CLIC Workshop 2014: Low Emittance Rings experimental program
CLIC DR STRIPLINE KICKER DESIGN AND DEVELOPMENT
C. Belver-Aguilar (IFIC)
On behalf of: A. Faus-Golfe (IFIC), F. Toral, M.J. Barnes (CERN)
http://gap.ific.uv.es
KICKER TECHNOLOGY AND PARAMETER CHOICES
PARAMETERS FOR THE STRIPLINES OF THE EXTRACTION KICKER OF THE
DAMPING RINGS
Characteristic impedance 50 Ω
Field inhomogeneity (%) [CLIC: 1mm radius] ± 0.01
Longitudinal beam coupling impedance (Ω per turn) < 0.05
Transverse beam coupling impedance (kΩ/m) < 200
FEEDTHROUGH TO PULSER (positive voltage input)
FEEDTHROUGH TO PULSER (negative voltage input)
FEEDTHROUGH TO LOAD
FEEDTHROUGH TO LOAD
BEAM
MAGNETIC FIELD
ELECTRIC FIELD
qEcEcEqF
BvEqF
2
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STRIPLINE KICKER OPERATION
ODD MODE: The electric field lines have an odd
symmetry about the centre line, and a voltage null exists between the two electrodes.
There is a virtual ground plane midway between the electrodes (capacitance = 2C12)
The effective capacitance between an electrode and ground is .
EVEN MODE: The two electrodes are at the same
potential, so there is no charge stored in the capacitance between them.
The resulting capacitance of either electrode to ground is .
COUPLED LINES → TWO OPERATION MODES: ODD AND EVEN MODE
Each mode has its own electromagnetic field pattern and its own characteristic impedance:
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HFSS SIMULATIONS
It is confirmed that a small stripline beam pipe radius results in closer values of even and odd mode characteristic impedance.
The even mode characteristic impedance of striplines is always higher than the odd mode.
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STRIPLINES GEOMETRY CHOICE
FLAT ELECTRODE
HALFMOON ELECTRODE
Matching characteristic impedances
Field homogeneity
Signal transmission
Settling time
Untapered longitudinal beam coupling impedance
Untapered transverse beam coupling impedance
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COMPONENTS CHOICE: ELECTRODE SUPPORTS In order to ensure the alignment of the electrodes along their entire length (1.639 m),
they are fixed outside the aperture by using four equally-spaced Macor rings, of 10 mm length each.
Once the electrodes are aligned and fixed to the Macor rings, this assembly is placed inside the stainless steel tube, and its angular position is guaranteed by a pin embedded in the striplines beam pipe wall.
The number of Macor rings and their length were selected by studying the mechanical requirements and the impedance mismatch introduced by the rings.
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Geometric parameters: = 1,8 rad = 1,7 m = 20 mm
BEAM COUPLING IMPEDANCE: LOW FREQUENCY STUDY
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At low frequencies:
Longitudinal impedance per harmonic:
Transverse impedance:
MATERIAL AND COMPONENTS CHOICES
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The beam pipe housing the stripline electrodes is a stainless steel tube of 1.712 m length. The internal diameter of the tube is 40,5 ± 0,2 mm.
Aluminium has been chosen for the electrodes, because it is relatively easy to achieve the tight tolerances required during manufacturing.
The electrode supports will be manufactured using Macor, which is a machinable glass ceramic.
All the materials and components chosen, such as feedthroughs, are compatible with ultra-high vacuum, of the order of 10-10 mbar.
FIRST TESTS AT CERN
S11 PARAMETER
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The frequency between peaks is ≈90 MHz, which corresponds to the two-way delay of the electrodes.
The electrode supports (Macor rings) increase the magnitude of the reflection parameter starting from 300 MHz, of every third peak.
The separation between these maxima corresponds to the distance, there and back, between the equally-spaced Macor rings.
ONGOING STUDIES: ELECTRODE HEATING
There are two ways of heating the electrodes:
- With the driving pulse: it is a priory not a problem
- With the beam
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Strategy:
1) Simulations of wake impedance with beam: get loss factor;
2) Eigenmode simulation to get the field distribution of losses;
3) Input power and field distribution and get temperature distribution.
ONGOING STUDIES: ELECTRODE HEATING
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Power deposition in the electrodes for the ALBA beam (T. Guenzel) < 1 W
U. Wienands, et al. (SLAC), High-Temperature Kicker Electrodes for High-Beam-Current Operation of PEP II. EPAC 2004.
𝑇 4=𝑃
𝜎 𝐴𝑒𝜀𝑒𝑓𝑓+(𝑇 ¿¿4 )𝑎𝑚𝑏¿ 𝜀𝑒𝑓𝑓=
𝜀𝑒𝜀𝑏𝑝
𝜀𝑏𝑝+3/2 𝐴𝑒
𝐴𝑏𝑝(𝜀𝑒 (1−𝜀𝑏𝑝 ))
(aluminium not polished)(stainless steel)
𝜀𝑒𝑓𝑓 (𝜀𝑏𝑝=0.6 )=0.07𝑇 (1𝑊 )=351𝐾=78
For the longitudinal expansion of the striplines due to heating, this temperature is not expected to be a problem.
FUTURE BEAM TESTS
1) Striplines not used as a extraction device and without inductive adder Longitudinal and transverse beam coupling impedance
2) Striplines not used as extraction device and with inductive adder Field inhomogeneity Pulse shape and repeatability Long term reliability of the system
3) Once long-term reliability is demonstrated: possible use as extraction device
Verification of the stripline dimensions.
Vacuum compatibility.
High voltage performance.
Longitudinal and transverse beam coupling impedance measurements..
FUTURE TESTS WITHOUT BEAM
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SUMMARY
The stripline design provides the performance specified for the extraction kicker of the CLIC DRs: excellent field homogeneity, good power transmission and reasonable broadband beam coupling impedance.
The stripline design has been carried out by using analytical approximations and simulations to optimize the stripline geometry.
Beam coupling impedance has been studied both analitically and with CST simulations, only for a low frequencies. The behavior of the kicker at high frequencies is an open question to be studied.
A prototype of the extraction stripline kicker for the CLIC DR has been manufactured by Trinos Vacuum Projects (Valencia, Spain).
Losses due to the circulating beam are presently being studied.
Laboratory tests have commenced at CERN labs. Results for the reflection parameter S11 match quite well with the results predicted by the simulations. Other laboratory tests will be done in the next months.
The stripline and the inductive adder will be finally tested separately and jointly with beam.
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