Slotfinger superconducting structure with RF focusing

1
Slot-finger superconducting structure with RF
focusing

• Yu. Senichev,
• IKP, FZJ

2
Supposed Scheme of HIPPI

• from JRA3 in the CARE proposal Version 26/09/2003
  with modification in annual report 2004

3
At present three candidates are considered in the
energy range W3-10 MeV

• Super-conducting CH-DTL (Frankfurt Uni.)
• based on TE211 mode
• with external triplet system and 10ß? focusing
  period length
• with growing phase velocity
• Normal-conducting RFQ-DTL (IHEP)
• based on TE111 mode
• with RF focusing
• with growing phase velocity
• Super-conducting Spoke cavity(FZJ,CEA)
• based on TE211 mode
• with external focusing

4
The type of structure

• Super-conducting
• higher efficiency
• higher accelerating gradient in cavity
• no requirement to shunt impedance
• but requires
• cryo-system
• Lorentz force detuning
• external quadrupoles (or strong solenoide)
• transition between the warmed-cold equipments
  decreases real accelerating gradient

5
The fundamental mode

• TM010 mode
• no accelerating field variation along cavity
• easily tuning
• TE111, or TE211 mode
• - quasi-electrodynamic potential

6
The transverse motion

• Focusing elements inside cryo-module
• larger acceptance
• higher current limit
• shorter drift space
• but
• requires strong field solenoide 10 T
• complicater system

• Focusing elements outside cryo-module
• simpler focusing system
• but
• smaller acceptance
• lower current limit
• additional place between cavities

7
Longitudinal motion parametric resonance
3.0 MeV ltkinetic energy of protonlt20 MeV.
8
RF defocusing

therefore
and defocusing kick
for initial energy 5-10 MeV the defocusing kick
17 T x Lcavity
9
Main reasons, decreasing the longitudinal and
transverse acceptances of SC accelerator

• Parametric resonances
• Long focusing period
• RF defocusing in transverse planes

10
New method of RF defocusing compensation
11
New method of RF defocusing compensation
12
The slot structure
13
The slot structure highest modes
14
The slot structure fundamental mode
The longitudinal component of the electrical
field in the center of the accelerating gap in
the slot and spoke resonators at Epeak40 MV/m
15
The slot structure focusing component
16
The slot structure field distribution
17
The slot structure quadrupole component
Now the field equation is
The average meaning of the slot function is
The motion equation in the slot structure is
18
The slot structure geometry optimization
Electrical field
Magnetic field
19
The slot structure geometry optimization
20
The slot structure comparison with spoke
CH-DTL
Slot structure
21
The slot-finger structure
22
The slot-finger structure highest modes
23
The slot-finger structure field distribution
24
The slot-finger structure flatness
Flatness
25
The slot-finger structure lattice
Three options for the RF and the slot gradient
functions
26
The slot-finger structure lattice
FOOD lattice
FOODDOOF lattice
where refraction angle is
27
The slot-finger structure
Longitudinal-transverse coupling resonance
28
The slot-finger structure
Longitudinal-transverse coupling resonance with
phase shift
29
The slot-finger structure
The family- structure resonances
Nf- number of focusing period with similar
cavities
30
The slot and slot-finger structureBeam dynamics

• the transverse motion equation taking into
  account the sliding factor caused by constant
  geometry in families
• the motion equation in the slot and the
  slot-finger structures
• the matrix formalism applied to the slot-finger
  rotated lattice
• the family structure resonances theory

31
The slot and slot-finger structurecavity features

• due to the geometrical symmetry of resonator the
  neighbour mode TE212 is removed
• due the TE211 choice the electrodes are
  transparent for the cooling liquid
• due to the lower potential between the extreme
  electrodes and the cavity wall we have the higher
  gradient in the central cells
• due to the rotation of every second cavity we
  provide the proper lattice FOODDOF
• due to the slots we decrease the RF defocusing

32
Conclusion

• We have developed the slot with and without
  finger structure based on the TE211 mode
• In comparison with the spoke it gives additional
  focusing and the technology is expected to be
  easier
• The slot-finger structure can be used in the
  range of 3-50 MeV
• The slot structure can be continued up to the
  high energy SC part
• We have investigated the beam dynamics and
  electrodynamics in the slot-finger structure
• We have analized the possible resonances in the
  slot-finger structure
• The slot-finger structure can be one of the
  candidates for the Low energy part of HIPPI

33
The slot structure
TM01 mode
What is common between the wave guide with disc
and the jungle gym guide?
TM01 mode