Marc Ross T9 – Snowmass 2001 Closing Plenary

T9 – DiagnosticsM. Ross/R. Pasquinelli

Thursday, July 19

RD:1)   determine mixing between z and x/y

2)   determine phase space halo parameters3)   develop effective collimation to localize

activationrelied 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; systemsSNS will use laserwire

Emittance propagation in linacs Linear Collider•Problem: Control wakes, dispersion () and coupling •Single bunch wakes and increase projected emittance usually unrecoverableFilamentation follows in chromatic systems

Practical approach: 1) BPM based emittance optimization2) Measurement of projected emittance3) Development of more direct diagnostics

1) BPM based (SLC-like):a) beam-based alignment quad dither/shuntb) dispersion-free steering correction of E generated distortionsc) 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

5mm Pb collimatorCsI Scintillator

Scattered

Movable table

12.8 m Laser wire systemPhoton Detector System

Laser monitorsystem

input system

Optical CavityLaser

Laser

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)

2sincos

2)

2(sin

22)

2(sin

22)( ttt tqatqatqatV

a pair of macro particles:

tq/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:

½ft = 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

RF InputCoupler

BeamDeflection

Irises withmode-lockingholes

z

Linear Collider

LC/FEL linacs use multiple compression stagesresult is highly distorted z phase

spaceTESLA, N/JLC z ~ 100m

RD: Resurrect deflection structure and test

SLAC FEL - LCLS Com

pres

sion

sta

ges

in F

EL li

nac

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 examplefill pattern:

Large ion gapsmall trains alternating between 9 and 10 bunches longtrain head intensity ramp4 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

Marc Ross T9 – Snowmass 2001 Closing Plenary

Beam Diagnostics:

•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