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RESULTS OF EXPERIMENTS WITH
SPIN-STABILISED HYDROGEN AND HYDROGEN
COMPOUNDS
W. Peschka, G. Sänger, G. Hietkamp
To cite this version:
JOURNAL DE PHYSIQUE CoZZoque C7, supp26ment; ax n o 7, Tome 41, juiZZet 1980, page C 7 - 1 6 5
R E S U L T S OF E X P E R I M E N T S W I T H S P I N - S T A B I L I S E D H Y D R O G E N A N D H Y D R O G E N C O M P O U N D S
X X X XXX
W. Peschka
,
G. Sanger and G.A. Hietkampx DFVLR, Institut fiir Technische Physik, 7000 Stuttgart-Vaihingen, PfaffenwaZdring 38-40, R.F.A.
+% Ostarode-Hmz, Rehbockweg 5, R.F.A.
+**Hoordwijkerhout, GuZdemondvaart 32, HL.
Resume.- Poursuivant un programme de recherche anterieur, nous avons maintenant realis6 une expb- rience pour stabiliser de l'hydrogene atomique. Alors qu'en 1970 de faibles densites atomiques
(1015 ~ m - ~ ) avaient BtB stabilisdes, des experiences recentes ont Btabli la possibilite de stocker environ 2 milligrammes d'hydrogene atomique
a
1 K, dans un volume effectif de l'ordre de 0,5 litre, pour une periode de quelques heures. Un champ magnetique allant jusqu'a 8 T etait appliqu6 grdce ddes bobines supraconductrices. Nous avons observe la propagation du son 2 1 K dans un milieu gazeux. Les resultats de l'experience conduisent d la conclusion que deux phases d'hydrogsne atomique orient6, solideetgazeuse, Btaient prdsentds dans la chambre de stockage de llexpQrience. I1 s'est avgre ~mpossible de determiner la superfluidit6 et la conductivite electrique du fait d'une panne du dispositif experimental. Grdce 2 une version modifiee de l1expQrience, d'autres etudes ont Bte entreprises sur le stockage d'hydrogene 2 forte orientation de spin dans des matrices de carbone et de lithium. Le resultat obtenu est que, en comparaison avec de l'hydrogsne atomique pur, l'hy- drogene polarisb posssde une stabilit6 plus grande en fonction de la temperature.
Abstract.- Following an earlier research programme, an experiment has now been made to stabilise hydrogen in its atomic state. Where in 1970 the stabilisation of small particle densities was achieved ( 1 0 ~ ~ / c m - ~ ) , the work ncw done has shown it to be possible to store about 2. milligrams of atomic hydrogen at 1 K in an effective volume of about 0.5 litres for a period of some hours. A magnetic field of up to 8 Tesla was applied by means of a superconducting magnet.Propagation of sound at 1 K was noted in a gaseous medium. The outcome of the experiment has led to the conclusion that both a solid and a gaseous phase of atomic, respectively spin-aligned hydrogen, were still present in the storage area of the equipment. An experiment to determine the superfluidity and electric conductivity could not be made due to equipment failure during an earlier test. Using modified equipment, further investigations were made into storing spin-polarised hydrogen in both carbon and lithium as matrixes. It was found that, in comparison with pure atomic hydrogen, spin- polarised hydrogen has an enchanced degree of stabilisation as a function of temperature.
1. Introduction To achieve the stabilisation of atomic hydrogen The principle of stabilisatior~ of hydrogen in useful quantities, one of our group (W. Peschka)
atoms is based on the alignment of electron spins proposed in 1958 the alignment of magnetic spin in a magnetic field at low temperature. This leads moments at low temperature with an external to the non-bonded triplet conditior. characterised nagnetic field. In principle, this process is by repelling forces between hydrogen atoms. Thus, similar to the paramagnetic saturation of atomic electron spin-aligned hydrogen atoms cannot re- hydrogen. Taking quantum mechanics into consider- combine, even in 3-body collisions, al-though this
may be important, of course, in other research fields. The reason for past experiments has been the very high specific entalphy of the recombina- tion reaction. Atomic hydrogen was considered an excellent energy store and the stored energy per unit mass would far exceed that of any other chemical, mechanical or electromagnetic energy store.
ation, it was shown that a magnetic field between 1 and 10 Tesla at a temperature below 1.3K is sufficient. At the same time, not much attention was paid to the possible disturhnce mechanisms. such as electron spin flips, which could alto-
( 3 ) gether prevent the stabilisation effect
.
