1. Lancaster University, Cockcroft Institute, Security Lancaster
Compact Radio Frequency Technology for Applications in Cargo and Global Security
Graeme Burt
Lancaster University, Cockcroft Institute, Security Lancaster

2. Smuggling and Global Trade
Illicit drug trade worldwide estimated to be $400bn
Illicit cigarette smuggling in EU alone €90bn, tax loss of around €16bn
Illegal wildlife trade $10-20bn worldwide
Counterfeit goods make 7% of world trade. In Europe alone it costs €400bn to legitimate trade

3. Current Contraband Threats to Europe
Arms Smuggling from North Africa via Italy, by some 3600 organised criminal gangs across Europe
Cigarettes in large quantities from Russia via Balkan states
Drugs from South America via Spain

4. Use of LINAC Based Inspection Systems
Revenue generation by collecting duties and taxes (Biggest benefit)
Protection from drug smuggling in large quantities (Second biggest benefit)
Deterrent to weapons and explosive smuggling

5. Examples of Effectiveness
UK Government deployed 10 scanners initially and within 2 years time, cross-channel cigarette smuggling fell by 70%, cutting it by 5 billion sticks per year and protecting £6 billion per year revenue
In Virginia USA 732 pounds of cocaine was seized in a cargo shipment of orange juice cans, street value of $644 Million(Dec 2013)
In May 2014, Spanish authorities found 2.5 metric tons of narcotic hidden in a shipment of pineapples
At Rotterdam port in Dec 2014, 3.5 Tons of cocaine was caught hidden in a shipment of cassava roots originated in Costa Rica
From I. Tahir, Rapiscan, APAE meeting

6. Cargo Screening Accelerators
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.

7. X-Band RF Applications
Low Energy, Low Output:
1 MeV, up to 2 cGy/min at 100 Hz.
Air cargo screening  inspect a full ULD:
No system currently exists to achieve the
required penetration and spatial resolution,
A 1 or 2 MeV based LINAC inspection system
has the potential to open up this new
market sector.
Mobile screening with a small exclusion zone:
Current mobile screening systems require
40m x 40m exclusion zone  protect public.
A low energy and dose rate LINAC can:
significantly reduce the exclusion zone footprint,
allow scanning in public areas i.e. sporting
events, car parks, concerts, etc.

8. Why X-band? (2rcavtshield + tshield2)p
For a mobile linac mounted on a robotic arm the weight of the linac is critical.
While the linac isn’t very big or heavy the shielding is.
X-band means that the shielding diameter is much less.
Area of shielding is given by
(2rcavtshield + tshield2)p
Availability of 9.3 GHz magnetrons

9. Cargo Screening Accelerators
X-band technology chosen due to:
availability of technology
compactness
technological limits to robustness
tolerances at high power in micromachining and brazing.
Existing Linac suppliers:
Varian (USA) – 65% market
Siemens (USA)
Nutech (China)
Linear Accelerators account for 90% of the sources used in high energy cargo screening.
It is expected that the global market is ~few hundred units/year.
In 2007, 250 units were sold internationally.
Data provided by Rapiscan Global Sales and Marketing (2007)

10. CLASP Ph-I Collaboration Team
Rapiscan Systems:
Ed Morton (Rapiscan PI)
Imran Tahir (Magnetron Controls)
E2v:
Stuart Andrews (Gun/Magnetron)
Cliff Weatherup (e2v PI)
Tushar Ghosh (Gun)
Trevor Cross (e2v PI)
Lancaster University:
Graeme Burt (Project Leader)
Praveen Ambattu (Linac)
Chris Lingwood (Linac)
Tom Abram (Mechanical)
Mike Jenkins (Linac) – Now at ASTeC
STFC, ASTeC Daresbury Lab:
Ian Burrows (Mechanical Eng.)
Peter Corlett (Project Manager)
Andrew Goulden (Cooling Sys.)
Paul Hindley (Installation)
Peter McIntosh (ASTeC PI)
Keith Middleman (Vacuum)
Rob Smith (Beam Diagnostics)
Chris White (Electrical Eng.)
Steve Griffith (electrical)
Travor Harnett (Electrical)

11. CLASP 1 MeV System (Funded Phase-I)
DC Electron Gun e2V collaboration
X-ray Target Rapiscan collaboration
Buncher and Accelerating Structure (1 MeV)
CI Proposal Scope
Phase-I
Magnetron
e2V collaboration
(8-12 GHz, 1-2 MW, Hz) Dynamic switching of amplitude and phase pulse-to-pulse)
Automated Control System
(Energy, rep-rate, dose)
Proprietary Rapiscan Imaging and Data Analysis

12. Stability against frequency detuning and losses
From the single chain model of ‘N+1’ coupled cavities, the eigenfunction for mode ‘m’ and
cell ‘n’, can be written as, k
Now incorporating frequency shift and losses to the cells, then the modified eigenfunction is given by,
Amplitude fluctuation can be caused by frequency errors caused from fabrication errors
Phase error can be caused by the cavity losses (wall and beam loading)
Mode
Amplitude error
Phase
error
zero
Δf/f
1/Q
p/2
(Δf/f)2
Nil p
1) T. Wangler, RF Linear accelerators, 2) E.A. Knapp, SW high energy linac structures, Rev. Sci. Instr. 1968

