# Presentation: 143743

## T9 – DiagnosticsM. Ross/R. PasquinelliThursday, July 19 

- T9 – DiagnosticsM. Ross/R. PasquinelliThursday, July 19

- RD:
- 1)   *determine mixing between z and x/y*
- 2)   *determine phase space halo parameters*
*3)   develop effective collimation to localize activation*
- relied upon for SNS ring

- Charge: 	Note promising RD;
- 	assess involved effort

- Selected _***5***__* fundamental*_ issues facing a variety of projects

- Issue 1:_emittance propagation in linacs_   *p* & *e*

- _Proton Drivers + VLHC_ (pseudo-linac):
-  *Problem*: understand diffusion mechanisms
- Diffusion limits high power performance  activation caused by beam loss
- SNS beam loss limits < 1W/m (10-6)
- SCRF cleanliness  severe limit on materials; systems
- SNS will use laserwire

## Emittance propagation in linacs 

- _Linear Collider_
*Problem*: Control wakes, dispersion () and coupling
- Single bunch wakes and  increase projected emittance  usually unrecoverable
- Filamentation follows in chromatic systems

- Practical approach:
- BPM based emittance optimization
- Measurement of projected emittance
- Development of more direct diagnostics

- _BPM based (SLC-like):_
- beam-based alignment  quad dither/shunt
- dispersion-free steering  correction of E generated distortions
- global correction  empirical orthogonalization minimalization
*Integrated  calibration, correction, analysis and error handling*

- RD:
*How well does this really work?*
- 		Tests: SLAC Linac, TTF

- Head-on image of ‘tilted’ beam 

- 20 nm achieved in FFTB - Cband

## Emittance propagation in linacs (2)

- _Linear Collider_
- _2) Transverse beam profile monitor_
*LASERWIRE **** the *LC replacement of wire scanner
- Vital projected emittance predictor of luminosity
- Wire/Laserwire monitors measure only projection  don’t directly provide source location

- RD: *Develop accurate monitor for projected emittance*
**High beam power; small spot sizes (resolution); large aspect ratio**
- 		Tests: ATF, TTF, CTF

- “Ability to make measurements at the diagnostic and predictive level as opposed to measurement of the end result”

- KEK – ATF ring laserwire

## Emittance propagation in linacs (3)

- _Linear Collider_
- _3) Direct measurement of beam ‘tilt’_
- Use cavity BPM dipole mode
- ‘crab’ structure in reverse
- for high disruption, *y – z* correlation serious concern

- RD: *Develop monitor for beam y(x)– z correlation*
*	**	*Test in FFTB, ATF
- 	( Develop monitor for ‘slice’ emittance FEL RD)

- a pair of macro particles:

- 

- t

- q/2

- q/2

- 

- EXAMPLE:
- Bunch length: t = 200 m/c = 0.67 ps
- Tilt tolerance	d = 200 nm
- Cavity Frequency	F = 11.424 GHz
- _Ratio of tilt to position sensitivity:_	1⁄2ft = 0.012
- A bunch tilt of 200 nm / 200 m yields as much signal as a beam offset of 0.012 * 200 nm = 2.4nm
- Need BPM resolution of ~ 2 nm to measure this tilt

## Issue 2:Bunch length & longitudinal dynamics - linacs

- _Linear Collider_
- LC/FEL linacs use multiple compression stages
**result is highly distorted z phase space**
- TESLA, N/JLC z ~ 100m

- RD: *Resurrect deflection structure and test*
*	*SLAC FEL - LCLS

- Compression stages in FEL linac

- Transverse deflecting structure -- ‘crab’

- Rotate (pitch/yaw) in order to display z on screen:

- _500 GeV streak camera_

## Issue 3:Single bunch instabilities

- _e+e- ring factories & LC & proton rings_
- _Emittance degradation from ambient particles – ions/electrons_
- e- cloud generated by SR/photo-electric effect; multiplied by secondary emission
- (e+ only; e- disperses cloud)
- Can cause _4x_ variation in *L* bunch/bunch
- Resonant behavior – bunch spacing; charge; vacuum chamber dimensions; local fields

- RD:
*Validate simulations by measuring cloud properties*
- (joint beam dynamics/diagnostics effort)
*Develop b/b L phenomenology*
- B-Factory operation/MD

- PEP-2 example
- fill pattern:

- Large ion gap
- small trains alternating between 9 and 10 bunches long
- train head intensity ramp
- 4 bucket spacing (design 2)
- _657 bunches filled out of ~ 1500 planned in design_

- Electron cloud analyzer - APS

## Issue 4: Integration

- _Example: SC proton collider rings_
- TeV/HERA/LHC
- Chronic operational limitation

- Remember GAN?

- RD: *Develop instantaneous chromaticity monitor for feedback*
- (CERN/DESY test)
- 	*Other optical stabilization?*

- Use head/tail (E) oscillation difference:

- “If it is difficult to accomplish locally – a very different approach is required for remote operation”

## Issue 5: Accelerator RD

- Example: -cooling
- m uses SC magnets and high gradient RF
- (Combination of *e/p*!)
- Measure profile inside cooling channel using:
- Thermal network on hydrogen vessel
- Scintillating fibers
- Very little space for diagnostics!

*RD in parallel between machine and its tools*

- Critical evaluation of emittance reduction experiment needed

## T9 – DiagnosticsM. Ross/R. Pasquinelli

- T9 participation representative of Snowmass diversity (~15)
- 	 Cross flow of information unique to Snowmass
- Active discussion
- RD interest from a wide variety of groups

- T9 – DiagnosticsM. Ross/R. Pasquinelli