P.W. Gorham et al.. TEST BEAM A SLAC Time relative to beam entry Antenna V/V rms Time relative to...

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P.W. Gorham et al..

TEST BEAM A SLAC

Time relative to beam entry

An

ten

na

V/V

rms

Time relative to beam entry

An

ten

na

V/V

rms

close to shower maximum

shower nearly dissipated

6 GHz bandwithoscilloscope

TEST BEAM A SLAC

insensitive to cherenkov and

transition radiation

sensitive to cherenkov and

transition radiation

7 ns decay constant, compatible with plasma cooling

classical bremsstrahlung theory assuming

coherence

P.W. Gorham et al..

Limitations of SLAC measurements

It has been proved only the existence of a microwave emission

• the absolute yield is not known precisely

--> this affect the uncertainty on the threshold in energy of

an air shower detector

With the AMY experiment we would like to overcome this limitations confirming and measuring precisely the absolute microwave yield and its frequency spectrum in the range between 1 and 25 GHz

• the spectrum in frequency has not been measured

--> it may give important informations on the underlying process

--> if there are bright lines the signal/noise of a telescope can be improved

--> if not, satellite televisions band are preferable to keep low the costs

THE AMY OBJECTIVE

The DAFNE Beam Test Facility

Energy range 25-750 MeV

Max. repetion rate 50 Hz

Pulse duration 1 - 10 ns

Particles/bunch Up to 1010

e-/e+

In comparison to SLAC the BTF beam provides a larger shower equivalent energy

ANECHOIC FARADAY CHAMBER

copper

2 antennas

RF adsorber SATIMO AEP 12 attenuation 1GHz: 30 dB > 6 GHz: 50 dB 2 m

2 m

4 m

beam axis

30 cm

choice of dimensions

• far field approximation (-> height and width)

• entrance and exit walls outside the antenna field of view (-> length)

2 antennas

2 m

2 m

4 m

beam axis

• spectrum analyzer -> frequency spectrum and absolute yield

• power detector & FADC (*) ->time evolution of the signal

(*) flexibility of a VME system (beam monitoring)

ANECHOIC FARADAY CHAMBER

EXPECTED FLUX DENSITY

depends on thedegree of coherence

= 1÷2

at the maximum energy deposit within the chamber

assuming an alumina target

beam-antenna distance

observed track lenght

€

≈1

2

alumina target alumina target

THE ANTENNA Rohde & Schwarz HL050

Log-periodic 0.85-26.5 GHz

from 1 to 25 GHz

Half-power beam width 650 -> 550

Cross-polarization factor 40 -> 35 dB

27.4 cm

SPECTRUM MEASUREMENT

amplifier ANTENNASpectrumanalyzer

Rohde & Schwarz FSV30

9 KHz - 30 GHz 40 MHz bandwidth

Gampl ≈ 25 dB

SPECTRUM MEASUREMENT

amplifier ANTENNASpectrumanalyzer

Expected signal at the maximum energy deposit

€

S = IBTF A e Gamp Δf

bandwidth

amplifier

antennaeffective area

€

Aeff = λ2G

4π≈

5⋅10−2

υ 2[GHz] m2

well above the expected instrumental noise (< -80 dBm)

quadratic scaling

linear scaling

TIME MEASUREMENT

amplifier ANTENNApower

detectorFADC

500 MS/s

4 channels

12 bit resolution

AD8317/8318

up to 10 GHzresponse time < 10 ns(no signal -10 dBm)

TIME MEASUREMENT

amplifier ANTENNApower

detectorFADC

• difficult to go above 10 GHz • minimum signals > -60 dBm

Constraints from power detector

Measuring the exponential decay with a 30-40 dB dynamic range high amplification gain

1) perform an initial measurement around a fixed frequency (commercial feeds in satellite bands)

2) once the spectrum has been measured, study the time signal evolution in the bands we will find interesting (above 10 GHz we may use frequency down converters)

C band

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Cherenkov electric field - 1 e-

Cherenkov: no target - quadratic scaling

density flux at the end of the camera after the adsorption (50 dB)

density flux at the antenna cross-polarized (40 dB)

MBR density flux at the antennamaximum shower development

For a realistic calculation:

• time separation between electrons coherence only if t << 1/f (0.04 ns < 1/f < 1 ns) 1 ns < bunch duration < 10 ns

• only particles within the chamber contribute to the signal

• modelling RF absorption

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Dealing with 1010 particles

Expected cherenkov signal in the spectrum analyzer in case of a copolarized antenna

> -10 dBm

An import goal of the test beam will be to measure the cherenkov radiation and to make a comparison with theoretical calculations

The experiment has been fully funded by INFN (~ 120 k€) and some of the instrumentation will be bought already during this year.

Agilent(?)

Agilent(?)

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