Particularities of normal conducting
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Particularities of normal conducting L-band deflecting cavities Valentin Paramonov , Institute for Nuclear Reseach of the RAS, 117312 Moscow, Russia. General remarks.

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Particularities of normal conducting l band deflecting cavities valentin paramonov

Particularities of normal conducting

L-band deflecting cavities

Valentin Paramonov,

Institute for Nuclear Reseach of the RAS,

117312 Moscow, Russia


Particularities of normal conducting l band deflecting cavities valentin paramonov

General remarks

1. In S-band frequency range Normal Conducting (NC) structures operating both in Traveling Wave (TW) [SLAC, CERN] and in Standing Wave [SPARC] mode are known. Structure base is Disk Loaded Waveguide (DLW).

2. For NC structures the L-band frequency range is near the border between TW and SW mode of operation, (in the domain of SW influence).

TW operation requires too much RF power.

2. SW operation – multi cell structure with operating p-mode for RF efficiency.

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Particularities of normal conducting l band deflecting cavities valentin paramonov

SW operation, efficiency vs. stability (DLW)

Efficiency Stability

DLW practically has just one degree of freedom – aperture radius Ra. Both Rsh and kc are defined by Ra value, kc increases with Ra increasing , Rsh decreases.

Deflection Coupling

H

E

Even in S-band range only short deflecting cavities are known (N=5) [D. Alesini et al, PAC 07; P. Craievich et al., PAC 09] due to stability limitation.

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


Particularities of normal conducting l band deflecting cavities valentin paramonov

S-band SW operation.

With lower frequency Rsh reduces, but Ra is already small ....

Let us decouple functions.

E-type

Deflection Coupling

H-type

V. Paramonov et al., Linac 06

E field H field

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


Particularities of normal conducting l band deflecting cavities valentin paramonov

Field distributions along axis

In the deflection participate transversal components both from electric and magnetic field.

In E-type DLW transversal components work in phase,

not so inH-type … Nevertheless…

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


Particularities of normal conducting l band deflecting cavities valentin paramonov

RF parameters

E type

H type

Rsh ~ 1/Ra

For L-band H type deflector has higher Rsh, higher coupling, but higher Esmax/E0. In last parameter it is not optimized finally.

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


Particularities of normal conducting l band deflecting cavities valentin paramonov

Aberrations

Free from aberration is just DLW (b =1) in lower HEM passband. Any deterioration of rotational symmetry automatically leads to aberrations.

Dependence of deflection in x-direction on the y position is dE0 ~ y2.

Depending on Ra value, dE0/E0 <1% for y/Ra <0.4 is achievable by nose shape optimization.

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


Particularities of normal conducting l band deflecting cavities valentin paramonov

Dispersion properties

Due to small transverse dimensions, Rc ~ 0.3 l, there is no HOM problem.

TM01

Operating point

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Particularities of normal conducting l band deflecting cavities valentin paramonov

Compensated RF structure (V. Paramonov,L.Krabchuk, Linac 2000)

Operating point

Branches due to waser+ stem

Has no stability problem (compensated, bg=0.32, b=1). Efficiency ~ 0.9 from previous case. More complicated in design and dispersion properties.

Field distribution for deflecting and coupling modes.

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


Particularities of normal conducting l band deflecting cavities valentin paramonov

Possible design

Vacuum RF input, WR650

Beam pipe

Tuning after brazing Cooling

RF probes

Possible parameters – Ra ~ 19 mm, Rsh ~ 38 MOhm/m, Ql ~ 7000, tt ~ 3 ms, L~ 1 m, P~30 kW, V~ 1 MV

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


Particularities of normal conducting l band deflecting cavities valentin paramonov

Summary

  • For application in L-band frequency range normal conducting standing wave deflectors are more effective.

  • As compared to Disk Loaded Waveguide structure, H-type structure has higher RF efficiency, essentially higher coupling and smaller transverse dimensions.

  • For H-type structure tolerable values both for aberrations and maximal surface fields can be obtained by appropriate shape optimization.

  • The high coupling value allows longer cavities without limitations for RF coupler position.

ICFA BD Mini-Workshop on Deflecting/Crabbing Cavity


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