Picosecond Laser Ablation and Ion Clusters for External Injection into the Extended EBIS
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Engineering topics
Kondrashev, Sergey
Publications and source records attributed to Kondrashev, Sergey.
Features of ion generation by a picosecond laser in the range of 10 11 –10 13 W cm -2 power densities
Picosecond lasers (ps-lasers) have significant advantages for the generation of low charge state ions compared to nanosecond lasers because the influence of heat conductivity on a solid target is almost negligible in the case of ps-laser ablation for laser pulse durations less than 10 ps. However, there is no comprehensive data on ion yields for different elements and target irradiation conditions for laser power densities at the target surface around and below 10 13 W cm –2 , which is of interest to our study of such plasmas as a source of low charge state ions for various applications, particularly for external injection of those ions into an Electron Beam Ion Source (EBIS). We investigated ion generation from Al, Ti, Cu, Nb and Ta target elements by a ps-laser with power densities in the range of 10 11 –10 13 W cm –2 at the target surface. A ps-laser with 1.27 mJ maximum energy within an 8 ps pulse and repetition rate up to 400 Hz has been used to generate a laser-ablated plasma. Dependencies of ion current versus time, total charge of registered ions as well as ion kinetic energy distributions are characterized using a Faraday cup. Significant difference in ion current dynamics between first, second and following shots onto the same target spot was found for all five target elements. The total charge of ions registered by the Faraday cup increases linearly with increasing laser pulse energy and is almost independent of the target element and number of shots onto the same target spot for all five target elements studied. The results obtained give us a basis for specification and design of the source of low charge state ions for external injection into EBIS.
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Picosecond laser generated plasma as a source of singly charged ions for external injection into an EBIS
The focus of this paper is on practical aspects of ion generation by picosecond lasers as a source of low charge state ions for external injection of ions into an electron beam ion source (EBIS). For a ps-laser, compared to a ns-laser currently used at Relativistic Heavy Ion Collier Electron Beam Ion Source (RHIC EBIS), the influence of heat conductivity in the solid target is almost negligible, which results in a lower target consumption rate and less vacuum pressure rise. By using a laser with high repetition rate, it is possible to produce quasi continuous 1+ ion beams for periods of tens of milliseconds, making it possible to take advantage of the ability of the EBIS to accumulate ions in the “slow” injection capture mode. Producing such an ion pulse train is now feasible since ps-lasers with pulse energy up to 10 mJ and rep-rate up to 10 kHz have recently become commercially available. The advantages of this lower current accumulation scheme include: (1) easier beam transport due to lower space charge of lower beam currents required compared to the present single pulse fast injection scheme, (2) better EBIS pulse to pulse ion output stability since pulse to pulse ion variations of the laser source are averaged over a long train of laser pulses, and (3) the possible addition of an isotope separator in which rare beams could be produced and selected at run time from less expensive (unenriched) targets. We studied the properties of plasmas generated by a ps-laser with 1.27 mJ energy within an 8 ps pulse and a repetition rate up to 400 Hz at Argonne National Laboratory to investigate feasibility and specify parameters for a laser ion source for RHIC EBIS using a “slow” injection mode. Al, Ti, Cu, Nb, and Ta targets were tested with various target translation speeds. Here, we demonstrated that a both “slow” and “fast” injection modes are accessible with a single ion source geometry and single injection line, providing the most attractive option for an ion source for external injection into RHIC EBIS trap based on a ps-laser.
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Study of Ion Generation by a ps-laser for External Injection into Electron Beam Ion Source
We investigated ion generation from Al, Ti, Cu, Nb and Ta target elements by a picosecond-laser in the range of 10 11 – 10 13 W/cm 2 power densities at the target surface. A ps-laser with 1.27 mJ maximum energy within a 8 ps pulse and repetition rate up to 400 Hz has been used to generate a laser-ablated plasma. Dependencies of ion current vs time, total charge of registered ions as well as ion kinetic energy distributions are characterized using a Faraday cup. Significant difference in ion current dynamics between first, second and following shots onto the same target spot was found for all five target elements. The total charge of ions registered by the Faraday cup increase linearly with increasing laser pulse energy and are almost independent on the target element and number of shots onto the same target spot for all five target elements studied. Target craters have been examined using a commercially available microscope (Nikon Eclipse LV150) and crater cross section areas were found to be in the range of 0.0076 – 0.0172 mm 2 within the first five shots onto the same target spot for different target elements. A linear dependence of crater cross section square on laser pulse energy has been observed for the Ta target. Ion energy distributions for all target elements have a plateau or a slight peak in the energy range of 10 - 100 eV and long low-intensity energy tail up to tens of keV.
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Cluster ion source for external injection and high capacity filling of light elements into the relativistic heavy ion collider electron beam ion source
An advanced Electron Beam Ion Source (EBIS) is the primary ion source to supply highly charged ion beams of different elements to the Relativistic Heavy Ion Collider (RHIC) and to the NASA Space Radiation Laboratory (NSRL). Intense beams of highly charged ions of various elements of the periodic table, ranging from helium to uranium, have been demonstrated since EBIS became operational in 2010. EBIS routinely provides ion beams to RHIC and NSRL quasisimultaneously with about 1 s switching time between different ion species. Such unique flexibility and rapid switching between ion species are based on external injection of singly charged ions into the EBIS trap either in “fast” or “slow” injection modes. At present, a Laser Ion Source (LIS) provides most of the ion species of solid materials using the “fast” injection mode into the EBIS trap and a Hollow Cathode Ion Source (HCIS) provides most of the ion species of gaseous elements using the “slow” injection mode into the EBIS trap. Gas injection into the EBIS trap is also possible and has been used but imposes some restrictions for the simultaneous generation of highly charged ions such as Au 32+ ions for RHIC and ions of gaseous species for NSRL. Because light ions have relatively high velocity inside the EBIS trap, efficient injection of hydrogen and helium ions and filling of the EBIS trap to high capacity is difficult from either LIS or HCIS. To overcome this restriction and enhance EBIS operational capability, we suggest injecting beams of hydrogen and helium cluster ions into the EBIS trap. Required parameters of cluster ion beam injection into the EBIS trap are estimated, and advantages of such an injection are highlighted. A cluster ion source with required high intensity is visible and will be designed, built, optimized, and tested.
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Development of highly efficient NEG pumping system for EBIS
Ultrahigh vacuum inside the ion trap volume is crucial for stable and reliable operation of an Electron Beam Ion Source (EBIS). We have developed and tested a compact linear pumping system based on the ZAO Non-Evaporable Getter (NEG) module with high pumping speed and enhanced sorption capacity for all active gases. Due to its minimal transverse dimensions, the system can be mounted adjacent to the ion trap inside a superconducting solenoid bore and will provide a pumping speed of the order of 1000 l/s for all active gases in that area. An externally supplied current (100 A DC) is used to heat the ZAO NEG up to 650 °C for more than 1 h, which is required for pump activation and/or reactivation cycles. The pumping system is being developed for use in the Extended EBIS Upgrade which is presently in progress at BNL. In conclusion, the design of the system and results of multiple tests are presented and discussed.
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