Mg run June 2006

 

Target issues

 

* UC2-320, W surface, laser ionization

* mass markers Mg/Na and Mn/K

* separator setup at 30.2 kV

 

* Yield check

Measured two times. The integration by hand gives for 29Mg ca. 1.4E6/uC and for 31Mg ca. 1.2E5/uC. Both numbers might be off by +-30%.

 

REX issues

 

Isotopes accelerated:    radioactive 29Mg9+ and 31Mg9+

                                    breeding time 28 ms, peak charge close to 9+

 

Currents:                      ~0.5 pA seen on 29Mg on BTS.FC20

                                    ~0.5 pA seen on 29Mg9+ on RFQ.FC20

                                    No currents seen for 31Mg

                                    31Mg beam very clean at Miniball

           

Efficiencies:

GPS.FC490 to REXTRAP inj plate: 70% or up to 100%. The reading of GPS.FC490 was not reliable for currents <100 pA.

 

TRAP: with 27 pA of 23Na on the trap inj plate and 14 pA on BTS.FC20 (maybe 10% Ne) => 50% trap efficiency

 

The total trap + EBIS + separator efficiency is 10% for 23Na9+ for 28 ms breeding time

 

            LINAC:             Transmission for A/q=3.5 75%

                                   Energy for A/q=3.5 2.75 MeV/u

 

technical problems:

            7-gap 3 tripped from time to time           

            BD kept on stopping, now fixed

Protons going to the beam dump even with proton request on

            GPS.FC490 reads unreliable values below 100 pA (a factor 2 too small)

            Control unit for IH-structure failed twice

            Bugs in mass scanner

                        B-field read-out doesn’t work

                        Saving name of mass scan

            Scaling of the working sets fails sometime, particular problem with XSEP.QP10

            Line heating stopped one night

Difficult to setup the mass separator and Linac as the Witch magnet was switched on until the beginning of the run

BEN.FC40 not working; BEN.FC100 has to be operated manually

 

comments:      

* No presetting for Linac, started late.

* The low count rate stated by Miniball

1.       was in fact not a factor 1000 lower than expected. The value of 8E5 30Mg/s was not an exceptional yield at Miniball but from the target.

Oct 2004          8E5 30Mg/s from ISOLDE

       2003         2E4 30Mg/s from ISOLDE

       2004         4E4 32Mg/s from ISOLDE

2.       had not a discrepancy of 100 between 29Mg and 31Mg

* Why A=29 could be seen on the GPS.SC483 and not A=31 was because of the yield factor difference of 12 (not 2 as stated in the beginning).

* Summary: REX lost quite so time trying to track down none existing anomalies!

* The 29Mg beam could not be used be the experiment due to the beam contamination

At Miniball        55-60% of A=29 seen (ratio Al:Mg:Na = 27:6:1)

                        4-45% of lighter element (14N or 16O from EBIS)

The move of the REXTRAP roughing pumps have resulted in 4 times larger Ne peaks in the REXEBIS residual gas spectrum.

 

lesson:

            Once again: the complete machine must have been working before the first beam time!