august 4-5, 2004 pep-ii post run 4 review 1 m. sullivan pep-ii post run 4 review august 4-5, 2004 ir...

August 4-5, 2004PEP-II Post Run 4 Review1

M. SullivanPEP-II Post Run 4 Review

August 4-5, 2004

IR Summary and Issues


Outline• Summary

• Issues

• Conclusions


PEP-II Interaction Region and the BaBar Detector

HER

LER

Collision point

BaBar

e e


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


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 !


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


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


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


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


Data from the two hottest NEGs

NEG temperatures

Pump pressure of 3147. The ion pump is between the two NEGs

3142

3149

3149


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


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


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


Upstream LER Ideal

Abstracted from Edward’s presentation

LER beam line from Q2 septum to about 63 m upstream


Upstream LER after summer down

Abstracted from Edward’s presentation


HER Upstream Q5 chamber

• We plan to replace this chamber

BaBar Deadtime

Diamond BW (HER)

NEG temp in Q5 chamber


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


HER upstream NEG screen

This is a post at the center of the chamber


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


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


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


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


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

august 4-5, 2004 pep-ii post run 4 review 1 m. sullivan pep-ii post run 4 review august 4-5, 2004 ir...

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