94,96Kr run July 2010
Target issues
* Target number #431 UC2, VD
plasma, cold line
* Beam on target (no converter)
* Ion source gas: 20%-Ne + 20% Xe + 20% Kr + 40% He
* HRS separator
* 17% ion source efficiency reached for Kr with 1.0 bar buffer-gas pressure
* RFQ cooler operated in cw mode
* Extraction electrode 68 mm (real gap)
* Uht(HRS,CCV)=30.13 kV, Uht(HRS, HT_target)=30.1530 kV, Anode=130 V, Uht(RFQ
cooler)=30.20 kV, RFQ extraction=0 V, Uht(trap)=30.00kV, Elec05=177 V
E-logbook:
“From data collected at tape station, figures
given in the focal plane of the separator:
92Kr : 4.2e7/muC (this is coherent with 15pA
peaks seen on HRS.FC490 at proton impact, the average 5pA is likely 92Mo from
VADIS ion source).
94Kr : 2.5e6/muC
96Kr: ???/uC
On A=96, there is also 96Mo, estimated at ca
5pA.
When using beam gate for, say, 100ms, we should
have ca 3e6 96Mo, and 5e5 96Kr from ISOLDE (with 3e13ppp). So beam delivered to
Miniball likely to be Mo, Kr, and Rb (as decay product within REX). “
Experimental issues
* Beam to Miniball
* IS485
Tuning
* Normal extraction from EBIS
* REXTRAP timing free-running relative to protons pulses
ISOLDE
Transmission including RFQ-cooler: 64%
for 83Kr
HRS.WG470 used throughout the run
Low energy
Stable beam 83Kr
Tperiod=66 ms, Tbeamgate=10%, Tbreeding=63.8 ms, Icol=212 mA
Trap inj. plate=22 pA, RFQ.FC20(23+)=8 pA
Trap+EBIS efficiency=1.6%
Did not manage to reproduce last year’s
efficiency (3.3%). Overall efficiency was better with 66 ms period than with 50
ms period for stable Kr.
Would have been better to keep 50 ms for the
96Kr beam (80 ms half life).
Linac transmission and
energy:
88% RFQ.FC20 to XL65.FC50 for A/q 4, 2.84 MeV/u
82% RFQ.FC20 to XL65.FC50 for 82Kr19+,
2.84 MeV/u
73% RFQ.FC20 to Miniball FC for 82Kr19+,
2.84 MeV/u
Difficult to steer the beam through Miniball. Need a lot of steering, cannot
fully cancel the scattered beam on the CD.
Total transmission (radioactive beam)
HRS.FC490_to_trap x Trap_EBIS
x Linac
0.60*0.016*0.73=0.7%
Delivered beams
92Kr22+
* Running with 17 pulses out of 38 pulses, 3E13 ppp
* At the REXTRAP injection plate we saw 30 pA in the peak
* RFQ.FC20=12 pA peaks, XL65.FC50=10 pA
* Miniball FC=3-4pA after reducing proton beam
to 1e13 ppp
94Kr22+
(forgot to record currents and running
conditions for this beam)
96Kr23+
* 17/38 3e13 ppp
* 2 pA on A=96 on the trap injection plate
* on RFQ.FC20:
10fA is fast radioactive mass 96 (effect of
stopping protons) – coherent with the 3000pps of radioactive beam seen at
Miniball.
25fA is mass 96, stable and
radioactive from target. (effect of
closing HRS beam gate)
70fA is everything from the EBIS as
A/q=4.174 (96X23+ + similar A/q).
(Effect of stopping bender in SEP).
* Particles rate at Miniball ~3000 pps (radioactive beam with mass 96 i.e.
including 96Rb)
Setting summary
For HRS we used:
* HRS_SEP_2010-07-21_30280V.csv
* RFQ-2010-07-21_30200V_132Xe.csv
* REX_RFQ_2010-07-21.csv
REX low energy settings saved as:
* REX-30kV-2010-07-29_HRS_83Kr.xml
* BTS-30kV-2010-07-29_HRS_83Kr.xml
* EBIS_100727_1557_83Kr_HRS_1.6%_final.csv
REX separator and linac base settings (A/q=4) saved as:
100722_1839_SEP_Aq4_2.84MeVu_86%_L65.csv
100722_1839_Aq4_2.84MeVu_86%_L65.csv
REX separator and linac settings optimised for
MB:
100729_1115_SEP_83Kr20+_MB.csv
100729_1115_83Kr20+_MB.csv
Technical problems
* Apparent REXTRAP efficiency 40-50%. In
reality much worse as about half of the beam was Ne+.
* Poor efficiency for the low energy part, at least a factor two less
than last year (not clear why).
Comments / Lessons learned
* Ebis running with O2 gas injection to avoid cathode poisoning (since beginning of the
year). Typical pressures Pcol 1E-9 mb and Pgun 4e-10 mb (computer readings).
* We saw about 2 pA beam on trap inj. plate for
96Kr which could not be explained. This beam is not going through the low
energy part. Could be a molecular beam. TaC2+ (A/q 96.5) is a possible
candidate.
* Linac transmission lower for heavier beams.
* Beam steering to Miniball.
1.
The alignment was checked before the run with an optical telescope looking
through the bender. The different apertures are well aligned relative to each
other (apparent misalignment less than 1mm).
2.
A good transmission can be reach easily to the Miniball FC but almost
impossible to avoid scattered beam on the CD. Suspect that the beam is
scattered on the collimator. Would need a different geometry for the
collimator.
3.
The best steering always involve X-Y steering after the bender and often
detuning of the bender. This suggests that the beam coming out of the bender is
not on axis. Would need a second collimator directly after the bender to check
this.
* Despite new shielding Miniball still sees a
lot of bremsstrahlung from the 9-gap. This could be reduced to almost nothing by
adding lead plates inside the tunnel. Need to add a second layer of lead on the
9-gap side. A small screen directly behind the 9-gap is also very beneficial.
* RF amplifier working well (also with A/q
4.3).