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AbstractStorage Ring Vacuum and Interface to Magnets
Hsiao-chaun Hseuh, NSLS-II Project
This presentation provided a quick overview of the storage ring vacuum system for the NSLS II project. A typical cell layout was detailed including the various cross section shapes and materials, valve locations and types as well as the pumps and instrumentation used. In addition, the types and locations of the various photon absorbers and chamber interconnects were presented. The second half of the talk focused on interface between the various storage ring magnets and the vacuum chambers. Most of the problems encountered were caused by the lack of consistency in the coil shape and the positioning of the coils on the yokes. Providing the vendors with 'go-gauges' earlier in the project could have prevented some of the troubles we encountered. The importance of collaboration and communication between the various groups as well technicians and engineers was highlighted. Finally, the limitation on the extraction of ID and bending magnet fans due to the magnet dimensions as discussed. *Work performed under auspices of the United States Department of Energy, under contract DE-AC02-98CH10886
Storage Ring Vacuum and Interface to Magnets
April 11th, 2012Prepared by: Charles Hetzel
Storage Ring Vacuum and Interface to Magnets
Presented by: Hsiao-Chaun Hseuh Prepared by: Charles Hetzel
Magnet WorkshopApril 11 – 12, 2012
SR Cell Layout
Vacuum System Details
Chamber-Magnet Clearance
Collaboration and Communication
Specification
1- Accelerator Tunnel
2- Experimental Floor
3 - 200 MeV LINAC
4 - 3 GeV Booster (C=158 m)
5 - RF Building, liquid He Plant
6 - Service Buildings
1
2
3
4
56
6
6 6
6
Nominal energy: 3 GeV
Nominal current: 500 mA
30 cells in 5 pentants
Ring circumference: 792 m
G3Dipole G4
Multipole G5Dipole
G2Multipole
G6Multipole
ID photon extraction
3PW photon extraction
3 pole wiggler (3PW)
Each 19-m cell (GV to GV) consists of 5 individual magnet/chamber girders. 3 focusing and 2 bending segments. With RF gate valves at both ends of the cell.
Photon extraction takes place at G4 and G6. Each cell is in-situ bakeable to > 130oC Design pressure: < 1x10-9 Torr at 500 mA.
Fast corrector andRF gate valve
Fast corrector
Fast corrector andRF gate valve
MM
MD
DS
S FCFC
FC
Multipole cross section Dipole cross sectionFast corrector
S4A/S5A cross section
ID beam lineFront End
BM beam line
• 90 multipole aluminum chambers, 3.7 – 4.5 m long• 60 dipole aluminum chambers, 3 m long• 60 short/narrow aluminum chambers - S4A, S5A• 90 fast corrector inconel chambers - FC
BM beam lineDipole
Multipole
ID/3PW fans
All metal RF gate valves isolate cells and straights. Double position indicators. Radiation resistant and bakeable. Large RF gate valves to isolate SC cavities.
All metal gate valves at injectors and front ends.
Right angle valves Roughing ports. Vacuum gauge/RGA isolation.
DN100RF gate valve
60 units
All metal gate valve~ 40 units
Right angle valve
200 l/s ion pump with TSP cartridgeand roughing valve
100 l/s ion pumpwith TSP cartridge
NEG strips in ante-chamber
Instrumentation located at dipole chambers.
CCG and RGA at G3
CCG and TCG at G5
Gauge tree with isolation valve.
Typical RGA scan
RGA trend during bakeout
Flange absorber21mm(V) X 64mm(H)< 200 W (< 16 W/mm2)
Absorbers intercept unused dipole radiation.
Protect downstream flanges and bellows
All absorbers are made of GlidCop Al15.
Stick absorber, X = 22 & 25mm< 700W (< 5 W/mm2)< 130°C, Tube < 119°C
Crotch absorber, X = +21mm< 1800W (< 57 W/mm2)
GlidCop < 180°C, Tube < 127°C
Requirements: Misalignment: +/- 2 mm Stroke: +10/-15 mm Angular deviation: +/-10 mrad Low impedance
GlidCop fingers
Finger retainer
Bellows weldment
Contact springsInconel 718 (w Ag)
Stainless Sleeve(w Ag)
Water cooled flange
Coil spring(Be-Cu)
inconel springs
GlidCop fingersStainless sleeve
Multipole cross section Dipole cross section
Multipole Chamber in Sextupole
MM
MD
DS
S FF
F
Grooves are machined for magnet poles
Chamber-Magnet pole clearance - ≧2mm Not a lot when you consider:
Extrusion shape tolerance. Bow and twist. Distortion due to machining. Machining tolerance. Positioning according to BPM.
Grooves were machined to accommodate magnet poles for 2mm clearance But coil dimensions are not well controlled which caused interference.
Current designShould have coil-chamber clearance of 4mm.Machine grooves for coil clearance? Additional cost Chamber stability under vacuum
Clearance gauges should have been provided to manufacturers at the prototype stage.
Clearance check should have been added to the pre-ship check list for first articles.Centering disk is required to ensure the profile is centered on pole tips. No centering disk = uneven gap
With centering disk = even gap
Early and extensive collaboration with other groups. Chamber design is driven by AP, Magnets, Diag., etc. Changes in BPM and mounting resulted in re-development of extrusion (> 1 yr). Some chamber materials were changed
RF bellows for slow correctors S4A material development (In SS Al)⇒ ⇒ Inconel for FC chambers
RF shielding was added for BPM rogue modes. Keep communication lines open
Attend other system meetings when possible. 3-D modeling can’t identified interference during assembly
Difficult to replace BPM buttons on girders Difficult to assemble bellows due to photon extraction pipes
Significant impact to vacuum chambers due to small changes in magnets. Increase in quadrupole length – 6 completed chambers were re-machined! Oversized coils in 90 mm dipoles – re-design chamber ports and stands
Current cross section
Original cross section
Pro-active communication and visits with manufacturers. Establish relations with potential manufacturers as early as possible. Visits early or before contracts are awarded can be very valuable
Is this allowed? Encourage manufacturers to become more than manufacturers.
Ask manufacturer inputs to improve design and fabrication methods Lack of quality control at some manufacturers – bi-metal flanges!
Close interaction between engineers and technicians. Develop required tooling as soon as possible. Use feedback from techs to improve and simplify the design and/or the fixtures. Reference drawings are more useful to techs than a stack of engineering drawings. Engineers should work through first few assemblies with technicians.
Establish a clear and complete set of specifications early on. These can drive fundamental choices that can’t be changed. i.e. comprehensive ray tracings early on for all possible insertion
devices and beam positions to define Geometric envelope vs. beam acceptance for SRP Protection of vacuum components from large beam deviation Allowable current without active interlock during commissioning
Maximum photon extraction openings are limited by the outboard dimensions of the magnets
QM2: < - 2 mr for ID fan QL2/QH2: < - 5 mr for BM fan
QM2
QL2