# Presentation: 186924

## Storage Ring Vacuum Systems

- H-C. Hseuh,  C. Foerster, J. Hu, G. Mahler, S. Pjerov, S. Sharma, J. Skaritka, C. Stelmach, ...
- October 10, 2006

## Outline

- Design Principles
- Vacuum Cell Layout
- Cell Chambers and Material - Al
- Chamber Cross Sections and Analysis
- Vacuum Pumping and Pressure Profiles
- Front End Vacuum
- Summary

## Design Principles

- Low outgassing and desorption after in-situ bake and pre-conditioning
- Intercept photons at discrete absorbers
- Located absorbers far away from the source
- Lower power density and simpler cooling
- High effective pumping speed (IP + TSP) at absorber locations

- Low Impedance:
- Beam channel with smooth cross sections
- Minimize no. of tapers, steps, gaps –  low Z
- Minimize no. of holes, slots for pumps and bellows – low Z/n
- Inner wall surface finish to ~ μm

- Adequate Apertures for Beam and Exit Photons
- BSC - 25mm x 70mm
- Chamber cross section precision to ~1 mm
- Chamber temperature stability « 1oC

## Vacuum Cell Layout

- 30 standard cells of ~ 19m eachLSS: 15 x 5m and 15 x 8mIsolatable with 60 gate valves

- 4m

- 3m

- 3m

- 5m

- 4m

- Cell chamber material: extruded aluminum 6063-T5
-      NSLS and APS experience; fabrication cost
-      thermal/electrical conductivity; ease of in-situ baking
- 60 bending chambers of 6**o** each, 3m long
- 90 multipole chambers of 3 different lengths/types
- > 20 day-one LSS chambers of various types
-       extruded Al with same cross sections as cell chambers

- Absorber locations

- FE

## AL-6063 (T5) Extrusion for the Cell Chamber

| Specifics | Al | SST | Cu |
| --- | --- | --- | --- |
| Initial PSD rate | High | Low | Average |
| Mechanical strength | Acceptable | Excellent | Good |
| Thermal expansion | Large | Small | Small |
| Thermal conductivity | Excellent | Poor | Excellent |
| Weldability | Good | Excellent | Good |
| Beam impedance | Low | High | Low |
| Bi-metal flanges | Yes | No | Yes |
| Cooling channels | Extrusion | Brazed | Brazed |
| Fabrication cost | Low | Average | Expensive |
| Ease of in-situ bake | Good | Poor | Good |
| Radiation shielding | Poor | Average | Excellent |

- Comparison of chamber materials

## Fabrication Steps for Cell Aluminum Chambers

- _Extrusion ($):_ only a few available (interested) vendors in the US
-              (due to the large cross sections and required dimensional precision)
-       	➱ > 1 yr to develop the correct parameters for each type
-                   before production can start
- _Stretching_: to straighten and eliminate the waviness of inner surface
- _Roll Bending ($):_ to obtain the correct curvature for bending chambers
- _Machining ($$$):_ ports for beam lines, BPMs, absorbers, pumps, ....
-               profiles at multipole, transitions, ...
- _Cleaning ($):_ to remove surface contaminants and reduce oxide layer
- _Welding ($$):_ photon exit ports, SS-Al bi-metal flanges, etc.
- _Assembly ($$$):_ BPMs, NEG strips, pumps, gauges, absorbers, ....

- (G. Goeppner/E. Trakhtenberg, APS, ANL)

## 3-D Models of Cell Chambers

- Bending chamber, ~ 3m long

- Special Bending chamber for IR lines

- Bending magnet/girder

- #3 Multipole magnets/girder

- Multipole chamber #3, ~ 5m long

## Chamber cross sections

- 3mm wall

- BSC: 25 x 70 mm**2**

- Dipole extruded cross sections

## Chamber cross sections – cont’d

- Multipole chamber extruded cross section

- @ sextupole

- @ quadrupole

- After Machining

- 3.9mm

- 3.2mm

- BSC: 25 x 70 mm**2**

## von Mises stress at sextupole location

- S**M** = 172 MPa
- (Localized)

