1

6

18µ

5560

25

Al2O3 ceramiceff = 9,8

periodicboundarycondition

magneticboundarycondition

electricboundarycondition

Al2O3

Ui

Ua

beam

pick-upframe

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

ε eff

3.02.52.01.51.00.5f [GHz]

continuous 0.762mmAl2O3 board

no Al2O3 board

slotted 1.905 mmAl2O3 board

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0.0

|Ua/

Ui|

3.02.52.01.51.00.5f [GHz]

continuous 0.762mmAl2O3 board

no Al2O3 board

slotted 1.905 mmAl2O3 board

t

t

t

t

2· t

2· t

4· t

BeamPU board

optionalamplifierboards combiner board

vacuumfeedthroughand flexibletransmissionline

amplifier

assumptions:

• transmission of slotline coupler: -0.92 dB = 0.9

• transmission of one Wilkinson combiner: -0.2 dB = 0.977

• transmission of a feedthrough with flexible transmission line: -0.5 dB = 0.944

• transmission of the amplifiers: 10 dB = 3.162

• noise figure of the amplifiers: 0.25 dB = 17.2 K

• electrode spacing: 25 mm

• frequency range: 1…2 GHz

result:100

80

60

40

20

0

90

70

50

30

10

nois

e te

mpe

ratu

re [K

]

30Kamps inside

80Kamps outside

amplifier inputamplifier outputslotline couplercombiner networkfeedthrough, flex linecoupler, combiner network,feedthrough, flex line

30K 80K

28.1K36.4K

47.0K

96.6K relative signal to noise ratio:

ampifiers inside, T=30K: 5.4 dB

ampifiers inside, T=80K: 4.6 dB

ampifiers outside, T=30K: 3.1 dB

ampifiers outside, T=80K: := 0.0 dB

Beam

cooled side wall (fixed)

flexible BeCu sheetfor em-shielding and

thermal conduction

Al2O3 board withslotline electrodes

Al2O3 board withWilkinson-combiners

antenna forbeam simulation

Al2O3 board withoptional Ampifier

milled pick-up frame(vertical movable)

contact clamps(amp. out, +3V, -1.5V, data, clock, ant. in)

contact clamp(amp. in)

6mm slotsmilled thru

Cu and Al2O3

Al2O3bridges

Cu or Au

thru holes thru holes

6mm slotsmilled thru

Cu and Al2O3

Au contactto frame

1.9 mm Al2O3

1st Wilkinson-combiner(100Ω/50Ω)

slotline/micro-strip-transition

Au contactto amp. board

Beam

Al2O3 board withslotline electrodes

Al2O3 board withcombiners or hybrids

antenna forbeam simulation

Al2O3 board withoptional Ampifier

milled pick-up frame(vertical movable)contact clamps

Investigations on Pick-Up and Kicker Electrodes for Stochastic Cooling

Claudius Peschke, Fritz Nolden (GSI, Darmstadt); Lars Thorndahl (CERN, Geneva)

1.0

f [GHz]

2.0

10

20

30

40

50

60

70

80

01.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

Zlo

ng

Ω[

]

GSI 6mm air gap92·53 mm2 quarter-aperture

FNAL slow wave55·53 mm2 quarter-aperture

CERN AC band 158·53 mm2 quarter-aperture

Slotline Pick-Up Properties of Different Slotline Types

Signal Combination and Noise Temperature

Pick-Up Module

An ideal slotline consists of a narrow gap in the conductive coating of an infinitely wide dielectric substrate.

In reality, the conductors are finite and the rear side of the electrode has to be shielded. This line acts more like a dielectric loaded waveguide with a cut-off frequency and a higher dispersion.

The numeric calculations were done using the Microwave Studio eigenmode solver. The line is built into a rectangular frame with a height of 55 mm. With a smaller box, the cut-off frequency would be in the operating frequency range (1-2 GHz). Below the slotline is 60 mm space to the center of the beam pipe. Symmetrically driven electrodes on each side of the beam pipe are simulated by a magnetic boundary condition at the bottom.

The first type of slotline has no substrate. The second type uses a continous 0.76 mm Al2O3-substrate. The third type is a compromise and uses a 1.91 mm substrate with a slot through the substrate.

The main task of the FAIR collector ring (CR) is stochastic cooling of RIBs and antiprotons. The CR should achieve a phase space volume reduction of 1.6·104 in 5 s for antiprotons and 1.3·106 in 1 s for RIBs. The pick-ups must have a large bandwidth, a high S/N ratio and a large aperture of 120·120 mm2. A new planar electrode is developed to meet these requirements.

The figure shows the square root of the longitudinal impedance (beam in center, longitudinal kicker mode) of a 2 m long array of 80 slotline electrodes, a 2 m long array of 23 CERN AC band 1 superelectrodes and a scaled FNAL slow-wave structure with 80 cells with a length of 32.5 cm without coupler.

To fulfill the signal-to-noise ratio requirements, one has to combine the signals of an array of electrodes. Due to the two different velocities it is necessary to use switchable delay lines for the phase consistent combination. A group of eight electrodes will be combined with fixed delays and the combination of the groups will be done with switchable delay lines. With an electrode distance of 25 mm and eight electrodes, the amplitude degradation compared with switchable delays on every electrode is only 4.6 % at 1.5 GHz.

One possibility to bring down the noise is to cool the pick-up modules to 80 K or 30 K.

Another possibility is to terminate the slotlines with electrically cold loads. A single electrode with the first combiner has a high reflection factor. An amplifier is therefore terminatad with its own cold input. Due to the different delays in the combiner network, an amplifier behind the module is terminated by the resistors of the combiners instead of the cold input.

The figures above show a possible layout of a pick-up module.

At the bottom of the module is the pick-up board with eight slotlines and the first combiner stages.

The board above establishes the connection between the pick-up board and the combiner board on top of the module. It also contains a small antenna for signal injection into each slot. This can be used to check the whole circuit of the module without a beam. The connection board can optionally contain the first stage of the low noise amplifier.

The pick-up module will be vertically movable to follow the cooled beam. This will be neccesary to get enough signal when the beam gets colder. Two BeCu springs establish the thermal connection to the fixed cooled side walls. These springs are also responsible for the electromagnetic shielding. An alternative to the mechanical complicatad long springs could be an simple gap with damping material on the sidewall and short springs for the thermal conduction.

A whole pick-up or kicker tank will probably consist of eight modules. Both ends will be closed with damping material and a thermal shielding.