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QuickTime™ e undecompressore
sono necessari per visualizzare quest'immagine.
QuickTime™ e undecompressore
sono necessari per visualizzare quest'immagine.
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
QuickTime™ e undecompressore
sono necessari per visualizzare quest'immagine.
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
QuickTime™ e undecompressore
sono necessari per visualizzare quest'immagine.
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(?)
QuickTime™ e undecompressore
sono necessari per visualizzare quest'immagine.