- S**Y** = 144 MPa for Al 6063-T5
- S**M** (D) = 54 MPa
- S**M** (Q) = 100 MPa

- Chien Pai, C-AD

## Deflection at sextupole location

- D**M** = 0.6mm x 2

- D**M** (Dipole) = 0.36mm x 2
- D**M** (Quad) = 0.57mm x 2

- Chien Pai, C-AD

## UHV Pumping and Pressure Profiles

- P**avg** < 1 nTorr

- In-situ baking of entire cells at 120 C x 40 hrs
-      To reduce thermal outgassing to < 1x10**-12** Torr.l/s/cm**2**
-            Total ring thermal gas load of < 1x10**-**5 Torr.l/s
- Pressure will be dominated by photon stimulated desorption (PSD)
-      # photons* *from BM ~ 1x10**+**21/s ≈ 7x10**-5** Torr.l/s
**       ****   **Assuming η (PSD) = 2x10**-**6 mol/*hv*  for Cu after ∫*hv*  > 1024/m
-      # photons* *from each 7m DW  ~ 6x10**+20**/s
-            with 15% intercepted by the ring absorber **➱** 7x10**-6** Torr.l/s
- NEG strips ~ 1,400 m @ > 100 l/s/m for active gases
-      Reside in ante-chambers as in APS
-      Pump thru the photon slots ( C = ~ 200 l/s/m)
- Ion pumps and TSP of ~ 500 l/s at absorbers
-      5 IP/TSP per cell + 2 for each ID location

## PSD Yield versus Photon Dosage

- measured at NSLS U9A & X28 beam lines

-  C. Foerster, et.al,
- J. Vac Sci. Technol. A14, 1273(1996).

-  C. Foerster, et.al,
- J. Vac Sci. Technol. A19, 1652(2001).

- Cu

- Al

- ~ 100A.hr at NSLS

## Preliminary

- Pressure Profiles (BM only) with Various Pumping Schemes

- By E. Hu & F. Makahleh

- Using Molflow and VacCal codes

- P**avg** ~ 1.5 nTorr

- P**avg** ~ 0.3± 0.1 nTorr

- Distributed NEG strips are critical to achieve low P**avg**!

**Preliminary**

## Preliminary

- Pressure Profiles with and w/o Damping Wiggler Radiation

- By E. Hu & F. Makahleh

- P**avg** ~ 0.27 nTorr

- P**avg** ~ 0.3 nTorr

- Absorber

- IP/TSP

**Preliminary**

## Beam Line Front End Vacuum

- Typical layout of Day 1 front end w/o beam line.

- Pressure of a few nTorr to protect the UHV SR vacuum
-       from HV beam line with window or differential pumping
- Entire FE to be bakeable to 200 C (all metal, UHV material, etc)
- IP/TSP combination (same as SR) at high heat load components

**PS: **photon shutter** **
**BS: **Bremsstrahlung beam stop
**IP/TSP:**** **ion pump/titanium sublimation pump
**GV:**** **gate valve

**GV**

**BS**

**PS**

**IP/TSP**

- Front end design depends on type of radiation source (BM or ID)
-       base on experience at NSLS and APS
- Details are being developed with the beam line determination

- _Front End Vacuum Systems_

## Typical layout of hard/soft x-ray beam line front end.

**IP/TSP**

**GV**

**BPM**

**BPM**

**SS x 2**

**CO**

**PM**

**PS**

**IP/TSP**

**GV**

**FV**

**BDA**

**PM: **photon mask**;**** CO: **collimator;** PS: **photon shutter;** BDA: **beam defining aperture;** SS: **safety shutter

- GV**: **gate valve; FV**: **fast valve;
- IP/TSP**: **ion pump and titanium sublimation pump

**IP/TSP**

## Major Goals for FY07 and FY08:

- Detail design of cell chambers and absorbers
- Fabricate or acquire (from APS?) a few prototype cell chambers
- Learn and develop expertise in NSLS-2 chamber fabrication
-        Establish formal collaboration with APS colleagues
-        Work with potential extrusion vendors ASAP
-        Refine the fabrication technique to meet the specifications
- Perform mechanical and vacuum evaluation on prototype chambers
-        Dimensional precision, support, alignment
-        NEG strip supports and installation
-        Vacuum performance
-        In-situ baking, NEG activation

## Summary

- Preliminary layout of cell chambers is progressing well
-         Improvements are made together with the lattice
- Stress and deflection of chambers at multipole locations are acceptable
- Detail chamber design can be started
- Ray tracing of SR fan continues to optimize the absorber design
- Simulation of the pressure profiles has started.
-         Including the PSD gas load from ID devices.
-         To be refined with the final chamber/absorber design
-         Pressure of < 1 nTorr is achievable with present pumping scheme
- Need to collaborate with APS colleagues on chamber fabrication
- Need to work with extrusion vendors soon