# Presentation: 850098

## ODR Diagnostics for Hadron Colliders

- Tanaji Sen
- FNAL/APC

- Acknowledgements:
-   A. Lumpkin, V. Scarpine, R. Thurman-Keup, M. Wendt

## Diffraction Radiation

- ODR for Hadron colliders

- Radiation emitted when a charged particle passes **in the vicinity** of a conducting target.
-          Two cones (angle ~ 2/γ ) of radiation in the forward and  backward direction
-           Key parameters: the impact parameter, beam energy and wavelength of radiation
-  Similar (and different) to transition radiation where a particle passes **through** the conducting target.
-  Main advantage: Non-invasive
-  Initial theory developed: ~ 1960s
-  First measurements reported: ~1995

## Possible Beam Diagnostics

- ODR for Hadron colliders

**Possible Beam Diagnostics**

- Diffraction Radiation Observables
- Near field (at or near target) intensity
- Polarization
- Frequency spectrum
- Far field angular distribution
- Interference between radiation from 2 sources
-  These can be combined to potentially measure
- Beam size
-  Beam position
-  Beam divergence
-  Energy
-  Recent measurements at KEK, APS, FLASH
-  Interest at other labs: CEBAF, BNL

## Diffraction Radiation - Layout

- ODR for Hadron colliders

**Diffraction Radiation - Layout**

**BDR**

- CCD or PMT

- Filter

- Polarizer

- Target

- Proton beam

- b  Impact parameter

- Beam

- 2Φ

- Φ

**Far field imaging at KEK**
- Phys. Rev Letters
- 90, 104801 (2003)
- 93, 244802 (2004)
**Near field  image at APS**
- PRSTAB:10,022802(2007)

- Target

**Effective source size**
**at target = (****γλ****)/2****π**

## KEK results (slit target)

- ODR for Hadron colliders

**KEK results (slit target)**

**Imax**

## KEK Summary

- ODR for Hadron colliders

**KEK Summary**

- Electron beam energy=1.28 GeV, γ=2505
- Bunch intensity = 1.2 x 1010
- Beam size = 10 μm,
-    divergence= 3.8x10-3(1/γ)
- Impact parameter ~ 5σy
- Detected wavelength λ = 0.56 μm
- Synchrotron radiation background from dipole 8m upstream; used a mask
- ODR intensity = 58% of OTR intensity
- Measured sensitivity to beam size ~ _14 __μ__m_

## APS 

- ODR for Hadron colliders

**APS **

- 10σ

- 10 σ

- 10 σ

- 16σ

## APS Summary 

- ODR for Hadron colliders

**APS Summary **

- Electron beam energy = 7GeV, γ= 13,699
- Bunch intensity ~ 1.9x1010 (3 nC). Tevatron proton intensity ~ 43 nC
- Beam sizes: σx = 1375 μm, σy = 200 μm
- Typical impact parameter ~ 6 σy
- Wavelength λ ~ 0.83 μm
- ODR signals observed up to 16 σy
- ODR signals (@ 6 σy) about 10% of OTR signal
- Sensitive to horizontal offsets of 50-100 μm
- Sensitive to beam size changes of 20-50 μm

## Hadron colliders: key parameters

- ODR for Hadron colliders

**Hadron colliders: key parameters**

|  | Tevatron |  RHIC |  LHC |
| --- | --- | --- | --- |
| Energy [GeV]
Bunch intensity
Target clearance [σ]
 Beam size [μm]
Wavelength[μm]
Beam div/opening angle
Far-field distance [m]   |  980
2.7x1011
12          8
399
14.4
2.9x10-3

2.5 |  250
 2x1011
12          8
1012
143
1.2x10-5

1.6 |  7000
1.1x1011
12         8
807
4.1
5.7x10-3

36.1 |

## Different target shapes

- ODR for Hadron colliders

**Different target shapes**

- Straight edge – APS (near-field), KEK (far-field)
- Rectangular slit – KEK (far-field)
- Round hole

## Round hole

- ODR for Hadron colliders

**Round hole**

- Intensity distribution from a single particle (PSF) depends only on these parameters
-           g, u, γθ
- Otherwise it does not depend on the inner radius a<
- Number of photons emitted (far-field)

-  Inner radius a<. Outer radius a>
-   Key parameters
-  Critical frequency  ωc = γc/a<
-  Radii ratio g = a>/a<
-  Scaled frequency u = ω / ωc

- ΔNγ = (β/π)αf u2 F(g, u) Δω/ω

## Far-field spectral distributions (round hole)

- ODR for Hadron colliders

**Far-field spectral distributions (round hole)**

- For g =1.1,
- Number of photons
- emitted /bunch/turn
-      ΔNγ  ~ 1.6 x 106

## Rectangular Slit

- ODR for Hadron colliders

**Rectangular Slit**

-  Angular spectral distribution from a bunch depends on
- Slit width
- RMS size
- Bunch transverse offset
- Observation angles
-     θx, θy

