# Presentation: 848507

## Brief review of motivation for the presently used layout
Discussion of adopted parameters and dimensions
Details of practical implementation

Conclusion and outlook

- Discussion of adopted parameters and dimensions
- Details of practical implementation
- Conclusion and outlook

- Status of Development of the ChopperF. Caspers [CERN-PS-RF]

## We are using a double meander type structure printed on an alumina substrate
Main advantages are:
Very good vacuum properties
Can sustain considerable doses of ionising radiation
Good heat conduction
Small lateral width
Printed circuit technology
All electromagnetic parameters ok

- Main advantages are:
- Very good vacuum properties
- Can sustain considerable doses of ionising radiation
- Good heat conduction
- Small lateral width
- Printed circuit technology
- All electromagnetic parameters ok

- Brief review of motivation for the presently used layout

## For a 2 ns rise- and fall-time (10%-90%) the external drivers could become very costly for a deflection voltage of 0-1 kV (peak, uni-polar) per deflecting plate.(1 kV into 50 Ohm requires 20 A !; for 500 Volt we still get 10A)
If we could produce deflecting structures with a width of, say, less than 5 cm, they would rather easily fit into dipole or quad magnets and we could simplify the design of this section.
We gain linear (in terms of kicker output power) with the length of the deflecting structures used.
Less voltage per kicker module would simplify the driver design (less signal combination thus better rise/fall time) and lowers the heat loss in the meander.  

- If we could produce deflecting structures with a width of, say, less than 5 cm, they would rather easily fit into dipole or quad magnets and we could simplify the design of this section.
- We gain linear (in terms of kicker output power) with the length of the deflecting structures used.
- Less voltage per kicker module would simplify the driver design (less signal combination thus better rise/fall time) and lowers the heat loss in the meander.

**How to reduce the cost for the driver?****(puls generator or wide-band amplifier)**

## We are considering a double meander structure e.g. 200mm long as shown below:

- 198+2mm (33 cells)

- 50 mm

- 42.5 mm

- 3 mm (50

- 

- )

- 6 mm

- 0.45 mm

- (100

- 

- )

- Substrate:

- 3 mm thick

- 

-  =

-  9.6

## 50 cm long structure, transmission measurements, 0-600MHz, time -domain display
The metal thickness of the meander has been increased to about 40 micron by electro-chemical deposition                                                

- The metal thickness of the meander has been increased to about 40 micron by electro-chemical deposition

- 1.65ns

- 1.98ns

## Critical  and limiting parameters for the double meander printed on alumina

- For the double meander type structure we are limited by
- Dispersion (phase nonlinear with frequency).This leads to pulse deformation, overshoot and ringing.
- Attenuation leads to a reduced kick, heating and, if frequency dependent, also to pulse deformation.
- Field coverage factor:leads to a reduction in effective deflecting field-strength.

## 50 cm long LANL structure, measured time domain response, EPAC paper 2000 by S.Kurennoy, 

**1 ns filter**

**2 ns filter**

## 50 cm long alumina structure, transmission measurements, 0-1000MHz; for comparison, on the right, measured data from LANL, Kurennoy, EPAC2000 [also 50 cm long but on RT duroid substrate with separating fins]

## 50 cm long  alumina structure, transmission measurements, 0-1000 MHz, phase after delay correction

## 50 cm long structure,transmission measurement, 0-1000 MHz, group delay variation vs frequency

## 50 cm long  alumina structure, field coverage factor (data provided by S.Kurennoy) peak value on axis =0.79 for the 50 Ohm meander in upper color bar.

**Relative color scale up to 100 %**

## Details of practical implementation

- We have tight constraints on the length of the chopper section (3 MeV)
- the possibility to place the chopper structure inside a (split ) quadrupole magnet is considered as a useful option
- The aperture between the chopper plates has been defined as 20 mm total (+- 10 mm)
- The deflecting plates will be operated with a triaxial feeding system. Inner coax = high frequencies, outer coax = low frequencies, RF- loads outside the vacuum

## Simplified layout of the chopper section

- Drawing by :A. Lombardi

- Vertical beam envelope

- Hor beam envelope

- Q

- Q

## Vacuum prototype of the chopper

- The total length of the chopper plates will be 700 mm; the first section is 400 mm, the second one 300mm (length of the 50 Ohm meander only!)
- This takes into account a generator voltage of 500 Volt (peak, into load) and a field coverage factor of about 80%
- Full aperture between both plates is 20 mm
- This leaves a certain safety margin
- We can accept 1 % beam loss
- Chopper plates may be inclined

## Layout of the chopper prototype (UHV version)

## Layout of the chopper prototype (UHV version)Detail #1 (electrical connections)

- 10 mm thick metal groundplane

- 3 mm thick alumina substrate

## Detail #2The 3 mm thick alumina plate

- Drawing (not exactly to scale) for the “400”mm long alumina plate
- Note the width of 60 mm (meander =42 mm) and the fixation holes
- Metallisation [meander only] will either be thickfilm or molymangan
- With about 30 micron silver added by el.chem deposition

- Fixation holes, 3mm diameter

## Detail # 3DC Isolator in the triaxial feedthrough

## Detail # 4Modified PMB coax feedthrough (CF16)

- This feedthrough is mounted
- on the rear of the electrically
-  floating metal support for the
-  alumina substrate.
- The ground of this feedthrough
- Is the outer conductor of the
- ” inner “ (=HF) coax  system

##                              Conclusion

This prototype of a 50 ohm double meander printed on 3 mm thick alumina is a competitive candidate for the SPL chopper
The structure can stand the radiation and heat load (if water cooled) and  has good vacuum properties
Wideband impedance matching has been achieved
The field coverage factor is slightly lower(79%) as compared to the LANL prototype (89% ) for 50 Ohm impedance.
Work for practical implementation of a first UHV version is in good progress

- This prototype of a 50 ohm double meander printed on 3 mm thick alumina is a competitive candidate for the SPL chopper
- The structure can stand the radiation and heat load (if water cooled) and  has good vacuum properties
- Wideband impedance matching has been achieved
- The field coverage factor is slightly lower(79%) as compared to the LANL prototype (89% ) for 50 Ohm impedance.
- Work for practical implementation of a first UHV version is in good progress