186,188,190,194,196,198Pb run 1-7 June 2011

 

Target issues
* Target number #447 UC2C surface Ta
* Beam on target (no converter). RILIS used.
* Mass markers: Tl, Pb (U and Ba as impurities)
* HRS separator
* Extraction electrode 60mm (real distance)
* Uht(HRS, HT_target)=30.30 kV, Uht(RFQ,CCV)=30.235 kV, Uht(trap, CCV)=30030 V, Uht(trap, AQN)=30088 V,Elec05=185 V

 

Yield measurements (from Logbook 1/6)
The preliminary estimate of the Pb188 yield is 2e6/muC and for Tl188 4e6/muC. But is to be checked for branching. No Pb188 with laser OFF, we just see Tl188.

 

Experimental issues
*
Beam to Miniball
* IS494


Tuning
* Slow extraction from EBIS 
* REXTRAP timing free-running relative to protons pulses

 

ISOLDE
   For 206Pb, 65-70% cw transmission from HRS.FC490 to the trap inj. plate.

 

Low energy
   Stable beam 206Pb
   Tperiod=250 ms, no beam gate, Tbreeding=248 ms (optimized 44+), Icoll=168 mA 
   Trap inj. plate=8 pA, RFQ.FC20(44+)=23 pA
   Trap efficiency=50-55%, Trap+EBIS efficiency=6.5%

 

Linac transmission and energy: 
   No stripper foils

   Transmission from RFQ.FC20 to XL65.FC50 at 2.84 MeV/u

   - 86.7% for A/q=4.333, 39K9+

   - 60.9% for A/q=4.3125, 138Ba32+

   - 40-50% for A/q=4.318, 190Pb44+
 

Total transmission (radioactive beam)
HRS.FC490_to_Trap x Trap_EBIS x Linac 
0.70*0.06*0.45=1.9%


Delivered beams

190Pb44+

With 2.8E13 ppp on the target we see 10 pA in the peaks on trap inj plate. Beam on BTS.FC20. 5.5 pA in the pulses. On RFQ.FC20 we had 20 pA in the peaks for the 0.4 uA proton beam. Tl contamination less than 10%.

 

188Pb44+

With 1.4 uA on the target, 3.0E13 ppp we have around 2 pA on trap inj plate. On RFQ.FC20(44+) 1.2 epA with the lasers blocked, 4 epA average with lasers on, 6 epA in the peaks. With beam blocked into trap we have no measureable current. XL65.FC50 2 epA on average, 3 epA in the peaks.

 

186Pb44+

0.1 pA on XL65.FC50 for 1.62 uA proton beam. No difference seen when the lasers are on or off. Thallium contamination >99%. No lead peaks in the prompt gamma spectrum at Miniball.

 

194Pb45+

With 1.5 uA proton beam, 3.1E13 ppp, we had 13 pA average current on the trap inj. plate, >25 pA in the peaks. On BTS.FC20 around 10 pA. On RFQ.FC20(45+) around 22 pA average current. On XL65.FC50=9.5 epA average current. Approximately 5-10% Tl in the beam.

 

196Pb46+

XL65.FC50 ~5epA, proton current 0.66 uA? Pb purity around 100%.

 

198Pb46+

No values


Setting summary
For HRS we used:
* HRS_SEP_203Tl_30300V_65%trans.csv
* RFQ_203Tl_30235V_65%trans.csv
* REX_RFQ_203Tl_30235V_65%trans.csv


REX low energy settings saved as:

* 110531_1208_TRAP_138Ba_HRS.csv

* 110530_1150_BTS_HRS_238U.csv

* EBIS_110601_1859_HRS_190Pb44+_5.5%_slow_extraction.csv


REX separator and linac settings saved as:
* 110602_1653_SEP_Aq4.273_188Pb44_L65_2.82MeVu.csv

* 110602_1654__Aq4.273_188Pb44_L65_2.82MeVu.csv

 

Technical problems

* Beam setup from ISOLDE delayed one day due to numerous technical problems (see below).

*Hardly any Thallium left as mass marker when we started. Did it evaporate away solely by the line heating?

* The target and line heating stopped several times (PLC problems) previous to and during the beam setting up.

* HRS.MAG90 had frequent communication problems / probe errors. Caused at least two ~ 1h stops for the users.

* During the setup period the REXTRAP vacuum system switched off every two 2 h. Due to an interlock limit being set too low.

* The controls for the XSEP.MD100 and XBEN.MD120 stopped working during the setup. Needed a reboot of cfv-170-rxpow1.

* The HRS.RFQINJ1 power supply stopped working. Beam to the users stopped for 2 hours.

* The transmission through the REX linac was only 40-50% for lead ions with q=44+ and 45+. For similar A/q~4.3 the transmission for 39K9+ was above 85%. Thus, it was shown that the poor transmission is due to charge exchange losses in the linac, mainly the RFQ section with a vacuum around 1E-6 mbar.

 

Comments / Lessons learned

* We had a 6 uSv/h alarm from monitor PAXY08 (next to REX separator) just after taking the 190Pb beam. The proton beam was thereafter limited to 0.5 uA during the 190Pb beam. Similar problem with 194Pb; had to reduce the proton intensity to 0.3 uA.

* The users did some of the beam changes themselves.