Impedance Compensationwith Meta-materials for HL-LHC Dimitris - - PowerPoint PPT Presentation

Impedance Compensationwith Meta-materials for HL-LHC

Dimitris Tsangaridis supervisor: Xavier Buffat special thanks: Nicolas Mounet

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Introduction Device properties Impedance Results

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Introduction

Purpose: The collimator’s impedance can make the beamunstable

• The collimator upgrade reduces the need of Landau Damping, by using

low resitivity material, thus reducing the imaginary part of the tune shift

• We are trying to minimize instabilities by moving the real part of the tune

shift closer to 0 to reduce the need for Landau damping further → Use negative permeability material

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Device properties

Device geometry

• thickness
• length → 1m
• halfgap

Meta-material properties

• negative permeability

µ

• resistivity ρ

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Tools

• Impedance Wake2D
• to calculate the wake fields that are left behind a

single particle

• DELPHI
• to calculate the effect of the device on the whole

beam

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Impedance

The real part of impedance for low frequencies is not 0 → Not physical

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Impedance

• only for halfgap = thickness and µr = -1 the impedance is physical
• To be further investigated, e.g. → µr (ω)

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Scaling with halfgap and thickness

The half gap (= thickness) has an inverse cubic relationship with the tune shift

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Scaling with resistivity

• Minimum of the impedance and its frequency for different values of

resistivity using only the meta-materialdevice

• Chose a half gap of 3 mm to be potentially compatible with the

collimation system

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Scaling with resistivity

• by moving the real part of the tune shift closer to 0 imaginary part is

increasing

• the reason is the corresponding (real/imag) part of the Impedance

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Expectations - Reality

• With our design the need for Landau damping is not reduced as the

reduction of the real part of the tune shift is coupled to an increase of the imaginary part

• Next steps :
• Study and understand why for some values of µ we don’t have 0

value of Impedance in low frequencies, re-optimise the device accordingly

• Consider negative permittivity material to reduce the imaginary part
• f the tune shift.

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

home.cern

Potential candidate

Terahertz Magnetic Response from Artificial Materials https://science.sciencemag.org/content/303/5663/1494

• In this article it is shown that with a µm scale thick meta material we can

have frequencies in the order ofTHz

• We need frequencies in the order of GHz which can be achieved with a

device in the order of mm

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Scaling with length

August 26, 2019 Impedance Compensation with Meta-materials for HL-LHC

Impedance vs halfgap and thickness value

2019-08-26

Impedance Compensation with Meta-materials for HL-LHC Results Impedance vs halfgap and thicknessvalue So to move the real part of the tune shift closer to 0 we have to make our device 85 meters long. We had the same result for other modes: chromaticity 0, 10, 15. So we had to make some optimizations to make

• ur device shorter. And we thought maybe we could change the resistivity
• f the meta-material ρ to achieve a shorter device.

Impedance vs halfgap and thickness value

2019-08-26

Impedance Compensation with Meta-materials for HL-LHC Results Impedance vs halfgap and thicknessvalue First we had to compute the Impedance. So by using Impedance Wake 2D with various values for permeability and then thicknesses and then halfgaps we created the left kind of graphs for every thickness and halfgap

• combination. Next we wanted the most effective permeability value which

corresponds to the minimum value of the Impedance in the whole graph. And after that the most effective for every thickness and after that the most effective for every halfgap. So we had the 3 best pairs of thickness- halfgap with their corresponding permeabilityvalues.