61,62Mn and 61,62Fe run
2008
Target
issues
* Target number #375 UCx, surface ioniser
* Mass markers: Rb and Mn+Ga
* Mn laser ionised
* HRS separator
* RFQ cooler operated in cw
mode
* Uht(HRS,CCV)=30.26 kV, Uht(HRS, HT_target)=30.2607 kV, Uht(RFQ cooler)=30.20 kV, RFQ extraction=0 V, Uht(trap)=30 kV
Measured 61Mn yield: 3.5e6 at/uC
Measured yield for 62Mn: 6.7e5 at/uC
Only Mn and Fe present in the delivered
beam. The surface ionized species would be 61Ga and 61Zn. 61Ga would be
post-accelerated but no gamma rays are known for 61Ga. Though, it decays to
61Zn and 61Zn decays with a 475 keV gamma ray. There
is no trace of this one in the miniball gamma ray
spectrum. (HRS comment JVdW)
During the run ~2.0E13 p/p were taken on the target. In
most cases 10/21 pulses.
Experimental issues
* Beam
to Miniball and to ionisation
chamber in 2nd beam line
* IS468
* In addition REX machine development to
investigate in-trap decay for acceleration of daughter nuclei
REX Tuning
* Normal extraction from EBIS
* In most radioactive beam cases the REXTRAP was triggered on the
PS booster and only 1 collection cycle per proton trigger
Low energy
Stable
beam 85Rb
ISOLDE : HRS.FC490=3.75
nA, HRS.FC746=2.78 nA, 74%
RFQ to
trap inj plate >95%
Trap:
Tperiod=30 ms, beam gate open
Trap inj plate=15 pA,
BTS.FC20=9.5 pA, 63%
EBIS: Tbreed=29 ms (optimised for 18+), Icoll~200 mA
RFQ.FC20(18+)=25.5 pA, trap+EBIS eff 9.4%
Stable beam 55Mn
Tperiod=30 ms, Tbreed=28 ms, no
beam gate
Trap
inj plate=42 pA, BTS.FC20=23 pA,
RFQ.FC20(15+)=100 pA (10 pA background of 22Ne6+)
Trap
efficiency=55%, Trap+EBIS efficiency=14.3%
(possibly
higher with correct Einzel lens setting)
Tperiod=300 ms, Tbreed=298
ms, breeding almost optimised
for q=21+
40 pA on
trap inj plate (no beam gate)
with 50 ms
beam gate => 11% trap+EBIS efficiency for
55Mn21+
Linac
Linac
transmission: 80% for A/q=4, from RFQ.FC20 to XL65.FC50
Transmission XL65.FC50 to
experiment ~33% with a 3mm collimator
Linac
energy: 2.90 MeV/u, energy spread +-0.7%
Total transmission
RFQ_cooler x HRS_to_trap x Trap x EBIS x Linac
x MB collimators
0.74 x 0.95 x 0.6 x 0.15 x 0.80 x 0.33 =
1.7%
Setting summary
For HRS we used:
RFQ_8-06-11_30200V_surface_85Rb.csv
HRS2REX_08-06-19.csv
REX low energy settings saved as:
REX-30kV-2008-06-19-HRS_85Rb.xml
BTS-30kV-2008-06-19-HRS_85Rb.xml
EBIS settings
attached
REX linac settings saved as:
080621_1040_Aq4_2.9MeVu_MB.csv
Beams
to users
61Mn and 62Mn
61Fe and 62Fe after decay in trap and EBIS
Ttrap scanned from 200 ms to 1100 ms
Tbreed=28 ms for 15+, Tbreed=203,
253, 293 ms for 21+
For 61Mn (3E13 ppp, 10 out of 21
pulses/sc):
1.2 pA
(average, 3 pA in peak) of beam was seen on the trap injection plate
1.5 pA (average, 3 pA in peak) of beam was seen on
RFQ.FC20
BEN.FC100 1 pA (average)
XL20.FC50 0.9 pA (average)
For 62Mn (2E13 ppp, 10 out of 21
pulses/sc):
~1 pA (average) of beam was seen on the trap
injection plate
~0.5 pA peaks seen on RFQ.FC20
Technical
problems
* Beam position on the HRS.MAG60 not fully reproducible (even
though HT_target, QP-array and magnet calibrations
non-changed).
* Erratic current measured at the trap injection plate when the beam gate was
active. Charging up effects also noticed. Suspect element at the injection side
of the trap.
* The database for REXTRAP cyclotron frequencies is missing.
* A coil in a power supply for the Cu-vapour
lasers burned
* Vacuum interlock fault switched occasionally off the electrostatic
elements in the REX mass separator and RFQ sections
* TRAP HT discharge, up to 0.04 mA. Coming from the local ion source.
* Oil pump to the lasers broken.
* REXTRAP TOF missed scans for very long trapping times (>500 ms).
* Setting low voltages (<1 V) for the cyclotron RF amplitude inside the
trap are not working correctly.
* Turbopump TP71 in the Miniball
beam line failed. The pump was isolated and the section pumped via neighbouring sections.
* 2nd cooling frequency was distorted after passing the 180
deg phase splitter.
Comments
* Linac RF stable, only a couple of IHS
restarts (the IHS instability seems to be going away with
time).
* Less Fe (daugther of Mn) seen at Miniball than hoped
for.
a.
In-trap decay not fully understood yet; could not yet establish where the
daughter ions are
lost.
b. Tried different trapping times; different breeding
times; higher REXTRAP trap potential (see
below).
c. Possibly needs to be followed up with another beam
time (e.g. with an easier K-Ca beam).
d. More extensive report will follow.
* Several positive result from the MD on in-trap/EBIS decay
experiment (see below).
1. Possible to apply two cooling frequencies simultaneously in the
trap. One freq for each 4 electrodes. Cooling applied
at both frequencies during the whole cycle. A clear enhancement of the
61Fe2+ trap TOF peak if cooling A/q=30.5 was applied.
2. Possible to pulse the injection barrier of the REXTRAP
(good for bunched RFQ injection). However, with the present power supply the
full rise time is long, some 100 us. Rising flank divided in steps.
3. A trap mass resolution of 200 Hz can fairly easily be
attained for long cooling times (few 100 ms) just by lowering the excitation
voltage to <1 V. Efficiency unknown. In this case no
active suppression of the contaminating ion species (i.e. no magnetron
excitation).
4. Possible to see 2+ ions in the TOF out of the
trap. Possible to gate out 1+ ions in the TOF between
the trap and the EBIS (can also be done by switching BTS.KI10).
5. Ions can be kept in the trap up to 1 s without major
losses (<20% loss for 55Mn).
6. Very good efficiency achieved for stable 55Mn15+ (neon-like
electron configuration); trap+EBIS efficiency
>15%. Achieved a reasonably good (~10%) trap+breeding efficiency for 55Mn21+ (high charge state,
only 4 atomic electrons left).
7. The trap barriers of the the REXTRAP
can be increased up to 240 V. Tendency to spark if injection barrier above 210
V. Could also increase Elec16 (inner gas diaphragm)
from 75 to 135 V without loosing trapping efficiency.