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Compact Radio Frequency Technology for Applications in Cargo and Global Security. Graeme Burt Lancaster University, Cockcroft Institute, Security Lancaster. Cargo Screening Accelerators. Aircraft ULD or pallets are too large for baggage scanners and too small for cargo scanners.
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Lancaster University, Cockcroft Institute, Security Lancaster
Aircraft ULD or pallets are too large for baggage scanners and too small for cargo scanners.
Currently searched by hand.
Luggage Scanning requires a few tens to hundreds keV. This can be delivered by traditional X-ray tubes up to 450 keV.
Ideal energy is around 1-2 MeV but no current source available.
Truck or shipping cargo is larger requires ~6 MeV. Industrial linacs can provide this.
DC Electron Gun e2V
Buncher and Accelerating Structure (1 MeV)
CI Proposal Scope
(9.3 GHz, 1.2 MW, 100-400 Hz) Dynamic switching of amplitude and phase pulse-to-pulse)
Automated Control System
(Energy, rep-rate, dose)
CI-SAC Dec 2011
5 mm beampipe diameter
3.5 mm iris thickness
1 mm coupling cell thickness
Structure was found to have poor matching and field flatness.
Low beta cells were further off frequency than could be tuned.
A 17 keV electron gun was specially designed for this project from a TWT gun.
The gun was modified to provide 200 mA with a 1mm spot size.
Gun has been successfully tested at Daresbury.
Substantial ringing is found on the ICT due to EM interference from pulse operation.
E2V engineers acceptance tested the magnetron at Daresbury.
Maximum power achieved ~ 1.1 MW but not sustainable due to arcs.
Operating at long pulse lengths (4 us) and high power (>1 MW) results in significant arcing within the magnetron.
Good quality full scale imaging requires dose of at least 0.03 Gy/min @ 1m @ 100Hz
So far the linac has produced a 750 keV, 1 mA beam as measured on the spectrometer and Faraday cup/ICT at the end of the diagnostics line (probably large beam loss prior to this).
This is limited by the cavity being slightly out of tolerance affecting the fields.
490 MHz wide
Contract placed with Comeb
60 MHz wide
We have developed a new X-band structure with much greater cell-to-cell coupling to increase tolerances.
Simple structure design with no slots to help tolerances (low fields and low voltage make this acceptable)
There is also interest in millimetre wave and THz scanning of personnel.
For this application we have been developing a 105 GHz Klystron.
To avoid issues with poor scaling of Klystrons to high frequencies we use a 3rd harmonic output cavity.
105 GHz output cavity
35 GHz input and intermediate cavities
To increase the size of the output cavity such that it could be made from conventional machining we use a higher order mode cavity (TM020-like)
Output coupler 94GHz
Input coupler 31GHz