The results 2escribed hereafter as well as the results shown in Fig. 7 suggest +.hat the disturb-
ance mechanisms are low at about 1.3K. During the most recent experiment, atomic Now, as a consequence of further experimental
hydrogen was stored in a crystalline solid H 2
and theoretical research by various groups of
scientists (3-15)
,
it has been established that matrix for more than 30 hours. From sample susceptibility measurements close to 0.33~ and spin-aligned hydrogen and deuterium in particular,based on other considerations, it is surmised but also other light atoms such as helium or
that there exist cooperative interactions and lithium hold great promise where quantum systems
are concerned. that localised regions of higher H concentrations behave as ferromagnetic domains.
JOURNAL D E PHYSIQUE
2. Basic Experiments
The early experiments aimed at demonstrating the possibility of stabilisation of atomic hydrogen During these experimentsf2), atomic H was produced bv means of a liquid nitrogen-cooled capillary glow discharge at a pressure of about 0.2 Torr.
Subsequently, the dissociated beam was cooled down rapidly by wall collisions on a liquid helium- cooled surface and directed via a quartz tube into a magnetic field of about 6 Tesla containing the stabilisation area which was cooled down by a He I1 bath to about 1.2K. The diagnosis of the atomic hydrogen was based on the recombination reaction resulting in an increase of the partial H pressure in the system measured by a mass
2
spectrometer.
No reproducible effects were observed when (2) the magnetic field was switched off
.
On the other hand, significant and reproducible results were obtained when heating the condensates. When molecular, non-dissociated hydrogen was condensed at low temperatures, either with or without the magnetic field, the heating of the condensates to 4.2K did not produce any changes in the partial hydrogen pressure
-
as was to be expected (see straight line 'a' in Fig. I ) .When H was dissociated and condensed into
2
the stabilisation area at a zero magnetic field, the heating of the condensates led to small changes in the Hz partial pressure (see curve 'b' in Fig. 1). The changes are interpreted as recom- binations of hydrogen atoms into molecules. Curves 'c' and 'd' represent the heating curves of two different test runs when the dissociated beam was condensed in strong magnetic fields at low temperature. The much more marked variation in the partial pressure of H2 is attributed to recombination processes. It is remarkable that the magnetic field was necessary only during the condensation process when the glow discharge was being operated. Thereafter, the magnetic field could be switched off without the Hz partial pressure being affected. The particle density of stored H could be calculated from the volume of the stabilisation area, the peaks of B partial
2
pressure and the conductance of the vacuum
15 3
tubing to about 10 /cm
.
3. Experiments into Higher Atomic Hydrogen Storage Densities
Owing to a grant from the Deutsche Forschungs- gemeinschaft in 1973, it was possible to carry out research into the subject matter in a more consist- ent manner.
3.1 Experimental Apparatus
The experimental set-up was mounted in a multi- purpose high vacuum chamber with a length of 6 m and a diameter of 2 m. This chamber had been con- structed for the purpose of inductive magneto- plasmadynamic (MPD) converter experiments. One of the end-sections accommodated the experiment; the other accommodated a high-flow cryopump for providing the necessary vacuum (see Fig. 2).
Fig. 3 illustrates the structure of this unique cryopump which was originally designed for main-
-4
taining a pressure of about 10 Torr against a high-speed flow of argon, respectively hydrogen plasma of up to 100 g/sec in an MPD converter experiment. The gases which have to be pumped first pass through the beam cooler
-
a multiple heat exchanger being operated by liquid nitrogen. They are then deflected by a cone-shaped LN -2
cooled radiation shield. After passing the LN2- cooled lateral heat exchanger, the gases are frozen on the centralzontainers. These consist of two separate cooling systems operated by liquid neon and-liqtiid helium respectively. The helium container is located between two neon containers which are interconnected by means of fins. The cryopump is completed by a system of liquid nitrogen storage containers near the end-section of the chamber and a cylindrical LN -cooled
2
radiation shield covered by superinsulation material for reducing the nitrogen losses. The LN circulation is effected by an outside
2
pump. The central containers are made of high quality pure aluminium and the heat exchangers consist exclusively of finned copper tubes. All other parts are made of stainless steel.
For the performance of the atomic hydrogen experiments, only the central LHe-filled container and the LN -cooled radiation shields were used.
2
Nevertheless, the pump speed was sufficient to maintain a vacuum of Torr during the experi- ments, even at hydrogen mass flow rates of up to
The entire hydrogen test apparatus is suspended inside a tubular frame which acts as a LN -cooled
2 radiation shield for the experiment (see Fig. 2 ) .
