Geosynchrotron emission from air showers at SLAC. Konstantin Belov UCLA

Transcription

1 Geosynchrotron emission from air showers at SLAC. Konstantin Belov UCLA

2 UHECRs in radio Radio technique got a new boost in recent years thanks to CODALEMA, LOPES and ANITA experiments. The precise energy and X max measurement of the UHECRs using only radio is a challenge Extensive and accurate Monte Carlo simulations are needed An experiment in a controlled lab environment will help to improve our understanding of the radio emission mechanisms and guide the new MC developments Directly compare MC simulations with the experiment where we control: target density refraction index magnetic field SLAC plans to offer up to 13 GeV electron beam in ESA this year. 2

3 Inside End Station A building Concrete wall Not to scale 11.2 m Concrete roof Inside Concrete tunnel target beam 13 m 4.3 m Beam dump 3

4 End Station A Crane Concrete tunnel roof Can be removed partially at the end of the tunnel Beam pipe. Will be shortened for us End of the concrete tunnel 4

5 End of the tunnel 30 cm Cable tray Beam pipe 51 cm 206 cm 269 cm Beam pipe support 251 cm 274 cm Put the scopes behind these concrete blocks. Move the blocks closer to the wall to reduce RF cable length 5

6 Proposed SLAC experimental setup Concrete shield for scopes End wall. Concrete. Antennas on the wall. 6

7 A target from bricks we have. ~ 140 cm long target is equivalent to 20 radiation lengths. A hybrid (ferrite + foam) RF absorber to suppress the Cherenkov radiation and reduce the effect of reflection/refraction at the side walls making the target a very poor wave guide. (TE mode cutoff frequency is ~30 MHz would otherwise be a problem). Alternative target materials and shapes are being studied. 7

8 A hybrid RF absorber HyPyr-Loss Series of RF absorbers From DJM Electronics. Ferrite tile with dielectric foam. Claim to be affective in 20 MHz-20 GHz frequency range. Suppressing RF reflections will be crucial for the experiment. Ferrite is effective from ~ 30 to 600 MHz Traditional dielectric foam is effective at 500 MHz and above. Combination of two with the impedance match is an effective RF absorber from 30 MHz to 20 GHz. Firrite density is > 4.5 g/cm 3 (more dense than alumina with g/cm 3 density which helps with refraction. 8

9 Other target configurations Irregular shape RF absorbing foam Lead brick - Destroys the wave guide - Eliminates the crack alignment problem Alumina bricks Ferrite 3 x 3 x 3 cm lead - No RF out - No TR our below 10 GHZ (experiments seems to contradict it see Gorham et al. arxiv:astro-ph/ v2) - Most difficult and expensive target Preshower up to Xmax in alumina or lead and exit into a low density material (aerogel) placed in magnetic field. 9

10 Graded Target Alumina/polyethylene in 10 density grades particles above critical energy cascade in alumina, but particles below critical energy stop in polyethylene track length and magnetic deflection takes place in a low density environment shower development occurs in alumina, compressing the longitudinal profile By David Seckel 10

11 Slanted surface target Shower is fully contained no TR to worry Cherenkov from the slanted surface to be measured Synchrotron is measured from the exit wall By Andres Romero and David Seckel 11

12 Best target material? Alumina (Al 2 O 3 ) looks like a good material for the target: It is non-metallic It is dense (~3.95 g/cm3) smaller magnet required to have the whole target in the magnetic field. 14 rad lengths of Alumina (~1 m) contain > 99.6% of charged particles (FLUKA) Has low loss tangent Some is already available from E-E 165 experiment Additional quantities can be purchased easily if necessary Was used to preshower in E-165 E experiment AD-90 alumina bricks 6 x4 x2 12

