11Be run
September 2010
Target issues
* Target number #436 surface ionizer Ta W
* Beam on target (no converter). RILIS used.
* Mass markers: Li, Be and K
* GPS separator
* Extraction electrode 55 mm (real distance)
* Uht(GPS,CCV)=30.20
kV, Uht(GPS, HT_target)=30.2008
kV, Uht(trap)=30.00kV, Elec05=140 V,
Yield measurements (from Logbook 17/9)
11Be measured. No time structure observed over less than 10s (FW comment: REX sees a time structure). About 6e6 11Be per uC protons in the focal plane of the separator. (FW comment: Most likely 70% separator/CA0 transmission.)
11Be yield reported from Miniball for 1.9 uA proton:
no Linac collimators => 1E6 pps
5
mm diameter collimator in XL65.FC50 => close to 3-5E5 pps
We believe the ISOLDE measurements underestimated
the yield. See also last entries 23/9 in GPS elogbook.
Experimental
issues
* Beam to Miniball
* IS430
Tuning
* Slow extraction from EBIS
* REXTRAP timing free-running relative to protons pulses
ISOLDE
For 7Li, 70-80% transmission from GPS.FC490 to the trap inj
plate
GPS.WG475 slit out
Low
energy
Operated with 20Ne from R. Scrivens at 7.6 V buffer gas pressure.
Stable beam 7Li
Tperiod=25.5 ms, beam gate open, Tbreeding=23.3
ms, Icoll=175 mA
Trap inj. plate=127 pA, RFQ.FC20(3+)=34.2
pA (background removed)
Trap efficiency=24%, EBIS efficiency=37%, Trap+EBIS
efficiency=8.9%
Stable beam 9Be
Tperiod=20 ms, Tbreed=17.3
ms (believe optimised for 9Be3+)
Trap inj plate 150 pA (+-20
pA, RFQ.FC20=30 pA
(background removed) => around 6.7% low energy efficiency
For 11Be3+ 7% low energy transmission (see below)
Linac transmission
and energy:
No stripper foils
At least 80%
for 40Ar11+ (A/q=3.636) RFQ.FC20 to XL65.FC50, 2.83 MeV/u
Total
transmission (radioactive beam)
GPS.FC490_to_trap x Trap_EBIS x Linac
0.70*0.07*0.8=4%
Delivered beams
11Be3+
* Running with 16 pulses out of 39 pulses, 1.95 uA
* At the REXTRAP injection 8.5 pA on average (12 pA in the peak); at BTS.FC20
on average 4.5 pA (main part in TOF Be)
* RFQ.FC20=1.8 epA for 11Be3+ on average, XL65.FC50=1.7 epA, Miniball FC 1.7 epA
With lasers off no beam measured
Setting
summary
For GPS we used:
* GPS_SEP_10-09-15_30200V_7Li.csv
* REX_GPS_2010-09-15_7Li_30200V.csv
REX low energy settings saved as:
* REX-30kV-2010-09-20_GPS_11Be3_7%.xml
* BTS-30kV-2010-09-15_GPS_7Li3+_8.5%.xml
* EBIS_100915_1751_GPS_11Be3_slowextr_7%.csv
REX separator and linac settings saved as:
100920_1919_SEP_11Be3+_2.83MeVu_mb.csv
100920_1919_11Be3+_2.83MeVu_mb.csv
Technical problems
* No reproducible Linac scalability in the A/q=2.75 region (11Be4+) for a beam energy of 3.07 MeV/u. Thus 11Be3+ was used with a lower beam energy of 2.83 MeV/u.
* The tube for 7-gap3 stopped working; was exchanged for a new; about 90 min stop.
* The controller for the GPS magnet (BH15) was exchanged during the setup due to malfunctioning.
Comments / Lessons learned
* Stripper foils weren’t used to separate 22Ne6+ from 11Be3+ as only 2000 pps of 22Ne was detected at Miniball.
* Noticed that a nominal efficiency of the low energy REX was attained with Trap delay=960 us and Injection time 20 us. That means the EBIS trap is closed before the ions are extracted from the trap?
* The efficiency was strongly dependent on the cyclotron frequency for the trap cooling.
* Miniball inserted collimators, mainly XL65.FC50, to improve the beam spot. With a 5 mm diameter collimator more than 50% of the beam was cut, meaning that the beam was very broad.