~ l l supply and exhaust tubes as well as the wiring for instrumentation pass through the 1.0 m 0 flange of the chamber (see Fig. 4). The heart of
the apparatus consFsts of three Dewar vessels con- taining a 4.2 LHe bath for dissociator cooling, the magnet vessel and the vessel containing a 1K He I1 bath which provides the cooling for the ex- periment. The evaporation rate of helium was measured by a Hastings flowmeter. The LHe-cooled tube (No. 4 in Fig. 2) was used as one electrode of the glow discharge dissociator. The other electrode (aluminium) was located outside
the vessel in a LN2-cooled quartz tube. This tube was fed through the main flange into the vacuum vessel, and its end drawn into a capillary of about 0.3 mm (d and 10 mm length.
The magnet vessel contained the superconducting NbTi, partially stabilised magnet (Siemenslhaving a horizontal bore of 90 mm effective diameter and a length of 400 mm. The maximum attainable field was about 7 Tesla at 4.2 K and about 80 A exci- tation current. At about 2.2 K, the maximum attain- able field was about 8.5 Tesla. To lower the temp- erature in the magnet Dewar and the 1K He I1 bath, two vacuum pump systems were used. During the ex- periment, all Dewars could be refilled automatic- ally with LHe.
The experimental area for the trapping of atomic hydrogen was mounted on a central 12 mm copper tube (Fig. 5
-
centre). A cylindrical section(Fig. 5
-
at right)was provided to carry the wirings and capillary tubes for the sensors mounted on the copper tube by means of teflon discs. A unit consisting of two search coils for detection of fluctuations in the magnetic field and piezo-probes for excitation and detection of acoustic oscillations could be slipped over the central section. The whole unit was then built into a thick-walled copper cylirder (400 mm in length, 85 ran0,
18 kg mass). The Atomic Hydrogen Trapping Section (AHTS) was connected to the bottom of the 1K HeDewar. BY soft-soldering, a thermally high conducting connection was obtained. All metal parts were manufactured of 99.95% electrolyte copper.The slope of heat conductivity as a function of temperature (Iw/cmK at 1 K, 3.5w/cmK at 4.2 K, maximum 40~/cm K at 20 K; ~ W / C ~ K at 300 K)
enabled an acceptable compromise between efficient cool-down and sufficient resistive damping of eddy currents due to field fluctuations from the magnet.
To guarantee a chemically stable surface, all copper parts were galvanised by a 0.01 mm gold sheet.
The instrumentation of the AHTS is shown in Fig. 6. The intake bore of the AHTS could be closed by a valve-like arrangement 'V' (leak rate about 0.1 litre per second).
Sensors were provided for:-
- fast temperature fluctuations (Au-Chrome1 thermo-
couple-
the junction covered by a small black leaf for detection of infrared radiation);- temperature (Allen Bradley glass carbon resist-
ors) ;
-
magnetic field intensity (high field: Hall probes; small field: SQUID arrangement);- fluctuations (SQUID and search coils);
-
acoustic waves (piezo-acoustic transmitter and microphones) ;- absolute pressure (capillary tube, 0.2
@, con- nected to Baratron sensor outside the vessel);-
hydrostatic pressure (capillary tubes ata vertical distance of 3 cm connected to a Baratron differential sensor outside the vessel);
- conductivity (aluminised mylar);
-
superfluidity (second sound probe consisting of a fast-responding heater, 5 Hz.
and a fast- responding Au-chrome1 thermocouple, the latter also being used for measurement of the gas temperature).
3.2 Sequence of Main Steps of Experiment
( 1 ) Pre-evacuation of vacuum chamber to 1 mTorr and flushing with hydrogen;
( 2 ) Cool-down of cryopump until vacuum of lo-' Torr;
( 3 ) Cool-down by LN2 of cold wall in experimental section:
JOURNAL
DE
PHYSIQUE(5) Final cool-down and filling with LHe of magnet Dewar ;
(6) Temporary starting of hydrogen glow discharge to clean discharge tube and surfaces within the AHTS;
(7) Flushinq of measuring capillaries by gaseous helium (excluding mass spectrometer because of larger diameter);
(8) Final cool-down and filling with LHe of residu- al Dewars;
(9) Starting of pump for the 1K Dewar and cool- down of AHTS to lo K;
(10) Temporary starting of glow discharge by use of a hydrogen-neon mixture (25 : 1 by volume) to cover inner surfaces of AHTS with solid neon) ;
(11) Excitation of superconducting magnet (persist-
ent mode) ;
(12) Running 2f glow discharge in a pure hydrogen atmosphere (3500 Vac, 70 mA) for H dissocia-
2 tion and H trapping) ;
(13) Shut-down of glow discharge and closing of AHTS inlet valve);
(14) De-excitation of magnet;
(15) Warm-up of AHTS by shut-down of He I1 cryo- stat evacuation.
