Progress of gasfilled RF hadron monitor study K

Progress of gas-filled RF hadron monitor study K. Yonehara APC, Fermilab 2/4/16 DUNE BIOS meeting, K. Yonehara 1

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 ($100 k/yr) – Evaluated a concept of the new hadron monitor – Prepare for phase II grant ($1 M/2 yrs) 2/4/16 DUNE BIOS meeting, K. Yonehara 2

Concept of gas-filled RF hadron monitor Fast-proton-impact ionizes N 2 and induces electron cascade N 2 gas High energy charged particle Beam-induced gas plasma RF field • Beam-induced gas plasma changes the permittivity of gas • Measure the permittivity shift by observing the RF modulation 2/4/16 DUNE BIOS meeting, K. Yonehara 3

Plasma permittivity Ionization electrons must be thermalized by gas via the momentum transfer interaction within one RF cycle! n: Electron collision frequency with gas ne: Number of ion pairs m: Electron mass wrf: Angular frequency of driving RF Variables tuned by RF parameters E, P Resonant frequency shift RF power loading K. Yonehara et al. , 2/4/16 http: //accelconf. web. cern. ch/Accel. Conf/IPAC 2015/papers/mopwi 018. pdf DUNE BIOS meeting, K. Yonehara 4

Schematic drawing of RF monitor 2/4/16 DUNE BIOS meeting, K. Yonehara 5

RF pixel and diagnostics 2/4/16 DUNE BIOS meeting, K. Yonehara 6

Set required position resolution for LBNF application Expected muon profile at muon monitor (P. Lebrun et al) 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 mrad 2/4/16 DUNE BIOS meeting, K. Yonehara 7

Assumptions in this analysis • No horn in event generator N. Mokhov – 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 ms, which is longer than beam spill time 2/4/16 DUNE BIOS meeting, K. Yonehara 8

Generate secondary beam in G 4 Beamline 120 Ge. V proton Carbon target @ z = 0 m 15 x 6. 4 x 1000 mm Secondary particles size = 1. 5 mm cycle time = 1. 33 s Pulse duration = 10 ms 84 bunches (120 ns bunch to bunch) 1. 2 1014 ppp @ 2. 4 MW Hadron monitor @ z = 200 m xy profile of all charged particles at hadron monitor Arrival time of protons at hadron monitor 500 mm -500 mm Most primary protons are arrived within 100 ps (= RF period) 2/4/16 DUNE BIOS meeting, K. Yonehara 9

Estimate RF energy dissipation • Record 6 D of charged particles generated in G 4 base simulator • Estimate number of ion pairs in RF pixel • Estimate dw for each ion pair • Sum dw to estimate W B. Freemire Number of ion pairs ~ 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 2/4/16 DUNE BIOS meeting, K. Yonehara 10

Evaluation for 120 Ge. V 2. 4 MW beam E = 0. 1 MV/m N 2 gas pressure = 1 atm RF energy dissipation in RF monitor • 12 x 12 pixels, 30 x 30 mm 2 • After single bunched beam passed • Orange curve is a normal fitting • Multiple scattering tail can be seen in this pixel size Beam center position sensitivity • Error is due to the normal fitting • Statistic error is 0. 5 % • Error increases when dx > 60 mm since the number of fitting points are less than 5 2/4/16 DUNE BIOS meeting, K. Yonehara 11

Sensitivity vs incident beam intensity 1 atm N 2 1 atm He Unity of W/U represents that all RF stored energy is consumed by the beam-induced plasma 2/4/16 DUNE BIOS meeting, K. Yonehara 12

60 Ge. V proton beam operation E = 0. 1 MV/m N 2 gas pressure = 1 atm • 8 x 8 pixels, 30 x 30 mm 2 RF resonator • It still detects the beam center within 1 mm spatial resolution 2/4/16 DUNE BIOS meeting, K. Yonehara 13

Long graphite target E = 0. 1 MV/m N 2 gas pressure = 1 atm • 12 x 12 pixels, 30 x 30 mm 2 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 2/4/16 DUNE BIOS meeting, K. Yonehara 14

Increase resonator sensitivity 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 2/4/16 DUNE BIOS meeting, K. Yonehara 15

Electronegative dopant • 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 N 2 + O 2 N 2 2/4/16 E = 0. 1 MV/m Gas pressure = 1 atm DUNE BIOS meeting, K. Yonehara We can measure the time domain hadron beam profile 16

RF frequency modulation E = 1 k. V/m f = 10 GHz N 2 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 2/4/16 DUNE BIOS meeting, K. Yonehara 17

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) 2/4/16 DUNE BIOS meeting, K. Yonehara 18

Estimated RF power Example f = 800 MHz E = 1 MV/m G. Kazakevic • Plot shows that the RF power source should provide ~2 k. W 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 2/4/16 DUNE BIOS meeting, K. Yonehara 19

Demonstration test (I) • Test 1: 800 MHz resonator at MTA to verify concept – All RF apparatus is ready – Need permission from Fermilab AD director Measure wider E/P than past test • Low gas pressure 1 - 10 atm • Low electric field 1 k. V/m - 10 MV/m • N 2, He, O 2 as dopant Experimental apparatus 2/4/16 M. Chung et al. , PRL 111, 184802 (2013) DUNE BIOS meeting, K. Yonehara 20

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 2/4/16 DUNE BIOS meeting, K. Yonehara 21

Demonstration test (III) • Test 3: 10 GHz resonator at MTA/Nu. MI for prototype test – Make a prototype RF monitor • Pixel structure – Buy/Make a new RF power source 2/4/16 DUNE BIOS meeting, K. Yonehara 22

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 Nu. MI/LBNF 2/4/16 DUNE BIOS meeting, K. Yonehara 23