmas and were found to be ideally suited to supplement the larger and more complex gas-cell analyzers by providing additional spatial and temporal information at a modest effort and cost.

Structure studies of carbon foils with the aim to improve the ability for heavy-ion stripping

Slackened carbon stripper foils of 3 to 5 μg/cm 2 produced by vacuum evaporation-condensation were graphitized by annealing at about 3300 K with a pulsed laser beam (1.06 μm). An average crystal size of 10 nm was measured by electron diffraction. The texture of the 002-plane is parallel to the surface of the foil as known from slightly annealed carbon foils. Radiation damages caused by high doses of heavy ions dramatically change the crystal structure. Electron diffraction patterns reveal newly formed graphite crystals with their 002-plane perpendicular to the texture. Compared to carbon foils of the same kind, but not graphitized, a lifetime prolongation of a factor of two was achieved for such foils tested in the terminal of the Munich MP tandem. The slope of the curve for heavy-ion transmission through carbon stripper foils varies for foils of the same kind and for different ion-beam conditions.