Steps 1 through 11 were normally performed within 100 hours. The remaining steps, represent- ing the actual experiment, were normally performed within 5 to 6 hours.
3.3 Experimental Results
Due to the work involved in performing steps 1 through 11, only six experimental runs could be carried out. The experiments were made with H
2' D and a H2
+
0.01 Vol% HD mixture. The results2
are largely in conformity with the different physical properties of normal hydrogen and deuterium. The H /HD experiment was carried out
2
to prove the non-existence of helium cold leaks within the system. Because it was possible to observe the mass 3 of the HD molecules during recombination within the warm-up period, any con- fusion between D; and ~ e + could be excluded with certainty.
Typical experimental results are shown in Figs
7 and 8. H2 with a purity of 99.9999% was used. Fig. 7 shows AHTS recordings between steps 13 and 15. Unfortunately, due to a malfunction,
the signals of both the superfluidity and con- ductivity sensors were erroneous.
The piezo-signal IT of the acoustic microphone was transcribed by hand from the original record- ing. As time progressed (from left to right), a continuous increase, starting from the noise level caused by the boiling liquids in the Dewsrs, could be observed when the glow discharge disso- ciator was being operated; this was followed by a continuous decrease after shut-down of the dis- sociator and closure of the AHTS inlet valve. pt and hp remained at approximately constant level whereas the microphone signal was decreasing continuously.
When the magnet was de-excitated (about 1 hour), a continuous decrease of pt, Ap and T could be observed.
Fig. 8 shows the recordings of the thermocouple signal Ts, the Hall probe signal BH, the inner wall temperature T and the pressures pt, Ap. Further recordings of the response from search coils B were transcribed by hand. Between the beginning and the end of the recordings, there was a time lapse of about one hour (see Figs 7 and 8 respectively).
During the warm-up period, an increase in the pressures within the AHTS was noted. When the wall temperature T was increased, the response from the infrared radiation detecting thermocouple gained in significance (see Fig. 9) and was accom- panied by a considerable increase in fluctuation
(equivalent to about 5K rms)
.
At about 2.3K,the wall temperature sensor responded very rapidly; the temperature rose to about 9K whilst pressures p and Ap increased also. The indication of
t
the Hall probe (BH) in relation to the SQUID signal (not shown) dropped sharply from about 20 Oerstedt to approximately zero. The response from the search coils indicated also an increase in magnetic fluctuation up to about
6
= 0.4 P V m s( 6
flux through the search coils; search coil2
The decrease in temperature T after the 9K peak can be explained by the equilibrium between
the AHTS heat capacity and the heat crnduction rate to the coolinq He I 1 D-war, assuming that a con- siderable amount of heat did arrive at the wall of the AHTS in a short time pulse. A calculation of the evaporation rate increase in LHe within the LH I1 Dewar produced a heat amount of about 400 wsec.
Using a special miniaturised piezo-transmitter and a piezo-microphone, the AHTS could be excited acoustically; the frequency was varied between 2000 and 3000 Hz by a sweep generator. As shown in Fig. 10, the maximum and minimum signals caused by axial standing waves in the AHTS could be detected. From the AHTS geometry and the frequency of maximum and minimum signals, a sound propagation velocity between 50 m/sec at 1K and 110 m/sec. at 2.3K can be derived.
3.4 Discussion of Results
With reservations to further experimental evidence, the following interpretation of the re- sults seems acceptable:-
Spin-aligned atomic hydrogen can be stored within the AHTS in a solid as well as in a gaseous phase.
AS shown by earlier
experiment^'^),
the external magnetic field appeared to be necessary only during the formation process of the two phases. The pressure curves shown in Fig. 7 show that the gaseous phase could be trapped within the AHTS in the presence of an external magnetic field. When the magnetic field was decreased, the pressure indication also decreased as if gas were leaking through the AHTS inlet valve. The trapping of the gaseous phase within the magnetic field may be explained by the paramagnetic susceptibility of atomic hydrogen. Similarly, the fluctuations in temperature and magnetic signals may be a conse- quence of recombination processes H+H=H2 '
The assumption that a solid phase must have been present also within the AHTS is based on the increase in pressure observed within the AHTS during the warm-up period from 1.1K to 2.3K, on the fluctuations in temperature and magnetic field observed there, and on the existence of a remanent magnetic field within the AHTS during more than one hour after shut-down of the magnet.
