MuCF07 System for Continuous Chemical and Isotopic Purification of Hydrogen for the MuCap Experiment A.A. Vasilyev a, I.A. Alekseev a, O.A. Fedorchenko a, V.A. Ganzha a, M. Hildebrandt b, P. Kammel c, P.A. Kravtsov a, C. Petitjean b, G.G. Semenchuk a, G.N. Shapkin a, V.A. Trofimov a and M.E. Vznuzdaev a a Petersburg Nuclear Physics Institute, Russia b Paul Scherrer Institute, Switzerland c University of Illinois at Urbana-Champaign, US 1
Why we need ultra pure hydrogen? q q Heavier elements Negative muons preferentially transfer from µp atoms to heavier elements with high rates. Once a muon has transferred to a µn Z atom, nuclear muon capture proceeds more than 100 times faster than on a µp atom. Thus, even tiny amounts of impurities in the hydrogen gas distort the observed µp lifetime spectrum. Consequently, muon transfer and subsequent capture must be suppressed by keeping the gas contaminants below a level of 10 ppb. Deuterium Isotopically pure hydrogen is required, since muons transfer to deuterium, where they pose a systematic problem for the MuCap experiment. Due to a Ramsauer-Townsend minimum in the μd + p scattering crosssection, μd atoms can diffuse over macroscopic distances and can either escape from the stopping volume in the TPC in a time-dependent way and can even reach the chamber materials, where muons are quickly captured. 2
Why we need continuous purification? Impurity capture events measured before purification system installation, shows the impurity capture event yield increasing in the hours after filling the hydrogen vessel through the palladium filter (better than 1 ppb). 3
Circulation Hydrogen Ultrahigh Purification System - CHUPS Reasons for Circulation system? - constant flux is necessary for the permanent gas purification. about 3 l/min - price of pure hydrogen is essential. about 1000 Eur/m 3 - stable pressure in TPC is important. 10 bar +/- 0.1% (10 mbar) Type of compressor? 10 bar absolute pressure 3 bar differential pressure 3-4 l/min flux ultra pure!!! Normal or Cryo-? 4
CHUPS P Simplified P-T diagram of a Compressor column P BV2 P BV1 Pushing to reserve volume Both check valves are closed P TPC Pumping from TPC T min T max T 5
Compressor unit Refilling port Purification unit CHUPS scheme CHUPS Gas/Liquid separator From Dewar F4 F5 V10 V11 C V11 V12 F11 CV12 CV21 F12 F21 T1 CV22 F22 CV31 F31 CV32 F32 MFC-1 MFC-2 MFC-3 LT1 T2 Relief T3 Vacuum line Membrane pump V13 V14 Oil-free vacuum line Vacuum line F6 T4 T5 F7 Refilling ports Oil free vacuum line Column1 Column2 Column3 L- nitrogen tank Upper L-nitrogen tank F10 F11 TT1 TT2 TT3 TT4 H1 H2 H3 H4 Compressor LT1 F9 Lo wer L-nitrogen tank F12 V21 HV pump ing system V35 V36 Vacuum system V19 FA1 FA2 Radiation shielding Purifier Control Gas Panel RV2 SV2 PT2 SV3 SV1 V2 RV1 V1 MFC-5 PT4 MFC-4 F8 PT3 V28 Reserve volume V6 V3 Oil free vacuum line V26 V31 DAC_24 TT5 Compressed air H10 TT10 TT6 V17 V15 V9 Sampling valve Sample V24 V29 PT1 HS F11 V32 V30 G V27 V33 V25 V5 V4 TPC V34 V37 V38 Release volume PT - pressure sensor TT - temperature sensor LT - level meter SV - operating valve V - manual valve F - filter F - filter-adsorber H - heater M - manometer MFC - mass-flow controller T - thrermalizer EF - electrostatic filter HS - humidity sensor LT - level detector G - getter - hydrogen line - pumping line - nitrogen line - compressed air line - electronic signal V16 V23 6
CHUPS, Hydrogen flux 3 l/min Temperature, K 180 170 160 150 140 130 120 110 100 90 80 00:00 00:30 01:00 01:30 02:00 02:30 03:00 Time Column 1 Column 2 Column 3 T max T min 7
Nitrogen purification The capture process µn Z N Z-1 +ν is identified by its distinct signature in the TPC 8
Nitrogen+Oxigen Chromatography measurements also track the purification process (-a). Oxygen traces dropped below the apparatus sensitivity of 5 ppb within two days after starting the circulation. Nitrogen concentrations below the apparatus sensitivity of 7 ppb. 9
Humidity 10
