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

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)

Beam current

VGCC3027

From Artem Koulikov

0

5

10

15

20

1.7 1.8 1.9 2 2.1 2.2 2.3

VGCC3027Pr

essu

re,

nTor

r

LER current, APreROD data, from Artem Koulikov

0

5

10

15

20

25

30

35

vgcc

4033

vp31

81vp

3164

vp31

47vp

3131

vp31

15vp

3075

vgcc

3075

vp30

54vg

cc30

54vp

3044

vgcc

3027

vgcc

2187

vp21

76vp

2167

vgcc

2099

vgcc

1143

Pres

sure

, nT

orr

A

IP

Beam

8.212.9

15.415.9

2459.68.2

12.9

PreROD, Artem Koulikov

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

Pump HistoryThe pressures before and after the ROD

show in general no dramatic changes

VP3181

VP3164

VP3147

VP3131

VP3054

VP3044

VGCC3027

VP3075

VP3115

Rod

Diamond History

Diamond East History

ROD

Time history From March 17 to March 31

LER current

2.2 A

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

Electron/gas separationUse of the end of the fill

VP3181

VP3147VGCC3027

VP3044

Fit of Electron component2nd order polynomial

(but cubic term present)

LER current (A)

VP3181 VP3164

VP3115VP3147

A typical preROD fill VP3044March 17, between 3pm and midnight

LER VP3044

DIAM-E DIAM-E vs VP3044

Time in hours

Thermal outgassing!

New method (least square fit)

Diam_E as function of time

VP3044

VGCC3027

VP3075

VP3147

COnstant

Just after the ROD

VP3044VGCC3027VP3075VP3147COnstant

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

Orbit changePressure history for March 29

Time in hours

VP3044

VP3075

50 nT

VGCC3027

VP3147

30 nT

70 nT

2 nT

Gap Voltage change, March 30 at 12.45 pm

VP3044

VP3075VP3147

VGCC3027

Time, in hours

Collimator March 31 at 11 pm

VP3044VGCC3027

VP3147VP3075

Time in hours

Diamond evoution

Days in March (32= April 1st)

1 point per fill

PreROD Level

Success on April 3

ROD

Sensitivity Coefficients history

VP3044

VP3075

VGCC3027

VP3147

Days in March

1 point per fill

RF voltage gap change

RODROD

X200 sensitivity change just after the ROD!!!

Coll open.

Fractions of the Diamond signal for each pump , fill by fill

Days in March

VP3044

VP3075

VGCC3027

VP3147

Zooming in on April 3

Days in March (34= April 3)

Asymptotic Diamond level

Pre ROD level

After collimator opening

After bunch pattern change

Fits April 3Before :

Large VP3044 and VP3147 components

Time , 10 sec units

DiamEast

VP3044VGCC3027VP3075VP3147COnstant

After coll opening, no more VP3044 component but higher VGCC3027

APril 3, after collimator AND bunch pattern changes

Negligible VP3044 AND VGCC3027!

Pressures History in April 3Once again, the story is not in the pressure

but in the sensitivity coefficients

VP3044

VP3075

VGCC3027

VP3147

Coefficients on April 3Coefficients

VP3044

Coll opening reduced VP3044 dramatically

Bunch pattern change reduced VP3147 by a factor 2

VGCC3023 coeff. Increased when coll was open but it was processed away

VP3075

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

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