(A careful survey of other magnetic materials and superconductive currents, which could have been responsible for a remanent magnetic field within the AHTS, produced negative results. Therefore, the surmise of some authors(7) that there are cooperative interactions and ferromagnetic domains which are responsible for a remanent magnetic field within a solid H-H2 matrix seems to be justified once again).
The short-pulsed amount of heat arriving at the AHTS wall can be explained only by a rapid recombination of atomic hydrogen. The equivalent of the 400Wsec energy observed is about 2 mg of atomic hydrogen stored in a deposit of solid H
2'
A total amount of about 4
2
0.5 gr solid hydrogen material trapped within the AHTS could be evaluated from the rise in temperature and pressure in time in relation to the conductance of the inlet valve leak. Therefore, the H : H ratio within the matrix2
should have been roughly 1 : 1000. A final evalu- ation of the results and experimental data is not warranted at this stage. There are still questions about the reliability of the experimental data and, therefore, about the conclusions based thereon. For example, there was the surprising fact that the Baratron sensors connected to the AHTS by long, capillary tubes worked satisfactorily. Obviously, the helium remaining within the capillaries after flushing worked as a pressured transmitter and prevented the capillaries from being plugged by frozen hydrogen.
4. Experiments on Spin-aligned Lithium-Hydroqen --- and Carbon-Hydrogen
4.1 General Considerations
The above mentioned results would seem to show that - at the current state of technology -
the achievable storage density of atomic hydrogen in a matrix of molecular solid hydrogen is very limited (less than 1%). What other possibilities exist?
Atomic hydrogen may be considered as the gaseous phase of the hypothetical metallic hydrogen.
Russian scientists claim to have produced it by applying a very high pressure in the following
JOURNAL DE PHYSIQUE
Normal solid molecular hydrogen was compressed between two blunted diamond cones. The electric resistance was very high and remained constant until a pressure of 3.5 - 5 Mbar was reached. The resistance then dropped by several orders of magnitude - actually metallic electric con- ductivity was measured. When the pressure was released, this high electric conductivity re- mained until a b u t 400 kbar; then the electric resistance increased rapidly by several orders of magnitude to its original value (Fig. 12). This wide hysteresis leads to the conclusion that once metallic hydrogen is achieve, it has a certain stability; only a small fraction of its recombina- tion energy of 53 kcal/~ol is required to prevent recombination. The energy which was still "pressed" into the metallic hydrogen at 400 kbar pressure should be applied in a different form, i.e. by an alloy. Alloys exist where one metal "compresses" another, so that intermediate phases become stable
(see e.g. the y-phase of the Cd-Sn alloys).
The energy which kept metallic hydrogen at 400 kbar is estimated at 7 kcal. This figure represents, of course, only the order of magnitude because it depends on the compressibility characteristic which is not accurately known.
Regarding this "high pressure" method, one may say that atomic hydrogen is already produced by means of the dissociator (hence, a pressure of several Mbar must no longer be applied), but must be con- densed in a suitable matrix or solid solution being capable of trapping the energy of 7 kcal in some form.
For the solid solution H / H ~ , this means that
-
at a concentration of atomic H of 0.4 Mol% - the heat of melting and-
at 3 Mol% - the heat of vaporisa- tion would be achieved. In other words, the mutual attraction of the hydrogen molec-ules is too weak to make it a potentially suitable material for high density storage of atomic hydrogen. For this reason, experiments have been performed with spin-aligned Li-H and C-H (Note: where the following text refers to H and H2, the experiment actually made use of HD). The set-up of the experiment was as follows:-4.2 Experimental Apparatus
A LHe-cooled trapping section TS (No. 19 in Fig. 13), surrounded by a superconducting magnet
(No. 4), was mounted in a turbo-pumped ultra-high vacuum (UIJV) chamber with a volume of about 200 litres (No. 1). This trapping section
(6
about 4 cm) was made of silver (110 g calorimetric value) and copper (14 g). It could be closed on the left- hand side (Fig. 13) by a slide valve (No. 11)which - when closed - had a leak rate of about
1 Torr litre/sec. The field intensity of the super- conducting magnet (No. 4) applied to the right- hand side of the experimental section (No. 19) was about 2 Tesla. An inhomogeneous field was applied as shown by the differently sized coils (No. 4)
(5800 and 3700 windings, max. current about 20 A).
