The Beam Test Facility at the SNS

Transcription

1 The Beam Test Facility at the SNS R.F. Welton, A. Aleksandrov, B.X. Han, Y.W. Kang, M.M. Middendorf, S.N. Murray, M. Piller, T.R. Pennisi, V. Peplov, R. Saethre, M. Santana, C. Stinson, M.P. Stockli and J. Tang Purpose of the BTF: develop an new SNS front end & stand alone 2.5 MeV research accelerator BTF description: Ion source & LEBT systems BTF operations & 1st beam measurements Timeline, status and outlook ORNL is managed by UT-Battelle for the US Department of Energy

2 A new 2.5 MeV beam test facility has been built at the SNS which accelerated it s first beam last week. The facility has 2 purposes: Prepare and validate the new Research Instruments RFQ accelerator as a potential replacement for the existing Berkeley RFQ Later serve as a stand alone 2.5 MeV research accelerator for (i) (ii) (iii) The Beam Test Facility (BTF) ion source development for the SNS (1.4MW) and PPU & STS (2.8MW) upgrades perform simultaneous 6D beam dynamic measurements for code validation conduct neutron moderator studies for the STS 2 NIBs 2016 Welton

3 Why consider replacing the Berkeley RFQ? BTF SNS Front End 3 NIBs 2016 Welton Risk associated with unexplained frequency and field distortions: over the last 16 years the Berkeley RFQ has had a history of largely unexplained de-tuning, field distortion events (-400kHz shift in 2003, -230kHz shift in 2009, field distortion in 2012) Unable to operate Berkeley RFQ at full design field with sufficient stability Stability is still not ideal at reduced field strength

4 Issues with the existing Berkeley RFQ Simulations show even µm scale mechanical displacement to the vanes can cause significant field and frequency distortions New RFQ design is mechanically and thermally much more robust Will require testing of beam energy, emittance and transmission before the decision is made to swap Typically observe 60-75% transmission for input current of ~50mA RFQ amplitude scans typically show little saturation with increasing drive power above our operating range PARMTEQH simulations using a measured source emittances suggest ~80% transmission for ~50mA at design field RFQ field amplitude is almost always limited by thermal instabilities during SNS operation before the optimum acceleration field is reached! 4 NIBs 2016 Welton Current operating range Design field range

5 BTF missions: ion source development Through direct MEBT beam current and emittance measurement, the BTF will be an ideal platform to develop and demonstrate ion sources for 1.4 MW operations as well as sources for the PPU and STS which requires significantly higher MEBT beam currents SNS-PPU upgrades the existing accelerator structure Increases neutron flux to existing beamlines Provides a platform for SNS-STS STS is optimized for highest neutron peak brightness at long wavelengths 5 NIBs 2016 Welton 1.4 MW Operation Energy (GeV) Macro-pulse length (ms) RFQ output beam current (ma) Macro-pulse un-chopped fraction PPU & STS Upgrade

6 BTF Missions: 6D beam dynamic studies & STS moderator development RFQ MEBT-1 Direct 6D phase space measurement after RFQ; includes cross-plane correlations. I S FODO BSM existing future Benchmark codes (community resource), evaluate diagnostics Study halo formation. Fully Funded Low power short pulse neutron source Up to 100 Watts on Li target 1-10 us 6m long neutron beam line Funded through LDRD FY15-16 then by STS Layout has been determined Most proton beamline components constructed but not installed 6 NIBs 2016 Welton

7 Major BTF components MEBT diagnostic beam line RFQ accelerator Isolation transformer enclosure HV Source electrical platform HV electrical conduit Lens 2 steering deck Ion Source cage LEBT chamber RF generator, ground rack 04 (not shown) 7 NIBs 2016 Welton

8 The SNS ion sources External Antenna Source RF Plasma gun Filter field Cs Collar 8 Cs 2 CrO 4 dispensers loaded into the collar Outlet aperture AlN Plasma Chamber PEEK cooling jacket Multicusp magnets Electron Dump Antenna Mounting flange Internal Antenna Source SNS ion sources: baseline source #2,3,4,5,6,7 & external antenna sources x2, x3 can be installed interchangeably on the SNS (8100), ISTF (8100) and BTF (8320) External antenna source highly developed, routinely runs on the ion source test stand makes persistent ~50 ma beams, usually tested for weeks, See RSI 87, 02B146 (2016) Nearly identical electrostatic Low Energy Beam Transports (LEBT) are also installed in each facility 8 NIBs 2016 Welton

