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Cryogenics and Superconductivity at
IUAC
Amit Roy
Inter-University Accelerator Centre
Introduction
Why superconducting Linac?
Challenges of Cryogenics for Linac
The IUAC facility
INTRODUCTION
Interaction of Cryogenics & Nuclear Science have produced
many spectacular breakthroughs. Some of these are:
Extreme low temperatures through nuclear adiabatic
demagnetisation.
Polarised targets for nuclear experiments.
High field magnets for particle accelerators.
Cryogenic detectors for high precision spectroscopy.
Superconducting Cavities for Particle Accelerators.
Why Superconducting Linac?
Large Accelerating Fields required.
Electric fields generated in Resonant
cavities.
Resonant cavities have Quality factors,
Q, whose value depend on resisitive
losses.
Skin Depth ~ few µm f > 100 MHz.
Surface Resistance is all important.
For Cu at 300 K,
RS = 7.8 [f(GHz)]1/2 mΩ
For Nb at 4.2 K,
RS = 105 [f(GHz)]2 exp[-18/T(K)] / T(K) nΩ
RS
Cu (300K)
Nb (4.2K)
at 100 MHz
0.078 mΩ
3.28 nΩ
300 MHz
0.96 mΩ
40 nΩ
1GHz
7.8 mΩ
328 nΩ
For Superconducting surfaces, additional contribution from
residual resistance, Rres
BCS surface
resistance of Nb
vs frequency at
4.2 K
(extrapolated to
1.8 K).
Frequency dependence of
the surface resistance at
77 K for polycrystalline
(full marks) and single
crystalline (open marks)
YBa2Cu3O7-δ
samples.
Solid line -Cu @77 K
Dashed line-Nb@7.7 K
Comparison
of surface
resistance of
Nb with A15
material
Nb3Sn
Power dissipated in a cavity, P = 2.π.f.U/Q
For Room temperature Cu Cavity, Q (max) = 10,000
Assume, U= 1 Joule, 1 MV/m E field@ 100 MHz ,
P = 6.3 kW
For Superconducting Nb Cavity At 4.2K, Q = 109
1 MV/m E field@ 100 MHz , P = 0.063 W
However, some power is required to provide liq He.
Add static heat load ~ 2W and with cryogenic
efficiency (hcr ~ 3. 10-3) factored in,
P = 2.1/hcr = 700 W
For achieving 4.2 K, require LHe, LN2 .
W
Dynamic Heat Load
W
Static Heat Load
W
Load of the Distribution system
Production of Cryogen.
W
Liquid helium refrigerator
W
Liquid Nitrogen supply for shields & precooling
Distribution of Cryogen.
W
Transfer Lines
W
Valve Boxes
W
Measurement of temperature, cryogen levels
Requirement of Cryogen for NSC Linac
Estimated Load@ 4.5 K Static Load
Dynamic Load
3 Linac Cryostats
60 W
180 W
Superbuncher Cryostat 5 W
5W
Rebuncher Cryostat
5W
10 W
Distribution
60 W
____________________________________________________
Total
130 W
195 W
Total Load @4.5 K
=
325 W (Eqv ~ 455 l/hr)
Estimated Load@ 80 K
Static Load
Dynamic Load
3 Linac Cryostats
1215 W
600 W
Superbuncher Cryostat
90 W
50 W
Rebuncher Cryostat
90 W
100 W
Distribution
600 W
Precooling of He
2025 W
____________________________________________________
Total
4020 W
750 W
Total Load @4.5 K
=
4770 W(Eqv ~110 l/hr)
Challenges of Cryogenics
Maintain cavity surface below Tc of Nb, 9.2 K
Feed RF power into the cavity from room temperature to
LHe temperature.
Large variable dynamic load.
Maintain alignment of the cavities to the beam axis.
Minimise the coupling of mechanical noise from outside to
cavities.
Minimise pressure fluctuations in the Helium system.
Large number of penetrations from outside to LHe
temperature.
Quick cool-down and warm-up of large mass.
Recovery & Purification of He gas.
Precautions for Power failures ( Important in India)
Gaseous He
Impure He
Purifier
Rebuncher
Storage Tanks
Dewar
Linac Modules
He Compressors
Superbuncher
Gas Bag
Recovery
Compressors
He Cylinders
Comparison of microphonics for a Nb
superconducting resonator
Witho ut any SS-b alls
With 8 0 SS-b alls
No. of occurrence
10 0 0 0 0
10 0 0 0
10 0 0
10 0
10
1
-6 0
-4 0
-2 0
0
20
40
Delta f (frequency variations) in Hz
60
First indigenous cavity, electron
beam welded at NSC
Cavity Resonator
being mounted in
the test cryostat.
TOP HAT
SLOW TUNER
NEW RF DRIVE
Valve Box assembly
Triple Jacketed
He transfer line
Insert Type
Superconducting
Solenoid
7.1 T @ 215 A
Inner Bore: 46 mm
Outer Diameter: 83 mm
Length: 150 mm
The Axial Field Profile of the Magnet at ~ 5Tesla
Magnetic Field [Tesla]
5
4
3
2
1
Field Homogeneity ~ 0.072% over 20 SDV
0
-14 -12 -10
-8
-6
-4
-2
0
2
4
6
8
Axial Distance From Mid Point [cm]
10
12
14
C vs LN2 level of Indigenous sensor
LN2 sensor
4E-10
sensitivity
= 3.7pf/ cm
3.5E-10
3E-10
2.5E-10
liquid level (cm ) ->
37
33
29
25
21
17
13
9
5
2E-10
1
capcitance in pf ->
4.5E-10
He Impurity Monitor
Superconducting Quadrupole Magnet for HYRA
World's First High Temperature Superconductor based
ECR source.
Thank You