On the left-hand flange of the vessel, a radio frequency powered hydrogen dissociator was mounted. It consisted of a quartz tube surrounded by a coil which was driven by a 27 Mc/sec. r.f. oscillator with a maximum power of 600 W. Normally, a power level of 200 W was applied. Hydrogen was fed into the quartz tube and a hydrogen plasma was produced by an inductive r.f. discharge at a pressure level of about 1 Torr. The atomic hydrogen content within the discharge was about 80%. A capillary hole on the right-hand side of the quartz and two holes (one each in the inner and outer shields) enabled the outflow of a gaseous H / H ~ beam from the dissociator into the trapping section (No. 19). Between the inner and outer shields (No. 8) of
- 5
the dissociator, a vacuum of about 10 Torr was maintained by a separate pump (No. 7). A small, tantalum crucible, heated electrically and shielded by a small LN -cooled shroud, could be
2
tilted through the opened slide valve into the trapping section TS. To this end, the LN2 tubes were bent as a swivel arm, so that a deposit of lithium could be placed on the inner walls of the TS.
4.3 Instrumentation
The pressure within the trapping section could be measured with a Pirani sensor (No. 10) connected to the trapping sqtion by a capillary tube.
The intensity of the magnetic field was measured by means of a Hall probe (No. 16) which was mounted closely to the magnet. The wall tempera- turebf the TS was measured by two Cu-Constantane therinocouples (Id reference) mounted on the out-
2
side wall of the TS (Fig. 13, Nos. 9 and 21).
Using a helium vapour pressure thermometer (No. 13), the temperature within the vessel of the super- conducting magnet could be measured.
4.4 Sequential Steps of Experiment
(1) Evacuation of UW chamber to about Torr and cool-down of radiation shield (No. 2); (2) Cool-down of magnet and TS by LHe;
( 3 ) Excitation of superconducting magnet; (4) Swinging of crucible into TS and evaporation
6
of Li at ,700 - 800° C into TS against a flow of cold helium gas fed into TS by means of a UHV leak valve and a capillary tube (No. 6). ~his'enabled the coating of the inner wall of the TS with amorphous lithium;
(5) Swinging of the crucible out of the TS and starting of r.f. dissociator for about one hour to trap H within the TS;
( 6 ) Shut-down of dissociator, closure of slide
valve (no. 11) and shut-down of magnet; (7) Warm-up of TS and observation of experimental
data.
4.5 Results of Experiment
Although experiments with hydrogen and deuter- ium as well as with H /D"HD mixtures alone have
2 2
been performed similar to those described in Chapter 3, this section is concerned only with Li-H and C-H experiments. Because no pumped helium bath was used, the temperature during the experi- ment did not fall below 4.2K, the boiling point of helium.
Therefore, 6 comparison with the experiments performed,at 1.1 K cannot be made because the important phenomena observed in those cases occurred at about 2.3 K.
Fig. 14 shows the typical behaviour of para- meters, such as pressure in the UHV chamber and the trapping section (TS), the magnetic field and wall temperature of the TS, and of the mass spectrometer recordings. Li6 and hydrogen were used.
Fig. 14 shows also the situation after a one- hour opei'etion period of the r.f. dissociator and de-excitation of the magnet. As--in the other experiments, a shut-down of the magnet did not produce any observable effect. During the warming- up period of about 5 minutes, no observable effects could be detected apart from a remanent magnetic field of unknown orig4n: of about 200 Oersted within the TS.
When the temperature in the %B reached about 6
-
8O K, the pressure within the TS increased,-2
within a few seconds, to 1.2.10 Torr; simultan- eously, the temperature of the TS increased to
14O K and -the pressure inside the vacuum chamber to 3 . T o n . The mass spectroq@ar.s indicated an increase of the atomic mass units 2, 3 and 4.
As the pressure in the TS was higher than in the vacuum chamber, the gas must have evaporated from the TS. Because this reaction was quite fast and generated heat, it is assumed that the above mentioned effects were due to the recombination of atomic hydrogen. From the available data, it was found that:-
-
the temperature increased from 6-8O K to 14O K;- the total heat released was 1.5 Wsec (equivalent
to stored atomic hydrogen 0.007 mMol);
- the total quantity of gas released was 0.4 cm
3NTP = 0.018 mMol H2;
JOURNAL DE P H Y S I Q U E
-
the maximum pressure within the vacuum chamber CONCLUSIONSwas 3. Torr; To achieve higher atomic density storage,
- the total amount of Li was 40 milligrams;
a. search-$hou?d'be made. for materials other than- the concentration of atomic H in
Li Was 0.1 Mol%. normal molecular hydrogen. With reservations tothe outcome of further experimental investigations, NOTE
-
we consider that C as a matrix offers advantagesObviously, with the recombination of atomic hydrogen,
for storing atomic hydrogen in higher densities. normal molecular H2 was also evaporated (the slide
valve was closed).
