Post on 18-Jan-2018
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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