# Presentation: 149955

## Recent drag rate measurements

- Recycler Departmental Meeting
- November 8th, 2006
- L. Prost, S. Shemyakin

## 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

## Drag rates ranged from 25 to 50 MeV/C per hour

- All but 6/15/06 data were taken with R38 <4>

## Comparison to current density profile: Better agreement ?

- Unexplained discrepancy (?!?!)
- Otherwise, good agreement between the two detectors

## Data may not be straightforward  to interpret because of a wobbling energy

- Pbars ‘drift’ before the jump

## 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**

## 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 ***P******i****** ***predicted from BYR01 positions ***Y******i*** as

**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**

## Energy jumps calibration/uncertainties

**Intended jump**
**(3.67 MeV/c)**

**100 mA, on axis**

**380 V**

**Error on jump (1********) = 0.23 MeV/c**

*GVMVLT gives 0.11 MeV/c for 1***

## 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*)

## 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 (1)
- Based on GVMVLT data, the estimated error is ~half the one calculated with position data
- But it is less sensitive

## 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