M. Sullivan Machine Advisory Committee Review December 13-15, 2004

1

IR NEG heatingM. Sullivan

MAC ReviewDec. 13-15, 2004

M. Sullivan

Machine Advisory Committee Review

December 13-15, 2004

IR NEG Heating and Upgrade

2



Outline

• History from last run

• Summer work

• Vacuum model

• Conclusions

3



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.

• MAC Review in April

• 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

4



Upstream LER plan view

136Fside

160Fside

150Fbot

130Fbot150F

bot150Fbot

Collimators Quad chambersDipole chambers

268F

425F453F

724F

LER current 2.2 A

5



Collimator

Collimator

724F

268F

453F

6



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

7



Data from the two hottest NEGs

NEG temperatures

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

3142

3149

3149

8



LER NEG Test chamber

9



Test NEG data over the summer

We held the test

NEG at our regen

temperature for a

month with a

Turbo pump

attached

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

10



Pressure in the test NEG

Pressure as a function of time in the test NEG.

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

Ave nTorr

0

2000

4000

6000

8000

10000

12000

14000

16000

6/29/040:00

6/29/0412:00

6/30/040:00

6/30/0412:00

7/1/04 0:00 7/1/0412:00

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

After the first 6 hrs

After about 48 hrs

11



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

12



LER upstream NEG work

• This summer:– We took out the nine NEGs with “c type” screens

and installed a small HOM absorber in each cavity– The total length of NEG pumping that was removed

is 5.5 m out of a total of 40.4 m– We removed the two movable collimators– We removed the Q4 NEG and have replaced it with

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

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

ion pumps in this region

13



Existing 3082 chamber

BPM

BPM

Chamber support

Cooling bar

NEG plenum

NEG heater

Quad extrusion

14



Chamber showninverted and plenum not shown for clarity

SiC HOM absorber

15



Part of one of the NEG pumps that was removed this last summer

16



One of the collimators that was removed

The NEG in this chamber was one of the hottest

17



HOM absorber to replace NEG pump

18



Drawing of installed extra pumping

19



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

20



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

21



Support tube Vacuum Design Model

Vacuum pressure in the support tube.

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

22



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 during the next downtime.

23



Upstream LER Ideal

LER beam line from Q2 septum to about 63 m upstream

24



Upstream LER after summer down

25



HER scrubbing

26



HER Upstream Q5 chamber

• We plan to replace this chamber

BaBar Deadtime

Diamond BW (HER)

NEG temp in Q5 chamber

27



The upstream HER NEGs and heater instrumentation

The upstream HER beam pipe is also blanketed with NEG pumps starting at 21 m and going out 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 screen is very similar if not identical to the “c type” screen seen in the LER

The collimator at 35 m has a TSP

The only chamber in this area without pumping is the fast kicker chamber

28



HER upstream NEG screen

This is a post at the center of the chamber

29



NEG heater temperature through heater resistance

• Stan Ecklund 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

This particular NEG pump can not be instrumented any other way

30



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

31



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

32



Upstream HER BLF NEG

This NEG is located 22-24.5 m from the IP

So far, this NEG looks OK

We think we will be OK for run 5

We have instrumented all of these upstream NEGs with TCs

33



Conclusions• We have fixed the NEG pumps in the upstream LER beam pipe that

were getting the hottest by removing the pumps and installing a HOM absorber in the pump cavity

• We removed the NEG pump that was closest to the septum chamber because HOM power was also heating up that pump and installed a HOM absorber in its place

• We removed the two movable collimators

• The run 5 beam parameters will increase the HOM power we have so far experienced by increasing the beam currents and shortening the bunches

• HOM power in IR2 will go up

• We have instrumented the upstream HER NEGs and we will be watching them very carefully during this coming run

Documents

M. Sullivan Machine Advisory Committee Review December 13-15, 2004