The European Spallation Source. Morten Jensen

Transcription

1 The European Spallation Source and its plans for RF Morten Jensen

2 Overview The European Spallation Source (ESS) will house the most powerful proton linac ever built. The average beam power is five times greater than SNS. The peak beam power will be over seven times greater than SNS The linac will require over 150 individual high power RF sources We expect to spend over 200 M on the RF system alone

3 What is ESS? ESS is a neutron spallation source for neutron scattering measurements. Neutron scattering offers a complementary view of matter

4 Short Pulse Neutron Spallation Sources The neutrons are cooled by a moderator downstream of the target The time constant of the moderation process is about 100 s Proton beam pulses shorter than 100 μsserve only to stress the metal target and limit the beam power Typical short pulse spallation sources have storage ring circumferences ~300 meters which produce 1 s beam pulses To build a storage ring with a 100 s pulse would require a ring 30 km in circumference The target stress from the short beam pulse places a limit on: proton beam power and ultimately neutron flux and brightness The proton beam power of SNS (Oak Ridge Tennessee, USA) is limited to 1MW (17 MW peak)

5 360 kj packed into a short pulse of 1 s (360 GW peak) would destroy a target ESS will not use a compressor ring The linac will send the beam directly to the target over a period of 3 ms at a rate of 14 Hz. Peak beam power on the target is less than 125 MW The tradeoff is that ESS will Have longer neutron guides between experiments and the target Require a neutron choppers for precision energy measurements Long Pulse Concept

6 What Will ESS Look Like? Target Instruments Linac

7 ESS is located in southern Sweden adjacent to MAX IV (A 4 th generation light source) To provide a world class material research center for Europe Where Will ESS Be Built?

8 How Much Will ESS Cost? Personnel Investment

9 How Will ESS be Funded? with in kind and cash contributions.

10 Top Level Requirements 5 MW of average beam power Pulse repetition rate of 14 Hz driven by neutron chopper constraints Pulse length of 3 ms Driven by instrument location And beam brightness Gives: Peak beam power of 125 MW 4% duty factor

11 Transition from construction to operations ESS Operations can be divided into three distinct phases: Initial Operations Phase ( , 4 years) Includes one year of activities to produce first neutrons (2019) and three years of activities to improve accelerator performance and to commission instruments (experiments by friendly users); Initial User Program Operations ( , 3 years) Includes support necessary for reliable operations with public users and provides the basis for future cost sharing; and, User Program Operations (Beginning in 2026 ) Routine operations including the completion and commissioning of the final 22 public instruments.

12 Summary Critical Path Licencing Accelerator Buildings Spoke & Medium Beta CM (Prod&Inst&Comm) Licensing ConvF AccSys NSS High Beta CM (Prod&Inst&Comm) Instrument Construction Ground break First installations on site (ACCSYS) First Beam on Target (570 MeV) Machine installed for 2.0 GeV Last of Instr 12 Const Instr HO to Op

13 Linac Design Choices User facilities demand high availability (>95%) ESS will limit the peak beam current below 65 ma Linac Energy of 2 GeV to accomplish 125 MW peak power. The linac will be mostly (>97%) superconducting Front end frequency is 352 MHz (CERN Standard) High energy section is at 704 MHz

14 Prototyping the ESS accelerator Sebastien Bousson Søren Pape Møller Roger Ruber Pierre Bosland Anders J Johansson CERN Roger Barlow The National Center for Nuclear Research, Swierk Ibon Bustinduy Santo Gammino

15 The ESS Superconducting Power Profile > 150 cavities/couplers 125 MW peak (4% duty) 5 MW average 26 Spoke Cavities 352 MHz 2*200 kw Tetrodes (Alternative under consideration 84 High Beta 704 MHz (5 cell) 1.2 MW IOT 1.5 MW Klystron as backup 36 Medium Beta 704 MHz (6 cell) 1.5 MW Klystrons Power splitting under consideration 1 RFQ and 5 DTL tanks 352 MHz 2.8 MW Klystrons

16 The RFQ and DTL will be similar to the CERN Linac 4 design. The RFQ will be 4.5 meters long and reach an energy of 3.6 MeV The DTL Will consist of five tanks Each tank ~7.5 meters in length Final energy will be 88 MeV Front End Section

17 Power distribution for the 5 Drift Tube Linacs One 2.8 MW for RFQ Five 2.8 MW klystrons for DLT Power split to two couplers per DTL tank CPI VKP 8352B Thales TH2179

18 Spoke Cavities 352 MHz Baseline solution: Combination of two 200 kw tetrodes Currently one RF source per cavity Courtesy of Yogi Rutambhara Options being considered to reduce cost: Larger modulator for several RF sources Large klystron split for 2/4/6 cavities Amplifier Prototype ordered for FREIA Test Stand in Uppsala

19 Baseline solution: (36+84) 1.5 MW klystrons Currently one RF source per cavity Possibility to feed >1 cavity per klystron Possible use of high KVA modulator Suppliers include: Thales, CPI and Toshiba Elliptical Cavities 704 MHz 36 Medium Beta g = cell cavities Maximum peak RF power = 800kW 84 High Beta g = = cell cavities Maximum peak RF power = 1100kW High Beta Cryomodule

20 One cavity per klystron Two klystrons per modulator 16 klystrons per tunnel penetration Elliptical (704 MHz) RF System Layout RF Gallery Layout Modulators Klystrons Me Waveguide Distribution Tunnel

21 Why do we need all these amplifiers? 2 GV, 125 MW DC supply wanted! ESS needs power at high frequency (352 and 704 MHz). Mains power is at 50 Hz! Convert mains AC to DC and then DC to high frequency AC Klystrons are typically used for high power accelerators. They exist at the power levels needed for ESS. They are really pretty good, reliable and quite efficient. IOTs at ESS parameters don t exist. They may be more complicated. They need to be developed and carry risk. Why all the fuss?

