http://www.surfacetreatments.it/thinfilms Thin Films for SRF – What might the future hold? (Charlie Reece - 20') Speaker: Charlie Reece - Jefferson Lab - Newport News (VA) USA | Duration: 20 min. Abstract While the great majority of applications which use superconductors for their low surface resistance properties in response to rf fields employ high-purity bulk niobium, there are inherent limitations with this material. One may imagine even a large number of desirable applications if but the high system costs could be brought down by factors of 2 to 10, or the supportable stable fields could be increased by factors of 2 to 10 over the best that niobium can sustain while remaining superconducting. So what do we dare dream of bringing onto the real plane? What might be realizable if we but sort out and control material properties appropriately? I’ll attempt to construct a brief survey taste of what might be possible via SRF thin films, while thoroughly ignoring the technical difficulties that lie in the path ahead.

1. Thin Films for SRF
What Might the Future Hold?
Charles Reece
Oct 4, 2010

2. SRF Thin Films
• The principal driver for pursuit of materials and surfaces with
vanishingly low surface resistance to rf fields (SRF) comes from
the particle accelerator field.
• So, what serves the customer’s needs?
• Low losses and high fields – of course
• Really, it is low integrated system cost per unit acceleration
{Resonator system, cryostat, rf drive, cryo system }
• The great majority of future applications for SRF will be CW
• Realizing lowest Rs is imperative
• Only with low Rs will high fields become usable.
• So what are the credible opportunities for SRF thin films to
make dramatic impact?
SRF Thin Film Wkshp – Oct 2010 cer 2

3. The Stage for SRF Thin Films
• For the customer, only the net price of each unit of
acceleration matters. The rest is “just details.”
• As a heuristic tool to guide us in dreaming not too far off the
real plane, I create a (simplified) model which includes the key
cost contributions for providing 100 MV of CW linac suitable
for accelerating a ~ 1 mA beam.
• For several applications, this is either the approximate need or a
suitable building block for much larger systems.
• I seek to link RF surface resistance, accelerating gradient, and cryogenic
and rf capital and 10-year operating costs required to provide 100 MV
acceleration. Increasing beam current would mainly increase RF costs.
• So where are the opportunities for SRF thin films to create a
significantly different future?
• Let’s dream of being limited by BCS losses:
SRF Thin Film Wkshp – Oct 2010 cer 3

4. The Landscape @ 1300 MHz
BCS surface resistance
It’s not yet clear
where MgB2 goes
on this plot.
Stay tuned.
BCS Rs calculated by
adaptation of Halbritter
program my Gigi Ciovati
SRF Thin Film Wkshp – Oct 2010 cer 4

5. Cost Model for 100 MV
• Cost100 MV (f, T, Eacc, Rs(mat’l), G, R/Q)
• I take the JLab upgrade cryomodule zone as a baseline from
which to scale.
• Model assumptions:
• Real estate is free.
• Static cryo load is linear with active length.
• RF power is constant cost, controls and distribution cost scale linearly
with length.
• Cryomodule cost is proportional to active length, i.e. once we know
what to do, doubling the accelerating gradient costs negligibly more.
• Cryo capacity designed to target load.
• Cryo capital cost and operating efficiency is per JLab expert model. (Rao
Ganni)
• Rs is BCS limited
• Cavity geometry fixed to clarify scaling patterns (would be tailored to
specific application).
SRF Thin Film Wkshp – Oct 2010 cer 5

6. Net Cost of 100 MV @ 2 K
Surface resistance has a dominant influence on system cost
SRF Thin Film Wkshp – Oct 2010 cer 6

7. The Landscape @ 650 MHz
BCS surface resistance @ 650 MHz
It’s not yet clear
where MgB2 goes
on this plot.
Stay tuned.
BCS Rs calculated by
adaptation of Halbritter
program my Gigi Ciovati
SRF Thin Film Wkshp – Oct 2010 cer 7

8. Net Cost of 100 MV @ 4.2 K
Conceivable economic opportunities for future SRF films at 4.2K
SRF Thin Film Wkshp – Oct 2010 cer 8

9. 100 MV Dream Solutions
R1 – 20 MV/m @ 1497 MHz, 2.07 K bulk Nb – (10M$) CEBAF Upgrade
Seven Dream Objectives - caveat emptor (cost/incremental 100 MV)
D1 – 40 MV/m @ 650 MHz, 2 K via Nb Film – (5.5M$)
Cheapest Nb solution, ~half the price of CEBAF acceleration
D2 – 20 MV/m @ 1300 MHz, 2 K, via NbN SIS Film – (5.9M$)
1st incremental application of SIS, 70% reduction in dynamic load
D3 – 50 MV/m @ 1300 MHz, 2 K, via Nb3Sn SIS Film – (8.9M$)
Compact FELs ? ILC ? 4GLS ?
D4 – 20 MV/m @ 650 MHz, 4.2 K , via NbN SIS Film – (7.1M$)
Driver for ADS?
D5 – 20 MV/m @ 650 MHz, 4.2 K, via Nb3Sn thick or SIS Film – (5.2M$)
Cheaper driver for ADS?
D6 – 60 MV/m @ 1300 MHz, 4.2 K, via Nb3Sn SIS Film – (4.1M$)
Cheaper ILC ? Commercial THz sources? Industrial processing?
D7 – 105 MV/m @ 650 MHz, 4.2 K , via Nb3Sn SIS Film – (4.2M$)
Compact, portable interrogation systems ?
Add MgB2 ? on the map? SRF Thin Film Wkshp – Oct 2010 cer 9