Similar measurements were performed with C as matrix. In these cases, the amorphous deposit
Ackncwledgements
was however made by means of a smoky propane
flame. The TS unit was, of course, dismantled The authors wish to thank Messrs. R. Eertram, and replaced with the C-deposit into the vacuum G. Schneider and 0. Goldschnidt for their much chamber again. To disorb any trapped gas, the TS appreciated
advice
and
assistance.was then heated to
%loo0
C for several days.The test sequence was as described for Li SUpplenent
(of course without steps 4 and.5). Here The transmission of acoustic waves led to the however, the gas release in the TS occurred when conclusion that atcanic H existed i n the gas phase
17 3
the magnetic field was reduced by a fraction (see (particle densityn/lO
at^
) a t 1. lo K (magnetic Fig. 15). The slide valve was open in this case. field 6 T) and also a t 2.3O Kafter
de-excitationof the superconducting magnet. Because the walls
From the available data, one will obtain for C as
of the TS were not covered with a s u ~ e r f l u i d He I1
a matrix:-
film, the out- of our experiments strongly
- Temperature increase from 6-8O K to 18O K; contradict the conclusion of other scientists *o
- Total heat released: 6Wsec (equivalent to r e p r t e d a t tkis sympsium that a m c hydrogen stored H 0.027 mMol); recarbines very quickly with solid
mlecular
3
-
Total amount of gas released: 1.3 cm NTP = hydrosen.0.06 rni-401; Considering the experimental set-up, we
naw
- Total amount of C: 5 milligrams;
assum thatsome
He-gas escaped f m the capilla--
Concentration of atomic H in C: 6 Mol%; r i e s of the Baratmn sensors which-
prior to-
Maximum pressure in TS: 1. ~ . I o - ~
Torr; the t e s t-
were f i l l e dwith
He, and covered the TS- Maximum pressure in vacuum chamber:
1. T o m . with an He film. The piezo-tr-tter evidently NOTE mrked mrrectly, but we cannot say what the gas Rere again, the normal molecular hydrogen had canpsition of Han3
Hewas.
According t o the gvaporated. vapour pressure of He a t 1. lo K,the
content ofL i t e r a t u r e
1 W. Peschka Uber d i e Verwendbarkeit von ato- marem Wasserstoff a l s T r e i b s t o f f fir F l u s s i g k e i t s r a k e t e n .
Proc. gth IAF-Congress, Ams t e r - dam 1958
Vienna, Springer pbbl
.
1959 2 R. Hess Untersuchungen uber d i e S t a b i l i -s i e r u n g von atomarem Wasserstoff m i t H i l f e t i e f e r Temperaturen und s t a r k e r magnetischer Fel der Thesis Univ. S t u t t g a r t 1971
3 J.T. Johnes C h a r a c t e r i z a t i o n o f Hdrogen Atom
jr. Systems
H.L. Mayer Ford Motor Comp. Publ. No. U-216
e.al. Vol. I. June 1958
4 C.K. Jen E l e c t r o n Spin Resonance o f Atomic S.N. Foner and Molecular free Radicals e.al. Trapped a t L i q u i d Helium Tempera-
t u r e
Phys. Rev. Vol. 112, 1958 p. 1169-1182
5 R. Hess Atomic Hydrogen
ESRO TT-42, A p r i l 1974
6 R.Hess Atomic Hydrogen S t a b i 1 i z a t i o n by High Magnetic F i e l d s and Low Temperatures
Proc. 1972 Cryogenic Engineering Conf. Plenum Press New York 1973
7 R,W,H, Behavior o f Atomic H i n S o l i d H2 Webel er. From 0,2 t o 0,8 K
NASA TMX-71732 1975
8 W.C.Stwalley Possible "New" Quantum Systems L.H. Nosanow Phys. Review L e t t e r s Vol. 36,
No. 15, 1976
10 F.J. Generation o f atomic H i n a hydrogen Zeleznik m a t r i x by t r i t i u m decay
Journ. Chem.Phys. Vol. 65, No. 11, 1976
11 G. Rosen Upper Bound on the E q u i l i b r i u m Con- c e n t r a t i o n o f Atomic H i n S o l i d Hz Physics L e t t e r s Vol. 61 A, No. 1,
1977, North-Holland Publ. Comp. 12 L.A. G r i t z o M e t a l l i c Hydrogen: A B r i e f Techni-
N.H. c a l Assessment
K r i k o r i a n Los Alamos Sci. Lab. LA-6172-MS UC-34a, Jan. 1976
13 R.D. E t t e r s Energy Storage P o s s i b i l i t i e s o f J.V. Dugan Atomic Hydrogen