9 The ion source cage RF isolation transformer RF directional coupler Port for ion source RF matching transformer Ion source water manifold RF matching capacitor 9 NIBs 2016 Welton

10 The ion source cage RF isolation transformer RF directional coupler Port for ion source RF matching transformer Ion source water manifold RF matching capacitor 10 NIBs 2016 Welton

11 Ion source / LEBT vacuum chamber Same as in SNS Built from spare SNS components 5 LEBT assemblies 11 NIBs 2016 Welton

12 The new RFQ accelerator Existing 12 NIBs 2016 Welton Manufactured by Research Instruments, GmbH Mechanically designed at ORNL using the Berkeley physics design Beam dynamics Same RF Similar, different in tuning Mechanical Stronger (solid Cu) Vacuum deformation: -18 vs -119 khz in existing Octagonal shape can provide better vacuum quality and mechanical strength (RF efficiency slightly decreases, but losses by stabilizers are much smaller) New

13 ITF diagnostics beam line layout quads BCM Emittance scanner Beam dump BPM 13 NIBs 2016 Welton

14 Tomco 2 MHz RF Generator Provides high power RF for ion source plasma generation TOMCO 120 kw Pulsed 2 MHz RF power amplifier Model BT120K Alpha Eight 15 kw solid state pulsed RF amplifier units Hybrid Combiners Operating Frequency: 2.0 MHz +/- 0.2 MHz Maximum duty-cycle: 8% Maximum Pulse Width: 1.3 ms Mismatch protection: withstands 2:1 VSWR indefinitely at full output power 14 NIBs 2016 Welton

15 Lens 2 steering deck -60kV Lens 2 supply HV enclosure +/- 3kV steering supplies HV platform 1phase isolation transformer HV insulators Provides control of beam direction entering the RFQ 15 NIBs 2016 Welton

16 Operating the BTF Log onto ics-srv-testf1 as testoper type: startmap-testf1 Type: startmap-btf BTF Controls Top Page 16 NIBs 2016 Welton

17 Operating the BTF: excerpt from operator training Verify PPS is in Operate All and MPS in Standby modes From this point forward operation is similar to the SNS front end in MEBT beam stop mode so we should follow our usual conditioning and cesiation procedure (Cs2CrO4_MEBT_startup'16b) Perform normal beam-based alignment using mechanical knobs located on the beam-left of the LEBT tank The preferred source restart method takes advantage of the smooth transition from low to high power of the TOMCO solid state 2MHz amplifier: Flow H2 gas / 13 MHz plasma ignition All LEBT voltages to nominal Slowly increase the solid state 2MHz power to nominal, 50-60kW (50-60% slider) Shift MPS from standby into 50us mode and measure MEBT beam current 17 NIBs 2016 Welton

18 LEBT beam current measurement BTF does not have a beam chopping capability like the SNS LEBT beam current measurements therefore require a dedicated +6kV (1-10 us, 10 Hz) pulsed power supply, deflecting beam to chopper target Full deflection will also require steering SNS LEBT beam current measurements: V=4.6kV (chopper) + 3kV (steering) = ~7.6 kv BTF LEBT beam current measurements: V=6kV (pulser) + 2-3kV (steering) = ~8-9 kv Lens-2: 46.0 kv Total deflection voltage with chopping and steering: 7.6 kv 18 NIBs 2016 Welton

19 Typical LEBT beam current measurement RFQ was off during these measurements LEBT beam currents typically 60mA range have been measured at the BTF for baseline source #6 with an 2MHz set point of ~60% Source #6 was also tested ~60 ma for multiple days of continuous running with no significant issues 19 NIBs 2016 Welton

20 LEBT beam current from source #6 LEBT Beam Current (ma) /17 8/18 8/19 8/20 8/21 8/22 8/23 8/24 8/25 Demonstration of continuous operation of source #6 on the BTF making about 60mA for 1 week. 20 NIBs 2016 Welton

