Developments in Nanosecond Pulse Detection Methods & TechnologyUHE Neutrino Detection using the Lunar Cherenkov Technique Lunatics - those who search for lunar ticks Prof Ron EkersDr Paul RobertsDr Chris Phillips Rebecca McFadden(PHD) Prof Ray PrthoeroeClancy James (PhD) A/Prof Steven TingayDr Ramesh Bhat
Outline • Lunar Cherenkov Technique • Characterisitics of Cherenkov Radio Pulse • Current ATCA Experiment • ATCA Upgrade • Future Experiments - SKA
UHE Neutrino Detection using the Lunar Cherenkov Technique neutrino photon shower Technique first proposed by Dagkesamanskii & Zhelezynkh (1989)and first applied by Hankins, Ekers and O'Sullivan (1996) using the Parkes radio telescope Image courtesy of R Ekers
Characteristics of Radio Pulse and Experimental Requirements • 100% linearly polarised • Broadband (0-3+GHz), continuous emission (See #0341 Clancy James for more details) • Very narrow unmodulated pulse (1-2ns) • Dispersed by ionosphere • Blurred by instrumental effects Require: Broad receiver bandwidth for ns time resolution High speed sampling Real time trigger to avoid excessive storage requirements Real time dedispersion to maximise SNR for trigeer
Advantages of using an Array of Small Radio Telescopes A rray geometry allows RFI discrimination based on the signal direction of arrival. The system temperature is dominated by thermal emission from the moon so there is little improvement in signal to noise ratio to be gained by larger apertures.With many small dishes, their spatial separation can be used to ensure that thermal emission from the moon is incoherent between elements thus increasing the signal to noise ratio. At frequencies in the 1-2GHz range, the primary beam produced by a 22m aperture (such as the Compact Array) can see the entire moon. Beamwidth is inversely proportional to aperture size, therefore a larger dish will see less than the entire moon and any minimal improvement in sensitivity from the larger aperture will be offset by decreased coverage of the moon.
Current ATCA Experiment using FPGA based Sampler Board • 3 Antennas fitted with custom built hardware • 1.2 GHz-1.8 GHz (600MHz) RF signal taken directly from antenna • Dedispersion on fixed analogue dedispersion filter • Real time trigger in FPGA • Ethernet connection to control room • Baseband recording for offline processing
Overall System Design for May 2007 Observing Term Baseband Buffer Offline Processing 1 Gbit Ethernet Link (TCP/IP)
1.2 – 2.5 Ghz Horn Polarisation and Band Splitter LNA 1.5 Ghz LNA 1.5 GHz LNA 2.3 Ghz LNA 2.3 Ghz Pol A Pol B Pol B Pol A L-Band RF Splitter Module (F10) S-Band RF Splitter Module (F11) L-Band Splitter (C22) S-Band Splitter (C23) 2.048 Gs/s 4096 samples, 2μs 5.1 σ 8 bit ADC Coincidence Test and Threshold Detect Buffer Ethernet Connection 8 bit ADC System Detail at Each Antenna Standard ATCA Receiving Path Customised Hardware Analog Dedispersion Filters 3 – 8 ns (night – day) ATNF BCC Interface 100Mb/s CABB Sampler Board
Differential Delay Statistics Histogram of VTEC for May 2006 Signal dedispersion is performed in analog microwave filters with a fixed dispersion characteristic. These filters were designed using a new method of planar microwave filter design based on inverse scattering . This results in a filter with a continuously changing profile, in this case a microstrip line with continuously varying width. The width modulations on the microstrip line produce cascades of reflections which sum to produce the desired frequency response. TEC data from NASA’s Crustal Dynamics Data Information System Δt = 0.00134 TEC (1/flo2 – 1/fhi2 ) Restricting data set to night-time hours (8pm-6am):Average TEC of 7.06 VTECU (May 2006) and 7.01 VTECU (May 2007)Over the 600MHz bandwidth (1.2-1.8 Ghz) this corresponds to an average differential delay of 5ns (May 2006) and 4.39ns (May 2007)
Field Programmable Gate Array • Semiconductor device containing programmable logic components • Can be programmed to duplicate logic functions (such as AND, OR, NOT, XOR) • Or more complex functions such as decoders or simple math functions (DSP applications: filtering, transforms, modulation) • A Hardware Description Language (HDL) can be used to define the FPGA's behaviour • High level design tools may be used to raise the level of abstraction in the design process
Introduction to ATCA Upgrade • Upgrade planned to increase current 600MHz bandwidth to 2 GHz – Compact Array Broad Band Upgrade (CABB) • Due to bandwidth and data storage limitations, the only way to exploit this new bandwidth is by implementing real time detection algorithms • These algorithms can be programmed into more complex FPGA boards currently being built by the ATNF for the CABB Upgrade
Wavefront 2 q2 Wavefront q D Path = D sin q Delay = D/c sin q D Additional Processing Power from FPGA Upgrade We can form multiple Beams to Cover the Limb of the Moon It will also be possible to implement real time dedispersion algorithms in this hardware and we have developed a technique for obtaining measurements of the ionospheric TEC which are both instantaneous and line-of-sight to the lunar observations. The ionospheric TEC can be deduced from Faraday Rotation measurements of a polarised source combined with geomagnetic field models, which are more stable than ionospheric models when the direction of signal propagation is parallel to the geomagnetic field vector.We propose to use this technique, with the polarised thermal radio emission from the lunar limb as our polarised source, to obtain instantaneous and line-of-sight TEC measurements.
Lunar UHE Neutrino Astrophysics with the Square Kilometre Array (LUNASKA) Work conducted by the Lunatic team will form a pathway for UHE neutrino detection using the proposed SKA radio telescope.The Square Kilometre Array will be 100 times more sensitive than the best present day radio instruments.The current designs proposed for the SKA consist of large numbers (~104) small dishes (6-12m) to achieve a square kilometre of collecting area in the 1-3GHz range.