High-precision measurements of

Superconducting cavities

Anirban (Krish)na Bhattacharyya

FREIA / HIGH ENERGY PHYSICS

Uppsala University

FREIA

2

FREIA

UU-ESS-IPNO-CERN &

Industry Collaboration(Thales, Electrosys, DB Elettronica, Siemens, NXP, ESRF, CERN)RF Source Development

(vacuum tube amplifier, solid-

state amplifier, SSA module &

combiner optimization)

High-power Spoke Cavity Testing (tuning system, dynamic load, electron emission, mechanical parameters and multipacting)

Digital LLRF

Combined THz/X-ray

source

Present & Future

• Acceptance testing of spoke

cryomodule ✓

• Test of prototype spoke

cryomodule valve box✓

• Test of prototype Single spoke

and Double Spoke

superconducting cavities✓

• Testing of crab cavities for

LHC upgrade

• ESS neutrino super beam.

Liquifier (He, N)

3

FREIA

Spoke Cavity(super - conducting)

Courtesy of P. Duthil

4

FREIA

Cryogens

5

FREIA

Spoke Cavity(super - conducting)

Courtesy of P. Duthil

Horizontal Cryostat

6

Cavity resonator

�� �ω�

��

�� � ω�� 2ω�� /����� �� ��

�� � ������ ��

7

Reflection coefficient

��

��

à ��

��

κ � 1 � ���δ

κ � 1 � ���δδ

���� � ��

������

tan θ�

Γ$ �1

1 � κ

� Γ$$ κ

1 � κ

κ ��

����

1

1%

� 1Γ

$$

Γ$critical coupling κ 1

over coupling κ & 1under coupling κ ' 1

8

Normal conducting cavity

Γ$$

Γ$

9

Superconducting cavity

Γ$ �1

1 � κ

� Γ$$ κ

1 � κ

κ �����

����

10

Reflection co-efficient, Q-circle and surface

Γ$ �1

1 � κ

� Γ$$ κ

1 � κ

11

Experimental setup

12

Reflection coefficient

Before cable compensation After cable compensation

13

Q-surface

14

Q-slope

Double-spoke cavity

15

Q-slope

Single-spoke cavity

16

THANK YOU

17

Digital loop delay

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Cavity conditioning

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