June 28, 2012

David Gassner

Gatling Gun Beam Diagnostics and Instrumentation

David Gassner

Gatling Gun ReviewJune 28, 2012

June 28, 2012

David Gassner

Outline

• Overview– Beam and machine parameters, challenges– Beam transport layout

• Current Monitors– Beam Integrating Current Transformer (ICT)– Cable Current Monitors

• Beam Profile Monitors– YAG Screen Viewer– Halo Detector

• Future Upgrades– Beam Position Monitor– Fast Current Transformer (FCT)– Pepper Pot

• Summary

Phase 1 diagnostics philosophy: Provide core diagnostics for the first beams, current and profile.

June 28, 2012

David Gassner

Beam and Machine Parameters

Electron Beam Parameters– Initial tests; 2 cathodes, 1 Hz operations– 2 beams ~ 15mm full with diameter at the profile monitor– 3.5nC charge per bunch– 1.5nS FWHM bunch length– Energy = 220 KeV

Challenges for instrumentation– 250kV potential voltages– Sensitive photocathodes

Vacuum 10-12 Torr range Bake out compatibility to 400C Outgassing and desorption concerns

June 28, 2012

David Gassner

Beam Transport Layout

GunCathodes

ProfileMonitor

Collector

Ceramic Break for HV

Beam CurrentTransformer230kV

Combiner Diagnostics stationis grounded

230kV Inside Collector cage

HaloDetector

June 28, 2012

David Gassner

Beam Current Transformer

Beam Line Device:

Bergoz off-the-shelf Integrating Current Transformer (ICT) 178mm ID, fits over 6” CF flange

Mounted around dedicated commercial ceramic breakGG transport beam pipe 3.67” ID

Removable copper image current shroud

Plan to bake beam pipe to 400C, will need coolingto ensure ICT does not exceed 150C.

Side View

Similar installation at C-AD

Detailed mechanical design not complete

June 28, 2012

David Gassner

Beam Current Transformer Electronics

Bergoz - Beam Charge Monitor (BCM) Integrate-Hold-Reset (IHR) electronics - Measure individual bunches & bunch trains- Integration gate width adjustable 0.1us to 7us Noise <1pC beam charge Calibrated

10kHz max individual bunch rate measurement

Planned beam intensity/bunch range100pC – 3.5nC

BCM-IHR Timing diagram

June 28, 2012

David Gassner

Cable Current Monitors

Beam makes 2 bends from gun photocathode to beam ICTPotential for measuring:

- Transport efficiency between gun, collector, and ground. - Beam losses - Cathode QE

These measurement present accuracy challenges (noise, matching, HV, etc…)Need to look at details, setting up some tests.

Monitor current pulses (3.5nC, 1.5nS) in cables at several locations.

Reasonable to pursuethis measurement?

ICT

June 28, 2012

David Gassner

Profile Monitor

GunCathodes

ProfileMonitor

Collector

Ceramic Break for HV

CurrentTransformer230kV

Combiner Groundedregion

200kV Inside Collector cage

HaloDetector

June 28, 2012

David Gassner

Transverse Profile Monitor – YAG:Ce Screen

Removable Optics Box

Virtual Resolution Target

Lens and CCD Camera

Semitransparentmirror

Linear Magnetic Actuator (2 position)

Transfer Engineering Inc.

PMM-Lite model

400C bake-out

YAG:Ce Screen 5cm diameter (4.5cm active)Thin coating on upstream side to bleed off chargeThickness = Few hundred microns

GigE CCD camera3-motor lens, zoom, focus, iris.Virtual target for optical

<100 microns optical resolution

Transverse beam size ~15mm round diameter Destructive measurement (low power)YAG screen normal to beamCopper mirror at 450 downstream

Electron Beam

Optics Box Courtesy Radiabeam

June 28, 2012

David Gassner

0 0.5 1 1.5 2 2.5 3 3.5 4 4.50

1

2

3

4

5

6

7

8

9

10

Pfeiffer [Pressure]

Varian [Pressure]

Current [uA]

Pres

sure

[1E-

8 m

bar]

Transverse Profile Monitor – YAG:Ce Desorption Concern

Q: Will we be able to see an image on the YAG screen without ruining the cathodes?

A: If our double bend inhibits ion movement similar to the 270o bend at Mainz then we hope to tolerate a few uA’s on the YAG screen and not damage the cathodes.

270o bend

YAG Screen(~10-8 torr)

Pressure Rise vs. Current on YAG screen Igor Alexander, B2/Mainz

Gun (~10-11 torr)

Mainz PKATTest Source

Mott Pol.

Source: B2/Mainz

Pressure doubles with 3uA on YAG, in 10-8 torr range

June 28, 2012

David Gassner

Halo Detector

GunCathodes

ProfileMonitor

CollectorCeramic Break for HV

CurrentTransformer230kV

Combiner Groundedregion

230kV Inside Collector cage

HaloDetector

June 28, 2012

David Gassner

Halo Detector Profile Monitor – Upstream of Collector

Collector230kV

Isolated molybdenum jaws- Quad configuration- Need shield from collector (not designed yet)

Electronics:Gated integrator

Signal processing on HV platform:Fiber optic connection to transfer data

Protect electronics from arcs.

Halo DetectorsQuad split (230kV)

Grounded shieldRaw signals from similar E-Lens Quad

Halo Detector, beam offset (green & red)

E-Lens Quad Scraper

ElectronRepeller (260kV) Ceramic

Break

June 28, 2012

David Gassner

Future Upgrades

Fast Current Transformer (can be installed along side of ICT)Measure individual bunch charge in bunch trains300ps rise time, 1GHz bandwidthCalibrated measurement, Fast scope DAQTrack charge evolution (QE) for each cathode

Beam Position MonitorMeasure bunch center of mass positions (when combiner field is rotating)Need space in beam transport for pick-upHigh temperature (400C) pick-up design

Pepper Pot Emittance MeasurementA preliminary design: Normalized emittance: xn/yn= 20.5µm/20.1µmSlit width: 1 mm, slit space: 1.5 mm (~ 5 beamlets)Drift space:  0.1 m < L < 0.3 m upstream of YAG profile monitorThickness: 1 mm (Tungsten, SS, or copper)Use horizontal and vertical slits one on upper part, one on lower part of the mask.

Toroid widthsICT = 32mm

FCT = 22mm

Side View

June 28, 2012

David Gassner

Summary

• Core Diagnostic for Phase 1– Proof of principle, 2 cathodes, 1Hz operation

YAG:Ce Screen (Transverse profile, destructive, low power) Quad Scraper (Near collector, halo monitor) Current transformers (Bunched beam, and on cables)

• Future Upgrades– More cathodes, higher frequency bunch trains

Beam Position Monitor (Non-destructive, fast) Fast Current Transformer (Bunch charge in long trains) Pepper Pot (Emittance, destructive)