Beam Instrumentation for HPM -with a strong focus on ESS Andreas Jansson Paris, France, 2011-07-01.

Beam Instrumentationfor HPM-with a strong focus on ESS

Andreas Jansson

Paris, France, 2011-07-01

P vs H-

• An H- beam allows for diagnostic methods based on laser-induced photo-neutralization.– All sorts of fun non-invasive measurements

possible– Not an option in a proton linac like ESS, so I won’t

talk about it.

NB. Due to concerns about losses, unnessecary use of H- is suppressed in e.g. Project X

Diagnostics types in HPA

• Diagnostics for daily operation– Beam Loss– Beam Current– Beam Position &

Phase– Target spot size

• Focus on reliability• Non-invasive.

• Diagnostics for commissioning and studies/optimization– Beam size/emittance– Bunch length/shape– Beam halo– Electron cloud(?)

• Focus on accuracy• Could be invasive

and/or use special beam.

ESS Beam Parameters

Beam Pulse Current: 50 mA (60mA from

source)

Bunch repetition rate: 352 MHz

Bunch charge: 140 pC

Bunch length (r.m.s.): 10-40 ps

Beam size (r.m.s.): 1-3 mm

Prel. ESS Diagnostics Specs• The beam loss monitoring system needs sufficient sensitivity to keep average losses below

1W/m, and enough time resolution/dynamic range to protect the machine from damage in case of (worst case scenario) uncontrolled fast beam loss.

• The beam position needs to be measured with an accuracy of a couple per cent of the beam size, or about 0.1-0.2 mm. The measurement should have a response time to changes of the order of 1 μs or better.

• The time of arrival, or phase, should be measured to a fraction of a degree of RF phase, or about 2-4 ps. A fast response to changes is not needed to phase the cavities, but may be useful for e.g. LLRF studies.

• The beam size needs to be measured with an accuracy of 10% or better. The beam size is about 2-3 mm at the available locations. The measurement can be an average over the 2 ms LINAC pulse.

• The bunch length needs to be measured with an accuracy of 10% or better. The measurement can be taken as an average over the pulse, or on a single bunch in the train. There is no need to measure the bunch length of all bunches individually. •

• Need to measure halo at the level of 10-5 or less of total beam. • The beam profile on target needs to be measured with an accuracy of 10%. Since non-linear

elements may be used in the final focus, this requirement is best expressed in terms of beam density rather than size.

Preliminary. Expected to change!

Important Assumption

• It is generally assumed that a “special diagnostics beam” would be low rep rate (perhaps 1Hz or less) and short pulse (perhaps 100us or less), but nominal bunch intensity.– Lowering beam current changes the optics of the

machine, making measurement results less useful– Means nominal bunch charge is unchanged for

diagnstics pulse• An exception to this rule could be that BPM data

from low current beam might be useful for early commissioning.

ESS Preliminary System Count

Based on discussions with Beam Physics in Lund, documented inhttp://eval.esss.lu.se/cgi-bin/public/DocDB/ShowDocument?docid=43 Intended as starting point for discussions. Expected to change.

Cryomodule & Diagnostics

Loss monitors

• Need to determine BLM system layout (part of MPS) – includes the type (speed, sensitivity and dynamic range) of detectors and location– Ionization Chambers– Fast photo-multiplier tubes– Neutron detectors– Diamond detectors

• Ongoing simulations (L. Tchelidze)– Transverse error studies – will generate loss map – result

of a several thousand runs with different error distribution.– Secondary particle shower map along all accelerator –

result of a multiple Monte-Carlo particle transport codes (Geant4, MARS, FLUKA).

Beam Position Monitors

• One dual-plane BPM per cell/cryomodule, could perhaps live with less in high energy end.– Most likely button BPMs in most of linac (simpler),

except in front end where striplines may be used.• Signal processing most likely digital, narrowband

with bandwidth of order 1 MHz.– Several collaboration/COTS options including

OpenHardware, Libera, Fermilab/ATF, ESS-B …• In the process of hiring engineer to work on this• Do we need special BPMs to measure/predict beam

position on target (large demagnification)?

Beam Current Monitors

• Several BCTs in front-end + one between main linac sections.– Except for the very front-end, will likely only be

used for early commissioning• Available off the shelf.

– Absolute calibration may be an issue.– Position dependence of reading

Target spot size

• SNS experience with CrAl2O3 coated target is good, would like to do something similar.

• ESS baseline target is now a He cooled solid tungsten wheel, need to adapt.

• Would like to see if we can measure spot size on beam window as well (using coating or OTR)

• “Cross-functional task force” with Target Division for integration issues

W. Blokland, BIW10

Bunch Length/ShapeA. Feshenko, LINAC04

• Due to very short bunches, Feshenko type monitor prime candidate

• Alternative design based on x-ray detection proposed by Ostroumov, may have significant advantages

• Both use physical wire in beam. Possibility to use ionization electrons (GSI)

Wire Scanners• SNS studies concluded that carbon

wires would work for short pulse.• Straight forward in NC linac.• GANIL wire sublimation test

suggests carbon wires bad for SC cavities, tungsten (and Nb) OK.

• Tungsten will likely have issues with thermionic emission, may need to measure downstream loss signal– Potential space/geometry issue,

need study• May be able to use welded bellows

-> simpler than SNS design• Wire scanner baseline profile device! SNS SCL WS

IPM/Gas Jet/BIF

• Except in front-end, IPM/BIF would likely need long integration time, possibly neeed to be operated in counting mode (slow), and may require gas injection.– Gas injection compatible with SC cavities?

• Gas jet to be investigated for use in SC linac (discussion with Cockroft Institute)

NB. Profile measurement is

primarily an issue in the cold linac

Kuehnel et al, EPAC08

Other profile/beam size options

• Electron beam scanner

• Quadrupole pick-ups

W.Blokland, HB2010

+

+

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Halo Diagnostics• Options for halo

measurements include instrumented scrapers, vibrating wires, and high dynamic range wire scanners– Best option may be

wire scanner with coincidence counting detector/telescope

LEDA WS, LANL

Vibrating Wire, Bergoz

WS Telescope, eg ANL

Other Diagnostics/Open Questions

• Specific front-end diagnostics (Faraday cups, slit scanners, …).

• Do we need to measure uncaptured beam?

• Do we need to measure e-cloud?

• Do we need to measure something else?

19

Diagnostics Girder/Side Spurs

19

It is foreseen to use a temporary movable diagnostics plate/girder with addtional destructive diagnostics only for commissioning

May make sense to design one of more permanent diagnostic side spurs

•Allows the use of (semi-)destructive diagnostics•May resolve the wire scanner contamination question•No throw-away diagnostics for initial commissioning•May help reduce the need of warm space between sections•Could potentially divert every Nth pulse for monitoring.•Side spurs may be useful in the future (e.g. parasitic experiments)•But needs to be designed into the lattice

50kJ pp20kJ pp5kJ pp

250kJ pp

Summary

• Work to define the ESS diagnostics is progressing– Have preliminary specs and systems count,

mainly based on discussions with Beam Physics in Lund

– Will be discussed with the persons responsible for the different parts of the linac, to make sure all needs are covered and enough space is reserved.

• Beam Diagnstics group in Lund is responsible for diagnostics in the entire linac, but we welcome your input and help.

• Conceptual design, locations/count and cost by 2012 (ADU), prototyping as part of P2B