Progress of gas-filled RF hadron monitor study K. Yonehara APC, Fermilab 2/10/16K. Yonehara1

Background Radiation robust hadron profile monitor is required for multi-MW beams Propose a gas-filled RF hadron monitor – Radiation robust – Accurate No space charge effect Awarded STTR phase I with Muons Inc., 2015 ($100k/yr) – Evaluated a concept of the new hadron monitor – Prepare for phase II grant ($1M/2yrs) 2/10/16K. Yonehara2

Concept of gas-filled RF hadron monitor 2/10/16K. Yonehara3 High energy charged particle N 2 gas RF field Beam-induced gas plasma Fast-proton-impact ionizes N 2 and induces electron cascade Beam-induced gas plasma changes the permittivity of gas Measure the permittivity shift by observing the RF modulation

Plasma permittivity 2/10/16K. Yonehara4 : Electron collision frequency with gas n e : Number of ion pairs m : Electron mass  rf : Angular frequency of driving RF Resonant frequency shift RF power loading Ionization electrons must be thermalized by gas via the momentum transfer interaction within one RF cycle! This condition is guaranteed with the present RF monitor design. Variables tuned by RF parameters E, P K. Yonehara et al.,

Schematic of RF monitor 2/10/16K. Yonehara5

RF pixel and diagnostics 2/10/16K. Yonehara6 RF phase lock signal Mixer to measure frequency shift ADC records raw RF signals

Set goal spatial resolution of beam center for LBNF application 2/10/16K. Yonehara7 I picked up the goal spatial resolution to be 1-2 mm at the hadron monitor even though the spatial resolution 5 mm is needed for 25  rad Expected muon profile at muon monitor (P. Lebrun et al)

Assumptions in this analysis No horn in event generator – High energy protons are dominant – Horn won’t change the profile of fast protons significantly No neutral particle involved – Assume it is an isotropic distribution – It may contribute as noise but it should not be significant No plasma recombination – Plasma lifetime will be > 10  s, which is longer than beam spill time 2/10/16K. Yonehara8 N. Mokhov

RMS size = 1.0 mm cycle time = 1.2 s (or shorter) Pulse duration = 10  s (84-2) x 6 bunches (20 ns bunch to bunch) ppp ( MW Generate secondary beam in G4Beamline xy profile of all charged particles at hadron monitor -500 mm 500 mm -500 mm 500 mm Arrival time of protons at hadron monitor 120 GeV proton Carbon z = 0 m 15 x 6.4 x 1000 mm Hadron z = 200 m Secondary particles Most primary protons are arrived within 100 ps (= RF period) K. Yonehara92/10/16

RF energy dissipation by plasma 2/10/16K. Yonehara10 ~ 100 ion pairs in 1 atm N 2 ~ 20 ion pairs in 1 atm He RF energy dissipation per RF pixel where i represents i -th test particle Number of ion pairs Record 6D of charged particles generated in G4 base simulator Estimate number of ion pairs in RF pixel Estimate dw for each ion pair Sum dw to estimate W B. Freemire

Evaluation for 120 GeV 2.4 MW beam 2/10/16K. Yonehara11 RF energy dissipation in RF monitor 12 x 12 pixels, 30 x 30 mm 2 ▸ Resonator size is determined from spatial resolution ▸ Number of data points are more than 5 which is needed for good fitting Observed beam profile after single bunched beam passed the monitor Orange curve is a normal fitting ▸ Beam center is found from the fitting in this analysis E = 0.1 MV/m N2 gas pressure = 1 atm

Empty target mode 2/10/16K. Yonehara12 RF pixel Primary proton beam at target Beam emittance = 30   rad (3  ) Square root of beta function = 4.5 m 1/2 Beam size = 3.2 mm (3  ) Divergence x’ = 75  rad (3  ) Only four RF pixels are hit the beam Beam is on one vertex of each RF pixel Beam position can be tuned by equalizing RF energy consumption in each RF pixel xy profile at RF monitor (z = 200 m) RF pixel RF monitor signal

Misalignment 2/10/16K. Yonehara13 Target 15 x 6.4 mm 2 0 mm dx 2 mm y profile x profile dx 4 mm y profile dy 4 mm dy 2 mm y x beam position on target For y direction: Beam center can be measured with 0.15 mm errors For x direction: Not enough spatial resolution to determine the beam center from the normal fitting

60 GeV proton beam operation 2/10/16K. Yonehara14 8 x 8 pixels, 30 x 30 mm2 RF resonator It still detects the beam center within 1 mm spatial resolution E = 0.1 MV/m N2 gas pressure = 1 atm

Long graphite target 2/10/16K. Yonehara15 12 x 12 pixels, 30 x 30 mm2 RF resonator It still detects the beam center within 1 mm spatial resolution Note: No Horn in this analysis! Hadron flux should be greater than the present result E = 0.1 MV/m N2 gas pressure = 1 atm

Tune resonator sensitivity 2/10/16K. Yonehara16 RF resonator is equivalent to a LCR circuit Concentrate E field A high capacitive resonator has higher sensitivity than a box resonator It is useful for a low intensity beam measurement Expected detectable beam intensity 10 9 to protons/bunch

Electronegative dopant 2/10/16K. Yonehara17 Oxygen is a good electronegative element to capture a free electron via the three body process dw of O 2 - is 50 times lower than electrons RF stored energy can remain even several bunched beams are traverse in the resonator N2 + O2 N2 We can measure the time domain hadron beam profile E = 0.1 MV/m Gas pressure = 1 atm

RF frequency modulation 2/10/16K. Yonehara18 E = 1 kV/m f = 10 GHz N2 gas pressure = 1 atm Integrated all beam spill Frequency shift can be measured very accurately by using a lock-in amp Challenging part is how the frequency of a RF source is stable

RF power source RF power source is the most cost driver Since required RF power is so small that the commercial power supply is available for RF monitor Magnetron is even cheaper (it is a source of microwave) 2/10/16K. Yonehara19

Estimated RF power 2/10/16K. Yonehara20 G. Kazakevic Plot shows that the RF power source should provide ~2kW power to a 800 MHz RF pixel to excite 1 MV/m RF field 1 MW power magnetron is available for this frequency which can cover 50 RF pixels Example f = 800 MHz E = 1 MV/m

Demonstration test (I) Test 1: 800 MHz resonator at MTA to verify concept – All RF apparatus is ready – Need permission from Fermilab AD director 2/10/16K. Yonehara21 Experimental apparatus Measure wider E/P than past test Low gas pressure atm Low electric field 1 kV/m - 10 MV/m N2, He, O2 as dopant M. Chung et al., PRL 111, (2013)

Demonstration test (II) Test 2: 2.45 GHz resonator at MTA for R&D – Make a new RF resonator – Test existing 2.45 GHz Magnetron Phase stability Amplitude stability 2/10/16K. Yonehara22

Demonstration test (III) Test 3: 10 GHz resonator at MTA/NuMI for prototype test – Make a prototype RF monitor Pixel structure – Buy/Make a new RF power source 2/10/16K. Yonehara23

Time line Propose STTR phase II grant (Spring, 2016) Get permission for demonstration test at MTA from Fermilab AD director Carry out test 1 (Summer, 2016) Analysis phase Make a new RF resonator Carry out test 2 (Winter, 2016) Analysis phase Make a prototype RF monitor Carry out test 3 (Spring, 2017) Make a practical RF monitor for NuMI/LBNF 2/10/16K. Yonehara24