ESS Spoke Linac section RF Anders Sunesson, RF group leader Rutambhara Yogi ESS Carlos Martins ESS Roger Ruber FREIA

Overview ESS status RF requirements Spoke Linac Technology choices Design Challenges Prototype plan Solution 2

ESS is in construction! 3 If you go on-site, chances are you will see concrete being poured Construction also means that we have to have solutions for the things we are asked to provide

RF requirements Spoke linac The Spoke linac has 26(+) cavities organized in cryomodules with 2 cav/CM The RF frequency is MHz The maximum RF power coupled to the cavity required is ≤350 kW (see power profile in next slide) With expected losses + overhead this becomes >400 kW The flat-top pulse width required is 2.86 ms, and the pulse repetition rate is 14Hz Amplitude and phase of the cavity field are required to be regulated to within 0.1% and 0.1° (rms deviation, value tbc) from the set-point to avoid excessive loss (beam physics) Has to fit gallery space 4

Spoke linac power profile 5

Schedule required The spoke RF sources need to be designed end 2015 Tender early 2016 Award contract mid 2016 Delivery start mid-end 2017, installation starts end 2017 Install last amplifier Mid-End 2018 This means prototyping needs to be ready well before design finalisation 6

Schedule spoke RF Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2Q3Q4Q1Q2B!Q3Q4 352 sources Spoke, 26 pcs Spec/design Procurement Construction Delivery 352 waveguide systems Spoke, 26 sets Specifications Procurement Construction Delivery 352 LLRF systems Spoke, 26 sets Specifications Construction Delivery Interlock systems Spoke, 26 sets Specifications Construction Delivery Installation 7

RF system components – LLRF- picks up phase/amp in cavity, provides tuning, maintains phase/amp in cavity – Predriver – amplifies RF signal to suitable level – Power amplifier – provides the high power RF – Power supply – powers the (power) amplifier – Distribution system – Fast(piezo)/slow(motor) tuning system 8 Focus on Amplifier

Technology choices for the RF sources Klystron Size scales with frequency not power – will be big Requires pulsed HV modulator – very bulky IOT Does not exist at this power level – new development needed Solid state Does not exist off-the-shelf at this power level Magnetron Would work for CW, very risky for pulsed Tetrode Possible off-the-shelf - this is the suggested solution 9

FREIA RF Power Source FREIA Laboratory, Uppsala University, to test – Prototype RF system (power amplifier and distribution) for ESS spoke linac – Spoke cavity and cryomodule tests Strategy – procurement of two (2) commercial tetrode based RF sources – Testing of RF sources – performance test of commercial prototype solid-state amplifier 10

A tetrode base solution was chosen The tube type is available off-the-shelf The tube type is well known and has proven performance The schedule does not permit prototyping for new concepts Extensive experience available from for example CERN regarding tetrodes For these reasons UU and ESS chose a tetrode based solution 11

Tetrode power source design The design uses the TH595 tetrode developed and marketed by TED The tube peaks at 200 kW A 2-tube solution is required External cavity couples to transmission Combiner set-up with hybrids and loads part of the power amplifier Tetrode gain is about 13 dB, so a predriver at about 10 kW is required 12

13 VAnode + s.switch VG2 + crowbar /s.switch VG1, Vf Load LLRF TH kW 205 kW VG1, Vf Load SSA ϕ A N-type (50 Ω)1-5/8 inch, 50 Ω 3-1/8 inch, 50 Ω 6-1/8 inch, 50 Ω WR2300(HH) Spoke Cavity H1: 90 o Hybrid H2: 90 o Hybrid 400 kW A LLRF with two outputs can be used instead at low-power end Power station layout R. Yogi

Tube TH595 test MHz 14 Gain = 15 dB η = 67% R. Yogi

Challenges with tetrodes for 352 MHz Requires coupling circuit (resonant cavity) – the anode is at potential One tube cannot supply enough power - combination Transit time limits frequency response (corner freq 200 MHz) Parasitics might cause problems for coupling to cavity Combination (one tube not enough) requires balancing of tube drives (in case of different gains and/or aging) Gain value means predrivers at≈10 kW required 15

