# Presentation: 371590

## Crystal Collimation at RHIC

-         Raymond Fliller III
- Brookhaven National Laboratory

- HALO03, Montauk, NY

## Collaboration

- BNL, Upton, NY
- Angelika Drees
- Dave Gassner
- Lee Hammons
- Gary McIntyre
- Stephen Peggs
- Dejan Trbojevic

-  IHEP, Protvino
- Valery Biryukov
- Yuriy Chesnokov
- Viktor Terekhov

## Crystal Channeling

## Crystal Channeling

- If particles entering a crystal are properly aligned to the
- crystal planes, they will follow the planes, even if the crystal is bent.

## How channeling works

- Particles entering a crystal with small angles will see the crystal
- structure.  If they move fast enough, the individual atomic
- potentials are smeared together into a transverse inter-planar
- potential, U(x).  As long as the kinetic energy of the transverse
- motion is small compared to the maximum interplanar
- potential           , then the particle is channeled.

- x  is the location where the particle will enter the lattice plane
- electron cloud, p  is the transverse momentum.

- c

- t

## The Critical Angle

- p is the momentum of the incident particle,
- v is the velocity

*The Critical Angle*

## Effect of the Beam Optics

- Assuming a particle distribution

- = unnormalized emmittance

- = rms momentum deviation

- p

- J = particle action

- = momentum deviation

- By  writing J=J(x,x',), and integrating over , it is
- possible to construct the particle distribution J,(x,x').
- This can be used to compute the angle of the crystal with respect
- to the orbit to achieve channeling (_channeling angle_), the _angular width_ of the channeling distribution, and_ channeling_ _efficiency._

## Channeling Equations

-               is the distance between the crystal face and the
-  beam orbit.

- Channeling angle:

- The width of the channeling dip  is highly dependant on the average impact parameter of the particles *dx*,  ,, and D. The expression for is quite complicated, and not displayed.

- 

- 

- From Equation 2.12 in *Crystal Channeling and Its application to High Energy Accelerators *the channeling efficiency is

## Placing the crystal at a place with a large  or D' means:

-  The channeling angle depends strongly on crystal position
-  The width of the channeling is increased.
-  The channeling efficiency is reduced because of the increased width.
-  Increased sensitivity to lattice errors.

- None of these are good for a collimation system.

-  It is harder to operate efficiently
-  Reduced channeling efficiency = reduced collimation efficiency

-  Unfortunately, all of the RHIC warm spaces have large !
- For a =2m lattice ,  = 460 m and  = -8.3 at the crystal.
- For a =1m lattice ,  = 1020 m and  = -39 at the crystal.

## ...Means rotating it!

- Because of the tilt of the ellipse

- Moving the crystal...

## Volume Capture

- This model does not account for volume capture

- Particles that enter the crystal, not aligned to the planes,
- can scatter so that they have the correct angle to the planes,
- then channel the remaining distance in the crystal.

## CATCH Code 

- CATCH written by Valery Biryukov

## Simulation of Data from RHIC 2001 Run

**Machine optics has a great effect on channeling efficiency!**

## Effect of Multiple Turns on Channeling Signal

- Particles not initially aligned to the crystal planes will scatter through the crystal,  and can return on a subsequent turn and be properly aligned and channel.  Mutliple turns can also allow the particle multiple chances to scatter in the crystal and be captured in the volume.

## RHIC Overhead View 

-        Channeling with
- Gold and Polarized Proton Beams

## Crystal Collimator Setup

- 8 Upstream PIN diodes

- 4 Downstream PIN diodes

- Data fill focus on upstream PIN diodes

## Crystal Vessel

- Beam Direction

- Crystal

- Crystal Motion

## Crystal

- 5mm

- Beam Direction

- Crystal Courtesy of IHEP, Protvino

## Tabulation of Data

- 

- at PHENIX

- *

- (m)

## Run 2003 Au Beam Data

## Analysis of the data

- The averages quoted here are results from fitting.  The
- fit tends to give a width wider than the data and the simulation.
- Simulation agrees with data.

## Hodoscope signal from 2001 RHIC run.  

- Hodoscope signal from 2001 RHIC run.

- During the shutdown, the hodoscope was inspected, and  Photomultiplier Tube  gains were increased.  The preformance of the hodoscope improved, but gains where too low still for coincidence measurements.

## 2001 Run Data

- Agrees with measured Twiss Parameters.

- Fitting the second peak is harder, so the expected agreement with the Twiss Parameters is less.

## Crystal Collimation

## Summary and Future Plans

-  Crystal Channeling seen at RHIC
-  Optics errors led to reduced channeling efficiency
-  Crystal was not helpful with collimation because of these errors.
-  Crystal Collimator will be replaced with a conventional collimation system.
-  Crystals may be used for microbeam applications at BNL's new NSRL.