Recent drag rate measurements

1. Recent drag rate measurements Recycler Departmental Meeting November 8th, 2006 L. Prost, S. Shemyakin

2. Data taken • Drag rate measurements with the electron beam on axis, +2 kV jumps • 100 mA – 400 mA • Nominal file (806) • Magnetic field realigned recently • Modified file 806 • SPB01I changed from 13.5 A to 14.5 A • From focusing optimization based on equilibrium changes of a cooled beam at 200 mA (1 mm offset) • Equilibrium to equilibrium • Check ‘old’ SA calibration • Got unexpected data due to slow energy oscillations • Additional output: • Energy vs y-position at R01 • Jumps calibration

3. Drag rates ranged from 25 to 50 MeV/C per hour All but 6/15/06 data were taken with R38 <4>

4. Comparison to current density profile: Better agreement ? Unexplained discrepancy (?!?!) Otherwise, good agreement between the two detectors

5. Data may not be straightforward to interpret because of a wobbling energy Pbars ‘drift’ before the jump

6. Slow (~6 minute period) energy oscillations are observed • Comparison of the Pelletron voltage variation dU recorded with GVM and the electron energy variations dE calculated from BYR01S • Both signals are averaged over 30 sec • Calibration from a jump (last week presentation) • 0.31 mm/kV • Source of these oscillations is unknown • Voltage regulation loop ? • Temperature ? This is a new observation

7. Taking advantage of the oscillations as an ‘independent’ measurement of the drag rate for small deviations • The blue curve shows the evolution of the pbar momentum Pipredicted from BYR01 positions Yias where P0 - initial momentum offset  = 33 hr-1 - drag rate coefficient D - coefficient translating the dispersion in BYR01S into the units of MeV/c per mm Y0 - beam position in BYR01S corresponding to an equilibrium energy

8. Energy jumps calibration/uncertainties 380 V 100 mA, on axis Intended jump (3.67 MeV/c) Error on jump (1s) = 0.23 MeV/c GVMVLT gives 0.11 MeV/c for 1s

9. Summary/Conclusions/Questions • Fastest drag rates ever recorded • Max ~50 MeV/c per hour for Ib = 300 mA • Better magnetic field alignment • Better alignment with pbars • Smaller emittances ? • Better focusing ? • In particular for 300 mA case • Should not matter on axis • May be slightly better agreement with estimation of the dependence of the drag force with the current density on axis • But still abnormally low drag rate for high electron beam current (e.g.: 400 mA) • ‘Standard’ data analysis (shown here) may be too simple for this set because of the energy wobbling continuously (see following points)

10. Summary/Conclusions/Questions (cont’) • Slow and relatively large energy oscillations were observed (with pbars and R01 position) for the whole duration of the measurements • New phenomenon/observation • Better (higher) drag force ? • Temperature variations ? • Relatively good agreement between the two ‘measurements’ using a linear model for the drag force • Small oscillations • Possibility to use an applied sinusoid for automated measurement of the drag force • Continue to use R01 position as a spectrometer • Estimated errors for the jump: 0.23 MeV/c (1s) • Based on GVMVLT data, the estimated error is ~half the one calculated with position data • But it is less sensitive

11. Not a real plan but… • We want to continue (and accentuate) the investigation of the friction force and cooling rates • More measurements will be requested • Visitors from BNL will come to Fermilab in December for that purpose • Very important for their project which goes into review in the Spring • Goals: • Improve cooling (FNAL) • Rates, lifetime,… • Understand cooling (FNAL, BNL,…) !! • Physics contribution of the Electron cooling project