21 First beam through the BTF RFQ! On ! 21 NIBs 2016 Welton

22 Past BTF Timeline July 2009 began writing equipment specifications for new RFQ March 2011 final RFQ design reviews and manufacture at RI begins Nov 2013 RFQ delivered to ORNL & assembly July 2013 Ion Source / LEBT systems design and acquisition work begins in earnest (weekly meetings) July 2014 RFQ acceptance test August 2014 installed 1 st ion source #6 July RFQ fully conditioned to 1ms, 60Hz, 550kW Aug st plasma and HV source operation March st beam in LEBT April st LEBT beam measurements August 2016 BTF operational readiness review Sept 2016 DOE authorization & 1 st accelerated beam at the BTF! 22 NIBs 2016 Welton

23 Future BTF timeline Fall 2016 High accuracy measurement of energy, emittance & transmission; high power beam test following commissioning plan Jan 2017 decision to perform RFQ swap: shut down BTF and begin transfer March 2017 install BTF RFQ on SNS Aug 2017 install Berkeley RFQ in BTF 23 NIBs 2016 Welton

24 BTF status and outlook Over several years a 2.5 MeV research accelerator has been designed, constructed and components tested individually (ion source, LEBT, RFQ, MEBT, diagnostics) Just obtained DOE approval to begin operations and produced 1 st beams! After full power measurements of beam transmission, energy and emittance of the new RFQ the decision will be made whether to install it on the SNS If installation occurs, the BTF will be re-commissioned with the Berkeley RFQ in about 1 year Lots of powerful ion source tools for developing accelerator-based ion source systems now exist at the SNS: 8 External and Internal RF driven H - ion sources, the BTF, the low energy and helicon test-stands, lots of ideas and a great community to explore them with! 24 NIBs 2016 Welton

25 25 NIBs 2016 Welton End of talk marker.

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27 LEBT beam current measurement The deflected beam current incident on the chopper target is drained through a 50 Ω resistor who s voltage drop is viewed by BTF Scope 3, channel 2. Beam current is sampled by deflecting 10us of beam current from every 6 th pulse at an arbitrary location on the 1 ms pulse usually at the 400us point. During CCR monitoring of the source/lebt operation this scope channel is used to alert an plasma outage LEBT chopper target By first making a LEBT beam current measurement with and without extreme steering and noting the ratio, the deflector supply and be run during RFQ inject to serve as a real-time monitor of LEBT beam current! 27 NIBs 2016 Welton

28 HV Isolation transformer Rack ITF02 Provides 110 & 208V AC power to the -65kV platform 110V single phase isolation transformer 208V 3 phase isolation transformer Total available power: 19 kva 28 NIBs 2016 Welton

29 LEBT beam current measurement B kv A kv kv C kv D SNS LEBT beam current measurements: V=4.6kV (chopper) + 3kV (steering) = ~7.6 kv BTF LEBT beam current measurements: V=6kV (pulser) + 2-3kV (steering) = ~8-9 kv 29 NIBs 2016 Welton

30 5kW beam dump with radiation shielding Beam dump Borated poly Steel Radiation outside the shield < 0.3 mrem/hr at full beam power Radiation can be up to 10 Rem/hr if beam misses dump 30 NIBs 2016 Welton

31 HV electronics platform for the source Provides a safe enclosure for ion source power supplies and diagnostics held at source potential (-65kV) 13MHz generator Edump supply Control chassis P-gun supply Control chassis Ethernet ports HV scope 1 HV scope 2 Thermocouples Design based on a minimum of 6 inches clearance for all HV structures 31 NIBs 2016 Welton

32 Ground Rack ITF04 Houses -65kV power supply and LEBT supplies and control chassis Breaker panel Control chassis Ground scope Control chassis Extractor Power supply Lens 1 Power supply HV supply controls HV supply 32 NIBs 2016 Welton

33 Rack ITF03 - AC power distribution Works with Hoffman & access control boxes Provides switched AC power to: ITF04 65kV supply ITF02 HV isolation transformer for ITF01 Lens-2 steering deck Receives power enable signals from: Door/panal interlock switches: ion source cage, ITF01-03 & steering deck vacuum system Hoffman box also provides signal to the access control box which can open/close the HV relays: 2x edump HV deck Lens 1 Extractor 33 NIBs 2016 Welton

34 34 NIBs 2016 Welton End of back ups.