The pressure build-up test of the 14 m-long

one cell in Taiwan Photon Source

Vacuum Group

Presenter: Ling-Hui Wu

L. H. Wu , T. Y. Lee, C. H. Chang, S. W. Chang, Y. C. Yang, Z. W. Chen, Y. P. Chang, C. S. Huang, Y. T. Huang,

C. C. Chang, S. N. Hsu, C. K. Chan, H. P. Hsueh, C. M. Cheng, B. Y. Chen, G. Y. Hsiung, and J. R. Chen

Outline

• Introduction a. Total 24 cells of Al vacuum systems in the electron storage ring

b. Explain the baking test

• Experiment a. Baking 24 cells was completed in the laboratory to achieve an

Ultra-high vacuum status

b. Pressure build-up method

• Results and discussion a. Outgassing rate

b. Pumping speed

c. Residual gas analysis

• Conclusion

1

2

Introduction

TPS status 1. The construction of Taiwan Photon Source (TPS), energy 3 GeV, since 2010.

2. Installation work has recently proceeded in the TPS tunnel

3.Vacuum chambers in the TPS storage ring are made of aluminium (Al) alloy

4.There are 24 cells of aluminum vacuum systems in the storage ring.

Baking procedure 1. The baking 24 cells was completed in the laboratory to achieve an ultrahigh

vacuum with pressure less than 1x10-8 Pa.

2. Water and other kinds of residual gases were removed after baking.

3. The RGA spectrum was continuously recorded during the vacuum baking.

The photos showed the

baking test condition

3

The assembled vacuum components is

shown below.The vacuum components

are assembled in the clean room (class

10000).

Introduction

The pressure and temperature of R24

cell, from the time of initial pumping until

the vacuum pressure build-up time.

∵ degas

∵ IP turned off

build-up

∵ Temp ↑

4

Experiment

Pressure build-up method

The outgassing rate and pumping speed can be estimated by the equation (1),

where Q is total outgassing rate (Pa∙m3∙sec-1), S is pumping speed (L∙s-1), P is pressure

(Pa), and V is volume of the system (m3). The equation (1) can be modified to be

where SNEG is pumping speed of NEG pumps (L∙s-1), and SIP is pumping speed of ion

pumps (L∙s-1).

It is assumed that S=SNEG+SIP . As the ion pumps turned off, SIP = 0, the equation (2)

can be rewritten to be

(1)

(2)

(3)

Here, the V × dP/dt value is calculated while ion pumps turned off in the first two

minutes. Theoretically, the NEG pumps activation effect is similar for each cell.

Thus, we compare the V × dP/dt value for each cell. We set the V × dP/dt = Δ Q

and Δ Q / A= Δ q, A is the inner surface area of the vacuum chamber (m2).

Besides, the pumping speed can be estimated directly from equation (4).

Experiment

5

(4)

The pumping speed can be estimated directly

from eq. (4). In the plot of log P with time (t),

the slope is S/V.

For R24 cell, the figure shows the pressure vs.

build-up time for IG4, IG5, and IG6.

R24 cell

6

Results and Discussion (1)

0 5000 10000 15000 20000 25000

0.0

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

1.0x10-5

1.2x10-5

1.4x10-5

1.6x10-5

Press

ure (

Pa

)

Time (s)

IG4

IG5

IG6

0 5000 10000 15000 20000 25000

0.0

5.0x10-8

1.0x10-7

1.5x10-7

2.0x10-7

2.5x10-7

3.0x10-7

3.5x10-7

4.0x10-7

4.5x10-7

Press

ure (

Pa

)

Time (s)

IG4

IG5

IG6

Compared the pressure after build-up time > 60 hrs

R24 cell / general case R05 cell / special case

For R24 , the general case of cell, during build-up period, the pumping action resulted from the NEG pumps and extractor gauges. The pressures increased to about 5x10-7 Pa with a duration more than 60 hours of build-up time. However, for R05 cell special case, the pressures increased to about 2x10-5 Pa with a duration more than 60 hours of build-up time. In order to improve the build-up pressure for R05 cell, we bake the ion pump separately.

Results and Discussion (2-1)

Bake Ion Pump separately

35000 40000 45000 50000 55000 60000 65000

0

1

2

3

4

5

6

7

Pre

ssu

re (

nto

rr)

Time (sec)

bakeIP3

IG4

R05 IP3

dP/dt = 2.97E-12 Torr/sec

IP3

T ↓

T ↓ CH4

7

The steepest slope dP/dt is 2.97E-12 Torr/sec. Compared with R05 cell build-up data, the slope order is similar. From RGA data, the residual gas source is mainly from CH4.

35000 40000 45000 50000 55000 60000 65000

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

Pre

ssu

re (

nto

rr)

Time (sec)

bakeIP4

Bake Ion Pump separately

IG5 T ↓

R05 IP4

dP/dt = 1.42E-14 Torr/sec

IP4

CH4 T ↓

Results and Discussion (2-2)

8

The second one is IP 4. The steepest slope dP/dt is 1.42E-14 Torr/sec. Compared with R05 cell build-up data, the slope order is much less than that of R05 cell. From RGA data, the residual gas source is from CH4.

30000 35000 40000 45000 50000 55000 60000 65000 70000

0.040

0.045

0.050

0.055

0.060

0.065

0.070

0.075

0.080

0.085

0.090

0.095

0.100

0.105

0.110

0.115

0.120

Pre

ssu

re (

nto

rr)

Time (sec)

IP5 bake (IG5)

IP5 bake (IG6)

Results and Discussion (2-3)

Bake Ion Pump separately

IG6

T ↓ R05 IP5

dP/dt = 1.05E-14 Torr/sec

IP5

H2, CH4 CO, CO2

T ↓

9

The third one is IP 5. The steepest slope dP/dt is 1.05E-14 Torr/sec. Compared with R05 cell build-up data, the slope order is much less than that of R05 cell. From RGA data, the residual gas source is from H2 CH4 CO CO2.

