224Ra run
30-31 August 2010
Target
issues
* Target number #433 UC2C surface W
* Beam on target (no converter).
* Mass markers: Na, Rb and Pb
* HRS separator
* Extraction electrode N/A mm (real distance)
* Uht(HRS,
HT_target)=30.310 kV, Uht(RFQ,CCV)=30.210
kV, Uht(trap)=30.00kV, Elec05=180 V?
· No yield measurements
· Part of the time 224Ra was delivered without protons on target; then came from 224Ac and/or 228Th.
·
0.07 uA of proton beam
was parasitically taken on the target between 09:00 Sun 29/8 and 05:00 Mon 30/8
to induce 224Ra activity in the target. At
a target temperature of 565A 1.2pA of 224Ra was seen on the trap injection
plate at 16:00 Mon 30/8. Target heating increased from 560 A to 585 A during
time without protons. See how the rate developed at
http://www.miniball.york.ac.uk/mblog/mb/9311.
·
From
20:00 on Tue 31/8 1.9 uA of protons were taken on the
target. The Ra current, measured at Miniball,
increased with a factor 10 compared with no protons on target.
·
From L.
Gaffney: The
average MB intensity without protons was 4.5E+04 pps
over a period of ~23 hours and with protons it was 4.2E+05 over
a period of ~11 hours. The integrated beam over the whole run is
2.0E+10 particles with an average of 1.4epA at MINIBALL. The francium
contamination was estimated to be 1 part in 10E+04. The beam was 99.99%
pure.
Experimental
issues
* Beam to Miniball
* IS475
Tuning
* REXTRAP timing free-running relative to protons pulses.
* Used EBIS slow extraction for part of the beam. RF pulse 700 us.
ISOLDE
For 87Rb, 78% transmission from HRS.FC490 to the trap inj. plate for 450 pA
Low
energy
Setup beam beam 223Ra
Tbreed=150 ms, Tperiod=200
ms, no beam gate, Icoll=167 mA
Trap inj plate 1pA
RFQ.FC20(41+)=1.8 epA =>4.4%
efficiency
Tperiod=357 ms, Tbreed=355
ms (not fully optimised), no beam gate
Icoll=higher than before
Trap inj plate=3.5 pA, RFQ.FC20(52+)=4.5
epA => 2.5%
Radioactive 224Ra beam
Tperiod=357 ms, Tbreed=355 ms, no beam gate.
Trap inj plate=0.4 pA (underestimated?)
RFQ.FC20=1.2 epA for 52+ =>5.8%
(probably overestimated)
Linac
transmission and energy:
Transmission from RFQ.FC20 to XL65.FC50 at 2.83 MeV/u
- 86% for A/q=4
- 60-65% for 224Ra52+
Total
transmission (radioactive beam)
HRS.FC490_to_trap x Trap_EBIS x Linac
0.78*(0.025~0.058)*(0.6~0.65)=1.2 to 2.9%
Delivered beams
224Ra52+
No protons on target; 12 h since 0.07 uA proton beam stopped.
RFQ.FC20=1.2 epA, XL65.FC50=0.75 epA, MB FC has 0.7+-0.1 epA
=>8.4E4
part/s at MB
Setting
summary
For HRS we used:
HRS_SEP_2010-08-09-30310V.csv HRS.WG470 slits
inserted
RFQ-2010-08-09_30310V_238U.csv
REX_RFQ_2010-08-12.csv
REX low energy settings saved as:
REX-30kV-2010-08-12_HRS_238U_3.8%.xml
BTS-30kV-2010-08-12_HRS_238U_2.7%.xml (cyclotron frequency to 204000 Hz for
224Ra)
EBIS_100830_1655_HRS_224Ra52_normalextr.csv
EBIS_100831_2011_HRS_224Ra52_slowextr.csv
REX separator and linac settings saved as:
100830_1651_SEP_224Ra52+-2.83MeVu_mb.csv
100830_1654_224Ra52+_2.83MeVu_mb.csv
Technical problems
* The ISOLDE target and the REX low energy part (incl RFQ cavity) was vented due to a faulty operation during the leak detection of the N2 venting line. Beam down for 2 ˝ h.
* Extractor 1 and 2 in the EBIS tripped (vacuum interlock?). Beam down for <1/2 h.
* The EBIS collector current varied between 180 and 225 mA.
Comments / Lessons learned
* No
dedicated heavy mass marker made the setup difficult. Not enough 238U was
present and the target couldn’t be heated as the 224Ra might leave it as well.
Thus, the more abundant 223Ra was used for the tuning.
* A long breeding time was
needed. By increasing the period time, without changing the breeding time, the
current on RFQ.FC20 goes down => part of the beam is lost in the trap.
* It was concluded that the 224Fr contamination was small, even with protons on target.
* During this running period (Pb,Rb,Na,Ra) the machine was scaled more than 10 times between different isotopes, stable and radioactive, light and heavy, without any problems.