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