# Presentation: 347310

## Monitoring Beam Intensity in the Tevatron Abort Gap Using Synchrotron Radiation

- Randy Thurman-Keup
*FNAL / AD / Instrumentation*

## Outline

- Motivation for Monitoring the Abort Gap Beam Intensity
- Synchrotron Radiation
- Synchrotron Radiation Devices in the Tevatron
- Some Results
- Other Odds and Ends

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Contributors

- Tom Meyer – AGI DAQ
- Eugene Lorman – Synclite
- Sten Hansen, Heide Schneider – Gating circuit
- Carl Lundberg, Dale Miller – Technical expertise
- Sasha Valishev – Synch. Rad., Acc. Phys., etc...
- Alan Hahn, Harry Cheung, Pat Hurh – Synclite
- Jim Fast, Ken Schultz, Mark Ruschman, Carl Lindenmeyer, Ron Miksa – Mech. Mods
- Morris Binkley – Big giant pulser
- Stefano de Santis, John Byrd – LBNL Gated PMT
- Stephen Pordes – Driving force

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Introduction

- The Tevatron operates with 36 bunches in 3 groups called trains
- Between each train there is an abort gap that is 139 RF buckets long
- RF bucket is 18.8 ns   Abort gap is 2.6 s
- In this talk, abort gap beam intensity measurements are usually normalized to beam around the ring

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Motivation

- During an abort
- Abort kicker magnet ramps up during abort gap
- Beam in the abort gap is directed towards magnets, CDF, etc...
- Quenches (in the past, 10 x 109 caused quenches)
- Recent experience......~40 x 109 did not quench (better collimation)
- CDF silicon detector damage
- DØ not impacted as much, protected by CDF collimator
- Previous monitors relied on counters external to the beampipe that were timed with abort gap
- Measured stuff leaving the abort gap, not stuff still in it
- Use synchrotron radiation to directly measure abort gap beam
- Want to be sensitive to a DC beam that is 1 part in 104 of the total beam

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Synchrotron Radiation History

- 100 yrs ago, calculations of radiation from circular paths
*Larmour, Liénard, Schott, Schwinger(later), etc...*
- 1947, Observed at 70 MeV e- synchrotron at GE
- 1944, Could have been betatron radiationif not for the shielding around the tube
- 1977, R. Coïsson calculates radiation from non-uniform magnetic fields such as magnet edges
- Significant radiation beyond the cutofffrequency which makes it possible to seeat high-energy proton machines
- 1979, First observation of protonsynchrotron radiation at CERN
- Early 90s, A. Hahn and P. Hurh produceprototype synchrotron radiation detector for Tevatron

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Synchrotron Radiation

- Radiated intensity  γ4
- Radiated intensity has a peak near the “critical frequency” and drops exponentially beyond
- Critical frequency  γ3
- Usually too infrared in proton machines
- Magnet edge enhances higher frequencies

**Dipole**

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Synchrotron Radiation @ FNAL

- TeV Dipole
- Critical wavelength ~ 2700 nm
- TeV Dipole Edge
- Critical wavelength ~ 220 nm

- System known as **Synclite**

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Synchrotron Radiation @ FNAL

- 200 nm

- 300 nm

- 400 nm

- 500 nm

- 600 nm

- 700 nm

- 800 nm

- 900 nm

- 1000 nm

- Illumination at the pickoff mirror

**980 GeV**

**This data generated by Synchrotron Radiation Workshop (SRW) calculation**

- Typical Proton Bunch
- Half million γ / 20 nm

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Expected # of photons

- Wanted to measure DC beam of 1 part in 104
- Total beam is 1013  want to measure 109 1.2 x 108 / abort gap
- Synchrotron radiation calculation
- # of 400 nm photons / 25nm / 6x1010 protons  ~  2 x 105
- Optical losses ~ 35% efficiency *(50% from beam splitter)*
- # of photons / 109 DC beam / 25 nm / rf bucket ~ 1
- Wavelength acceptance ~ 200nm
- Gating duration ~ 30 buckets
- PMT Quantum Efficiency ~ 15%
- Typical # of photoelectrons ~ 40

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Made use of existing synchrotron light system
- Measures beam profile, including abort gap, using lens and camera
- Added beam splitter and gated photomultiplier tube

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Synclite Device

- X-Y Mirror

- X-Y Mirror

- Pickoff Mirror

- Beampipe

- Beam Splitter

- 25:1 Filter

- CID Camera

- Filter Wheel

- Synchrotron Light

- Quartz Window

- PMT Module*

- Lens

- Proton Optics Box

- _PMT Module_*Contains optional 100:1 Filter

- 25:1 and 100:1 filters are Neutral Density Filters

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Synclite Device

**Future home of PMT**

**Proton Synclite Box**

**Antiproton Synclite Box**

- Picture taken beforePMT installation

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Synclite Device

**Synchrotron light spot**

**~ 9 in**

**Beam splitter**

- Picture taken with small CCD camera
- The specks are radiation-damaged pixels

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

**Synchrotron light box**

**Abort Gap PMT**

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Made use of existing synchrotron light system
- Measures beam profile, including abort gap, using lens and camera
- Added beam splitter and gated photomultiplier tube
- Photomultiplier had to be gateable and insensitive to light present just before the gate (bunch intensity is several thousand times brighter than DC beam)
- Rules out just gating the output of the PMT

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Made use of existing synchrotron light system
- Measures beam profile, including abort gap, using lens and camera
- Added beam splitter and gated photomultiplier tube
- Photomultiplier had to be gateable and insensitive to light present just before the gate (bunch intensity is several thousand times brighter than DC beam)
- Rules out just gating the output of the PMT
- Custom gating circuit for generic photomultiplier
- Pulse two dynodes

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Two dynodes are capacitively coupled to pulsed voltage source.
- When pulsed, the dynodes are pushed to their nominal voltage level.