13 Coils SLAC found coils for us: 566 mm OD, 416 mm ID 2.5 thick 64 turns Imax = 700A at 70 C water temperature 400G at 500A according to Carsten. Calculations for Helmholtz coil 1600G at 700A. Water cooled 110 pounds of weight. Can double up the coils to get to ~3,000 G. Tests for pulsing the coils to be conducted at SLAC. 24 more coils to be removed in February. SLAC coils at UCLA. 13

14 Magnetic field setup Black calculated Color mapped at UCLA at 21 A scaled to 700A Coil OD 0.6 m, ID 0.24 m Distance between coils 0.26 m 64 turns Current 700A X-axis distance in cm from the Helmholtz coil axis Color distance along the axis from the center b/w coils Magnetic field tension. Helmholtz coil configuration. Target Low density material Coils beam 14

15 A small backup magnet This monster does fit into the tunnel. Any idea how to use it? 15

16 Goal: FLUKA simulations to see the shower development within the target with a magnetic field Cross-check with GEANT4 that is used for e-field e prediction Needed for SLAC RP team to estimate the radiation doze Alumina target 150 cm x 20 cm x 20 cm Alumina target 40 cm x 20 cm x 20 cm Pb target 3 x 3 x 3 cm Surrounded by imaginary cylinder 2 m diameter 10 m long centered around the target. 13 GeV and 4.5 GeV electron beam along X-axisX 1000G magnetic field along positive Z direction covering 120 cm of the target along the beam direction particles for the simulations Number of electrons in bunch at SLAC is upto 1.56x10 9 ( 0.25 nc) Simulation run by John Clem 16

17 FLUKA simulations. Shower development. Xmax is at 4.5 rad lengths. In agreement with GEANT4. Alumina rad. length is 7 cm Moliere radius is 3 cm Mag field is along z-axis About 90% of the shower is contained within 0.5 rad length or about 3 cm. 17

18 FLUKA energy distribution of charged particles at different shower development stages Target is about 20 rad lengths 18

19 FLUKA. Charged particles crossing 2m cylinder around the target electron simulation. 13 GeV. Upper plot - # charged particles crossing imaginary 2 m radius cylinder around the target Lower plot angular distribution around the cylinder: 0 degree is vertical direction pointing up. Energy distribution of the charged particles on 2 m cylinder for the radiation dose calculation 19

20 RF calculations in GEANT4 (Thanks Andres) Time domain method from Alvarez-Muniz, Romero-Wolf and Zas [Phys. Rev. D 81, (2010)] GEANT tracks limit < 1mm Calculating vector potential from the track The shower is propagating with the speed c, but RF is propagating with c/n. Synchrotron signal will be amplified at the Cherenkov angle ( about 1 o for the air and 56 o for alumina target n=1.73 ) For tracks with the high energy, the peak in the frequency spectrum is above 1 GHz, but there are many lower energy tracks due to low energy knock on electrons 20

21 GEANT4 simulation example GeV electrons scaled to 0.25 nc SLAC charge Target occupies all space Magnetic field is 1000G n=1.73 For the observer at the shower axis Plots by Andres Romero-Wolf 21

22 Spectra at different angles Noise is due to only 1000 particles were simulated. Plots by Andres Romero-Wolf 22

23 Synchrotron contribution at the Cherenkov angle Preliminary GEANT4 + ZHAireS simulations. Alumina (n=1.73) filling the entire space The ratio improves significantly for a less dense medium such as polyethylene. 23

24 Conclusions The proposed experiment at SLAC will help to improve the models of the radio emission from extensive air showers and help to validate MC simulations There are many challenges to scale the results to the air showers: Overall scale of the experiment (10m vs 10 km) Changing density and index of refraction in the air We have full mental support from SLAC. Material support might be limited this time Beam is expected this year (April will be the earliest) The energy might be limited to 4.5 GeV due to funding situation for the magnets at SLAC We are in the process of simulating different targets/materials/magnetic fields using GEANT4 + ZHAireS Plans to add RF into FLUKA (John Clem) 24