Se run
Target
issues:
Before the run:
* Automatic stable beam scan to be made before taking
and after taking protons.
* Monitor stable Se80 at nominal target temperature.
Too much 82SeO can saturate REXTRAP (which was not the case during the run).
* p-beam scan and yield
measurements on 80Rb
* Look for 68Se in germanium detector set up. Measure
mass 98 and sum up yields in order to determine GeS
and AlBr production. Collection of
70SeCO on foils in
Note: Do not take more than 2.5uA of p-beam (with the
option of increasing towards the end of the run).
* Yields measured before
the run (all in ions per uC and transmission
corrected to the focal plane) from the ZrO2 target:
Mass 98: 70SeCO+ 3E5
Mass 101: 73Se 1.1E8
Mass 73: 73Se+73Br+73Kr 1E8
73Ga 2.7E7
73As >1E9? (to
be checked when short-lived activity gone)
Mass 77: 77Kr+77Rb 7E5
77Br 3E8
77Ge 7E7
77Se ca. 100 pA
(comes from mass marker)
* Conclusions:
1. The SeCO+/Se+ ratio (difficult to measure
on mass 70) looks OK on mass 73, i.e. there is enough CO2 coming to the ion
source to make an efficient SeCO+ sideband.
2. We did not observe 71Se which indicates a slow Se release. I guess
the 70Se yield could be enhanced by heating the target more. I propose to sit
on 70Se coming out of REX and monitoring the 70Se current in MINIBALL while
slowly heating the target to 600 A if needed.
The yield
dropped slowly during the run, with a factor ~
isotope run: 70Se19+
breeding time: 58 ms (limitation in Linac freq), peak
charge at 19+ and 20+
currents:
* at
* 1-2 pA on the trap
injection plate for A=98
* 0.7-1 pA
after the trap, mainly Mo
* no
current seen after the EBIS on Se A/q, but ~1 pA on
the Mo peaks
* in the beginning of the run
around 7000 Se/s were expected at Miniball
efficiency (measured with 82Se12C16O):
*
* Trap 85% for an extracted mixture of CO, CO2 and SeCO. Around 50% for SeCO
alone.
* EBIS >5% (checked with 82SeCo, maybe even 6.5% if
ZrO+ and O+ out of the trap is discounted for)
* Linac
>80%
comments:
* breakup
of molecule in EBIS and not in trap
* no 66Ge16+ seen after the
EBIS (because of the charge state choosen 3.684)
* scaling of the linac from
A/q4 and test with 22Ne6+ as pilot beam worked very well
technical problems:
* Difficult to have a high transmission from
* Console computers and FECs
stopped, partly due to general network intervention.
* 2 Danfysik power supplies
broken (IH inner tank triplet, 7-Gap doublet).
* 200 MHz system still unstable (Prefl>).
lessons
learned:
* Have to readjust beam transport and ion injection
into the trap in case the ISOLDE ion source is retuned. Anode voltage to retune
the energy
* EBIS efficiency very dependent on Ugun and Uanode.
* The dipole excitation voltage in the trap should be maximum also for a flat molecule adjusted trap.
* 200 MHz amplifier has to be less sensitive to
reflected power