J r . Proc. lth World Hydrogen Energy R. Palmer Conference
Miami Beach 1976, Pub: Mc Graw H i l l 14 J.V. Dugan Ground S t a t e P r o p e r t i e s o f T r i p l e t
J r . Atomic Hydrogen
R.D. E t t e r s Chemical Physics, 1973
15 R.D. E t t e r s Binding.Energies f o r Clusters o f Atomi c-Tri p l e t Hydrogen
Physics L e t t e r s Vol. 42 A, No. 6 1973
16 Dr. Ye Yakovlcv Ncw Scientist, 2 Scpt. 1P7G
C 7 - 1 7 4 JOURNAL DE PHYSIQUE
Fig. 1
- Mass Spectrometer Signals during
Wan-up of H ~ / H Matrix
(a) Hz intake, dissociator off; O magnetic field, (b) Hz dissociation by operating dissociator;
0 magnetic field,
(c) H2 dissociation by operating dissociator
Fig. 2 - Principle of experimental apparatus
(1 Cryopump section, (2) Superconducting magnet,
( 3 ) Atomic Hydrogen Trapping Section (AHTS)
,
(4) He-cooled electrode for dissociator,( 5 ) LN2-cooled radiation shield,
( 6 ) LN2-cooled hydrogen dissociator
(15 min.); magnetic field: 6 Tesla, Fig. 3
(d) H dissociation by operating dissociator 3-stage cryopump
2 ( 1 ) LN2coo1ed parts,
(30 min.); magnetic field 6 Tesla
(2) LNe-cooled parts
( 3 ) LHe-cooled part
Fig. 4
View of main flange (0 1 m) carrying all feed- throughs (No. 28) into vacuum system.
( 1 ) Helium refrigeration line (20K, 300W); (2) LN -cooled hydrogen dissociator, (3) L H ~ transfer lines,
(4) Valve battery and Baratron sensors for feeding gases into experiment.
Fig. 5 - View of Atomic Hydrogen Trapping Section
Fig. 6
- Principle of Atomic Hydrogen Trapping Section
(AHTS )-
Supercondycting Magnet (SM),
-
V-valve device,-
Conductivity Probe (CP),-
Piezo-transmitter (PI) and microphone,-
Hall probe (HP),-
Superfluidity probe (SF)-
Fast-responding thermocouple (Th),
-
Temperature sensor (TI,-
Mass spectrometer connection (MS),-
Sear coil connections (B)-
Pressure sensor connections (P, HPI, HP2),-
SQUID probe (SQC)Recordings of pt Absolute Pressure
hp
- differential pressure
BH
-
magnetic signal TS-
thermocouple signal B- search coil response
T - wall temperature within AHTS during warm-up
Fig. 7
Recordings of Absolute Pressure Pt and Differential Pressure Ap within AHTS T
-
microphone signalspi- H-beam pressure at capillary exit of dissociator SF- superfluidity probe signal (erratic)
Fig. 9
Response from Thermocouple signal TH
(responding time 100 msec; chart speed 2 cm/min.)
F i ? . 10
JOURNAL DE PHYSIQUE
Fig. 11
-
Correlation Chart of Diagnostics SignalsResatance,ohms Retation bitween the
electrtcul reststance o f the hydrogen at 4.2 K and the force applred to the anvils. A Large hvsteresis is visible. W h e n the pressure is removed from the anvils, the conductivtty of the solid hydrogen does not immediately return torts inittal value. This indicates that metallic hydrogen could possrbly etist
an a metastable state over a wide range o f pressures,
lo2
'Dl
0 1 2 note though is close that not to the 0. when It hydrogen is important the pressure retains to Compress~on force larb~trary unltsl its metallic properties at pressures considerably lowet. Lhan those necessary for the initial transformatton to the metallic stateFig.
12
E'reesure
vacuum chamber
Pressure
( TS )time
1Min
6F i g .
1 4r Recording
of
Pressure ( V C )
Yressure (TS)
,
Temperature
(TS:
and Mase epectr.
using
an
arnorphoue Li-Matrix
~ i g . 13 - Principle of L ~ = - H and C-H Experiments (1) Vacuum vessel; (2) LN2 Cold wall.; ( 3 ) Turbo-
pump; ( 4 ) ~uperconducting magnet; ( 5 ) r. £.
dissociator; 16) leak valve for gaseous helium inlet; (7) dissociator pump; (8) dissociator shield; (9) and ( 2 1 ) thermocouples; (10) swing- arm and connections for ~i~ crucible; (11) slide valve; (12) crucible; (13) vapour pressure thermo meter; (14/15/17) helium feed and vent-lines;
(16) magnetic sensor; (18/19) LHe-cooled section.
