192Pb run 16-18 August 2010

Target issues
* Target number #433 UC2C surface W
* Beam on target (no converter). RILIS used.
* 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,

Yield measurements (from Logbook 13/8)
190Pb: 4.0e6 at/uC from ISOLDE target
192Pb: 1.0e7 at/uC from ISOLDE target

Experimental issues
* Beam to Miniball
* IS494

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

ISOLDE
For 87Rb, 78% transmission from HRS.FC490 to the trap inj. plate for ~12 nA

Low energy
Stable beam 208Pb
Tperiod=255 ms, beam gate 10 ms, Tbreeding=230 ms (optimized 45+), Icoll=230 mA
Trap inj. plate=9.2 pA, RFQ.FC20(45+)=22 pA
Trap efficiency=43.5%, Trap+EBIS efficiency=5.3%

Tbreeding to 200 ms and rep rate to 5 Hz for radioactive beam

Linac transmission and energy: 
No stripper foils

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

- 87% for A/q 4+

- 62.5% for 238U55+ (large error bars)

- 67% for 192Pb45+

Total transmission (radioactive beam)
HRS.FC490_to_trap x Trap_EBIS x Linac
0.78*0.053*0.67=2.7%

Delivered beams

192Pb45+
* Running with 14 pulses out of 39 pulses with 3E13 ppp, 1.41 uA

At the REXTRAP injection 18 pA on average (uncertain, slowly decaying with inj. plate out)

RFQ.FC20 = 25 pA for 192Pb45+ on average, XL65.FC50 = 17.5 pA

* Running with 14 pulses out of 39 pulses with 1E13 ppp, 0.49 uA

XL65.FC50 = 4.5 pA, Miniball FC = 4.2 pA

Setting summary
For HRS we used:
* HRS_SEP_2010-08-09_30310V.csv
* RFQ-2010-08-12_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_3.8%.xml

TRAP and BTS settings same as for 238U, but with cyclotron frequency at 238000 Hz.

* EBIS_100816_1841_HRS_192Pb45+.csv

REX separator and linac settings saved as:
100816_1838_192Pb45+_2.84MeVu_60%_mb.csv
100816_1838_SEP_192Pb45+_2.84MeVu_60%_mb.csv    

Technical problems

* Had to reduce proton beam intensity due to RP alarms:

16/08/10, A. Dorsival

Alarme PAXY08 niveau B (> 6 µSv/h) dûe à l’accumulation d’ions Pb-192 en sortie de l’aimant séparateur de REX. Les ions destinés à l’expérience MINIBALL ont une charge 45+, les autres ions n’ayant pas cette charge s’implantent dans la chambre à vide en sortie d’aimant. Environ 50% des ions sont perdus dans le TRAP et 45% dans l’aimant séparateur de REX. H*(10) = 300 µSv/h au contact et 15 µSv/h à 40 cm de la chambre entre l’aimant et DB2 (slits) pour une intensité de protons de 1.5 µA.

Tension d’accélération des ions 21 kV, soit une énergie de 21*45/192=5 keV /u.

Balisage du risque d’exposition de part et d’autre de l’aimant séparateur de REX et intensité réduite à 0.5 µA. Le run Pb durera environ 3 jours.

* Unstable e-beam current, had to adjust O2 gas

* Half of the night 17-18/8 was unintentionally run with laser-off/out-of-tune due to communication problems with laser staff.

Comments / Lessons learned

* The monitor PAXY08 next to REX separator has a first alarm threshold at 3 uSv/h (EBIS platform considered as a working place). This triggers the flashing sign in the control room, the second alarm threshold (6 uSv/h) triggers an alarm in the CCC.

* Could reach nearly 100% transmission through Miniball with no scattering on CD. Although a large horizontal steering was required, +2.2 A. REX collimators fully open, Miniball collimator 9.8 mm diameter.

* The beam was pure of contaminants and more intense than proposed. The yield (~5e6Hz) is at the limit that can be taken at MiNIBALL (when bombarding 2mg/cm2 target) without slow extraction from EBIS.