Vacuum technology Ultrahigh vacuum effect – much lower pressures can be generated than before. UHV under scrutiny The deployment of high-compression-ratio turbopumps in this way represents a win-win for UHV system innovation. Most notably, upfront investment and cost of owner ship are favourable when compared with conventional approaches to UHV generation (for example, the use of an ion getter pump in tandem with a turbopump, with the latter deployed as backing pump). The new approach is also a lot simpler in terms of implementation, field maintenance and service intervals (typically longer than four years). As such, this is a pumping set-up that will suit scientific users who want a UHV system that pulls the vacuum and is 100 % reliable, 100 % of the time. It’s also one switch to do it all, with a single programmable controller to drive the turbopump and the dry backing pump. In their experimental study, the Pfeiffer Vacuum team used a small-scale vacuum chamber (500 mm diameter, 120 mm high) that was baked for seven days at 120 °C. The scientists then evaluated the UHV performance of the compact and powerful turbopump (hydrogen compression ratio 1×10 7 ) when paired with four separate dry backing pumps (a rotary vane pump; a multistage Roots pump; as well as a two-stage and three-stage diaphragm pump). The time span for each measurement was one day, using hot-cathode and cold-cathode ionization gauges to track chamber evacuation for each backing/main pump pair (see table). Pump type Backing pressure (mbar) UHV (mbar) Rotary vane pump 3 x 10 -3 2.4 x 10 -11 Mulitstage roots pump (ACP 15) 3.2 x 10 -2 2.5 x 10 -11 Three-stage diaphragm pump (MVP 20) 1.0 2.7 x 10 -11 Table: backing pumps shape up for UHV performance For relatively simple vacuum chambers, like the one in the own lab, it was found that even a small diaphragm pump is sufficient as the backing pump in combination with the turbopump. The team also concluded that a multistage Roots pump in tandem with the turbopump provides an ideal backing/main pump combination to generate low UHV conditions for chambers of 100 l capacity or more. This is particularly relevant in a big-science context, where users need to generate UHV in the vacuum tubing of a particle accelerator without particulate contamination from the pumping system. In fact, for an accele- come up with vacuum innovations that make rator setting the optimum set-up would see the turbopump paired with multistage Roots backing pumps – both of which are fluorinefree and can operate with an extended cable connection of up to 120 m between the control electronics and pump location (to keep the electronics away from harsh radiation environments). Right now, the priority for the team is to educate the R&D customer base about the merits of UHV generation using high-compression- ratio turbopumps – specifically, the 300 H series and its sister product the 700 H (with hydrogen compression ratio 2×10 7 ). The company’s webinars on the subject have been well re ceived by the research community, with most of the commercial interest to date coming from universitybased vacuum customers. The 300 H series turbopump is a really good pumping option for UHV, but we’re still trying to make it better. Ultimately, our job is to life easier for our R&D customers. This is a solution that does just that. The Author: Dipl.-Ing. Andreas Schopphoff, Head of Market Segement R&D, Pfeiffer Vacuum GmbH, Asslar, Germany Two-stage diaphragm pump (MVP 15) 3.0 2.8 x 10 -11 since 1974 WATER JETTING TECHNICS HIGH-PRESSURE TECHNICS HIGH-PRESSURE SYSTEMS HIGH-PRESSURE PLUNGER PUMPS HYDRAULICS PROCESS TECHNICS APPLICABLE IN VARIOUS APPLICATIONS surface and components cleaning │oil, petro chemistry and gas chemistry │ process industry │ mining www.kamat.de/en get further information
