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 GLM.

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 ~10 after 5 days with protons on target.

REX issues

isotope run: 70Se19+

breeding time: 58 ms (limitation in Linac freq), peak charge at 19+ and 20+

currents:

* at GPS.FC490 between 6-10 pA (not reliable) at A=98 (>90% was stable 98Mo)

* 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):

* GPS.FC490 to REXTRAP injection plate 60-75%. After target-ion source adjustment it might have been below 50%.

* 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 GPS to REXTRAP right!!

* 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