David Saltzberg, 24 Nov. 02 ANITA meeting Slide 1 Review of Accelerator Measurements of RF shower...
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Transcript of David Saltzberg, 24 Nov. 02 ANITA meeting Slide 1 Review of Accelerator Measurements of RF shower...
David Saltzberg, 24 Nov. 02ANITA meetingSlide 1
Review of Accelerator Measurements of RF shower emission
OutlineMini review of RF detection (emphasis on tricky points)
- Antenna response to signal
- Noise
Measurements of Askaryan Effect
David Saltzberg, 24 Nov. 02ANITA meetingSlide 2Basic Anatomy of an Antenna
+Receiver
E
E
E field
Z0 = 377/n
balun
coaxcable
Rr=50 or 75 (typical)
Rr=50 or 75 (typical)
V
Balun impedance matches AND isolates outside of cable shield from radiator, BUT is difficult to make broad-band
Rr=“radiation resistance”= impedance looking into back of balun
David Saltzberg, 24 Nov. 02ANITA meetingSlide 3
Electric fields and Antennas
View I: Electric fields & Effective height E field measured in V/m Antenna described by effective height, heff, where
Careful, V is the “open circuit” voltage, i.e. if antenna is looking into infinite impedance. For a matched load, divide by 2
effhEV
David Saltzberg, 24 Nov. 02ANITA meetingSlide 4
Electric fields and Antennas
View 2: Pointing Flux and Effective Aperture S = E2/Z (E is instantaneous E(t)…careful factors of 2), where
Z0=377 in free space (W/m2)
- P=A*S
- In media, Z0= 377 *
Power delivered by antenna into a matched load is called “effective aperture”. (assuming no ohmic losses)
- Careful, note difference in defintion wrt heff
If load is known, can go between two views:
r
effeff R
ZhA
40
2
David Saltzberg, 24 Nov. 02ANITA meetingSlide 5
Noise
R.F.I. : Radio Frequency Interference, typically manmade. If impulsive, could mimic signals without increasing system
temperatureEven if not impulsive, can raise system temperature If narrow band, can be removed by notch filtering (online) or
by making a cut on signal duration (offline). Even “broadband” RFI can usually be removed offline by
cutting on durationDo not expect EXTREMELY broadband (100-1000 MHz)
and short duration from RFI.Even if not impulsive, can raise system temperature
David Saltzberg, 24 Nov. 02ANITA meetingSlide 6
Noise
Thermal noiseBroadband and is ultimate background since can look like
signal If antenna aperture is filled by source at temperature T,
expect power delivered to matched load to be P=kB*T*B, where B=bandwidth
Gives V fluctuating as Gaussian with Vrms=sqrt(P*R) where R is input impedance of detector (typ. 50). This is a bit more complex when bandwidth≠100%
290K filling aperture, connected to matched load:- P=-174 dBm/Hz
- Vrms=0.45 nV/sqrt(Hz) if 50 system
David Saltzberg, 24 Nov. 02ANITA meetingSlide 7
Recommended Reading
J. Kraus, “Antennas, 2nd ed”, esp. chapter 2 C. Balanis, “Antenna Theory” ARRL “The Antenna Book” M. Schwartz, “Information Transmission, Modulation, and
Noise” (you can skip the part on vacuum tubes!) Horowitz & Hill (amplifiers, noise…)
David Saltzberg, 24 Nov. 02ANITA meetingSlide 8Lunacee II and III
(July 2000 and June 2002)
Askaryan Experiments at SLAC:SLAC/FFTB 30 GeV e- < 1mm bunch size 1-3%X0 radiators up to 1019 eV in ’s
Only photons leave the vacuum window no TR
30 GeV e-e- &
e- to dump
<E>=4 GeV
radiators
30 GeV linac
FFTB
David Saltzberg, 24 Nov. 02ANITA meetingSlide 9
Lunacee II and III
SLAC, Final Focus TestbeamAl Odian contacted us after seeing
Lunacee-I preprintBremsstrahlung photons from 28 GeV
electronsVery small beamsize (<<1mm)Real charge excess developsphoton beam so no Transition Radiation
David Saltzberg, 24 Nov. 02ANITA meetingSlide 11
Target Geometry
Lunacee II
Lunacee III, similar geometry but built with salt bricks
David Saltzberg, 24 Nov. 02ANITA meetingSlide 12
Bandlimitted pulses
E.g., 1.7 to 2.6 GHz
With radiator out, saw mV/m fields.
In general, t ~ 1/BW
# cycles ~ 1/ frac. BW
David Saltzberg, 24 Nov. 02ANITA meetingSlide 13
Absolute field emission check
Also took data in 2002 run to check coherence out to ~12 GHz. To be analyzed
0.01
0.1
1.
V/m
/MH
z at
1m
David Saltzberg, 24 Nov. 02ANITA meetingSlide 16
Shock wave
Speed of radio propagation in sand=0.6 c
Measured speed = (1.00.1)c CR shock wave
Shock wave at Cos-1(1/n)~51O
``Snelled’’ to 29O
David Saltzberg, 24 Nov. 02ANITA meetingSlide 18
T.I.R.
Anita needs to see signals that are transmitted from ice to vacuum (chance of total internal reflection)
Tested at Lunacee-II, from sand to air, and saw a 36 dB suppression
Antarctica’s firn layer should help somewhat. Still will be loss due to Fresnel Coeff.
David Saltzberg, 24 Nov. 02ANITA meetingSlide 19
Transition Radiation
TR is made whenever a charged particle crosses a dielectric boundary
Closely related to CR and all the coherence arguments of Askaryan hold
In Lunacee –I sent a 15 MeV electron beam through a foil. Found X10 disagreement with prediction. Perhaps because we were not monitoring beam at its last stage
Lunacee –III created an electron beam from the SLAC photon beam using a lead brick & aluminum plate. Calcuated E field (0.28 V/m) was consistent with observed (0.31 V/m).
David Saltzberg, 24 Nov. 02ANITA meetingSlide 20
Summary & ideas
Askaryan effect is established (or why would you be here?)
Other tools we may needUser module to provide parameterized E-fields to MC
simulationsBetter parameterization of angular distribution of emission
(including airy peaks)Antenna design codeDigital signal processing codeApply to understanding transmissivity of Firn (hard to do
experimentally?)