PowerPoint Prsentation des FZ Rossendorf

1
Experiences with the TESLA cavities in
cw-operation at ELBE P.Michel, A.Büchner
,H.Büttig, M.Justus, U.Lehnert, C.Schneider,
G.Staats and J.Teichert, Institut of Radiation
Physics Forschungszentrum Dresden-Rossendorf
e.V., 01314 Dresden

• Introduction to ELBE beam time statistics
• ELBE cw modul
• Results experiences
• intrinsic Q-factor
• field emission cavity processing with
  pulsed RF
• microphonics phase jitter
• energy drift problem
• HOM damping
• Conclusions

2
(No Transcript)
3
door knob
4
ELBE statistics
Beam time distribution at present 31
Bremsstrahlung 10 Channeling 34 FEL 25 Machine
Development What users would like to have cw
beam / pulsed beam 83 Energy 5.34 MeV
..more!! Current nA..1 mAmore!!
Bremsstr. Chann. Rad.FEL
Bremsstr.Channeling Rad.
Test Operation
3 shift operation
5
Some general statements
Cold compressors helium plant (220 W _at_ 1.8 ,
Linde) works stable Warm up cleaning after 3
month operation increase of He flow adjustment
to CC-characteristics heaters in
cryomodules RF couplers modified for cw
operation work well implementation of window
diagnostics (pressure, temperature,
sparks) setting proper Interlock thresholds No
problems on tuning system were observed no
tuning necessary if He-pressure is kept
stable no fast tuning correction is needed for
pulsed RF operation
6
Q-factor
after assembly and 4 years operation
before assembly (2000)
Maximum energy _at_ ELBE 35 MeV (design
value 40)
7
Field emission

• Limitation of gradient due to field emission
• C2 particularly problematic

8
Higher energy by RF pulsing
Macro pulse
Phase control
Amplitude control
Pickup signal
RF ramp
Beam on
11 ms
0-25 ms 1-25Hz Dmax 63 (beam)
Maximum energy in RF pulsed mode 48 MeV _at_ D1
9
Improving of max. gradient by pulsed RF processing
RF processing procedure 11ms(ramp)8ms(stable) _at_
10Hz 5 h _at_ 12,5 MV/m 5 h _at_ 13,5 MV/m 7 h _at_ 14
MV/m
10
Long-term behaviour ??
11
Interaction between two cavities ??
strong correlation observed !
source-amplifier effect
12
Microphonics
Modul 1
Modul 2

• Differences between modules 1 and 2
• Origin of most lines is unclear
• Effect on phase jitter ???

13
Phase jitter

• Real phase jitter divide by control loop
  factor (70) lt 0.1 deg
• Origin of the differences between the modules
  ????

14
Energy drift

• Beam energy drifts up over hours after switching
  on of RF Monday morning user run begin
  delayed
• Energy drift depends on gradient unstable
  beam energy after each energy change

15
causes of energy drift ?

• Energy drift is correlated to RF power
• field emission drift
• Pickup signal remains constant
• no (very small) temperature rise
• on pick up antenna
• HOM-coupler temperatures
• rise with RF power but the
• time scales are quite different
• Field degradation at pickup
• due to a temperature rise of
• the HOM coupler ??
• better cooling of HOM coupler ???

16
HOM coupler
17
HOM coupler temperature
No superconductivity even at RF off
18
Compensation of energy drift

• Measurement of beam position in
• dispersive sections by stripline BPMs
• Control of one gradient to keep
• energy constant
• Using optimized PID controller

0,1
19
HOM damping
Beam current 240µA cw
20
Damped HOM power
Damped HOM power of dipol modes lt 100mW
21
Conclusion

• TESLA cavities work successfully in cw mode for
  more than 4 years
• gradient in cw mode is limited to lt 10MV/m
  (field emission)
• RF trips due to microfonics _at_ 10MV/m
• there are not understood differences in
  microphonics between modules 1 2
• energy drifts after RF switch on (energy
  stabilisation)
• HOM couplers are not sufficiently cooled
• damped HOM power _at_ ELBE ist low (do we need HOM
  couplers at all ?)

22
Acknowledgment
FZ Dresden J. Claussner, B. Eppendorfer, J.
Erber, M. Freitag, F. Gabriel, F. Herbrand, R.
Jainsch, D. Pröhl, B. Reppe, A. Schamlott, R.
Schlenk, Ch. Schneider, R. Schurig, J. Stephan,
J. Voigtländer, A. Winter, U. Wünsche, B.
Wustmann DESY Hamburg, HEPL Stanford, ACCEL
23
Radiation Source ELBE
superconducting Electron Linac
of
high Brilliance and low Emittance
nuclear spectroscopy nuclear astro physics
?-radiation 0 20 MeV
radiobiology metal physics
X-rays 10 100 keV
Electrons 40 MeV 1 mA cw
semiconductor physics radio chemistry biophysics
IR-radiation 3 150 µm
transmutation research material research
neutrons 0 30 MeV
semiconductor physics defects in materials
positrons 0 30 keV
24
ELBE CW-Linac