20140401 Accelerator Vacuum at DESY

Accelerator Vacuum Systems at DESY

Part I:

Experiences with the operation of the PETRA III vac uum system

Part II:

Undulator chambers for PETRAIII, FLASH & XFEL

Lutz Lilje, Torsten WohlenbergDESY, 1.4.2014

L. Lilje | Accelerator vacuum systems at DESY | 1.4.2014 | Page 2

Experiences with the Operation of the PETRA III Vac uum System

> PETRA III History

> 1976 built as an electron – positron collider

� 1978 to 1986 in this collider mode.

> 1988 to 2007

� PETRA II was used as a pre-accelerator for the HERA

> 2007 – 2008

� Conversion into a synchrotron light facility.� e+ operation (2009 – 2012)

• 2009 commissioning with beam

• 2010 “friendly users”,

• 2011 regular user operation

• 2012 regular user operation

� e- operation (started Jan 2013)• 2013 regular user operation


PETRA III Layout


PETRA III Future Plans

> PETRA III continues as a 3rd generation synchrotron light source with very high brilliance and very low emittance

> PETRA III Extension

� Currently, two more sectors are being upgraded from old FODO lattice to DBA cells for insertion devices

� In total 10 more experimental stations are being built

� Large user demand

� DORIS III switched off

> Increase availability

� Aimed for 95 %, achieved 94%• Close, but not good enough

• Mainly due to RF system


PETRA Extension: Halls North and East


„Vacuum“ Problems

> All of the subjects are related to the vacuum system

� Some of which are closely related ….

� … more or less in order of appearance

> “Stichabsorber”

> RF contacts

> Laser window

> Undulator

> Cavities

� Visual ports

� Couplers


“Stichabsorber”

> During commissioning sudden increases in pressure in in the new DBA sector

> Investigations show that a flange was too warm

> When beam orbit was slightly pointing upwards no heating observed

> Heating due to synchrotron light from upstream dipole

> Absorber design needs to be modified

ca. 4.5 Watt/mA

Synchrotron light fan can pass below the absorber

Shadow of “Stichabsorber“


“Stichabsorber“ Old design

New design

> Lesson learned (again)

� Beam physicist says: „Beam will always be in nominal orbit.“

� Engineer optimises for lowest power deposition

� Shallow angle solution

� Commissioning will prove physicist wrong

� Mike Seidel in OLAV1 2005

� “→ build your system passively safe if possible; any orbit that circulates will occur!”

Side view


RF-Contacts in RF-shielded Bellows


RF-Contacts in RF-shieldedBellows

> RF contacts on the inside are tricky

� Several tests were done beforehand tomake sure that contacts have contact

> But:

� Only when the RF-shielded bellow isoverextended RF fingers loose contact

> Re-Design needed

� RF-Fingers on the outside

> Limited the current in the 40 Bunchmode to 80 mA until 2012


Laser Window for Diagnostics

>2010 Leak in PETRA old section SWR

>Laser focal point in window plane

>Leak small

�Quick intervention withglue

>Exchange duringregular maintenance


Undulator Crash


Undulator Crash


Undulator Crash

> 2010

> Firmware upgrade to motorcontrol

> Hard end switches not in optimal position

> Chamber was still leak tight!


2011: Undulator Chamber has a dent…


Part of a Film Badge Found

> Counter measure:

> Visual Inspection of all undulatorpoles after maintenace daysbefore machine operation whengaps were opened

> Are there technical solutions tothis elsewhere?


