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

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

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

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

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

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

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

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)

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

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

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

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/0410281

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