The Impact of Dissociator Cooling on the Beam Intensity and Velocity Spread in the SpinLab ABS M. Stancari, L. Barion, C. Bonomo, M. Capiluppi, M. Contalbrigo, G. Ciullo, P.F. Dalpiaz, F.Giordano, P. Lenisa, L. Pappalardo and M. Statera University of Ferrara, Italy and INFN Ferrara

ABS Intensity over time Is there an emperical limit on the intensity of an ABS, perhaps due to intra beam scattering? (Novosibirsk, PST01) Evidently not! (PST 03, SPIN 04)

SpinLab ABS1 Dissociator Cooling We observe that : all temperatures rise with input flow for fixed cooling power but do not change with increased microwave power ( W) the beam parameters are not sensitive to variations in the cooling water temperature the beam parameters are sensitive to variations in the collar temperature

SpinLab ABS1 Procedure: change the collar temperature, and monitor Inlet Pressure Nozzle and Skimmer Chamber Pressures Beam Density and Time of Flight with QMA (both hydrogen atoms and molecules separately)

QMA measurements S 1,S 2 Advantage: Quick measurement (30 seconds) available during temperature changes Disadvantage: (Transverse) beam density instead of beam intensity Beam Density Time of Flight Advantage: provides both beam density (  f(v) ) and beam intensity (  vf(v) ) Disadvantage: requires 10 minutes measuring time and thus a thermally stable system f(v) S(t)

Time of Flight Sensitivity Scan of nozzle temperature Scan of input flow Molecular Beam Studies

Chamber pressures Nozzle temperature = 115 K Beam Response to Collar Temperature Changes 75 sccm H sccm O 2 4 mm nozzle at 115 K Inlet Pressure

molecules atoms Chamber pressures Nozzle temperature = 115 K Beam density Beam Response to Collar Temperature Changes 75 sccm H sccm O 2 4 mm nozzle at 115 K Inlet Pressure

Velocity Distributions atomsmolecules v drift T beam v drift T beam

atoms 4 mm nozzle molecules 4 mm nozzle Beam Intensity and Collar Temperature 100 K:  = 92-95% 115 K:  = 94-95%

atoms 4 mm nozzle molecules 4 mm nozzle molecules 2 mm nozzle atoms 2 mm nozzle Beam Intensity and Collar Temperature Preliminary observations More intensity loss for higher nozzle temperature larger nozzle diameter 100 K:  =72% 115 K:  =66% Higher % loss for molecules  Importance of molecule-atom collisions?

Velocity Distributions Difference in mean velocity between atoms and molecules is greater for 4 mm nozzle 2 mm nozzle4 mm nozzle v drift T beam v drift T beam 100 K atoms1400 ± 5021 ± ± 2022 ± 2 molecules1350 ± 5022 ± 51280± 2026± K atoms1500 ± 5024 ± ± 2026 ± 2 molecules1420 ± 5026 ± ± 2031 ± 2

Beam Response to Oxygen Flow Chamber pressures Beam density molecules atoms Inlet Pressure 75 sccm H 2, 4 mm nozzle, 100 K 1-5 sccm O 2 50 K collar

Oxygen Scan Details Almost constant dissociation Some broadening of velocity distributions at high O 2 flow? moleculesatoms Molecules: T beam from 25 to 29 K Atoms: T beam from 21 to 24 K

Conclusions A correlation between the dissociator cooling and the beam intensity has been established. Further studies about how to increase the intensity of atomic beam sources are planned in the future.

Possible Explanations Expansion changes, less forward peaking as collar temperature increases? Unlikely - both chamber pressures increase. Increasing rest gas attenuation in large skimmer chamber? Unlikely - chamber pressure increases only 4%. More intra-beam scattering as the collar temperature increases?  Atom-atom collisions or molecule-molecule collisions? Little or no change in velocity spread is observed.  Atom-molecule collisions?

Time of Flight Cross Check 20% 10% 60% 40% 100% 80% Molecular Beam measurements: Red numbers – H2 input flow in % of 250 sccm Time of Flight Beam Density

Water Cooling Tubes

Collar Photograph

Some Characteristics of Current Sources HermesNov.Wisc.ANKERHIC Input (mbar l/s) B pt (T) d mag (cm) v drift (m/s) ~1530 T beam (K) ~18 length (m) d ct (cm) Intensity (10 16 atoms/s)