Moisture measurements in CHUPS with TPC 0.016 312 Humidity, ppm 0.014 0.012 0.010 0.008 0.006 H2O_sensor, ppm TT5, K (H2O sensor) TT6, K (TPC) 310 308 306 304 302 300 Temperature, K 298 0.004 TPC connection 296 0.002 294 0.000 20.03.2006 00:00 21.03.2006 00:00 22.03.2006 00:00 23.03.2006 00:00 24.03.2006 00:00 Time 25.03.2006 00:00 26.03.2006 00:00 27.03.2006 00:00 292 28.03.2006 00:00 11
CHUPS results N 2 less than 5-7 ppb O 2 less than 5 ppb H 2 O about 20 ppb 12
General layout of the cryogenic column 13
Condenser 14
Reboiler 15
Vapour flow in the column at reboiler power ~20W 105 39.2 100 37.4 Vapour flow rate, mol/h 95 90 85 35.5 33.6 31.7 Vapour flow rate, sl/min 80 0 1 2 3 4 5 6 Pressure, bar 29.9 16
Saturated vapour pressures and separation factors Separation factor 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1 1.06 1.05 1.04 1.03 1.02 Alfa o-p Alpha D-H p-h2 o-h2 HD 1200 1000 800 600 400 200 0 Saturated vapour pressure, kpa vapour (atomic fraction y) liquid (atomic fraction x) Temperature = const At dynamic equilibrium the content of low-boiling component is a-times higher in liquid. Separation factors: a a o- p D-H = = P P Sat. Para Sat. Ortho P P Sat. H2 Sat. HD 1.01 20 22 24 26 28 30 32 T, K 17
Height equivalent to a theoretical plate (HETP) Bubble cap plate Non-regular packing G, y* Plate height Vapour Liq uid HETP L, x* Typical plate height ~15 cm Efficiency = 70% Theoretical plate a part of the column, where composition of outgoing liquid and vapour flows are in equilibrium. (Abstract equivalent of the bubble cap plate with efficiency = 100%) Height Equivalent to a Theoretical Plate (HETP) Atomic fractions: x - in liquid y - in vapour a Separation factor: * * x /(1 - x = * * y /(1 - y * in dica tes equilibriu m comp osition ) ) 18
Packing Characteristics: Type: spiral prismatic Size: 2x2x0.2 mm Free volume fraction: 0.82 Specific surface: 3490 m 2 /m 3 Packed density: 1430 kg/m 3 Material: stainless steel Total volume of packing in the column = 560 ml Total packing surface in the column = 1.95 m 2 19
Ortho-Para Hydrogen Chromatogram 30 25 (Natural hydrogen, Column pressure = 1.2 bar; Reboiler power = 10W) Hydrogen composition: Top: Para=72.5% Ortho=27.5% Bottom:Para=5.0% Ortho=95.0% Top Bottom 20 15 10 5 0 Para Ortho 1500 2000 2500 3000 3500 Time 20
Ortho hydrogen concentration 100 90 Ortho H 2 concentration, % 80 70 60 50 40 Bottom Top 30 20 1 1.5 2 2.5 3 3.5 4 4.5 Column pressure, bar 21
Separation ratio (SR) 70 60 50 a o-p (P) 74.4 Experimental points Separation ratio 40 30 20 10 0 1 2 3 4 5 Pressure, bar SR N = a - Fenske equation for total reflux mode (N the number of theoretical plates) HETP=Packing height / N SR = X Bottom X Top / / ( 1 - X ) ( 1 - X ) Bottom Top 22
Expected HD concentration profile 160 140 Feeding point 120 Height, cm 100 80 60 Pure protium withdrawal Purging point 40 20 0 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1 10 100 HD fraction, ppm Feed flow rate = 1 L/min; Pressure = 1.5 bar; Purging flow rate = 0.015 L/min; HETP = 2.2 cm Initial HD concentration = 6 ppm (deuterium atomic fraction = 3 ppm) 23
Deuterium purification results The final measurements of the probes were performed on the new 200 kv Tandem accelerator built for isotope analysis in Zurich. A special ion source was constructed giving extremely low backgrounds of hydrogen ions from walls, etc. The walls are continuously sputtered to keep the background low allowing measurements during 2 hours. The existence of the zero samples from the DRU system turned out to be crucial, since the accelerator gives a different background if the ion source is not fed with hydrogen gas. First zero sample measurement gave zero deuterium concentration at 70 ppb sensitivity. Thus, it contains less than 70 ppb of deuterium. 24
Conclusions q q Separation column performance: q q Height Equivalent to a Theoretical Plate (HETP) value of 2.2 cm corresponds to the best medium power cryogenic column results. HETP value is almost constant in wide range of vapour flow rate. Output deuterium concentration better than 70 ppb does not depend on the initial concentration (natural hydrogen can be used!). It is possible to produce pure ortho- or para- hydrogen (99%) in the continuous mode. 25