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