SRF Work Packages

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SRF Work Packages
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Accelerating RF Cavity HOM ? BPM

• Naturally narrow band cavity QL 104 , ?? 1
  µs
• single bunch,
• but not bunch to bunch BPM

Centering accuracy and BPM resolution better
than 50 µm (TTF, 2004)
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1) Measurement of cavity alignment in the
cryomodule

• Measuring the Cavity misalignment in Cryomodule
• Experiment performed last week at TTF module 4
  (ACC4)
• (N. Baboi, J. Frisch, L. Hendrikson, R.
  Paparella, et al.)
• Accelerating gradients set to zero in all 8
  cavities
• Reference straight trajectory across the module
  set by 2 BPMs on both sides of the module
• Modes used TE1116, TE1117, TM1105, TM1106
• PRELIMINARY RESULTS ( problems of reproducibilty
  of HOM center reconstruction w.r.t. steering
  ranges !! )

4
1) Monitor cavity alignment in the cryomodule

• PRELIMINARY RESULTS ( problems of reproducibilty
  of HOM center reconstruction w.r.t. steering
  ranges !! )

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2) Inta-cavity Bean Position Monitor
Angular scan resolution and accuracy lt 50 µrad
Relative position resolution 4 µm (cf. M. Ross
and J. Frisch).
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3) Trapped modes

• HOM measurements of beam excited trapped mode was
  successfully applied to
• The detection of the 2.6 GHz dipole mode (Qext
  106)
• The qualification of superstructures
• It will be necessary if for the qualification of
  Low Loss and Reentrant cavity types at SMTF
  and STF.

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Two Challenges for HOM-BPM
I) Mode to mode systematics em. centre and
polarisation
Systematic center position offset 100 µm (M.
Dohlus)
last 2 columns reversed !!
Mode center spread 100 µm (TTF measurements,
2004)
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Two Challenges for HOM-BPM
II) Measuring the Pitch of the fondamental
mode The pitch angle between the 1.3 GHz
accelerating mode and the beam trajectory (200
µrad) is the main cause of songle bunch emittance
growth in the linac.

• Can one measure it through the HOM couplers ?
• other monopole modes of the 1st passband through
  the 2 ports ??
• systmetics of the dipole mode vs. 1.3 GHz mode
  pitchs ??

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HOM-BPM Programme

• Thesis of Rita Paparella (Saclay-DESY) at Orsay
  University (Oct. 2003 Sept. 2006)
• The 40 cavities of TTF will be equipped with the
  SLAC electronics.
• Use for the ILC much debatted question 36,
  Cost vs. Performance ?

• The association to CARE will allow
• 3-6 months extension of Ritas PhD contract (6
  month delay in the thesis program)
• Participation of Claire Simon (CARE/SRF temp
  stall on WP11/BPM) to the test and commissioning
  of the SLAC electronics at SLAC (1 month) and at
  DESY
• Scientific cross-benefit CARE-ILC to the debate
  on HOM monitors

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HOM-BPM Programme

• The 40 cavities of TTF will be equipped with the
  SLAC electronics.

Project Cost and Schedule Table 1 TTF VUV-FEL
HOM BPM electronics cost.
The system will be delivered before October 31,
2005. At that time, the group will work at DESY
to commission the system using the TTF beam. The
prototype cycle will be complete July 31, 2005.
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HOM-BPM Programme

• The 40 cavities of TTF will be equipped with the
  SLAC electronics.

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New BPM mechanics

• New design of the cavity BPM ( For the cleaning,
  12 holes of diameter 5mm have to be added)

• Resonant modes with the new design (simulated
  with HFSS)

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Cold Re-entrant BPM
Linearity and Centering Accuracy
New design
Old design
Voltage ?/S a.u
40 µm
Voltage ?/S a.u
Position of the beam (mm)
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SRF/WP1/BPM Planning

• Sept. 05 - Dec. 05 Fabrication of the 1st BPM
  cavity (TTF room temperature).
• Oct.05 Test and commisioning of the old type
  BPM in ACC1
• Oct. 05 - Jan. 06 Fabrication of the 2nd BPM
  cavity (TTF cryogenic temperature).
• Jan. 06 RF tests with beam at DESY
  (installation of the BPM cavity need an
  oscilloscope with a bandwidth gt2 GHz).
• Feb.06 - Apr. 06 Validation of the RF board
  Programming and validation of the digital
  electronics.
• May 06 - June 06 Tests at DESY (2 weeks) on the
  cavity which is at room temperature with its
  electronics but without control-command
  interface. The tests will be done with
  displacement of the beam to know the noise, the
  dynamic range and do the calibration of this
  system.
• Feb. 06 - Sept. 06 Installation and preparation
  of the cold BPM cavity.
• Oct. 06 Tests of the cold cavity with the beam
  and electronics without the control-command
  interface.
• Nov. 06 - Feb. 07 Programming of the
  control-command interface.
• March 07 Tests of the cold cavity and its
  electronics.