Tetrode power source Power supply Supply voltage up to 18 kV, baseline design is a 2x18 kV anode supply for pulsed delivery Supplies are also needed for filament, screen, and grid 16

- 40 kVA Anode power supply 18kV / 2.2 A T1a T1b HV capacitor charger HV capacitor bank HV series switch 150 mm x 150 mm x 250 mm High voltage Anode Power supply Tetrodes C. Martins 17

18kV / 2.2 A T1a T1b -Integrated system (short HV and control cables, integrated control and interlock system) -Minimal stray inductance of the HV cables -Use standard off-the-shelf modules -Time to repair is short (one rack system) -Series of 26 units makes some cost reduction (series effect) -Many companies in HV can design, build and test this kind of system High voltage Anode Power supply C. Martins 18

High voltage Anode Power supply C. Martins 19

Prototyping 20

Prototype: FREIA RF Power Station #1 Uppsala University tendered 21-Feb-2013: tender published – 1 station with option for 2nd station – allow for alternative technology – allow for sub-system bids 08-Apr-2013: 12 replies – 4 for tetrode system – 3 for solid-state system – 1 for IOT system – 4 for sub-system parts 14-Jun-2013: published decision 28-Jun-2013: contract signature – Craftec (Delta) for filament power supply – Electrosys for all other parts based on 2x TH-595, water+air cooled SSA pre-amplifier crow-bar with fast solid-state switches commercial power supplies Delivery end Dec Jul-2013: design modifications – 400 kWp output power – solid-state crow bar – two series switches from Astrol – capacitor charger from Technix – Re-designs (for example capacitor charger) changes delivery time to Feb Dec-2013: design modifications – reduce footprint <5.5 m2 – several minor modifications 21 R. Ruber

FREIA RF Power Station #1, continued 03-Feb-2014: Electrosys asks to delay delivery to April 24-Feb-2014: delay to May 10-Mar-2014: FREIA notices that Electrosys has financial problems – work to completion estimated 2.5 months – discussion starts how Uppsala can support completion of the contract, but no workable solution is found 09-Jul-2014: Electrosys under court protection 24-Oct-2014: proposal that Elenos takes over Electrosys, pending approval by court 22 R. Ruber

Scenario A 23 A deal is reached and the court agrees The various challenges are overcome Company operational end November Time to complete power station about 4 months Expected delivery Uppsala if everything works out April 2015 R. Ruber

Parts for the power stations at Electrosys 24 R. Ruber

FREIA RF Power Station plan B Commercial tender 10-Oct-2014: tender published – 1 station with option for 2nd station – allow for alternative technology – allow only for full system bid – specifications as previous tender, but more stringent requirements on financial stability of tenderers 19-Nov-2014: final date for replies 28-Nov-2014: foreseen publish decision 09-Dec-2014: foreseen contract signature 31-May-2015: foreseen delivery to Uppsala 25 R. Ruber

FREIA RF Power Station Plan C Solid-state based Industry development: Siemens prototype financed by company based on commercial 1kWp transistors system of five 19" racks – 4 racks with 100 kW each – 1 rack with final combiner stage and controls May-2015: foreseen shipment to Uppsala for evaluation and performance test In-house development amplifier modules – optimized >1 kWp transistor – minimum amount of soldered components final combiner stage – 100 kW compact non-resonant combiner technology demonstration – preparing a 10 kW prototype amplifier 26 R. Ruber

Continuation after delivery power station RF power station tests at FREIA Validation of the concept Lessons learned Implement changes (if any large) in updated design 27

ESS Spoke Linac RF solution Technical solution: 26 dual tetrode stations Peak Power 450 kW, MHz, duty 5% Total size of RF power source 2600 mm x 800 mm x 2400 mm This fits the gallery layout ESS has adopted this as baseline design 28

Supply plan The sources planned to be delivered by in-kind partner Elettra, Italy Contract planned end 2014 The RF distribution system planned to be delivered by in-kind partner Huddersfield University, UK, contract pending The LLRF systems planned to be delivered by in-kind partner ESS Bilbao, HoA November 2014 The interlock systems – no partner yet 29

Layout in gallery 30

Thank you 31