Thermal effects in PEP-II Consequences for BABAR

1. Thermal effects in PEP-IIConsequences for BABAR • The thermal effects in PEP-II • Origin and characteristics • Before and after the ROD • The drivers of BABAR background: VGCC3027, VP3044, VP3075 and VP3147 • Detailed time history of the sensivity coefficients • A possible model

2. Overview of Thermal effects in PEP2 • The sustained running at high currents in the LER causes heating in some PUMPS which then OUTGAS (mainly Ion pumps but 150°F has been also observed on NEG pumps) • The source of the heating is High Order Modes getting into the core of the pump • The associated time constants are order of HOURS • The pressure rise causes higher beam-gas background • The single beam LER background is now a function of : f(I_Ler, Time_since_refill)

3. VGCC3027 Beam current From Artem Koulikov

4. PreROD data, from Artem Koulikov

5. 15.9 12.9 8.2 59.6 24 15.4 8.2 12.9 PreROD, Artem Koulikov

6. Before and after the ROD • This effect has always been present. IT rises critically with current • BUT before the ROD, even at 2.2 A, BABAR was not very sensitive to it • During the ROD on March 24, the NEG were activated (ie heated around 500°C: this throws gas way which is then reabsorbed with higher efficiency) • Just after the ROD. It was noticed that the pressure on the pumps has increased (ex VP3147) while most of them decreased • BUT the main effect was that BABAR sensitivity to the thermal HEATING was INCREASED by a huge factor • The main sensor is BAckward East Diode/East Diamond • Since then, the operators try to process the extra gas by constantly running at the maximal allowed value of SIG9 • The current was then raised from 1.5A on March 25 to 2.23 today

7. Pump HistoryThe pressures before and after the ROD show in general no dramatic changes Rod VP3164 VP3181 VP3147 VP3115 VP3131 VP3075 VP3054 VGCC3027 VP3044

8. Diamond History ROD Diamond East History 2.2 A LER current Time history From March 17 to March 31

9. Study of LER vacuum problems using detailed time evolutions • Most ideas discussed here stem from discussions/presentations by Witold and Artem • Identification of the sources using very detailed time histories thru BABAR ambient database, fill by fill. • Characterization of Babar background as ftcn of LER pressures in pre-ROD data using the 4 pumps sensitive to HOM and showing heat-related effects (plus a constant term*LER) • VP3044, VGCC3027, VP3075 , VP314 • Post ROD data -Identical sources BUT Large changes in sensivity (Underlying mechanisms: Thermal outgassing , large current sensivity when equilibrium reached

10. Electron/gas separationUse of the end of the fill VP3181 VP3044 VGCC3027 VP3147

11. Fit of Electron component2nd order polynomial (but cubic term present) VP3164 VP3181 VP3115 VP3147 LER current (A)

12. A typical preROD fill VP3044March 17, between 3pm and midnight VP3044 LER Thermal outgassing! DIAM-E vs VP3044 DIAM-E Time in hours

13. New method (least square fit) Diam_E as function of time VP3044 VGCC3027 VP3075 VP3147 COnstant

14. Just after the ROD VP3044 VGCC3027 VP3075 VP3147 COnstant

15. Main Discrete events • March 29 12 pm Orbit change • March 30 12.45 pm Gap Voltage • March 31 23 pm Collimator change • April 3 9 am Collimator change • April 3 17 pm Bunch pattern change

16. Orbit changePressure history for March 29 VP3044 30 nT 2 nT VGCC3027 VP3075 50 nT 70 nT VP3147 Time in hours

17. Gap Voltage change, March 30 at 12.45 pm VP3044 VGCC3027 VP3147 VP3075 Time, in hours

18. Collimator March 31 at 11 pm VGCC3027 VP3044 VP3075 VP3147 Time in hours

19. Diamond evoution ROD 1 point per fill Success on April 3 PreROD Level Days in March (32= April 1st)

20. Sensitivity Coefficients history ROD ROD Coll open. VGCC3027 VP3044 X200 sensitivity change just after the ROD!!! VP3075 VP3147 1 point per fill RF voltage gap change Days in March

21. Fractions of the Diamond signal for each pump , fill by fill VP3044 VGCC3027 VP3147 VP3075 Days in March

22. Zooming in on April 3 Asymptotic Diamond level After collimator opening After bunch pattern change Pre ROD level Days in March (34= April 3)

23. Fits April 3 Before : Large VP3044 and VP3147 components DiamEast VP3044 VGCC3027 VP3075 VP3147 COnstant Time , 10 sec units After coll opening, no more VP3044 component but higher VGCC3027

24. APril 3, after collimator AND bunch pattern changes Negligible VP3044 AND VGCC3027!

25. Pressures History in April 3Once again, the story is not in the pressure but in the sensitivity coefficients VGCC3027 VP3044 VP3075 VP3147

26. Coefficients on April 3 Coefficients VGCC3023 coeff. Increased when coll was open but it was processed away VP3044 Coll opening reduced VP3044 dramatically Bunch pattern change reduced VP3147 by a factor 2 VP3075

27. Dead time issue on April 3 VGCC2187 drives BABAR dead time. It was reduced a) on coll opening b) on bunch pattern change VGCC2187 pressure BABAR Dead time (in %) Time in hours Time in hours Babar Dead time VGCC2187

28. Conclusions • PEP exhibits thermal outgassing in (at least) 4 locations related to HOM losses which then induce BABAR beam gas background • BABAR sensitivity was significantly increased after the ROD: Best hypothesis: outgassing of heavy Gas, although the pressures themselves did not change much • A detailed fit to the time evolution of the background signal as a linear combiantion of each pump alows to extract the sensitivity coefficients fill by fill. • The main contributors were: • VP3044 and VGCC3027 in th week following the ROD • VP3147 came into play after 1 week , triggered by the RF voltage change • The fix to the background problem was -processing -reduction of HOM heating by opening collimators and change in bunch pattern