30000 40000 50000 60000 70000 80000

0

1

2

3

4

5

6

Pre

ssu

re (

nto

rr)

Time (sec)

bakeIP6

11:45

9:00

Results and Discussion (2-4)

Bake Ion Pump separately

IG6

R05 IP6

dP/dt = 1.45E-12 Torr/sec

IP6

CH4

T ↓

10

The final one is IP 6. The steepest slope dP/dt is 1.45E-12 Torr/sec. Compared with R05 cell build-up data, the slope order is similar. From RGA data, the residual gas source is mainly from CH4.

Compared the pressure

IG 4

IG 5

IG 6

P UHV Pbuild

R05 cell R05 cell

after ion pump baking R24 cell

2.77E-8 2.05E-5

6.93E-9 2.17E-5

6.00E-9 2.69E-5

5.29E-9 2.00E-5

5.61E-9 2.15E-5

6.19E-9 2.69E-5

7.55E-9 1.08E-7

5.55E-9 8.64E-8

6.03E-9 1.45E-7

Table 1. The pressure before build-up (PUHV) (Pa) and pressure after build-up

time more than 60 hours (Pbuild) (Pa) of R05, R24

P UHV Pbuild P UHV Pbuild

Results and Discussion (3)

11

We found that the PUHV is similar for R05, R24 cell. PUHV of R05 cell is indeed improved after ion pump baking. It results from the decreasing amount of CH4. However, the Pbuild is not improved obviously after ion pump baking. Why ?

Results and Discussion (4)

Calculation of outgassing rate and pumping speed

(V × dP/dt = Δ Q , Δ Q / A= Δ q) (V: ~1 m3) (A: ~5m2)

Table 2. The outgassing rate per unit area(△q) (Pa.m.sec-1) . Pumping speed(S)(L.sec-1)

estimated from equation (4), of R05, R24

IG 4

IG 5

IG 6

△ q S

R05 cell R05 cell

after ion pump baking R24 cell

△ q S △ q S

2.64E-10 1.33

2.85E-10 2.00

3.60E-10 2.63

9.81E-11 1.57

1.06E-10 1.56

1.36E-10 2.20

3.76E-11 1.82

3.12E-11 1.91

4.69E-11 2.23

12

The △q value of R05 cell is improved after ion pump baking but is greater than that of R24 cell. The pumping speed, estimated from eq.(4), is similar for both R05 cell and R24 cell.

Results and Discussion (5)

13

Analyze residual gas with ion pump baking effect

The residual gas analysis

shows that after ion pumps

baking, the amount of CH4 is

obviously decreased and the

amount of Ar is not reduced.

Besides, in order to decrease

the outgassing of argon gas,

the vacuum chambers were

also baked separately.

However, the amount of Ar is

not reduced obviously.

The source of argon residual

gas is still not clear.

R05 cell /

special case

From Y. C. Yang /Vacuum / NSRRC

40 40 16

16

Results and Discussion (5)

0

10

20

30

40

16 1812 132 4

Percen

tag

e (

%)

m / e

percentage

16 1814 15 36 40 4428 32

14

0

10

20

30

40

Per

cent

age

(%)

Percentage

12 132 4

m / e

16 1814 15 36 40 4428 32

R24 cell / general case R05 cell / special case

The RGA is recorded during

pressure build-up period,

shown in figure.

The residual gas proportion

is estimated after build-up

time more than 60 hours.

For R24 cell, the main

residual gas source is from

H2, and CH4.

For R05 cell, the main

residual gas source is from

CH4, and Ar.

Since four ion pumps turned

off for more than 60 hours, it

is inferred that the vacuum

pressure could increase to

~10-7 Pa or ~10-5 Pa, mainly

dependent on proportion of

the amount of argon gas to

total amount of residual gas.

0 200 400 600 800 1000 1200 1400 160010

-12

10-11

10-10

10-9

10-8

10-7

Cu

rren

t (A

)

Build-up Time (s)

mass2

mass4

mass12

mass13

mass14

mass15

mass16

mass18

mass28

mass32

mass36

mass40

mass44

0 200 400 600 800 1000 1200 1400 1600

10-13

10-12

10-11

10-10

10-9

10-8

Cu

rren

t (A

)

Build up Time (sec)

mass2

mass4

mass12

mass13

mass14

mass15

mass16

mass18

mass28

mass32

mass36

mass40

mass44

> 60 h build up time > 60 h build up time

15

Conclusion

Pressure build-up test 1. This paper was focused on the pressure build-up test for 14 m-long

vacuum chambers of Taiwan Photon Source (TPS).

2. As one cell arrived in UHV status, pumped by IP and NEG, the lowest

vacuum pressure can achieve ~10-9 Pa in the assembling laboratory.

3. The pumping speeds were estimated and the composition of

the residual gas is analyzed.

R05 cell (special case) 1. Since four ion pumps turned off for more than 60 hours, the vacuum

pressure could increase to ~10-7 Pa or ~10-5 Pa, mainly dependent on

proportion of the amount of argon gas to total amount of residual gas.

2. The ion pumps and the vacuum chamber were baked separately.

However, the amount of argon residual gas is not reduced obviously.

3. The source of argon residual gas is still not clear.

Acknowledgements

Thanks for assistance and friendship from every member of vacuum group in NSRRC

16

Thank you for your attention.

17