Storage Ring Components ↓

Absorbers

Intensity Absorber - Photon Shutter

Technical Description

The Absorber serves to absorb the synchrotron radiation and to carry away the related heat capacity of the absorber body by way of water cooling.

The absorber insert consists of

the basic flange (DN 100 CF),
the absorber body,
in standard design made of OFHC copper or Glidcop®,
an OFHC copper coil (6 x 1) vacuum-brazed to the back and serving as water cooling,
-a bar-like support assembly which is atmospherically sealed using a membrane bellows, and
-a pneumatic cylinder equipped with 2 proximity switches used as end switches.

The pneumatic cylinder is double-acting. In case of a loss of media (compressed air, voltage) the absorber moves into the beam path.
The electrical proximity switches can be exchanged against mechanical micro switches.
The positioning and arrangement of the intensity absorber in the front end is made together with a 150l/s ion pump, the all-metal gate valve, a fast-closing valve and a small chamber on a separate steel column with an x, y, z adjusting frame.

Technical Datas

Overall dimensions -Base flange: -Height:	CF 100 ( bigger O.R. ) about 750 mm
Active length in beam direction:	appr. 80 mm
Aperture:	appr. 20 x 10 mm²
Heat load:	appr. 4 kW
Absorber material:	OFHC-Copper or Glidcop^®
Absorber stroke:	50 mm
Cooling water connection:	Swagelok
Cooling water pipe:	tube 6x1, copper
Leakage rate:	<1 x 10^-10mbar • l • s^-1
Compressed air:	6 bar

Radiation Absorber

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Radiation Absorber

Crotch or Photon Absorber

Technical Description

This kind of absorber is located in the crotch part of the dipole chambers. It absorbs a part of the synchrotron radiation power density by about 50W/mm2
(Remark: This value permits the use of OFHC copper as absorber material).
The absorbers for the synchrotron radiation can be also made of GlidCop^® (for higher density). The Photon or Crotch Absorber has a direct water cooling system. They are fitted into an orifice which is connected with the keyhole of the vacuum chamber (see reverse side - figure 1). An ion pump is connected directly under or beside the absorber on the same orifice.
The Cooling is done by four pin holes with a 6x0,5 mm tube for the incoming water. A wire is wound around the inner tube in order to enhance the heat transfer. The water velocity is 3m/l.
The cyclic temperature changes and the corresponding strains lead to fatigue of the material which can lead to failure. In order to reduce the strain the absorber is split into two halves with a comb like structure each with two cooling channels (see reverse side - figure 2). The comb structure of the upper and the lower part fit together with 1 mm separation. Due to an angle between the synchrotron radiation and the normal of the absorber no radiation can pass the absorber. Since the synchrotron radiation now hits alternating small sections of the upper or lower part of the absorber which are slightly separated, the hot sections can expand slightly and thus the maximum stress is reduced [1].

FMB produces two modifications of Crotch Absorber:
- Fixed Absorber (see reverse side - figure 3, the left one),
- Adjustable Absorber (see reverse side - figure 3, the right one).

References
[1] S.Hermle, D.Eilenfeld, E.Huttel, E.Wiedemann,
“Layout of the Absorbers for the Synchrotron Light Source ANKA”, PAC 1999, New York

Figures

Figure 1 Photon Absorber in a Quadrupole Chamber (PSI – SLS)
Figure 2 Splitted Crotch Absorber
Figure 3 Straight Vacuum Chamber Riva- CGM2 incl. two absorbers (PSI – SLS)

Straight Chambers

Narrow Gap Vessels

Technical Description

For the DLS contract a total of 10 aluminium vessels have been manufactured with bimetal CF flanges:

8 pieces of a length of 947mm and
2 pieces of a length of 4900mm.
These vessels have been delivered with exactly fitting bakeout jackets from the company Horst.
In the storage ring these vessels rest on stands. On the top these stands are fitted with an adjustable clamping device where the Al vessel is clamped and held on both outer sides.

Each vessel includes:

1 profile section,
2 CF bimetal flanges,
4 stiffeners,
4 sealing plugs,
4 Swagelok threaded fittings,
1 exactly fitting strong back and
one interior NEG coating.

The actual vessel profile section is an extruded aluminium section with the outer dimensions of 208mm x 20mm.
In the centre there is an elliptical channel of 74mm x 11mm. On the left and right from this ellipse there is a through hole on each side with a diameter of 6mm. These through holes are used for water–cooling the vessel section after installation in the storage ring.
At the section ends these channels are closed using plugs. The required cooling water is passed into the longitudinal channels via 2 additional bore holes each (made from the narrow outer side of the profile section.
The connecting joints are threaded fittings made by SWAGELOK. A flexible Al gasket is used as a sealing.

Bimetal blind flanges made by the company ATLAS are used as connecting flanges.
The flange face of these flanges consists of high–quality stainless steel (316L) and the rear side of an Al alloy (6061–T6) which can be welded well.
Both flange halves are connected via explosion bonding.
Titanium and copper are used as bonding materials between stainless steel and copper.
These bonding materials are used as thin sheets.

Flanges and vessel profile section are welded using HF and TIG welding techniques.
Stiffeners are tack welded between the outer diameter of the flange and the vessel profile section in order to additionally increase stability of the welds.
Additionally it is recommended to perform each transport after mechanical completion by using a strong back which is "made to measure".

This strong back consists of:

two transit blocks each (The transit blocks are two solid Al plates, which are fixed above and below the vessel via form fitting at the two ends of the Al vessel and whose front sides are at the same time mounted against the rear sides of the bimetal flanges. This ensures the perpendicularity of the bimetal flanges towards the vessel axis in both directions at right angles towards the beam axis and prevents an overstressing of the Al weld.) and
a connecting section. Depending on the length of the Al vessel additional folding holders are welded on to this section, which prevent the whole vessel from deforming.
Transit blocks and connecting section form a unity and are screwed with one another.

Interior coating of the Al vessel – NEG (non– evaporable getters) coating (approx. 1µm)

Getters are materials capable of adsorbing gas molecules by chemical forces.
Before NEG– inside coating of the vacuum vessel: It must be cleaned according to a special technology of CERN, to dissolve the native oxide layer completely.
At room temperature NEGs are able to pump most of the gas with exception of rare gases and methane and other light hydrocarbons.

NEG thin films have several advantages comparable to a well–known NEG–strip and pumps:

They trap the gas coming from the substrate materials.
After activation a NEG film is a clean metal surface resulting in a large pumping speed and reducing degassing (both thermal and ion/photon/electron induced).
These NEG– films do not need space, electrical feedthroughs or insulation.

Technical Datas

vessel length:	4900mm (2x) and 947mm (8x) – for DLS
Layer thickness:	approx. 1 µm (variations ±20%) The interior elliptical profile section (74mm x 11mm) has been coated using 3 electrodes simultaneously. The variations in layer thickness result from the respective distances to the electrodes. The resulting layer thickness was substantiated on a test coupon.
Coating company:	SAES Getters in Lainate / Italy
Number of possible activations of the layer:	approx. 20 times