# Presentation: 580495

## The Development of Large-Area Psec-Resolution TOF Systems

**Henry  Frisch**
**Enrico Fermi Institute and Physics Dept**
**University of Chicago**

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## OUTLINE

**Introduction;**
**Three Key Developments since the 60’s: a) MCP’s,          200 GHZ electronics, and End-to-end Simulation;**
**HEP Needs: Particle ID and Flavor Flow, Heavy Particles, Displaced Vertices, Photon Vertex Determination; **
**The Need for End-to-End Simulation in Parallel;**
**Other Areas?  Other techniques?**
**What Determines the Ultimate Limits?**

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## Introduction

**Resolution on time measurements translates into resolution in space, which in turn impact  momentum and energy measurements. **
** ****Silicon Strip Detectors and Pixels have reduced position resolutions to ~10 microns or better.**
** ****Time resolution hasn’t kept pace- not much changed since the 60’s in large-scale TOF system resolutions and technologies (thick scint. or crystals, PM’s, Lecroy TDC’s)                         **
**Improving time measurements is fundamental , and  can affect many fields: particle physics, medical imaging, accelerators, astro and nuclear physics, laser ranging, ....**
** ****Need to understand what are the limiting underlying physical processes- e.g.  source line widths, photon statistics,  e/photon path length variations. **
** ****What is the ultimate limit for different applications? **

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## Possible Collider Applications

**Separating b from b-bar in measuring the top mass (lessens combinatorics => much better resolution)**
**Identifying csbar and udbar modes of the W to jj decays in the top mass analysis**
** ****Separating out vertices from different collisions at the LHC in the z-t plane**
**Identifying photons with vertices at the LHC (requires spatial resolution and converter ahead of the TOF system**
** ****Locating the Higgs vertex in H to gamma-gamma at the LHC (mass resolution)**** **
**Kaon ID in same-sign tagging in B physics (X3  in CDF Bs mixing analysis****)**
**Fixed target geometries- LHCb, Diffractive LHC Higgs, (and rare K and charm  fixed-target experiments)  **
**Super-B factory (Nagoya Group, V’avra at SLAC)**
** ****Strange, Charm, Beauty and Baryon Flow in Heavy Ion Collisions.. Etc.**

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## K-Pi Separation over 1.5m

-  Assumes perfect momentum resolution (time res is better than momentum res!)

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## Accelerator  Applications

**Momentum (velocity times known mass) Analysis in a beam (e.g. test beam).****  ****4 single-module stations (this is our proof of principle- first step after laser)**
**6D Muon Cooling (muons.inc, hopefully) measurements- two 25-module stations replace a  magnetic spectrometer (need pos. tho still 2 places)**
**Accelerator folks interested (per Patrick LeDu at LHC)**

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## Why has 100 psec been the # for 60 yrs?

**Typical path lengths for light and electrons are set by physical**** ****dimensions of the light collection and amplifying device.**

- These are now on the order of  an inch. One inch is 100 psec. That’s what we measure- no surprise! (pictures from T. Credo)

- Typical Light Source (With Bounces)

- Typical Detection Device (With Long Path Lengths)

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## Major advances for TOF measurements:

- 1. Development of MCP’s with 6-10 micron pore diameters

**Micro-photograph of Burle 25 micron tube- Greg Sellberg (Fermilab)**

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## Major advances for TOF measurements:

- 2. Ability to simulate electronics and systems
- to predict design performance

**Output at anode from simulation of 10 particles going through fused quartz window- T. Credo, R. Schroll **

**Jitter on leading edge 0.86 psec**

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## Major advances for TOF measurements:

- 3. Electronics with typical gate jitters << 1 psec

**Simulation with IHP Gen3 SiGe process- Fukun Tang (EFI-EDG)**

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## Major advances for TOF measurements:

**3a. Oscillator with predicted jitter ~5 femtosec (!)**
** ****(basis for PLL for our 1-psec TDC) .**
** **

**Most Recent work- **
**IBM 8HP SiGe** **process See talk by Fukun Tang (EFI-EDG)**

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## A real CDF Top Quark Event

-  **Fit t****0**** (start) from all tracks**

**W->charm sbar**

**W->electron+neutrino**

**B-quark**

**B-quark**

**T-quark->W+bquark**

**T-quark->W+bquark**

**Cal. Energy**
**From electron**

**T-Tbar -> W****+****bW****-****bbar**

**Can we follow the color flow through kaons, cham, bottom?   TOF!**

**Measure transit time here**
** ****(stop)**

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## Geometry for a Collider Detector

