TechnologyDepartment

ZS Ion Trap Development

G. Raffaele and R.A. Barlow

Acknowledgements: B. Balhan, M.J. Barnes and B. Pinget

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Content• Present system and why upgrade

• Specification and Gantt Chart

• SPS ZS HV breakdown signals collection

• PSpice electrical modelling studies

• New ion trap HV box design

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The ZS has sparked since introducing LHC type beam. High spark rates damage the ZS and reduce their lifetime. [1]

ZS outgassing represents another important limiting factor affecting the vacuum. It depends strongly on beam parameters, especially the bunch length. [1]

In 2011 the cathode power supply was set to -100kV in order to reduce sparking. It makes difficult to achieve fast multi-cycling due to the high voltage and long equivalent time constant of the system (~8s). [2]

A system of interlocks is needed to guarantee reliability.

Present system and why upgrade

Influencing factors

Beam parameters ZS main electric field and ion trap fields Electron cloud System impedance (image current) Scrubbing and surface conditioning

(beneficial).

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Specification and Gantt Chart

An official document is located in EDMS (1469236) concerning the technical specification for the new Ion trap HV box design.

A Gantt Chart has been devised to provide a roadmap for the design process.

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HV breakdown signals collectionAn official document is located in EDMS (1487194) providing an overview of the HV breakdown signals collected in BA2 (ZS1 and ZS2), BA6 ZS6 and in the 867 ZS test bench during LS1 (Jan. 2015).

Cathode waveforms do not change significantly in BA2 and BA6, suggesting the occurrence of cathode sparks with different kinds of anode coupling.

Despite grounded anode, waveforms could still be observed on the anode sensing circuit.

The anode sensing circuit in 867 is provided with a 1:25 attenuator since signals collected show a higher amplitude w.r.t. those measured in BA2 and BA6. Possibly it is due to the effect of the length of the cables.

Signals collected in 867 display rapid oscillations both on the cathode and on the anode sensing circuit. It is mainly due to the effect of the cable length and possible source and/or load impedance mismatch.

Extremely difficult to deduce relationships between measured waveforms and operational conditions of the ZS and Ion trap system.

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PSpice electrical modelling studiesCOUPLING

MODEL

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PSpice electrical modelling studies

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PSpice electrical modelling studies

The achieved coupling model is speculative, but however demonstrates reliable empirical results:

the same topology is used for each kind of spark event and it is possible to reproduce some of the

real world measurements through careful choice of component values.

Very interesting scientific paper: “High Voltage vacuum discharge characteristics” [3] suggests the

occurrence of a pinched plasma column during the breakdown event. An inductive component is to

be taken in to account which could be related to the coupling model devised for the ZS.

System model seems to be reliable to evaluate effects of hardware modifications for the Ion trap.

Actions

Collect more signals in BA2 (especially for ZS3, ZS4 and ZS5), BA6 and 867 when possible.

Cable analysis with vector signal analyzer.

Source/Load impedance mismatch to be investigated.

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New Ion trap HV box design Experience from the past showed that the redesign of the Ion Trap circuit was tricky: several ZS damaged

despite good results in the lab [4].

New version of HV box circuit is being devised and candidate components identified.

A test bench is set up (HV cage1 lab, 865-2D-17) with a spare HV box.

An FSU job is to be planned to suits the need for new hardware.

Improvements planned:

Anode grounding.

Reduce Ion trap 1MΩ impedance.

Umon up and Umon down signals to be acquired.

Spark Ion trap up and spark Ion trap down signals to be acquired.

Oil suppression.

NEW SIGNALS ACQUISITION

IMPEDANCEREDUCTION

ALARA

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References [1] – M.J. Barnes, “LIU-SPS ZS Electrostatic Septum Upgrade Review”,

20-02-2013.

[2] – B. Balhan, “Design and operation of existing ZS”, LIU meeting 20-02-2013.

[3] – S.K. Handel, F.R. Nordhage, “High voltage vacuum discharge characteristics”, European Physical Journal of Applied Physics n.15/2001 (pp. 207-2012).

[4] – J. Borburgh, “Possible ZS improvements”, LIU meeting 20-02-2013.