1. Conceptual Design of a Programmable Cone Generator for SK and T2K
D. Casper, J. Dunmore University of California, Irvine

2. Motivation Hardware simulation of single- and multi-ring events
Vertexing
Efficiency
Ring-counting
POLFIT
Use identical source in 2km detector and Super-K

3. IMB-Style Cone Generator
Advantages
Simple, proven technology
Easy for 1-ring topology
Use existing laser systems
Disadvantages
Hard to adapt to more complex geometry
Hard to vary relative intensity for 2+ rings

4. The “Death Star” Make an icosahedral device
Maybe solid, or maybe just a wire-frame
Drive each cone-generator with an LED
Vary intensity of each cone independently of others
Many different topologies possible depending on which LEDs are activated

5. Other Advantages
Electronic system will be completely portable between 2km and SK
Truly identical source
LEDs are very stable over time
Can potentially swap-in different colored ones too…
No need to take jig in and out of water to to change configuration
No need to manually rotate jig by hand
Possible to simulate specific kinematics, e.g. 0 mass constraint

6. Constraints Size of access ports is finite
“About 20 cm diameter” (Nakahata-san)
Cone-generator must be very compact!
LED pulse must be short (~ 1-2 ns)
10 cm circumscribed radius
9.5 cm edge
2.5 cm radius for
cone-generator aperture

7. How to make it small?
Need to use lenses and/or mirrors to produce cone pattern
Interesting observation:
The image of a point-source at the focal distance of a cylindrical lens is a line
Hmm…
Then the image of a point source at the focal distance of a toroidal lens is a ring…
~1.5 r

8. A Compact Single-Cone Source
Transparent, conical Cap (Air/Water interface)
Outgoing, conical rays
Toroidal Lens R ~ r for n ~ 1.45
and  = 41˚
LED (Programmable)

9. How Small?
The geometry of the toroidal lens is determined by the Cherenkov angle, and the index of refraction of the lens material
For a typical plastic lens material with n = 1.49, the minor and major radius of the torus are virtually equal: r/R = 1.0
So the “donut” has no hole
The absolute scale is determined by the size of the LED
The radii of the torus must be large enough that the LED is effectively a point source

10. Ray-Tracing Simulation
I’ve written a ray-tracing simulation to verify the imaging characteristics of the toroidal lens, and to study the effect of a finite-sized source
Includes the lens, mask near center of lens, conical shield, and water interface
Assume LED is a disk of variable size
Include realistic angular distribution for LED
The physics is straight-forward (Snell’s Law at each surface)
Reflectivity/Transmission vs. angle not included yet, probably not very important

11. Angular distribution (looks good!)
Simulation Results
R = 1 cm r = 1 cm n = 1.49
rLED = 1.2 mm
1/2 = 60˚
Assumed LED Angular Distribution
Angular distribution (looks good!)
Example LED
(OSRAM LB P473)
 ~ 465 nm

12. LED Pulses
1-2 ns LED pulses have been used in a variety of applications
High-energy physics
Fluorescence spectroscopy
Several pulser designs are published in the literature, but the specific LED models used are no longer in production
Idea is to make a small “base” with diode mounted, and larger programmable controller unit that sits on top of the tank
Width of LED Pulse (ns)
Blue UV
B.K.Lubsandorzhiev, Y.E.Vyatchin physics/

13. Status and Questions Optically, the concept appears to work well
Blue surface-mount LEDs with 1.2mm radius are commercially available
UV LEDs tend to be larger (~2.5 mm radius)
Maybe use a pinhole or lens to make the source appear smaller?
No practical problems with making ~4 cm diameter toroidal lens
Waiting to hear back from manufacturer with quote
Still need to address the electronics
More research needed, but doesn’t look like a show-stopper
Advice, references welcome