22 The ESS Redesign Before November 2012 Limited procurement time Modulator and Klystron Strategy *** Buy Lots and Right Now!*** MW Capable Current plan MW Operation MW Capable (Medium Beta) Buy standard klystrons for the Medium Beta Investigate IOTs for High Beta MW Capable (High Beta)

23 Where next? The ESS Requirement Time to develop Super Power IOT Accelerating Structure Freq. Quantity Max Power (kw) (MHz) RFQ, DTL ** Spoke ** Elliptical Medium Beta ** Elliptical High Beta ** Power saving from high beta 20 GWh per year ** Plus overhead for control

24 Resonant Multi-Level (RML) topology 400V, 3 phase, 50Hz ~1 kv ~1 kv ~1 kv Standard of the shelf LV components Special HV components & assembly Keypoints: Lower cost due to usage of standard LV components into a great extent; Reduced footprint/volume due to minimal sub systems count; Compatible both with PULSED and CW operations and with different types of RF amplifiers (Klystrons, IOT s, tetrodes, etc.); Improved efficiency (~94%), due to minimal number of conversion stages in capacitor chargers; Excellent AC grid power quality (flicker free, sinusoidal current absorption, unitary power factor); Courtesy of Carlos Martins

25 Cathode (DC Beam) Source Beam RF input Klystron (Velocity Modulated) Control Acceleration Deceleration = RF Output RF output Collector IOT (Density modulated) RF input Magnetic field Reduced velocity spread compared to klystrons Higher efficiency Biased Control Grid RF output No pulsed high voltage Cheaper modulator

26 The Performance Comparison Klystron/MBK Back-off for feedback Operating Power Level Courtesy of CPI P P out P in +6 db sat ~ 65-68% ESS ~ 45% High gain IOT s don t saturate. Built-in headroom for feedback. Low Gain ~ 70% IOT MB-IOT 100 Short-pulse excursions possible Long-pulse excursions possible Typical Example of 80 kw IOT Tuned for kv P in 80 Klystrons: Back off for feedback cost 30% IOTs: Operate close to max efficiency P out (kw) P in (W) Courtesy of e2v

27 IOT Advantages High Efficiency and Minimal Energy Consumption is Mandatory for ESS Modulator Efficiency 90% to > 95% Power Saving from High Beta section 3.3 MW Heat from collectors can still be recovered RF Efficiency 43% to > 60% Efficiency higher still at low current Modulator capital cost is lower saving 6 10 M EUR Smaller form factor affecting space/cost of the building Lower voltage, no oil tanks

28 700 MHz HOM IOT Experience CPI VHP-8330A IOT RF Input Design Parameters value units Power Output 1000 kw (min) Beam Voltage 45 kv (max) Beam Current 31 A (max) Frequency 700 MHz 1dB Bandwidth 1 ± 0.7 MHz (min) Gain db (min) 31kV % (min) Diameter 30/76 in/cm 0.7 Height 51/130 in/cm Weight /450 lbs./kg Collector 0.5 Coolant Flow 220 gpm Body 0.4 Coolant Flow 10 gpm O/P Window 0.3 Cooling (Air) 35 cfm Output power 0.2 Efficiency P o (M W ), efficiency Test Results (pulsed) Ib (A) Gun Solenoid, O/P Cavity RF Output Collector

29 IOT Options Power requirement for 500 kw 1.5 MW Narrow band (single output cavity) Single beam Large cathode High voltage High cathode loading Oil in the modulator and gun Multi beam Several smaller cathodes Higher total perveance > Lower voltage Scalable for higher power levels ( kw per cathode)

30 Single Beam or Multi beam? Single beam limits current High supply voltage ( > 95 kv for >1 MW) Multi beam allows higher current Lower supply voltage (50 kv for > 1 MV) No oil, simple protection circuits Higher efficiency if designed for low space charge per beam Examples of MB Klystrons CPI VKL MW 1.3 GHz Thales TH MW 1.3 GHz Toshiba E3736H 10 MW 1.3 GHz

31 Parameter Frequency 704 MHz Comment Maximum Power 1.2 MW During pulse plus overhead for regulation Pulse length Up to 3.5 ms Beam pulse 2.86 ms Pulse repetition freq. 14 Hz Duty factor 5% Gain Target IOT Parameters for Prototype Build (Currently out for tender closing date 29 Feb 2014) > 20 db Overhead margin 30% Short duration only High voltage < 50 kv No oil for the PSU nor the gun tank Efficiency at 1.2 MW 65% Design target Design lifetime 50,000 hrs Design target comparable with klystrons Grid bias / Idle current No idle current May be gated between pulses Prototypes required 2 Preference for two separate manufacturing sites Series production 84 Plus initial 10% spares, plus ongoing supply

32 Schedule Considerations MW on target High beta power source installation 2015 First tests Early 2014 Tender awarded 2019 First Neutrons 2017/18 Decision for high beta power source 2018 Medium beta klystrons installed Early 16 High power test Original plan: Use the same klystron for medium and high beta Tender out for IOT tech. demonstrator May 13 IVEC Jan 13 CERN Collaboration Nov New base line review 704 MHz klystron prototype nearly ready safe backup Modulator development in parallel Financial rather than project risk but cost recovered in operation

33 Thank you