Technological aspects of Electron Lenses, errors and control

Vsevolod Kamerdzhievfor Fermilab Beam-Beam Compensation team

LARP Mini-Workshop on Beam-Beam Compensation, July 2-4, 2007

V. Kamerdzhiev for BBC team Technological aspects of Electron Lenses, errors and control 2

Tevatron Electron Lenses

TEL2

The TEL2 magnetic system consists of eight conventional solenoids, the 65 kG SC main solenoid, four short 8 kG and two long 2 kG SC dipole correctors.

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Magnetic field measurements

•Short corrector 1, I = 191.42 A

•0

•0.5

•1

•1.5

•2

•2.5

•3

•3.5

•4

•4.5

•5

•5.5

•6

•-350 •-300 •-250 •-200 •-150 •-100 •-50 •0 •50 •100 •150 •200 •250 •300 •350•Longitudinal pozition z, mm

• Ma

gn

eti

c f

ield

, k

G

Magnetic field quality along the electron beam path has been verified using 3D Hall probe

in addition, a laser based technique was used to check the straightness of magnetic field lines in the main solenoid (<100 m).

V. Kamerdzhiev for BBC team Technological aspects of Electron Lenses, errors and control 4

Electron gun

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Using the tube based modulator

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First TEL2 e-beam

Cathode current

Collector current

Modulator grid

Trigger pulse

Was improved to better than 5%

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TEL1 e-current ripple

0.4 Hz15 Hz

~1% variation

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Using the Marx generator

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Modulator vs Marx generator

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Marx generator

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TEL2 in pulsed mode (Marx)

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TEL2 e-current ripple, timing jitter

60 Hz<1 %

cure found

fixed< 1ns now

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Marx generator failure

Schottky power

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Emittance growth vs e-beam noise

TEL2Δ

ε/Δ

t

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Emittance growth vs e-beam noise

TEL1

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The e-beam world

gun

collector

BPMs

Isolated electrodes

L-shaped pickup

Reliable position measurement for all tree beams is challenging due to very different spectral content. Currently we can achieve ~100 m accuracy/resolution

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Summary

The e-beam quality in both TELs reached the level that made reproducible demonstration of beam-beam compensation possible.

Generating dc e-beam does not appear very challenging, however generating pulsed beam (individual compensation of all bunches) does.

Though the voltage itself is not a challenge – short rise time and high rep rate requirements make the development of the e-gun driver very challenging.

The solid state Marx generator proved to be a reliable electron gun driver (with radiation shielding installed).

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Plans

• Further reduce e-beam noise and ripple

• Simulate the effects of e-beam noise, ripple on beam lifetime and emittance growth (Lifetrac)

• Upgrade HV pulse generators (second generation Marx and solid-state modulator based on a summed pulse transformer scheme), multi-bunch BBCompensation

• Install gaussian electron guns and perform head-on compensation studies (dc or pulsed)

• Study the effect of electron beam size on protons (lifetime, halo, Schottky) in both TELs

• Improve position measurement