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Made use of existing synchrotron light system
- Measures beam profile, including abort gap, using lens and camera
- Added beam splitter and gated photomultiplier tube
- Photomultiplier had to be gateable and insensitive to light present just before the gate (bunch intensity is several thousand times brighter than DC beam)
- Rules out just gating the output of the PMT
- Custom gating circuit for generic photomultiplier
- Pulse two dynodes
- ~200 ns settling time after gate application
- Relatively inexpensive
- Not all PMT’s work correctly
- End window tube had 10 μs transient after application of gate
- Side window tube worked better, installed for several months
- Some sensitivity to pre-gate light

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Test stand used a pulsed blue LED to simulate the beam bunches and a constant low level green LED to simulate the DC beam

- End-window tube gating transient

- Pre-gate light sensitivity

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Made use of existing synchrotron light system
- Measures beam profile, including abort gap, using lens and camera
- Added beam splitter and gated photomultiplier tube
- Photomultiplier had to be gateable and insensitive to light present just before the gate (bunch intensity is several thousand times brighter than DC beam)
- Rules out just gating the output of the PMT
- Custom gating circuit for generic photomultiplier
- Hamamatsu gated regular PMT (inexpensive, $5K)
- PMT module  complex circuitry would be in tunnel
- Exhibited same sensitivity to light as FNAL gating circuit

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Made use of existing synchrotron light system
- Measures beam profile, including abort gap, using lens and camera
- Added beam splitter and gated photomultiplier tube
- Photomultiplier had to be gateable and insensitive to light present just before the gate (bunch intensity is several thousand times brighter than DC beam)
- Rules out just gating the output of the PMT
- Custom gating circuit for generic photomultiplier
- Hamamatsu gated regular PMT (inexpensive, $5K)
- Hamamatsu gated MCP style PMT on loan from LBNL
- Expensive! (~$20K /tube)
- 2-stage Micro Channel Plate PMT – Gain of <= 106
- 5ns minimum gating time w/no noticeable settling time
- No sensitivity to pre-gate light
- Very large extinction ratio

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## DAQ Systems

**Synclite DAQ System**

**Abort Gap DAQ System**

- Average 1000 turns of data in each of the 3 abort gaps.

- For abort gap:
- Average 200 camera frames of data, each containing ~75 turns

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity (Synclite)

- Peak is ~7 x 109

- CID Camera Image

- Raw

- Background Subtracted

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Abort Kicker Turn-on

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Calibration

- Two options:
- Calibrate by gating on a bunch (with attenuators in place) and comparing to FBI intensity
- Calibrate by turning the TEL off and then back on and comparing to the DCCT measurement of the accumulated beam intensity

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Calibration

- Periodically check this using TEL trips.  Seems to vary by 40-50%

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Abort Gap Intensity Monitor

- Abort gap beam intensity after longitudinal damper went berserk and started shaking beam everywhere (AGI saturates at ~70E9)

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Microbunches

- Longitudinal profile in the end of an abort gap
- Captured beam should be bunched in the center of RF buckets

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## DC Beam Elsewhere

- Take 1 6-bucket sample between each bunch and ~10 in each abort gap
- ~30 hour store duration (sample # = time)

**Sample #**

**Position #**

**Position #**

**Sample #**

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## DC Beam Elsewhere

- Measure every bucket in 1 train except the 5 centered on each bunch
- Compare change from beginning to end of store as a function of bucket

- Intensity (E9)

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## DC Beam Diffusion

- Expected Diffusion Direction

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Issues

- No automatic pedestal subtraction
- Pedestal varies by ± 1 E9 over time
- Pedestal very sensitive to beam synchronous EM noise
- Will be helped by new PMT (see Future)
- No automatic gain measurement
- Checked periodically (TEL trips)
- Correlation between TEL and bunch calibrations
- Cross-talk from Synclite
- Need synchronization for any automatic solutions
- OAC?

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Pedestal behavior

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Pedestal behavior

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Summary

- Abort Gap Monitoring PMT has been in use for nearly 2 years
- Integral part of TeV operations
- Checked by the sequencer before normal beam aborts
- Watched by CDF and MCR
- i.e. I get paged when it hiccups

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Future

- 2006 Shutdown
- Replace LBNL PMT with newly purchased PMT
- Hamamatsu R5916U-50 ++
- 3 stage MCP vs. 2 stage (better S/N; N being EM pickup)
- 10% duty cycle vs. 1% duty cycle for gating
- Install second one in antiproton box
- Typical proton bunch intensity is 250-300 E9
- Pbar bunch intensities now approaching 100 E9
- Efforts to see pbar abort gap beam in Synclite have not seen anything large (maybe possibly hints of < 1E9 at beginning of store, but complicated by pickoff mirror movement)
- Possibly attempt to automate gain and pedestal measurements
- OAC?

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006

## Stuff

- R. Coïsson,
- Opt. Commun. 22, (1977) 135*On Synchrotron Radiation in Non-Uniform Magnetic Fields*
- Phys. Rev. A20 (1979) 2*Angular-Spectral Distribution and Polarization of Synchrotron Radiation from a “Short” Magnet*
- R. Bossart, *et. al.*,
- Nucl. Instr. and Meth. 184 (1981) 349*Observation of Visible Synchrotron Radiation Emitted by a High-Energy Proton Beam at the Edge of a Magnetic Field*

- R. Thurman-Keup  -  AD Seminar

- 2/21/2006