System for Continuous Chemical and Isotopic Purification of Hydrogen for the MuCap Experiment

Size: px

Start display at page:

Download "System for Continuous Chemical and Isotopic Purification of Hydrogen for the MuCap Experiment"

Duane Parsons
5 years ago
Views:

1 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

2 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

3 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

4 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

5 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

6 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

7 CHUPS, Hydrogen flux 3 l/min Temperature, K :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

8 Nitrogen purification The capture process µn Z N Z-1 +ν is identified by its distinct signature in the TPC 8

9 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

10 Humidity 10

11 Moisture measurements in CHUPS with TPC Humidity, ppm H2O_sensor, ppm TT5, K (H2O sensor) TT6, K (TPC) Temperature, K TPC connection : : : : :00 Time : : : :00 11

12 CHUPS results N 2 less than 5-7 ppb O 2 less than 5 ppb H 2 O about 20 ppb 12

13 General layout of the cryogenic column 13

14 Condenser 14

15 Reboiler 15

16 Vapour flow in the column at reboiler power ~20W Vapour flow rate, mol/h Vapour flow rate, sl/min Pressure, bar

17 Saturated vapour pressures and separation factors Separation factor Alfa o-p Alpha D-H p-h2 o-h2 HD 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 T, K 17

18 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

$2 mm Free volume fraction: 0.$ Packed density: 1430 kg/m 3

19 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

20 Ortho-Para Hydrogen Chromatogram (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 Para Ortho Time 20

21 Ortho hydrogen concentration Ortho H 2 concentration, % Bottom Top Column pressure, bar 21

22 Separation ratio (SR) a o-p (P) 74.4 Experimental points Separation ratio 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

23 Expected HD concentration profile Feeding point 120 Height, cm Pure protium withdrawal Purging point E-7 1E-6 1E-5 1E-4 1E HD fraction, ppm Feed flow rate = 1 L/min; Pressure = 1.5 bar; Purging flow rate = L/min; HETP = 2.2 cm Initial HD concentration = 6 ppm (deuterium atomic fraction = 3 ppm) 23

24 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

25 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

HYDROGEN DISTILLATION AT THE DEUTERIUM REMOVAL UNIT OF MuCap EXPERIMENT

HYDROGEN DISTILLATION AT THE DEUTERIUM REMOVAL UNIT OF MuCap EXPERIMENT I.A. Alekseev, E.A. Arkhipov, S.D. Bondarenko, O.A. Fedorchenko, V.A. Ganzha, P.A. Kravtsov, V.A. Trofimov, A.A. Vasilyev, T.V. Vasyanina,