PETRA III Vacuum SystemProgress ReportM.Seidel, DESY-MVA
• bakeout times reconsidered
• standard arc (7/8 of ring)
• insertion octant (undulator chambers, SR absorbers, keyhole chambers)
DESY MAC 11/08/2004
Pressure and Conditioning
• pressure is determined by desorption q and pumping speed S’ per length
• desorption is proportional to the photon rate and improves inversely with the dose
'qPS
=
( ) /q n n n nγ γ γ γη∝ ⋅ ∝
DESY MAC 11/08/2004
Required Pressure• assume typical gas composition (<Z>=3.6):
25% CO, 75% H2• inelastic scattering:
• for Ptot = 2·10-9 mbar→ τ = 94 h
• elastic scattering: → τ = 660 h
( )0,
0.695[ ] [ ]ln[ ]
iE i
i
h P pbarX m
τδ
−=
⋅∑
(larger thanTouschek)
DESY MAC 11/08/2004
Required Dose to Achieve This
• desired pressure, pumping speed and photonflux in arc of 4·1017 s-1m-1 result in required desorption coefficient of η < 6·10-6
• this is reached after 50..125 Ah• with average current of 75 mA it takes 700 to
1700 hours of operation• however, after a tenth of this time lifetimes
beyond 5h should be possible already
DESY MAC 11/08/2004
Standard Arcs – Elements between Dipoles
• vertical orbit correction with sextupole → space of correction coil gained for bellows unit
• support of beam pipe at BPM housing; decoupled from quadrupoles
quadrupole
dipole dipole
bellows sextupoleBPM
DESY MAC 11/08/2004
Standard Arc – Chamber Profile•extruded aluminum profile
•120m of prototypes made;
bending tests (200m radius) under way
•cost remarkably low, eg. 4k€ for tooling
DESY MAC 11/08/2004
New and Old Profile
•new profile is tighter
• water cooling both sides
•integrated NEG pumps instead of integrated ion getter pumps
•continuous pumping slot
(old)
DESY MAC 11/08/2004
NEG Pump Design
issue: NEG strip expands during electrical heating and contracts afterwards → risk of electrical shortage to chamber
here: chain of ceramic fixtures, the distance between them is fixed by steel elements; this guarantees an equal distribution of the strip excursions
HOM’s in pump channel: power deposition small; impedance smaller than old chamber with pumping holes
DESY MAC 11/08/2004
Aluminum – Steel JointsUHV joint sample made by US company ATLAS; explosion bonded
• expensive!
• high reliability; applicable for UHV
sample cut under small angle →10x enlargement
DESY MAC 11/08/2004
RF Shielded Bellows
• CuBe fingers sliding on outside of steel cylinder
• water cooled SR absorbers on both sides
• SR shadowing:
step-back
horizontally 7mm, vertically 1mm
DESY MAC 11/08/2004
Bellows Impedance
1500-128anticipated machinebudget
126-0.2200 shielded bellows7mm horiz., 1mm vert.
1290-4200 shielded bellows7mm step-back
444-4312 cavities(7 cell)
kick parameter k┴[V/pC m]
loss parameter k║[V/pC]
component
bellows has cavity-like shape; HOM’s potentially harmful
consider longitudinal and transverse loss factors (R.Wanzenberg)
DESY MAC 11/08/2004
Issue: NEG Strips• planned to use strip ST707: activation at 400°C vs. 800°C(ST701) – reduced mechanical stress
• observation at HERA: significantly reduced pumping speed after ~20 activations; partially loss of NEG material from strip!
• ongoing: quantitative investigation of remaining pumping speed of HERA strips and consultations with company SAES Getters
DESY MAC 11/08/2004
New Octant
• flat stainless steel chambers; 4 Cu absorbers to localize radiation power deposition
• ion-getter/Ti lumped pump units
• steel chambers with integrated NEG pumps
• undulator chambers (probably) simple Al profile with NEG coating (similar to ESRF design)
DESY MAC 11/08/2004
Undulator Chamber• working solution: aluminum chamber with NEG coating; water
cooling; extruded profile; similar to ESRF design• advantages: cheap and simple; even frequent exchanges would be
possible• disadvantages: activation temperature of 200°C is close to
tolerable limit for aluminum alloy
undulator-chamber
(schematic)
DESY MAC 11/08/2004
Steel Keyhole Chamber• wide chamber-> 4mm steel; Cu impossible!
• NEG pump in welded side channel
• produced from steel sheets
DESY MAC 11/08/2004
Issue: Accidental Heating of Steel Chambers by Synch. Rad.
• HERA IR: burned and deformed steel chamber; 4mm wall
• at PETRA better interlock required!
• even tighter interlock needed for undulator beams
inside: steel molten!
DESY MAC 11/08/2004
Absorber Units• massive Cu absorbers, produced by wire EDM and brazing
• cooling from top and bottom
• conceptual design stage, eg. pumping etc. still missing
DESY MAC 11/08/2004
Outlook• arc chamber production starts mid 2005• design of new octant should be finished by fall 2005;
production already started• present activities: detailing of new octant; preparation of
arc production (decision on NEG strip)• large quantity of special components to be designed:
injection section; RF section; diagnostic components; transport lines; collimators→ manpower tight; countermeasures are:
– termed employments on project money– DESY central design group– external companies, drawing offices