RF STUDY AND OPTIMIZATION OF THE TOTEM ROMAN

RF STUDY AND OPTIMIZATION OF THE TOTEM ROMAN POT Nicola Minafra Dipartimento Di Fisica di Bari INFN, Sez. Di Bari CERN PH-TOT Doctoral Student 2 nd Workshop on Detectors for Forward Physics at LHC 29/05/2014

Outline • The TOTEM experiment • The RF problem o Heating and interactions with the beam o Simulation of the equipment • The New Roman Pot o Cylindrical design o Shielded Box design • Prototyping and Testing Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 2

TOTEM experiment at LHC The TOTEM experiment has been designed to measure the total proton cross section and to study elastic and diffractive scattering at the LHC energy. The total cross-section is measured with a luminosity independent method that allows to achieve a precision of the order of 2%. Using the Optical Theorem: CMS T 1 220 m T 2 Roman Pot Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 3

TOTEM after LS 1 Pileup resolution To IP 5 • Mitigate multi-track ambiguities adding silicon strip detector tilted around the beam axis by 8° • Attribute the leading protons to the correct vertex using a timing detector Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 4

Outline • The TOTEM experiment • The RF problem o Heating and interactions with the beam o Simulation of the equipment • The New Roman Pot o Cylindrical design o Shielded Box design • Prototyping and Testing Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 5

The beam and the cavity Every cavity is excited when a bunch passes through it and the excitation could live enough to perturbe the passage of the following bunches. The beam tranfers energy to the cavity, producing heating and instabilities. Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 6

The Impedance of a cavity The Impedance is a complex value (depends on the frequency) that gives indication about the RF behaviour of a cavity CST Particle Studio is one of the software used to compute the impadance of equipments facing the beam Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 7

Power loss: heating The power dissipated on the wall of the cavity can be computed knowing the Impedance of the cavity and the Power Spectrum of the beam. • The Impedance is computed using numerical simulations • The LHC beam Power Spectrum is measured LHC revolution frequency Number of buckets: 1782 LHC Power Spectrum Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 8

Effective longitudinal impedance It is an indication of the dispersion of the beam through the cavity. Frequency (MHz) Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 9

Outline • The TOTEM experiment • The RF problem o Heating and interactions with the beam o Simulation of the equipment • The New Roman Pot o Cylindrical design o Shielded Box design • Prototyping and Testing Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 10

The Box Roman Pot The present Roman Pot has a box shaped detector housing Lot of empty space: Small detector packaging Huge cavity facing the beam Problems with ferrite Simplified model for the numerical simulation: Front Side Nicola Minafra - RF study and optimization of the TOTEM Roman Pot • PEC and Ferrite only Geometrical impedance • No thin windows Small effects on the results 02 March 2021 11

The Cylindrical Roman Pot With the Cylindrical Roman Pot, the space between the detector housing and the flange is reduced: J More space for the detector J Small cavity facing the beam The cavity is smaller with the new design but still present to allow the insertion of the Roman Pot: A ferrite ring has been introduced to further reduce the heating. Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 12

Shielded Box Roman Pot A RF shield has been designed to reduce the impedance of the existing Roman Pot without modifying its structure. The shield is a copper and stainless steal foil with holes for ventilation and it does not interfere with detected particles: Small detector packaging J Good Impedance J Usage of current infrastructure Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 13

Heating computation Flat top Power Spectrum with a bunch spacing of 50 ns; the beam current has been chosen 0. 6 A Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 14

Simulation results s the t l su by e R ed ov RN e r p CE nc ap a ed p Im Team Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 15

Outline • The TOTEM experiment • The RF problem o Heating and interactions with the beam o Simulation of the equipment • The New Roman Pot o Cylindrical design o Shielded Box design • Prototyping and Testing Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 16

Prototype Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 17

Wire measurement A thin wire is used to create an electrical line and the reflection and the transmission are measured using a Network Analyzer. Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 18

Probe test A probe is inserted inside the equipment and the reflection is measured using a Network Analyzer. Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 19

Beam Pipe as reference Both methods perturb the measurement: • The impedance of the wirebeampipe needs to be matched (ripples) • The probe is introducing some resonances that depends on its position Wire test Probe test Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 20

Test results Simulation (with wire) Wire test Probe test Cylindrical RP without ferrite: 40 mm from centre (garage position) Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 21

Test results Wire test for Cylindrical Roman Pot with and without Ferrite 2. 50 E-02 2. 00 E-02 1. 50 E-02 1. 00 E-02 5. 00 E-03 0. 00 E+00 2. 00 E+08 4. 00 E+08 6. 00 E+08 8. 00 E+08 1. 00 E+09 1. 20 E+09 1. 40 E+09 1. 60 E+09 1. 80 E+09 2. 00 E+09 9 to 1 visible resonances! Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 22

Conclusion • New TOTEM Roman Pot designs • Cylindrical RP • ~ 5 times less heat • ~ 35% lower Effective Longitudinal Impedance • Shielded Box RP • ~ 6 times less heat • ~ 30% lower Effective Longitudinal Impedance • Extensive RF (and other) tests on prototypes • Good agreement with simulations • Clear effect of the ferrite Waiting for last approval from CERN Impedance Team Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 23

Q & A References RF Characterization of the New TOTEM Roman Pot CERN-TOTEM-NOTE-2013 -003 TOTEM Upgrade Proposal CERN-LHCC-2013 -009 RF Optimization of the New TOTEM Roman Pot LHC students poster session, 5/3/2014 Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 24

Box RP Impedance with the RP inserted at 1 mm from the beam Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 25

Cylindrical RP Impedance with the RP inserted at 1 mm from the beam Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 26

Shielded RP Impedance with the RP inserted at 1 mm from the beam Nicola Minafra - RF study and optimization of the TOTEM Roman Pot 02 March 2021 27