RF Cavities and Couplers

> PETRA III Project re-used HERA- (and PETRA)-style cavities

� 500 MHz Hardware was available

� Best cavities and couplers moved to PETRA

> Problematic

� Original RF design not really for high currents but rather for large voltage

� High bunch charges and HOM issues

� Limiting the 40 bunch operation (sometimes)


Cavities

> Visual ports on cavities for coupler observation (comes next)

> Occurred once in 2011

� Attributed to wrong glas material> Re-occurred when 40 bunch mode

reached 100 mA beginning of 2013

> Size of the port is large enough for HOM RF (1-3 GHz)

> Heating up to 200°C

� Windows rated for 300°C> But when machine operation is

suddenly inhibited cooling rate too fast: >> 3°C/ min

> Implemented Copper mask to shield RF


RF Cavities

> Visual ports on cavities for coupler observation (comes next)

> Occurred once in 2011

� Attributed to wrong glas material> Re-occurred when 40 bunch mode

reached 100 mA beginning of 2013

> Size of the port is large enough for HOM RF (1-3 GHz)

> Heating up to 200°C

� Windows rated for 300°C> But when machine operation is

suddenly inhibited cooling rate too fast: >> 3°C/ min

> Implemented Copper mask to shield RF


RF Couplers


RF Couplers

> Optical sensor shows

� Clear evidence of plasma• Not necessarily a bad thing

� Clear evidence of local heating• Probably field emission

> Old RF system

� Cleaning methods cannot be compared to nowadays standards

� Several surface defects can be observed e.g. particles, drying stains etc.

> Improvement program started

� Dry-ice cleaning of RF components e.g. couplers• Was successfully tested for SRF cavities and normal-conducting RF-Guns

� Tests of freshly etched and rinsed cavities• Application of pure and ultra-pure water standards


END of part 1

Sven Lederer (MVS) Lutz Lilje (MVS) Torsten Wohlenberg (MVS)and many MVS colleagues DESY, HAMBURG

OLAV IV April 01-04, 2014 NSRRC, Hsinchu, Taiwan

Undulator vacuum chambers for PETRAIII,FLASH & XFEL


24Outline� Requirements of the different accelerators for the undulator vacuum chambers� PETRAIII on the example of PU1

� Development of the PU1 vacuum chamber� 3D-model � Realisation� NEG coating not discussed in this presentation

� FLASH on the example of FLASH2� Development of the FLASH2 undulator vacuum chambers� 3D-model� Realisation

� European-XFEL� Development of the European-XFEL undulator vacuum chambers� 3D-model� Special requirements on surface roughness & oxide layer

� Support system for the undulator chambers� Detail of the alignment system

OLAV IV April 01-04, 2014 NSRRC, Hsinchu, Taiwan Undulator chambers for PETRAIII FLASH & XFEL Torsten Wohlenberg MVS DESY, Hamburg


25

Requirements of the different accelerators for the undulator chambers


PETRAIII FLASH1/FLASH2 XFEL

Pressure requirements Average pressure ˂1�10��

mbarNEG coating required

Average pressure ˂2�10��

mbarAverage pressure ˂2�10��

mbar

Beam dynamic requirements Surface roughness & oxide layer„normal“

Surface roughness & oxide layer„high“

Surface roughness & oxide layer„very high“

Magnetic gap Tunable magnetic gap, minimal 9.5-12.5 mm

Fixed magnetic gap of 12 mm (FLASH1)Tunable magnetic gap, minimal 9.0 mm (FLASH2)

Tunable magnetic gap, minimal 10.0 mm

ApertureMinimal wall thickness

Horizontal: 56-57 mmVertical: 7-10.5 mmMin. wall thickness 0.75 +0.025 – 1.0 +0.1 mm

Horizontal: 9.5-15.0 mmVertical: 7.7-9.5 mmMin. wall thickness 0.45±0.02 – 1.0 mm

Horizontal: 15 mmVertical: 8.8 mmMin. wall thickness 0.4 + 0.025 mm

Tolerance of alignment Horizontal:±0.5mmVertical : ±0.1mmAngel: 0.1mm to the magnet pole area

Horizontal:±0.2 mmVertical : ±0.1 mmAngel: 0.05 mm to the magnet pole area

Horizontal:±0.1 mmVertical : ±0.1 mmAngel: 0.05 mm to the magnet pole area

Particle free (ISO5) Not required Required Not required


26PETRAIII undulator vacuum chambers on the example of PU1


� Simulated chamber deformation caused by the pressure difference (C. Martens , DESY, ZM1)

