MI Departmental Meeting February 3 rd , 2010 Lionel PROST, Alexander SHEMYAKIN

1. 24-hour Drag Rate Measurements(Data taken between 4 am on January 26 and 4 am onJanuary 27 continuously & some more on January 29) MI Departmental Meeting February 3rd, 2010 Lionel PROST, Alexander SHEMYAKIN Thanks to Arden Warner for helping with the ACL scripts that make taking the data more consistent and easier

2. Experimental plan • With the proton source downtime, we had the (unique) opportunity to complete measurements that require a small amount of pbars (<1.5e10) and a lot of time • Re-alignment of the cooling section magnetic field • Electron cooling clearly deteriorated over the past few months • Characterization of a DC beam with short (microseconds) interruptions (we called this mode of operation ‘negative pulsing’) to remove ions trapped in the beam potential • Ions are source of non-linear fields that we cannot correct for • Already shown that these short interruptions modify the optics i.e. do remove at least some of the ions trapped • More quantitative on: what frequency is needed ? What pulse width ? • Try to explain the drag rate distribution from June 2009 for300 mA • Or rather, does using negative pulsing help smooth the beam distribution ?

3. Alignment of the magnetic field in the CS • Same procedure as what was successfully done after the Summer shutdown • See March 21st, 2007, RR meeting (in Indico) for detailed explanation for one solenoid (Sasha’s talk) • Beams Document 3461-v1 for the whole present procedure • As-found drag rate measurements of each individual solenoid • Did not adjust all solenoids but only the 3 worst • ‘Zero-in’ all BPMs with end correctors for final alignment Solenoid modules BPMs Electron beam trajectory • The beam is kicked far from axis with the exception of the module to be measured • Autotune fixes the beam trajectory on axis at the entrance and exit of the module being measured • 8 dipole correctors in this module are changed by the same amount to find maximum drag rate

4. Results from field alignment • Increased the drag rate on-axis by 30-40% • ~25 MeV/c per hour to ~35 MeV/c per hour • Increased cooling rate (on-axis) by 60-70% transversely • Marginal improvement longitudinally • Emittances for the last shot to the TeV were closer to/at their historical values • < ~4 p mm mrad (Schottky) while stashing, constant 1.8 p mm mrad (FW) during extraction, 1.1 eV s per 2.5 MHz bunch Stashing Extraction New’ tune’ implementation 4 p mm mrad 2 p mm mrad

5. Negative pulsing - Frequency scans for optimum ion clearing • Frequency is limited by the power supplies utilized in the dome • 15 Hz at 300 mA, 35 Hz at 100 mA • Settings for 100 mA were optimized without negative pulsing while they were optimized with negative pulsing for 300 mA (hence the different behaviors) • Pulse width (2-30 ms) did not have any measurable effect on the drag rate Not a fit 300 mA (2 ms width, on-axis) 100 mA (2 ms width, on-axis) Likely need more than 15 Hz but less than 50 Hz

6. 100 mA (Dec’07) 300 mA (Jun’09) 2.5 1.5 Y, mm -2.5 -1.5 -1.5 1.5 X, mm X, mm Situation with 300 mA DC – No negative pulsing (June’09) • Coarse 2D distribution of the cooling forceacross the electron beam (default interpolation from MathCAD plotting package) Color map scaling not normalizedContour levels in MeV/c per hour Appears as if we have 3 distinct ‘good cooling’ regions More indicative of a quadrupole effect

7. Drag rate as a function of the electron beam position • 28 data points • Average of all measurements if several at same location • F(x,0), F (0,y), F (x,y) at 45 for r = 1 mm and r = 2 mm • Same unormalized colormap as previous plots • Max drag rate measured:70 MeV/c per hour • No very sharp peaks • Effective size (for cooling) much improved • Best cooling is not on-axis • Likely results from the way settings were optimized i.e. minimizing the longitudinal emittance equilibrium with the electron beam off-axis Feb’10 Y, mm MeV/cper hour X, mm

8. Cooling ‘Profiles’ with and without negative pulsing (300 mA) Drag rate as functions of X (Y=0) and Y (X=0) offset between the centers of the electron and pbar beams. Error bars: ±10% (goodness of the fit guesstimate) No negative pulsing Negative pulsing(15 Hz, 2 ms) • Optimum focusing for each case • Search for optimum: on-axis for ‘no negative pulsing’; off-axis for ‘negative pulsing’ mode

9. Interpretation of the instability on January 7th • Used 300 mA beam with negative pulsing to cool the stash after mining • Started with the beam offset by +1 mm • Moved the beam further out in steps when we observed too low(< 1.8 p mm mrad) FW transverse emittance • Instability after the 6th bunch was extracted A more appropriate offset for final cooling with an electron beam with such a cooling force distribution • By moving the electron beam in the positive direction, we actually were increasing core cooling (or, at the very least, not decreasing the cooling strength) !! Profile with negative pulsing indicate that it may be beneficial to try final cooling with negative offset to cool the tails efficiently and avoid overcooling the core

10. Conclusions • Re-aligning the cooling section magnetic fields improved the drag rate by 30-40% (100 mA, on-axis, 2 kV jump) • We might have to do this every several months • Alternative: keep adjusting procedure • Significant improvement to the cooling rate transversely • Not much longitudinally  May require aligning ALL solenoids • Drag rates with negative pulsing show a much less perturbed distribution at 300 mA (i.e. much reduced non-linearities) • Efficiently getting rid of the trapped ions likely require a higher pulse frequency than currently available (for high beam currents) • EE Support is considering building a 50 Hz ‘pulser’ (new modulator) • Our attempt to do final cooling at 300 mA and which resulted in an instability can be explained by the cooling force ‘profiles’ that we measured • Should be interesting to try again with a negative offset to take advantage of the slow rising slope • May be interesting to revisit settings obtained from YAG measurements (pulsed beam  no ion accumulation)