10,11Be run Nov 2006
Target
issues:
* Ta #340, MK8, laser ionisation
* Li and Be mass markers
*
* Yield values:
The
experiment estimated ~5E4 11Be/s at their setup
Into
the trap we measured ~1 pA (large error bars) ->
6E6 11Be/s
=>
total efficiency ~1%, a factor 3 lower than REX
estimates with stable beam
Experimental issues:
* Second beam line
* IS438 and
IS444
isotopes
run: 10Be3+ stripped to 4+ after 9-gap
(C 25ug/cm^2) to suppress remaining 20Ne and 40Ar
11Be4+
also stripped after 9-gap (C 25ug/cm^2) to suppress 22Ne, 11B?
breeding
time and extraction: 15 ms for Be3+
and 25 ms for Be4+
slow extraction, ramping time 550 us
RF
on for 800 us
Only
20 Hz repetition rate due to conservative operation
efficiency
and currents:
39K10+
With Tperiod=20 ms, Tgate=10
ms, Tbreed=12 ms and ~10 pA
on trap injection plate, the total efficiency ~15%
7Li3+ With Tperiod=20
ms, Tgate=10 ms, trap inj
plate 61 pA
BTS.FC20=15 pA => trap eff =25%
with Tbreed=18
ms, RFQ.FC20=11 pA => EBIS eff=24.4%
Total efficiency >6%
7Li2+ optimal Tbreed for 7Li2+ was 7 ms, total efficiency 3.4%
9Be3+ with Tperiod=50 ms, Tgate=5ms,
Tbreed=15 ms, trap inj plate
56 pA => 5% total efficiency
Radioactive 10Be3+ with 22Ne buffer gas
Injection plate = 50pA
BTS.FC20 = 12pA
RFQ.FC20 = 10pA (2.5pA
background)
Trap+EBIS
eff = 5%
BL2.FC10 = 6.0pA (0.4pA
background)
Users FC = 2.6pA
Linac
eff (6-0.4)/4+ / 7.5/3+ = 56%
Radioactive 10Be3+ with 4He buffer gas
Injection plate ~60 pA
The trap efficiency is
around 10% (down a factor ~2)
RFQ.FC20 ~4 pA 3+ (background of 1 pA substracted).
Trap+EBIS
eff = 2.2%
Total efficiency down
about a factor 2 compared with Ne gas
At BL2.FC10 ~2 pA (10Be4+)
11Be currents
Trap injection plate
1-2 pA
No current seen at least after the
low energy part.
Count rate: 5-10/s on
experiment target
linac transmission and energy:
10Be3+ 2.93MeV/u 82%
11Be4+ 2.92MeV/u 80%
11Be4+ 2.71MeV/u 77%
Technical
problems:
* RILIS unstable
* Ran out of 22Ne gas (part of it inexplicably wasted when remounting
gas system?)
* Contamination in trap
* Difficult to steer the beam on to the experimental target
* Could not run the linac and separator at at A/q=2.5 due to scaling limitations
* Updates of the CS for the beam optics and RF (unstable java
applications)
Comments
and Lessons learned
* Isotopically purified 22Ne and 4He buffer
gas used for 10Be run
* Isotopically purified 20Ne buffer gas used
for 11Be run
* Newly installed buffer gas system suppressed the gas contamination
inside the trap
* Unfortunate with breaks during the run => loose time for restart of
the machine
* When using slow extraction it is a prerequisite to record a trigger
spectrum at the experimental setup to assure that no beam is lost outside the
RF window of the accelerator
* Difficult startup of both 10,11Be -> light beams need
extra startup time