**“****r” is expensive- need a thin segmented detector**

**Coil**

**2” by 2” MCP’s**

**Beam Axis**

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## Generating the signal

**Use Cherenkov light - fast**

**A 2” x 2” MCP- actual thickness ~3/4”**
**e.g. Burle (Photonis) 85022-with mods per our work**

**Incoming rel. particle**

**Collect charge here-differential**
**Input to 200 GHz TDC chip**

**Custom Anode with **
**Equal-Time Transmission**
** ****Lines + Capacitative. Return**

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## Anode Structure 

**RF Transmission Lines**
**Summing smaller anode pads into 1” by 1” readout pixels**
**An equal time sum- make transmission lines  equal propagation times**
**Work on leading edge-  ringing not a problem for this fine segmentation**

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## Tim’s Equal-Time Collector

**4 Outputs-  each to a TDC chip (ASIC)**
**Chip to have < 1psec resolution(!)**
**-we are  doing this in the EDG (Harold, Tang).**

**Equal-time transmission-line traces to output pin**

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## Anode Return Path Problem

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## Capacitive Return Path Proposal

**Current from MCP-OUT**

**Return Current  from anode**

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## Solving the return-path problem

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## Mounting electronics on back of MCP- matching

- dum

- Conducting Epoxy- machine deposited by Greg Sellberg (Fermilab)

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## End-to-End Simulation Result

**Output at anode from simulation of 10 particles going through fused quartz window- T. Credo, R. Schroll **

**Jitter on leading edge 0.86 psec**

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## EDG’s Unique Capabilities - Harold’s Design for Readout

- dum

**Each module has 5 chips- 4 TDC chips (one per quadrant) and a DAQ `mother’ chip.**
**Problems are stability, calibration, rel. phase, noise.**
**Both chips are underway**

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## Simulation of Circuits (Tang)

- dum

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## Readout with sub-psec resolution:

_***Tang’s Time Stretcher- 4 chips/2x2in module***_

**Readout with sub-psec resolution:**

**Receiver**

**“****Zero”-walk Disc.**

**Stretcher**

**Driver**

**11-bit Counter**

**2 Ghz PLL**

**REF_CLK**

**PMT**

-  Front-end chip

- 1/4

**CK5Ghz**

**Tang Slide**

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## Diagram  of  Phase-Locked Loop

**1N**

**Diagram  of  Phase-Locked Loop**

**PD**

**CP**

**I****1**

**I****2**

**LF**

**VCO**

**F****ref**

**F****0**

- Uc

***PD: Phase Detector***
***CP: Charge Pump***
***LF: Loop Filter***
***VCO: Voltage Controlled Oscillator***

**Tang Slide**

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## Microphotograph of IHP Chip

- Taken at Fermilab by Hogan –
- Design by Fukun Tang

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## IBM SiGe BiCMOS8HP Process

**130-nm technology**
**SiGe hetero-junction bipolar transistors**
***f******T****** (high performance): 200GHz, BVceo=1.7V, BVcbo=5.9V***
***f******T****** (high breakdown):   57GHz,   BVceo=3.55V, BVcbo=12V***
**High-Q inductors and metal-insulator-metal capacitors**
**4 types of low-tolerance resistors with low and high sheet resistivity**
***n+ diffusion,  tantalum nitride,  p+ polisilicon and  p- polisilicon***
**Electrically writable e-fuse**
**CMOS transistors (VDD=1.2V or 2.5/3.3V)**
***Twin-well CMOS***
***Hyperabrupt junction and MOS varactors***
**Deep trench and shallow trench isolations**
**5 copper layers and 2 aluminum layers (3 thick layers)**
**Wire-bond or controlled collapse chip connect (C4) solder-bump terminals**

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## 2GHz VCO Design

**Simplified VCO Schematic**

- Purely hetero-junction transistors
- Negative resistance
- 130Mhz tuning range
- On-chip high-Q LC tank
- High Frequency PN diode Varactors
- Capacitor voltage dividers
- Full differential 50-ohm line drivers
- Deep trench isolation

- CORE

- Core

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## VCO Schematic & Post Layout Simulation Setup

_***VCO Schematic & Post Layout Simulation Setup***_

- av_Extracted (RCL)

- Schematic

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## Av_Extracted Back Annotation View

_***Av_Extracted Back Annotation View***_

- Node_Tn:
- C=119.8f
- L=73pH

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## VCO Post Layout Transit Simulation