13. Bi-periodic cavity
p/2 modes are more stable than p modes as the contribution from the modes above and below cancel and they have a large separation to the next nearest mode
high shunt impedance
p-mode
high field stability
p/2-mode
p/2-mode
bi-periodic L
both !
L a p
Coupling cavity
Accelerating cavity
Beam sees a p-mode high acceleration
RF sees a p/2-mode field highly stable

14. RF bunching and focusing
Solenoids are unacceptable for compact applications. Hence RF focusing from the linac structure is used
Radial focusing
(long. Debunching)
Initially the DC bunch see’s all phases, bunching phases are captured
The captured bunch then is accelerated moving towards the peak acceleration
The bunch is then moved to a radially focussing phase until the linac exit which unfortunately starts to debunch the beam.
CI-SAC Nov 2010

15. 1 MeV Buncher/Accelerator
17 keV

16. 1 MeV Linac Design 5 mm beampipe diameter 3.5 mm iris thickness
Parameter
Value
Energy
1 MeV
Frequency
9.3 GHz
Length
130 mm
Rsh max
116 M/m
Pin
433 kW
Pulse Length
4 s
Pulse Rate
250 Hz
Peak Beam Current
70 mA
Average Beam Power
70 W
5 mm beampipe diameter
3.5 mm iris thickness
1 mm coupling cell thickness
Gradient (MV/m)
E (MeV)
Ibeam (mA)
Spot Size (mm)
20 (nom)
1.08 70
1.6
+10 %
+11 %
-4 %
+58 %
-10%
-27 %
-33 %
-55 %
Voltage (kV)
E (MeV)
Ibeam (mA)
Spot Size (mm)
17 (nom)
1.08 70
1.6
+10 %
+0.8 %
-3.5 %
+48 %
-10%
-7 %
-20 %
-15 %

17. Beam Tracking Analysis
Particle Tracking initially performed in ASTRA.
Collaboration with Tech-X UK to verify Linac electron beam capture and tracking.
Using VORPAL code to validate PIC transport.
Good comparison was found between both methods.

18. Launch radius=0, Momentum vs Z
2.09 MeV
1.58 MeV
1.19 MeV
0.59 MeV
Here ‘phi’ is the particle launch phase with respect to the phase giving maximum energy

19. Linac Fabrication Fabrication commissioned with UK industry:
Shakespeare Engineering, Ltd
Geometric tolerances of 10 m required.
Diamond machining and vacuum brazing processes employed.

20. Cavity Tuning
Structure was found to have poor matching and field flatness

21. Lancaster/STFC X-band structure
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)
Built by Comeb, Italy

22. Diagnostics Line
In order to fully diagnose the beam from the linac we have a diagnostics line fitted to the output.
We have a motorised section which can either provide a slit, a screen, a tungsten target or vacuum.

23. Beam properties Spot size measured on phosphor screen at 3 mm.
This is a few cm away from the linac so we still need to work out the size at the linac exit.
We capture around 30-40% of the current emitted from the gun.

24. 3-4.5 MeV S-band linac Higher energy reach. Simpler to manufacture.
Pi mode structure.

25. From J. O’Malley AWE, APAE meeting

26. Higher Energy LINACs As Gamma-Ray Source
Recent theoretical/experimental work shows that a gamma beam from LINACs with energies higher than 10.6MeV can excite stable nitrogen isotope in explosive (N14) to radioactive isotope (N13), emitting positrons. The positron produces two 0.5MeV photons that are easily detectable
Same technique can be used to detect land mines as well using 17MeV LINAC
As Photo-neutron Source
Intense photo-neutron beam can be a reliable way of detecting explosives and nuclear materials
LINACs with energy levels above 8Mev and with converter materials such as Be and D2O in the X-Ray beam path can produce intense photo-neutron beams
From I. Tahir, Rapiscan, APAE meeting

27. Potential Linac solution
Could a high gradient linac offer 17 MeV electrons in 35 cm?
Its 50 MV/m which is certainly less than achieved using CLIC technology, but impedance is the issue.
There would not be space for an XL-5 or several smaller tubes.
Lets limit to a 7 MW with a PC.
Using a structure almost identical to an undamped CLIC structure would meet the requirements for this application.
Changing the beam current will allow the voltage to be adjusted.

28. Other Current/Future developments
Time of flight Compton Backscatter
Alloys 3D images to be created with access to only one side. Handling distortion cased by intensity dropping with distance is a challenge. Improved resolution can be achieved with smaller pulse lengths with higher current. Needs a higher current due to low backscattered dose.
CW linacs
Lower peak dose, and easier for detector to deal with temporally.
Phase contrast
Offers better contrast for low Z materials (a weakness in X-ray scanners).

29. Conclusion
Through PNPAS, a strong UK collaborative team has been formulated to successfully demonstrate a working system solution.
A new S-band linac has been developed
Future applications will need higher repetition rate and/or higher energies
A CLIC/VHEE like structure with a 7 MW klystron and a PC could meet the high gradient requirements.