Scraping, beam intesnity optimizations and nuching were set up and optimized during the day.
Initial findings
- Very long cooling times are needed after deceleration to cool the decelerated beam.
- Electron energy and decelerated beam are not well matched.
- 229Th is cooled even later after the other ions
- Even after scraping some contaminats remained that were either rebunched and show side bands. or move around as a "cloud".
- This can be seen on the detectors (e.g. particle dector, but also PMTS) as a flat bump in the folded "accu" spectra. the signal decreases with time. I.e., It moves around the ring with a frequency matching the one of the wanted species but with some "phase offset" of about half a ESR revolution. The signal is ratger stron but vanishes ("decays") after some time. Probably finally scraped og
- It is very tigth to set the scrapers correctly (and the particke detector).
- Fortunately the ion beam optical setting is such that the scraper in the south is in optimal position just at its "Endlage inne" (values see below)
- SIS intensiteis have increased but are still on average a factor 3-4 lower than one year ago.
- As a sidenode: For optimal scraping, the beam decelerated, debunched, cooled, scraped and rebunhced. Thus, one can see if there are contaminants, and, in consequence clean the beam better from unwanted species.
- The bunches are still quite long given the number of ions, increasing of the bucket fill from 1.0 to values large than 1.4 gives problems such as phase shifts , ande changes even inbetween a waiting/measurement time. to be discussed with the specialists on monday
Mitigation Solution
- The cooling energy is set 100V higher - which also matches better to a recalculated scanning range; ( PTB 104513 V, Ohmlabs 1040509 V). This better matching improves cooling times but is till not optimal. It is noted, tha tthe cooling times are long since a broad cloud of ions is decelerated, and the electron current is low (was 50 mA, now 60 mA).
- Electron current increased 50 mA -> 60 mA.
- Scrapers are moved in in two steps with an intermediate posiions to mitigate the problem of overshoots when driving. Before rebunching they are slightly moved out to make room for the slightly larger
bunched beam.
- Due to the change of the voltage the bunching frequency has changed (see post of the start of the test measurements); electron cooled DC beam and bunched beam are (alomost) matched using the RSA in 100kHz scale. The new reference frequency on the RSA are (old: 243.750625MHz, rev. frequency 1.542728 MHz, 158 harm - new: 243.815 MHz, 1.54313 MHz).
[New settings for timing and scraper position will be attached as fotos; an emergency backup of the settings are stored in an earlier post).
- The cooler actually drags the ion very slowly to its final position after ~30 s just before rebunichng (visible by the shift of the peak relative to the marker just before rebunching). This is interpreted as and effet of the power supplies only very slowly reaching a final value to within a few kHz.
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