_***VCO Post Layout Transit Simulation***_

**Transit Output Waveforms**

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## VCO Schematic and Post-layout V-F Transfer Function Plots 

- Schematic V-F Transfer Function

- Post Layout V-F Transfer Function
- F=2GHz@VC=1.35V
- Tuning Range=130MHz

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## VCO Post Layout Phase Noise Simulation 

_***VCO Post Layout Phase Noise Simulation ***_

**Output Phase Noise**

***VCO Cycle-to-cycle timing jitter can be estimated by following formula:***

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## Phase Detector and Loop Filter Design

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***Characteristics of Four-quadrant Multiplier Phase Detector Differential Outputs with over-driven Inputs***

******

******

******

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## Open loop (PD+LP) Sensitivity: 50uV/ps.

***Open loop (PD+LP) Sensitivity: 50uV/ps.***
***  ******20ps timing jitter at ref_clock generates about 33fs jitter at local clock!***

***2mV ripple with 2Ghz fundamental frequency at loop filter output is observed, PLL timing jitter is dominated by this ripple, which equivalents to ~66fs. ***

***A example showing Phase Detector & Loop Filter Open Loop Responses to the Ref_clock phase variation (1-20ps)***

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## DAQ Chip- 1/module

- Jakob Van Santen implemented the DAQ chip functionality in an Altera FPGA- tool-rich environment allowed simulation of the functionality and VHDL output before chip construction (Senior Thesis project in Physics)
- Will be designed in IBM process (we think) at Argonne by Gary Drake and co.
- Again, simulation means one doesn’t have to do trial-and-error.

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## Why is simulation essential?

- Want optimized MCP/Photodetector design- complex problem in electrostatics, fast circuits, surface physics, ....
- Want maximum performance without trial-and-error optimization (time, cost, performance)
- At these speeds (~1 psec) cannot probe electronics (for many reasons!)
- Debugging is impossible any other way.

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## Simulation for Coil Showering and various PMTs 

**Right now, we have a simulation using GEANT4, ROOT, connected by a python script**
**GEANT4:  pi****+**** enters solenoid, e- showers**
**ROOT:  MCP simulation -  get position, time of arrival of charge at anode pads**
**Both parts are approximations**
**Could we make this less home-brew and more modular?**
**Could we use GATE (Geant4 Application for Tomographic Emission) to simplify present and future modifications?**
**Working with Chin-tu Chen, Chien-Minh Kao and group, - they know GATE very well!**

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## Interface to Other Simulation Tools

**Interface to Other Simulation Tools**

- ASCII files:             Waveform time-value pair

- Tube Output Signals from Simulation

- Tube Output Signals from Scope

- System Simulation Results

- IBM 8HP PDK

- Cadence Virtuoso Analog Environment
- Or
- Cadence Virtuoso AMS Environment

- Custom Chip Schematic

- Spectre Netlist (Cadence Spice)

- ASCII files:                            Waveform time-value pair

- Spectre Netlist

- Spectre Library

- Cadence Simulator

- Tang slide

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## Questions on Simulation-Tasks (for discussion)

- Framework- what is the modern CS approach?
- Listing the modules- is there an architype set of modules?
- Do we have any of these modules at present?
- Can we specify the interfaces between modules- info and formats?
- Do we have any of these interfaces at present?
- Does it make sense to do Medical Imaging and HEP in one framework?
- Are there existing simulations for MCP’s?

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## Present Status of ANL/UC

**Have a simulation of Cherenkov radiation in MCP into electronics**
**Have placed an order with Burle/Photonis- have the 1****st**** of 4 tubes and have a good working relationship  (their good will and expertise is a major part of the effort): 10 micron tube in the works; optimized versions discussed;**
**Harold and Tang have a good grasp of the  overall system problems and scope, and have a top-level design plus details**
**Have licences and tools from IHP  and IBM working on our work stations. Made VCO in IHP; have design in IBM 8HP process.**
**Have modeled DAQ/System chip in Altera (Jakob Van Santen); ANL will continue in faster format.**
**ANL has built a test stand with working DAQ,  very-fast laser,  and has made contact with advanced accel folks:(+students)**
**Have established strong working relationship with Chin-Tu Chen’s PET group at UC;  Have proposed a program in the application of HEP to med imaging.**
**Have  found Greg Sellberg and Hogan at Fermilab to offer expert**** ****precision assembly advice and help (wonderful tools and talent!).**
**9. Are working with Jerry V’avra (SLAC); draft MOU with Saclay**

