P-Carbon CNI polarimeter upgrades. Vacuum system. Target drives. Targets. Polarimetry Workshop, July 31, 2009 A.Zelenski for polarimetry group

December 4, 2009

New target motion mechanism.

 Additional set of detector ports will facilitate new detectors development, while keeping the established technique intact.  Two sets of targets will extend the period between target replacements and reduce the machine downtime.  Additional polarization and emittance measurements can be done with extra set of targets (polarization and emittance measurements during the energy ramp).  A new carbon target production technique (by the laser ablation developed at TRIUMF, Vancouver, Canada) will be also tested.  The polarimeter upgrade project is funded by CAD ($150k) and RIKEN ($75k) and planned to be completed by the end of December 2008 for operation in 2009 polarized proton run.

p-Carbon polarimeter operation in Polarimeter survived all the upgrades. Reliable operation in switching mode (between vertical and horizontal planes) was demonstrated after a few software glitches were fixed. Beam intensity profile measurements made essential contribution to emittance calibration and knowledge of absolute values. Rate problem for polarization measurements. Maximum carbon rate up to 8 million event/s, ~1 events/bunch crossing (for 72 strips). About 3-5 rate variation was observed for the regular target thickness. It looks like thinner target lifetime is the same (or better?) than thicker targets. To accumulate required statistics ~ 20 millions events target should sit longer time in the beam. The effect to the beam emittances and luminosity is negligible at store. The only problem would be target lifetime.

Vacuum system upgrade. Polarimeter chamber is pumped by two pumps (ion pump ~1000l/s and NEG cartridge ~ 2000 l/s hydrogen) isolated by vacuum valves. Diam. 8.0” (ID) nipples and valves provide sufficient conductance to utilize full pump capacity. Isolation valves will allowed proper pump conditioning and faster turn around time after the venting. In future we plan to setup some moderate chamber baking after testing of polarimeter components (targets, detectors, Am-sources) tolerances to temperature. ~ 1.5*10^-10 vacuum was obtaine after two weeks pumping.

March 22

P-Carbon CNI polarimeter. Target speed steps/sec → 15 mm/sec linear speed was used for emittance measurements steps/s for polarization measurements. ~ 100 mm RHIC beam 180 mm 10 mm-SSD Scattering angle ~0.5 deg ~1.6 mm

The target ladder.

Target alignment jig.

Yellow targets effective thickness spread

Blue targets effective thickness spread

Y-1, V#5 (12)

Blue-1, V#4 (3)

Blue-1, V#2 (8)

Blue-2, H#1, (2)

Y-2, V#5, (2.8)

Carbon targets Evaporation (glass slide, mask preparation). Floating. Picking. Measurements (reproducibility). Attachment to the ladder. Ladder installation. Pumping. Target motion. Beam exposure.

Plans. Work out new procedure for more reproducible (thin) target production. Test new laser ablation evaporation technique (TRIUMF). Set-up target width measurement. Much more manpower will be required. There is a plan to hire a dedicated technician (~50% time shared with instrumentation group). If laser ablation works well, we can try to set up similar facility at CAD (Masahiro Okamura).

Target lifetime Carbon strip target is only 5-10  m wide and 4-5  g/cm 2 thick. This corresponds about atoms in the beam. The recoil Carbon production rate is about 10^8 atoms/s at present very high RHIC beam intensity), therefore after one hundred (10 s) measurements about 0.1% of carbon atoms are knocked out of the strip. Some targets survive for two weeks which corresponds to about 300 measurements.