Thomas Jefferson National Accelerator Facility Marcy Stutzman

Marcy L. StutzmanThomas Jefferson National Accelerator Facility

P.Adderley, M.Poelker, G.R.MyneniM.Baylac, J.Brittian, J.Clark, J.Grames, J.Hansknecht

Thomas Jefferson National Accelerator Facility Marcy Stutzman

•6 GeV Nuclear PhysicsLaboratory

•3 Experimental Halls

•200 uA, 80% polarized electron beam

•UHV Photoelectron guns

Thomas Jefferson National Accelerator Facility Marcy Stutzman

304 Stainless Steel ChambersPressure ~1e- 11 Torr (Extractor Gauges)100 kV CeramicOpen to beamline during operationDifferential Pumping cans with NEGSGaAs PhotocathodeProcess with Cs and NF3 in chambers

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Quantum Efficiency across cathode after running beam

Cathode lifetime vs. Chamber Pressure

>15.0E-11 Torr

~5.0E-11 Torr

~2.5E-11 Torr

J. Grames Jefferson Lab 2003

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Main Pump

Test Vacuum Chamber

Bake Pump

Ext

ract

or

Spi

nnin

g R

otor

Ext

ract

or Orifice

RG

A

Extractor Gauges Orifice Spinning Rotor Gauge

Thomas Jefferson National Accelerator Facility Marcy Stutzman

APCQ ∆⋅

= AV

tPQ ⋅

∆∆

=

Orifice Method Accumulation Method

•Bake Chamber (250 ºC, 30 hours)•Eliminate Pumping•Track Pressure Rise with Spinning Rotor Gauge

•Calculate Outgassing Rate:

•Bake Chamber (250 ºC, 30 hours)•Equilibrate ~12 hours across orifice•Measure pressures with extractor gauges•Flow Rate through orifice = C·ΔP with C the conductance of the orifice•Calculate Outgassing Rate:

Recommended practices for measuring and reporting outgassing data, P.A.Redhead, JVSTA 20, 1667 (2002)

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Rate of Rise with Spinning Rotor Gaugefor Three Vacuum Chamber Materials

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

3.0E-04

0 20 40 60 80 100

120

140

160

180

200

220

240

260

280

300

320

340

Time (hours)

Pres

sure

(Tor

r) 304 Stainless

6061 Aluminum

316L Stainless

1.26x10-101.96x10-96061-T6 Aluminum

2.16x10-102.46x10-9316L Stainless Steel

1.67x10-101.85x10-9304

Stainless Steel

Pump Pressure

Chamber Pressure

Orifice Measurement Data for Three Vacuum Chamber Materials

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Outgassing Rates for Three Chamber Materials

1.E-13

1.E-12

1.E-11

304 StainlessSteel

316L StainlessSteel

6061-T6 Aluminum

Chamber Material

Out

gass

ing

Rat

e (T

orr*

l/s*c

m^2

)

orificeROR

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Activation protocol check…

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Ion Pump

Test Vacuum Chamber

Bake Pump

Extra

ctor

Spin

ning

R

otor

Extra

ctor

Orifice

RG

A

RG

A Leak Valve

•SAES WP-950 getter cartridges •ST-707 getter material•Leak valve loaded with UHP Hydrogen

Rated Pump Speeds 3x10-6 Torr, 23 ºCHydrogen: 430 L/sOxygen: 280 L/sCO: 170 L/s Nitrogen: 65 L/s

Recommended practices for measuring pumping speeds,M.H.Hablanian, JVSTA 5, 2552 (1987).

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Modified Flowmeter:

Ion Pump

Test Vacuum Chamber

Bake Pump

Extra

ctor

Spin

ning

R

otor

Extra

ctor

Orifice

RG

A

RG

A

Leak Valve

M.H.Hablanian Recommend Procedure for measuring pump speeds, JVSTA, 1987

−

−−

= 1022

011

ppppCS

Orifice Method:

0ppQS−

=

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Extractor Gauge ROR data NEG chamber

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

0.00 20.00 40.00 60.00 80.00 100.00Time (hours)

Pres

sure

(Tor

r)

No Negs

NEG 1 ion 30A

NEG1 Ion 37A

NEG1 turbo

NEG2 bake

NEG2 ion

NEG2 turbo

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Pump Speed vs. Process, Equilibrium Method

0.0056

2.1 2.5 2.2

4.5

9.5

6.7

1.1

0

2

4

6

8

10

12

Empty C

hambe

r

Baked

Ion 30A

Ion 37A

Turbo 3

0ABak

e

Ion 30A

Turbo 3

0A

Pum

p Sp

eed

(L/s

) Older NEG Pair New NEG Pair

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Pump Speed and Pressures (NEG2 baked)

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

0.00 10.00 20.00 30.00 40.00

Time (min)

Pres

sure

(Tor

r)

0

5

10

15

20

25

30

Pum

p Sp

eed

(L/s

)

P2

P1

S

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Ti/Zr/V coating600V, Argon dischargeOrifice measurement for outgassing rate

Uncoated Tube: ~2x10- 12Torr L/s·cm2

Coated Tube: -9x10- 13Torr L/s·cm2

Conclusion: The coating does pump, orifice to ion pump makes pump speed calculation extremely complex.

Thomas Jefferson National Accelerator Facility Marcy Stutzman

2

Process:

•Turbo pump stand•Pump Down for 24 hours•Bake at ~180ºC 24 hours•Pump for 48 more hours•Record pressure

Chamber Pressure after Pumpdown and Bake Process

02E-104E-106E-108E-101E-09

1.2E-091.4E-091.6E-091.8E-09

StainlessSteel

TiN Coating Thin SiO2 Thick SiO2 ExternalSiO2

Pres

sure

(Tor

r)

Methods for Reducing Hydrogen OutgassingC.Dong, P. Mehrotra and G.R.MyneniHydrogen in Materials and Vacuum SystemsAIP Conf.Proc.671:300-306,2003

Thomas Jefferson National Accelerator Facility Marcy Stutzman

Maybe SiO2 ROR data?

Coat inside of chamber with NEG, outside with SiO2, TiN?

Thomas Jefferson National Accelerator Facility Marcy Stutzman

•Outgassing rate is limited not by the material at this level, but rather by the technique that we are using for our bakeouts

•NEGs do reduce ultimate pressure, but measured pump speeds are lower than expected and activation protocol is notyet optimized

•To achieve XHV in our gun chambers, more work towardstechnique, materials, and coatings is still needed