M. Sullivan High Luminosity workshop (HL6) November 16-18, 2004

November 16-18, 2004Belle High Luminosity Workshop1

M. Sullivan

High Luminosity workshop (HL6)

November 16-18, 2004

IR Vacuum Summary and Issues


Outline

• NEG story

• Vacuum modeling

• Conclusions


PEP-II Interaction Region and the BaBar Detector

HER

LER

Collision point

BaBar

e e


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


Upstream LER plan view

136Fside

160Fside

150Fbot

130Fbot150F

bot150Fbot

Collimators Quad chambersDipole chambers


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

NE

G p

ress

ure

(n

To

rr) 350 °F


NEG temperatures

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

3142

3149

3149

Data from the two hottest NEGs

LER beam current


Hydrogen Concentration Torr l/g

Hyd

roge

n E

quili

briu

m P

ress

ure

(Tor

r)

200°

C

300°

C

400°

C

600°

C

500°

C

St707

Em

britt

lem

ent

Lim

it (2

0 T

orr

l/g)

NEG heaters on NEG heaters off

Ion pumps off

Ion pumps on

•Heat NEGs for 1 hr•400-450 degC•Time 11:45-12:45•Tubro cart pump: 220 L/s •Pressure at pump about 10-5 Torr

Some regeneration details


LER NEG Test chamber


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

nT

orr

NEG temperature 725 °F


Pressure in the test NEG

Ave nTorr

-2000

0

2000

4000

6000

8000

10000

12000

14000

16000

6:00 7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36

Pressure as a function of time in the test NEG.

Holding the NEG at the regen temperature of 725 F (400 C).


LER upstream NEG work

• This last summer:– Took out the nine NEGs with “c type” screens and

installed a small HOM absorber in each cavity– The total length of NEG pumping removed is 5.5 m

out of a total of 40.4 m– We have removed the Q4 LER NEG and replaced it

with a HOM absorber (another 1.6 m)– We then added extra pumping at the port between

the Q4 and Q5 chambers– In addition, we have added extra screening to the

ion pumps in this region– We also removed the movable collimators


One of the NEGs that was removed last summer


One of the collimators that was removed

The NEG in this chamber was one of the hottest


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 check on screen conductances and on outgassing values from SR fans

• Nevertheless we can get some idea about what happens to the vacuum pressure profile with the above LER NEGs removed


Chamber Model Layout

HER downstream

LER upstream

LER downstream

HER upstream

Support chamber

Q5 NEG

Q5 NEG

66.114 m

69.33 m

ST plot

plot

plot

plot

plot

12

3

4

5 6


Support tube Vacuum Design Model

Vacuum pressure in the support tube.

The model predicts a pressure peak at the IP of about 20 nTorr.


No radial ion pumps

We lost these pumps a couple of years ago.

One developed an Argon instability before it died . Both pumps do not work right now.

We intend to replace these pumps this coming summer.


Upstream LER Ideal

LER beam line from Q2 septum to about 63 m upstream


Upstream LER after summer down

One can see the pressure bumps where the NEG pumps have been removed

Keep in mind that we believe the vacuum pressure to be better than this due to the beam scrubbing from the high LER beam current.


HER scrubbing


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


Conclusions• This last run we discovered that NEG pumps in the upstream LER

were heating up due to HOM power getting through the screens. The high beam current in the LER and high beam bunch currents increased the HOM power levels. In addition, we verified that the movable collimators were a significant source of HOM power. (These screens would have probably worked with the original PEP-II design parameters)

• This past summer we have fixed as many of the NEG heating problems as we could:

– 9 LER “c type” chambers have been modified

– The upstream LER Q4 chamber NEG has been removed

– The two LER upstream movable collimators have been removed

– Intend to replace the HER upstream Q5 chamber this coming summer

• These fixes should make recovering from a NEG regen much faster

• The upstream HER NEGs will need to be watched more closely

Documents

M. Sullivan High Luminosity workshop (HL6) November 16-18, 2004