� Final design for the extrusded aluminum profile by MIFA Experience Precision

� Result after several design studies with manufacturers

� Wall thickness 0.7 mm� Deformation 80 µm/side

� Development for PU1

�horizontal width: 57 mm tolerance 0/+0.1

�vertical high: 10.5 mm tolerance: 0/+ 0.15

� chamber height: 12.0 mm tolerance 0/+0.05




� Aluminium welding � Aluminium DN100CF flange, DLC coated

� Vacuum chamber: � PU1 length 5400 mm � NEG coating

� Aircoils

� 3-D Model




� Realisation PU1


29FLASH2 undulator vacuum chambers


� Wall thickness 0.5 mm � deformation 1µm/side

� Development for FLASH2




�vertical high: 7.7 mm tolerance +/- 0.05mm

�horizontal width: 10.0 mm tolerance +/-0.1

� chamber height: 8.6 mm tolerance +/-0.02




�Friction welding flanges transition SS/Al

�Vacuum chamber: FLASH2 length 2618mm

�Aluminium laser welding

�Holes for correction coils

�Holes for cherenkov fibers

�Aluminium laser welding

� 3-D Model




� Realisation


32European-XFEL undulator vacuum chambers


� Wall thickness 0.4 mm

� Deformation is < 50 µm

� Development for European-XFEL




�horizontal width: 15 mm tolerance: 0/+0.1

�vertical high: 8.8 mm tolerance: -0.05/-0.15

� chamber height: 9.6 mm tolerance +0.02/+0.05




Friction welded flanges, transition SS/Al

Water cooling

Cross section of the 5.4 m long undulator chamber

10 pockets for online dosimetry

Picture taken from talk:Beschleunigerbetriebsseminar Grömitz, 18.–21.3.2012 Lars Fröhlich, Elettra–Sincrotrone Trieste

Two wire correctors (inner channels)

� 3-D Model�Vacuum chamber: European-XFEL length 5.4mm




� Roughness & Oxide layer� AFM treatment on a 5 m long test chamber

� Measurement preparation and equipment

Mitutoyo (Surftest SJ-210)

Sketch of sample preparation

Sample for series of measurements




� Roughness & Oxide layer� Result of the AFM treatment on a 5 m long test chamber (Polishing only in one direction!)

� Results point out that it is essential to polish in both directions!

�Target line :80 nm Ra

�Entrance of the chamber

�Center of the chamber

�Exit of the chamber




� Roughness & Oxide layer� Oxide layer research with TEM on AFM polished aluminium samples

after different times at air.� → result shows no growth of the oxide layer after the passivation

�Sample 26 one day at air

�Sample 21 one week at air

�Sample 22 two weeks at air

3-5 nm oxide layer on all samples


37Support system for the undulator vacuum chambers


� Detail of the alignment system� Proof of principle of this alignment concept wasdone at sFlash, FLASH2 and PETRAIII where theundulator gap could be closed to design value:

sFlash 9 mm, FLASH2 9 mm & PETRAIII 12.5 mm

�Horizontal adjustment

�Vertical adjustment�Angular

adjustment

�Undulator vacuum chamber

�PETRAIII

�sFLASH & FLASH2


�End of Part 2

38

OLAV IV Apil 01-04, 2014 NSRRC, Hsinchu, Taiwan Undulator chambers for PETRAIII FLASH & XFEL Torsten Wohlenberg MVS DESY, Hamburg


Summary and Outlook

> PETRA III achieved full beam current of 100 mA in all modes:

� 40, 60, 480, 960 Bunches

> Extension project is ongoing

> Continued work on availability needed

> Undulator chambers for various accelerator applications have been built

� Universal, flexible and precise support system being implemented

> Requirements are demanding and need vigorous control

� Geometry and Alignment

� Surface roughness

� Oxide layer


Thanks for your attention!

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20140401 Accelerator Vacuum at DESY