David Saltzberg, 24 Nov. 02 ANITA meeting Slide 1 Review of Accelerator Measurements of RF shower emission l Outline äMini review of RF detection (emphasis

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


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


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


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


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


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


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


Two SLAC runs

July 2000June 2002


Target Geometry

Lunacee II

Lunacee III, similar geometry but built with salt bricks


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


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


Coherence


Shower profile


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


Polarization Tracking


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.


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).


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?)

Documents

David Saltzberg, 24 Nov. 02 ANITA meeting Slide 1 Review of Accelerator Measurements of RF shower emission l Outline äMini review of RF detection (emphasis