138Kr run Aug 2009

Target issues
* Target number #405 UC2C, Ta VD5+Cu, cold line
* Beam on target (no converter)
* Mass markers: 95% Ar + 5% Xe
* HRS separator
* Extraction electrode 50 mm
* Uht(HRS,CCV)=30.20 kV, Uht(HRS, source)=30.20 kV, Uht(HRS, HT_target)=30.1997 kV, Uht(trap)=30.00kV, Elec05=170 V

* Ion source efficiency around 15%

* Yield measurements performed on 138Xe: awaiting input from Giles/Stora

* Count rate at Miniball: awaiting input from the users

Experimental issues
* Beam to Miniball
* IS415

Tuning
* Slow extraction from EBIS, optimized on 126Xe
* REXTRAP free-running relative to proton impact

ISOLDE
136Xe: HRS.FC490=6.1nA, HRS.FC748=4.7nA, trap inj plate=4.37nA

RFQ eff=77%, HRS-to-REX eff=72%, no slits inserted

Low energy
* Stable beam 138Xe (normal extraction)

Icoll=190 mA, Tperiod=183 ms, Tbreed=180 ms (almost optimised for 33+), Tbeamgate=18 ms

Trap inj plate 3.1 pA, RFQ.FC20(33+)=7.5 epA => total efficiency=7% 

(very difficult to read as the Keithley is jumping)

* Radioactive beam 138Xe (slow extraction)
Icoll=185 mA, Tperiod=163 ms, Tbreed=160 ms (too low, high rep rate)

Trap inj plate average 42 pA, RFQ.FC20(33+)=58 epA => 4.2%

Linac transmission and energy:
Accelerated radioactive beams: 138Xe33+(4.1818)

Energy: 2.865MeV/u +/-0.3% FWHM

RF pulse length 700 us

Transmission: A/q=4 RFQ.FC20 to XL65.FC50 85%

126Xe30+ A/q=4.2 RFQ.FC20 to XL65.FC50: 73%

Total transmission
HRS.FC490_to_trap x Trap_EBIS x slow_extraction * Linac x experiment collimator
0.72*0.06*0.95*0.73*0.75=2.5%

Delivered beams
138Xe33+
15 out of 34 pulses, 8E12 ppp, 0.5 uA
Current varying significantly
Trap inj plate 42 pA
RFQ.FC20 average 58 epA
XL65.FC50 average 35 epA (NB. Beam defocused -> not all recorded)

Setting summary
For HRS we used:
* HRS-SEP-9-08-18-30340.csv
* RFQ-9-08-18-30200.csv
* RFQ-REX-9-08-18-30340.csv

REX low energy settings saved as:
* REX-30kV-2009-08-21_HRS_138Xe.csv

* BTS-30kV-2009-08-21_HRS_138Xe.csv

* EBIS_2009-08-21_Aq41818_slowextraction.csv

REX separator and linac base settings saved as:
* 090820_1730_SEP_Aq4.1818_2.85MeVu_70%_MB.csv

* 090821_1630_Aq4.1818_2.85MeVu_tunedMB.csv

Technical problems
* IHS switched off due to a fuse for the water cooling tripped. Down time 1 h

* 7gap amplifier stopped. Down time 15 min

* HRS MAG90 lost its communication. All units had TGM timeout. Reboot of dsc Disopow sorted out the situation. Down time 2 h.

* 9GP.MQ30 stopped due to overheating. Cooling circuit flushed, worked thereafter. Problem occurred before the actual beam time.

Comments / Lessons learned
* The linac transmission for heavy and highly charged 126Xe30+,31+,32+ was around 70-75% while the transmission for light A/q=4 (20Ne5+ and He+) and A/q3.666 (20Ne6+) was 85-86%. Linac scaling working so not the reason. We suspect that a poor vacuum, around 1E-6 mbar, in the DB3 / buncher section causes beam scattering and/or charge exchange. To be verified.

* The users were limited in the amount of beam they could handle. Thus, a very low proton current on the target of ~0.1 uA was taken. Apparently the users inserted a slit in the linac to reduce the intensity even further.