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August 4-5, 2004 PEP-II Post Run 4 Review 3 PEP-II Interaction Region and the BaBar Detector HER LER Collision point BaBar ee ee
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August 4-5, 2004PEP-II Post Run 4 Review1
M. SullivanPEP-II Post Run 4 Review
August 4-5, 2004
IR Summary and Issues
August 4-5, 2004PEP-II Post Run 4 Review2
Outline• Summary
• Issues
• Conclusions
August 4-5, 2004PEP-II Post Run 4 Review3
PEP-II Interaction Region and the BaBar Detector
HER
LER
Collision point
BaBar
e e
August 4-5, 2004PEP-II Post Run 4 Review4
Summary
• We have achieved y*s of 10 mm
• With x*s of 30 cm
• Total beam currents of 2450 on 1550 (1590 on 2540 on last shift)
• No sign of SR backgrounds• Total current in the support tube up to 4.1 A!
• Heating in the IR (from Q2 to Q2) OK so far
• Discovered NEGs being heated by HOM power
Stan will talk about this
August 4-5, 2004PEP-II Post Run 4 Review5
Issues• Run 5 goals that affect the IR
• LER current of 3.3 A• HER current of 1.8 A• Higher bunch currents more HOM power• Shorter LER bunch length more HOM power• Lower y
*s to 9 mm• Lower LER x
* to 30 cm • Increase LER emittance to 50 nmrad
• BSCs
• NEGs
Total of 5.1 A !
August 4-5, 2004PEP-II Post Run 4 Review6
BSCs
Present machine parameters
LER x*= 30
cm and LER x = 22 nmrad
LER x* may
be a little low, but it is the value for run 5
BSC just clears the present Q2 chamber on the forward side
Plenty of room on the backward side
August 4-5, 2004PEP-II Post Run 4 Review7
BSCs
Expected LER beam size for run 5
LER parameters: x
* = 30 cm x = 50 nmrad
BSC is defined as 15 + 2mm (uncoupled)
BSC violated at the septum
Just enough room for the beam
New chamber being built for summer 2005
August 4-5, 2004PEP-II Post Run 4 Review8
Summary of the NEG story
• When we regenerated the NEGs in IR2 on March 24 we began to wonder if some of the NEGs were starting to heat up from HOM power.
• We confirmed that some were getting hot shortly thereafter but we did not get a full picture until the next ROD on June 3 when we instrumented every NEG in the upstream LER beam line.
Regeneration temperature is about 750 °F
August 4-5, 2004PEP-II Post Run 4 Review9
Lab test data of NEG outgassing as a function of temperature
LER NEG Pump Temperatures
Upstream LER side
NEG Pressure vs NEG Temperature
0
1
10
100
1000
10000
0 100 200 300 400 500 600 700
NEG temperature deg F
NEG
pre
ssur
e (n
Torr
) 350 °F
August 4-5, 2004PEP-II Post Run 4 Review10
Data from the two hottest NEGs
NEG temperatures
Pump pressure of 3147. The ion pump is between the two NEGs
3142
3149
3149
August 4-5, 2004PEP-II Post Run 4 Review11
Recent test NEG data
We held the
test NEG at
our regen
temperature
for a month
Ave NEG pressure -- nTorr
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
6/27 7/2 7/7 7/12 7/17 7/22 7/27 8/1
Time
nTor
rNEG temperature 725 °F
August 4-5, 2004PEP-II Post Run 4 Review12
LER upstream NEG work
• This summer:– Take out the nine NEGs with “c type” screens and
install a small HOM absorber in each cavity– The total length of NEG pumping that will be
removed is 5.5 m out of a total of 40.4 m– We will remove the Q4 NEG and replace it with a
HOM absorber (another 1.6 m)– We then add extra pumping at the port between the
Q4 and Q5 chambers– In addition, we will add extra screening to the ion
pumps in this region
August 4-5, 2004PEP-II Post Run 4 Review13
Aside: Vacuum model
• We have started building a vacuum model of straight 2
• Had great help getting started by a summer student (Edward Young)
• We have a preliminary model of the LER upstream beam pipe
• Still need to work on screen conductances and on outgassing values from SR fans
• Nevertheless we can get some idea about what happens when the above LER NEGs are removed
August 4-5, 2004PEP-II Post Run 4 Review14
Upstream LER Ideal
Abstracted from Edward’s presentation
LER beam line from Q2 septum to about 63 m upstream
August 4-5, 2004PEP-II Post Run 4 Review15
Upstream LER after summer down
Abstracted from Edward’s presentation
August 4-5, 2004PEP-II Post Run 4 Review16
HER Upstream Q5 chamber
• We plan to replace this chamber
BaBar Deadtime
Diamond BW (HER)
NEG temp in Q5 chamber
August 4-5, 2004PEP-II Post Run 4 Review17
Other upstream HER NEGs and heater instrumentation
The upstream HER beam pipe is also blanketed with NEG pumps starting at 21 m and going up to up to about 45 m from the IP
There are a total of 4 vacuum chambers in this region with NEG pumping (6 long NEGs). All of the pumps are below the beam chamber.
The collimator at 35 m has a TSP
The only chamber in this area without pumping is the fast kicker chamber
The screen is very similar to the “c type” screen seen in the LER
Stan instrumented one of these NEG heaters the last week (they all look like they have the same design) by putting a small current (10 mA ) through the heater circuit and measuring the heater resistance
Next slide
August 4-5, 2004PEP-II Post Run 4 Review18
HER upstream NEG screen
This is a post at the center of the chamber
August 4-5, 2004PEP-II Post Run 4 Review19
NEG heater temperature through heater resistance (work in progress)
• Stan has installed a circuit that measures some of the heater rod resistances
• He has instrumented:– LER upstream
• Q4 + Q5 (same circuit)• BV1 + next outboard (3042) (same circuit)
– HER• Q5 downstream• Q5 upstream• BLF upstream
August 4-5, 2004PEP-II Post Run 4 Review20
Temperature plot of first “c” chamber in LER (BV1)
Temperature plot of first “c” chamber in LER (BV1) using resistance measurement
Agreement is no better than about 20%. The signal is complicated by the resistance being the sum of the leads plus another NEG heater
BV1 NEG
August 4-5, 2004PEP-II Post Run 4 Review21
Q5 NEGsQ5
downstream
Q5 upstream
The upstream Q5 NEG resistance matches the TC we have in that NEG
Conclusion: Downstream HER Q5 NEG is hotter than the upstream HER Q5 NEG
August 4-5, 2004PEP-II Post Run 4 Review22
Upstream HER BLF NEG
This NEG is located 22-24.5 m from the IP
So far, this NEG looks OK
We should be OK for run 5
We need to instrument all of these upstream NEGs especially the ones closest to the collimator
August 4-5, 2004PEP-II Post Run 4 Review23
Conclusions• The run 5 beam parameters will fill more of the IR aperture,
especially for the LER• HOM power in IR2 will go up • We will violate the LER BSC (as defined) on the upstream septum
• This summer we will try to fix as many of the NEG heating problems as we can– 9 LER “c type” chambers will be modified– The upstream LER Q4 chamber will be modified– The two LER upstream movable collimators will be removed– Hope to replace the HER upstream Q5 chamber
• These fixes should make recovering from a NEG regen much faster
• The upstream HER NEGs will need to be watched more closely
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