30Mg run 2008

Target issues

* Target number #391 (UC2-C W)

* Beam on target (no converter)

* Mass markers: Mg, K

* GPS separator

* Laser ionisation

* Uht(GPS,CCV)=30.2 kV, Uht(GPS,HT_source)=NaN, Uht(GPS,HT_target)=NaN, Uht(trap)=30.00kV, Elec05=160 V

Yield measurements

- 29Mg ~5e6/uC

- 30Mg 2.3e6/uC

- 31Mg 9.4e5/uC

- 32Mg 1.8e5/uC

Yields of 23Mg and 27Mg were also found to be good. Mg is released fast, with difficulty measuring a rising time constant which is under 10ms.

Experimental issues

* Beam to Miniball

* IS470

* Delivered beams: 30Mg7+

REX Tuning

* Normal extraction

* REXTRAP timing free-running relative to protons pulses

Low energy

Stable 39K from ISOLDE

Tperiod=20 ms, Tbreed=9 ms (optimized for 9+), Tbeamgate=2 ms

Trap inj plate 23 pA

Trap+EBIS eff=19.8% (9+, closed shell)

Stable 26Mg from ISOLDE

Tperiod=20 ms, Tbreed=8 ms (optimised for 7+)

Trap inj plate 16.6 pA

Trap+EBIS eff = 14% (7+)

Radioactive 30Mg7+ (18 of 42 proton pulses, 3E13 ppp)

Tperiod=20 ms, Tbreed=8 ms

Trap cyclotron freq optimised 1524823 Hz

0.5 pA on trap inj plate, 0.5 pA on RFQ.FC20, 0.3 pA on XL65.FC50

4E4 part/s at Miniball

Linac transmission (RFQ.FC20 to XL65.FC50) and energy:

80% for A/q 4 at 1.83MeV/u, ~70% for A/q 4.2857

70% for 133Cs31+ (A/q 4.2903) at 2.845MeV/u (+/-0.4% FWHM)

Total transmission (radioactive beam)

GPS.FC490_to_trap x Trap_EBIS x Linac 95%*14%*70%=9.3%

Setting summary

For GPS we used:

* GPS_SEP_30200V_8-10-14.csv

* GPS_CAO_REXstandard.csv

REX low energy settings saved as:

* REX-30kV-2008-10-31_GPS_Mg30.xml

* BTS-30kV-2008-10-31_GPS_Mg30.xml

REX separator and linac settings saved as:

* 081031_0958_30Mg7+_Aq4.2272_1.8MeVu_MB.csv

* 081031_0958_SEP_30Mg7+_Aq4.2272_1.8MeVu_MB.csv

Technical problems

* The buncher was set to the debunching phase. The phase was shifted by 180 deg between 09/09, when we last had 84% transmission for A/q 4 at 2.9MeV/u, and 20/10. The phase was probably already wrong during the Hg run where we had low transmission throughout the run. The cause for this sudden phase shift is not known.

20/10/2008 (now) 25/04/2008 (start-up this year)

The larger peak corresponds to the debunching phase (larger energy spread).

* The IHS is running with a “DIY” automatic restart system made by Lee. This prevented many interruptions but is problematic when the timing is changed (restart system is going into a loop as the tuner is not moving fast enough). It would be very useful to have an improved version of this system (with tuner reset) implemented in the PLC.

* Some capacitors in the BEN.MD120 power supply exploded during the stable Kr run (Miniball calibration) on Sat night 3/11. The run had to stop. The power supply could be repaired Mon 3/11.

Comments / Lessons learned

* The beam is very unstable after the 9GP when the 9GP is running. This is possibly caused by charging-up on the collimator wheel in DB4 which is directly exposed to the electron beam from the 9GP. This should be improved when the quadrupole and DB are swapped (this shutdown).

* The transmission of the linac is decreasing with larger A/q, we can get >80% at A/q 4 but only 70% for A/q 4.3.

* The count rate at Miniball is not consistent with a total REX transmission of 9.3%. We expect 2.7E5pps on the target instead of 4E4pps. Reason unknown.