- tx= γθx,  ty = γθy

## Far-field spectral distributions (slit)

- ODR for Hadron colliders

**Far-field spectral distributions (slit)**

- Wavelength dependence

**LHC**

**TEV**

- Beam parameter dependence

## Far-field spectral distribution(straight edge)

- ODR for Hadron colliders

**Far-field spectral distribution****(straight edge)**

- Characteristic  λc = 2πb/γ
- At b = 4.8mm, λc = 28 μm (TEV)
- Spectrum at ω > 0.2 ωc
- Photon yield/bunch/turn
- At ω = 2 ωc or λ=14 μm,
-                     ΔN = 4.4 x 106
-                photons/bunch/turn

## Interferometry

- ODR for Hadron colliders

**Interferometry**

- Beam

- Interference from multiple apertures

- Forward DR from 1st target interferes with backward DR from 2nd target
- Interference pattern is sensitive to beam divergence
- Distance between targets should be comparable to far field distance. Rules this out
- for the LHC
- May be difficult for very
- small beam divergences

- FDR

- BDR

## ODR location in the Tevatron

- ODR for Hadron colliders

**ODR location in the Tevatron**

- Drift space around C0 is 11m
- 4 dipoles upstream, 2 dipoles downstream in the proton direction
- Beta functions are in the range 60-85m
- Preferable to image pbars closer to the 4 dipoles ?

- 11 m

- protons

- Optics around C0

## Empty space in C0

- ODR for Hadron colliders

**Empty space in C0**

## LHC Insertion

- ODR for Hadron colliders

**LHC Insertion**

- Regular arc dipoles are ~260m from IP
- Weak separation dipoles (~1.5T) at 60m from IP
- ODR monitor would be stationed between the detector and 1st quadrupole – left and right side of IR

- 260m

- 260m

## Measuring β*, α*

- Beam size, hence β, is measured at +L, -L
-  α* = [β(-L) – β(+L)]/4L
- β* = ( [< β>2 + 4(1+ α*2)L2]1/2 - < β>)/2)
-     < β> = [β(-L) + β(+L)]/2
- This measurement of β*, α* is independent of optics errors

- T. Sen; 10/18/2007

- ODR for Hadron colliders

- IP

- -L

- L

## Layout in the LHC

- ODR for Hadron colliders

**Layout in the LHC**

- IP5: Horizontal Crossing Angle

- IP1 : Vertical Crossing Angle

- b

- b

- BDR Cone

- BDR Cone

- Target at 45  to
-  beam direction

**Beam 1**

**Beam 2**

## Design decisions

- ODR for Hadron colliders

**Design decisions**

- Location of the target; both beams should not be present simultaneously, far enough from dipoles, ...
- _Determine the synchrotron radiation background at the target_
- Determine the optimal shape and material of the target
- Near-field/Far-field imaging or both
- Determine the optimal wavelength range
- If IR, deal with the challenges of IR detection (sensitivity, water vapor absorption, window material, ...)

## Choice of window

- ODR for Hadron colliders

**Choice of window**

- Quartz has almost no transmission between 10 and 50 microns. Might work for RHIC (~140microns)
- Diamond would be the material of choice for IR

- Courtesy: FLASH

## Goals for Tevatron measurements

- ODR for Hadron colliders

**Goals for Tevatron measurements**

- Install ODR monitor in 2008 shutdown
- Measure two beam parameters with good reproducibility for a single beam
- Either beam size and beam position
-    OR
- Beam size and beam divergence
- Measurements in both planes ?
- Measure parameters for several bunches
- Update measurements every N turns

## Pros and Cons of ODR in the LHC

- ODR for Hadron colliders

**Pros and Cons of ODR in the LHC**

- _Pros._
- Non-invasive
- Beam size measurement near the IP on both sides, hence beam size at the IP
- Measurement itself will not be influenced by optics errors
- This can be used to diagnose gradient errors in the IR.
- Relative beam position measurements can be compared against BPM measurements in the IR.
-  A tomographic reconstruction of transverse phase space may be possible from measurements over several turns.
- _Cons_
- Slower than synchrotron light monitor. Signal will have to be integrated over several bunches.
- Errors associated with the measurement are not well known at the moment.  Installing a device in the Tevatron would determine the limits of resolution with this device.
- The ODR monitor would be installed between the TAS and the 1st quad. Impact on the machine-detector interface needs to be better understood.

## Major LHC issues

- ODR for Hadron colliders

**Major LHC issues**

- What are the major benefits of imaging close to the IP?
- How do the errors associated with the ODR measurement compare to the errors from propagating the synchrotron light monitor measurement in the arcs to the IP?
- How fast can the ODR measurements be made?
- What is the level of synchrotron radiation background at the ODR target?

## Next Steps

- ODR for Hadron colliders

**Next Steps**

- Design ODR setup in the Tevatron – E0 preferable.
- Develop a collaboration with US labs and CERN
- Present proposal to the LARP collaboration for funding a LARP task (April 2008)
- Proceed with experiments
- Develop ODR facility for the LHC
- Determine potential for future machines: muon collider, ILC,...