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## The Future of Psec Timing-                    Big Questions:

**From the work of the Nagoya Group, Jerry Va’vra, and ourselves it looks that the psec goal is not impossible. It’s a new field, and we have made first forays, and understand some fundamentals (e.g. need no bounces and short distances), but it’s entirely possible, even likely, that there are still much better ideas out**** ****there.**** **

**Questions:**
** ****Are there other techniques? (e.g. all Silicon)?**
** ****What determines the ultimate limits?**

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## Smaller Questions for Which I’d Love to Know the Answers

**What is the time structure of signals from crystals in PET? (amplitude vs time at psec level)**
**Could one integrate the electronics into the MCP structure- 3D silicon (Paul Horn)?**
**Will the capacitative return work?**
**How to calibrate the darn thing (a big system)?**
**How to distribute the clock**
**Can we join forces with others and go faster?**

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## The Future- Triggering?

**W->charm sbar**

**W->electron+neutrino**

**B-quark**

**B-quark**

**T-quark->W+bquark**

**T-quark->W+bquark**

**Cal. Energy**
**From electron**

**T-Tbar -> W****+****bW****-****bbar**

**Can we follow the color flow of the partons themselves?**

**Measure transit time here**
** ****(stop)**

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## Time-of-Flight Tomograph

**Time-of-Flight Tomograph**

- Can localize source along line of flight - *depends on timing resolution of detectors*
- Time of flight information can improve signal-to-noise in images - *weighted back-projection along line-of-response (LOR)*

-  x  = uncertainty in position along LOR
-        = c **.** t/2

-  x

**Karp, et al, UPenn**

**Slide from Chin-Tu Chen (UC) talk at Saclay Workshop**

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**Notes:**
One normal variation in PET cameras is the “time-of-flight” or TOF design. By measuring the difference in arrival time at the two detectors, the positron source can be localized along the line of flight. Doing this does not improve the spatial resolution, but improves the signal to noise ratio (the mechanism will be described in more detail in the next slide) — the variance improves by a factor of 2D/ct, where D is the diameter of the radionuclide distribution, c is the speed of light, and t is the TOF resolution. Several TOF PET systems were built in the 1980’s with barium fluoride or cesium fluoride scintillators. They achieved ~500 ps timing resolution, which results in 8 cm localization. For objects the size of the human head (which was what most PET cameras imaged in the 1980’s) the net result is a tomograph with a factor of ~2 lower variance than a non-TOF BGO tomograph.
Problems arose from the use of barium fluoride as a scintillator. It is less dense than BGO, and so the spatial resolution is degraded. In addition, the wavelength of its fast emission is in the hard UV, which made it difficult to work with (i.e. expensive) because it does not penetrate glass-windowed photomultiplier tubes or any known glue (to couple the crystal to the photomultiplier tube). Finally, it was difficult to keep these cameras in tune. Thus, TOF PET largely died at the end of the 80’s. However, the advent of LSO and other new PET scintillators (that can provide excellent timing resolution without the material drawbacks of barium fluoride) makes TOF a promising direction for modern PET.

## That’s All...

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## Backup Slides

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## π+ Generation, Coil

- Showering
- GEANT4

- Input Source code, Macros Files
- Geometry
- Materials
- Particle:
- Type
- Energy
- Initial Positions, Momentum
- Physics processes
- Verbose level

- PMT/MCP
- GEANT4 - swappable

- Get position, time

**Pure GEANT4**

- Have position,
- time, momentum,
- kinetic energy of
- each particle for each step
- (including upon entrance to PMT)

- Need to redo geometry (local approx.➔ cylinder)
- Need to redo field
- Need to connect two modules (python script in placefor older simulation)

- Shreyas Bhat slide

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## π+ Generation

- GATE

- Input Macros Files - precompiledsource
- Geometry
- Materials
- Particle:
- Type
- Energy
- Initial Positions, Momentum
- Verbose level

- Solenoid Showering
- GATE

- Physics processes
- macros file

- PMT/MCP
- GATE - swap with
- default “digitization”
- module

- Get position, time

**GATE**

- But, we need to write
- Source code for
- Magnetic Field, recompile

- Shreyas Bhat slide

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## A real CDF event- r-phi view

-  Key idea- fit t0 (start) from all tracks

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## MCP’s have path lengths <<1 psec:

- Can buy  MCP’s with 6-10 micron pore diameters

**Micro-photograph of Burle 25 micron tube- Greg Sellberg (Fermilab)**

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